Chem Soc Rev Dynamic Article Links Citethis: DOI: …polymer.zju.edu.cn/biomaterials/uploads/Publications/...Chem. Soc. Rev. This journal is c The Royal Society of Chemistry 2012 capsules

This journal is c The Royal Society of Chemistry 2012 Chem. Soc. Rev.

Cite this: DOI: 10.1039/c2cs35088b

Layer-by-layer assembly of microcapsules and their biomedical

applicationsw

Weijun Tong, Xiaoxue Song and Changyou Gao*

Received 22nd March 2012

DOI: 10.1039/c2cs35088b

Nanoengineered multifunctional capsules with tailored structures and properties are of particular

interest due to their multifunctions and potential applications as new colloidal structures in

diverse fields. Among the available fabrication methods, the layer-by-layer (LbL) assembly of

multilayer films onto colloidal particles followed by selective template removal has attracted

extensive attention due to its advantages of precise control over the size, shape, composition, wall

thickness and functions of the obtained capsules. The past decade has witnessed a rapid increase

of research concerning the new fabrication strategies, functionalization and applications of this

kind of capsules, particularly in the biomedical fields such as drug delivery, biosensors and

bioreactors. In this critical review, the very recent progress of the multilayer capsules is

summarized. First, the advances in assembly of capsules by the LbL technique are introduced

with focus on tailoring the properties of hydrogen-bonded multilayer capsules by cross-linking,

and fabrication of capsules based on covalent bonding and bio-specific interactions. Then the

fabrication strategies which can speed up capsule fabrication are reviewed. In the following

sections, the multi-compartmental capsules and the capsules that can transform their shape under

stimulus are presented. Finally, the biomedical applications of multilayer capsules with particular

emphasis on drug carriers, biosensors and bioreactors are described (306 references).

1. Introduction

The capsules have great applications in fields of medicine,

catalysis, cosmetics and so on. Nanoengineered multifunctional

capsules with tailored structures and properties are of special

interest due to their potential applications and fundamental

importance as new colloidal structures. Particularly, this type of

MOE Key Laboratory of Macromolecular Synthesis andFunctionalization, Department of Polymer Science and Engineering,Zhejiang University, Hangzhou 310027, China.E-mail: [email protected]; Fax: +86-571-87951108;Tel: +86-571-87951108w Part of a themed issue on supramolecular polymers.

Weijun Tong

Weijun Tong is currently anassociate professor of materialsscience at Zhejiang University.He obtained his PhD inmaterials science in 2007under the supervision of Prof.Changyou Gao at ZhejiangUniversity, China and Prof.Helmuth Mohwald at Max-Planck-Institute of Colloidsand Interfaces, Germany. Hismain scientific interests are inthe areas of supramolecularassembly, microcapsules,functional colloids and theirapplications in biomaterials.

Changyou Gao

Changyou Gao is currently aprofessor of materials scienceat Zhejiang University, awinner of the National ScienceFund for Distinguished YoungScholars of China, and aCheung Kong Scholar ofMinistry of Education ofChina. He obtained his PhDin polymer chemistry andphysics in 1996 under thesupervision of Prof. JiacongShen at Jilin University,China. His research interestsinclude self-assembled micro-capsules, nano and colloid

biomaterials and their interaction with cells, biomaterials fortissue regeneration and cell migration.

Chem Soc Rev Dynamic Article Links

www.rsc.org/csr CRITICAL REVIEW

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http://dx.doi.org/10.1039/c2cs35088b



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Chem. Soc. Rev. This journal is c The Royal Society of Chemistry 2012

capsules may supply revolutionary solutions to the problems

in biomedical fields, including but not limited to therapeutic

delivery and diagnostics.1,2 One of the promising methods

which can fabricate such a kind of capsules is layer-by-layer

(LbL) assembly3,4 of multilayer films onto colloidal particles,

followed by selective core removal (Fig. 1).5,6 Besides the

traditional electrostatic interaction, other driving forces such as

hydrogen bonding,7,8 covalent bonding,9 base-pair interactions,10

guest–host interactions11 as well as van der Waals interactions12

have been recently utilized to fabricate multilayer capsules. These

developments are invaluable because they allow a diverse range

of materials to be assembled into the capsule walls and additional

control over the structures and properties of obtained capsules.13

Therefore, by using this technique capsules with well-controlled

size and shape, finely tuned wall thickness and variable wall

compositions can be obtained.14 Furthermore, the templates

also can supply additional opportunities for the control of

capsule structures.15,16 The ability of precise manipulation of

capsule structures enables the tailoring of permeability,17

loading and release,18–21 mechanical properties22,23 as well as

biofunctionalities24 of the capsules.

At the beginning the studies on LbL multilayer capsules are

mainly focused on the fabrication and basic physicochemical

properties.14 However, the past decade has witnessed a rapid

increase of research concerning their functionalization and

applications, particularly in the biomedical fields such as drug

delivery, biosensors and bioreactors.25 Very recently, several

excellent articles have reviewed the progress of LbL capsules

as drug delivery systems,8,26–34 optical biosensors35 as well as

reactors.36,37 Another tendency in this field is the continuous

development of new fabrication strategies, which can endow

the capsules with novel structures and properties.8,38 In this

critical review, we will highlight the very recent (i.e. the last

5 years) progress of the LbL multilayer capsules. First, we will

focus on the advances in assembly of capsules by the LbL

technique, emphasizing on tailoring the properties of hydrogen-

bonded multilayer capsules by cross-linking, and fabrication of

the capsules based on covalent bonding and bio-specific inter-

actions. Then we overview the fabrication strategies that can speed

up and scale up capsule fabrication. In the following sections,

we will introduce the multi-compartmental capsules and the

capsules that can transform their shape under stimulus. Finally,

we will describe the biomedical applications of LbL capsules, with

special emphasis on drug carriers, biosensors and bioreactors.

2. Advances in assembly of multilayer capsules by

the LbL technique

2.1 Cross-linking to tailor the properties of hydrogen-bonded

multilayer capsules

Cross-linking is an effective way to enhance the stability and

tune the properties of multilayer capsules. Even for the multi-

layer capsules assembled through electrostatic interaction, in

some cases cross-linking is still necessary for the capsules to

survive through harsh conditions such as high ionic strength,

extreme pH and strong polar organic solvent.39–43 Moreover,

cross-linking can effectively manipulate the permeability and

mechanical strength of capsules.39,42,43 The LbL assembly of

multilayers through hydrogen bonding has been extensively

developed.7,8,13 However, further stabilization is required for

biomedical applications since most of these multilayers will be

disassembled under physiological conditions.44,45 The first cross-

linking method is carbodiimide chemistry.46–48 Uncross-linked

components can be selectively released at higher pH, yielding

single component and hydrogel-like microcapsules.49,50 These

capsules exhibit reversible pH-responsive swelling and shrinking,

which can be used for loading and releasing macromolecules.

Fig. 1 Schematic illustration of the polyelectrolyte deposition process

and of subsequent core decomposition resulting in hollow capsules.

Reprinted with permission from ref. 6. Copyright 1998, Wiley-VCH.

Fig. 2 PMASH–PVPON capsule wall (a) under LbL polymer deposition

conditions, (b) cross-linked at physiological pH, and (c) under cellular

reducing conditions. Reprinted with permission from ref. 53. Copyright

2009, American Chemical Society.

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One of the significant advances in this issue is the revisable

stabilization of hydrogen-bonded LbL capsules via disulfide

bonds.8,51 In this strategy, the key step is to modify at least one

of the components, for example, poly(methacrylic acid) with

thiols (PMASH), which can be further cross-linked under

oxidative conditions to stabilize the capsule wall. The

uncross-linked component poly(vinylpyrrolidone) (PVPON)

can be selectively removed, yielding stable single component

hydrogel capsules. Under reductive conditions, such as inside

cells, the disulfide linkages can be cleaved by glutathione,

resulting in disassembly of the capsules (Fig. 2). Subsequently,

the influences of thiol content, molecular weight of PVPON,

oxidation reagents, cross-linking way as well as layer number

on the properties of capsules such as degradation rate, perme-

ability and cargo retention are systematically investigated.52–55

The obtained knowledge can be used to optimize the prepara-

tion conditions and precisely control the properties of the

capsules, highlighting the virtues for encapsulation and delivery

of diverse therapeutic substances.56–58

Click chemistry with the features of high efficiency and

selectivity under mild conditions is another powerful tool

for cross-linking of the hydrogen-bonded multilayers and

microcapsules.59–65 In a general strategy, one component is first

modified with alkyne moieties and then alternately assembled

with another component on silica particles via hydrogen-

bonding. The films are cross-linked with a bisazide linker,

followed by removal of the template and uncross-linked

component at physiological pH through hydrogen bonds

disruption, yielding single-component hydrogel capsules

(Fig. 3). By choosing different alkyne-modified polymers,

bisazide linkers as well as the multilayer assembly sequence,

the properties of the capsules can be well manipulated. For

example, assembly of alkyne-modified PVPON (PVPONALK) and

poly(ethylene glycol) (PEG) results in low-fouling capsules60,62

while combination of pH sensitive alkyne-modified polymers

and reduction-sensitive bisazide linkers yields dual-responsive

capsules.65

2.2 Capsules directly assembled by covalent bonding

Zhang et al. first fabricated the covalent LbL microcapsules

through the reaction of N-methyl-2-nitro-diphenylamine-

4-diazoresin (NDR) and m-methylphenolformaldehyde resin

(MPR) in methanol.9 Similarly, microcapsules with a high

modulus and stability are fabricated through a coupling

reaction between epoxides and amines in organic solvent.66

The obtained capsules are very stable against harsh conditions

due to the covalent structure.9,66 More importantly, assembly

in organic solvents greatly expands the range of materials

adopted by the LbL technique. The reaction between amine

and aldehyde is fast and efficient in aqueous solution at room

temperature, and thereby is suitable for the covalent LbL

Fig. 3 LbL assembly of low-fouling PVPONAlk capsules covalently cross-linked by click chemistry. Hydrogen-bonded multilayers of PMA and

PVPONAlk are assembled onto colloidal silica templates precoated with a layer of PVPON. Free alkyne groups are then used to covalently cross-

link the PVPONAlk in the multilayer by click chemistry with a bisazide linker containing a disulfide bond. After removal of the template particle

and subsequent release of PMA at pH 7, low-biofouling PVPON capsules that can be degraded in reducing environments are obtained. Reprinted

with permission from ref. 60. Copyright 2009, American Chemical Society.

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assembly in aqueous solution. Using this feature, single poly-

electrolyte (PE) component multilayers and microcapsules are

fabricated through glutaraldehyde (GA)-mediated covalent

assembly.67,68 This method can be extended to other biomacro-

molecules such as polysaccharides, polypeptides, and proteins.69

However, the main drawback of the above-mentioned methods is

that the obtained capsules may largely lose their stimuli-responsive

properties due to the uncontrollable covalent reactions.67,68 One

solution to this problem is to carefully control the content of

reactive groups in polymer chains, leading to a controllable

reaction degree and a number of functional groups. This concept

was first demonstrated by Such et al.70 Poly(acrylic acid) (PAA)

molecules grafted with minor amounts of either alkyne

(PAA–Alk) or azide (PAA–Az) are alternately assembled on

silica particles through the click reaction, yielding hollow micro-

capsules after core removal. Due to the carboxylic acid groups in

PAA, the capsules show reversible swelling and shrinking by up

to 70% in response to acid–base pH cycling. A detailed study is

further performed to investigate the influences of assembly

conditions such as pH, ionic strength as well as grafting degree

of PAA on the structures and properties of the obtained films

and capsules.71 Through this method, degradable microcapsules

also can be produced using dextrans modified with alkyne and

azide groups through hydrolysable carbonate esters.72,73

As a natural protein, bovine serum albumin (BSA) is con-

sidered to be biocompatible and biodegradable. It has a defined

structure with high content of charged residues of amino acids,

such as aspartic and glutamic acids, lysine, and arginine.74,75

GA only cross-links the amine group of lysine,76 while the other

charged residues of amino acids still exist. Consequently,

pH response of the resultant products can be expected.

Moreover, the GA cross-linked albumin microspheres are

relatively non-immunogenic and biodegradable in muscle without

adverse tissue reactions.77 Therefore, the GA cross-linked

BSA spheres/capsules are promising for pharmaceutical

applications. In a recent study,78 BSA was first assembled on

the surface of colloidal particles, which were then suspended in

GA solution to cross-link the adsorbed BSA layer and activate

the surface for next covalent assembly of BSA. This procedure

is repeated several times until the desired layer number is

reached. Hollow capsules are obtained by removal of the cores.

The capsules show reversible pH-controlled permeability, which

can be used to encapsulate macromolecules.

Recently, Jia et al.79 introduced biocompatible, biodegradable,

stable and nontoxic polysaccharide-based microcapsules, which

were fabricated by covalent LbL assembly of chitosan (CS) and

alginate dialdehyde (ADA) through amine and aldehyde reac-

tion. In this strategy, polysaccharides such as alginate, heparin as

well as starch can be modified with aldehyde groups which can

react with the amine groups in CS. However, electrostatic

interaction may also contribute to the multilayer assembly in

the CS–ADA system. Interestingly, the prepared (CS–ADA)5/CS

microcapsules display intriguing autofluorescence without any

external fluorochromes. This phenomenon resulted from the

n–p* transition of the CQN bonds in the Schiff base formed

between amino and aldehyde groups.80–82 These autofluorescent

microcapsules can avoid external fluorochromes used in bio-

logical tracing, showing great promise in biomedical applications.

In the following work of the same group,83 low-molecular-weight

and redox-responsive cystamine dihydrochloride (CM) is

assembled with ADA to fabricate microcapsules, which exhibit

pH- and redox-responsive as well as autofluorescence (Fig. 4).

2.3 Capsules assembled through bio-specific interactions

The specific interactions between complementary DNA bases

are stable enough under physiological conditions in nature.

Therefore, the biocompatible and biodegradable DNA is very

Fig. 4 (a) LbL assembly of autofluorescent polysaccharide-based microcapsules uploading docetaxel (Dtxl) against tumor cell proliferation. The

formulated Schiff base and disulfide bonds form capsules with pH- and redox-responsive properties for pinpointed intracellular delivery based on

physiological difference between intracellular and extracellular environments. The as-obtained microcapsules could be degraded into ADA and

mercaptoethylamine (MEA). (b) Typical CLSM images of the microcapsules excited at 405 nm and collected 500–550 nm (green). (c) Fluorescence emission

spectrum of the selected region in the CLSM image of (ADA–CM)5 capsules. Adapted with permission from ref. 83. Copyright 2012, Wiley-VCH.

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attractive if it can be prepared into multilayer films and

capsules. This was first demonstrated by the Caruso group,10

and the factors governing the structures and properties of the

films and capsules were systematically investigated.84–89 It is

necessary for the pre-adsorbed DNA to be available for the

subsequent layer to hybridize, thus the oligonucleotides with

multiple nucleotide units are needed.84 Furthermore, the

oligonucleotide length plays an important role, and at least

10 bases per hybridizing block in the DNA diblocks are

required for successful multilayer film formation. Also the

stability and melting temperature of the films increase along

with the increase in oligonucleotide length.86,88 The use of salt

in forming DNA multilayers is crucial in promoting and

maintaining hybridization of complementary base pairs by

screening the repulsive forces between the negatively charged

DNA main chains.89 The obtained DNA capsules shrink after

template removal,85 and the shrinkage can be greatly inhibited

by hybridizing additional oligonucleotide sequences that can

crosslink the films.90 Since modern biotechnologies enable the

precise control over the sequences of DNA, the properties of

consequent DNA films and capsules can be well tailored. For

example, capsules assembled from a DNA with restriction-

enzyme cut sites can be only degraded in the presence of a

specific enzyme.91 These results are important for precise

control of the structures and properties of DNA films and

capsules, which have great potential applications in the fields

of sensing, diagnostics, and drug/gene delivery.

Furthermore, DNA sequences can be grafted to diverse

polymers to form DNA–polymer conjugates, which can be

further assembled into multilayer thin films. For example,

DNA-grafted poly(N-isopropylacrylamide) (PNIPAM)micelles

are assembled into multilayer thin films through specific base

pair interactions, resulting in further DNA–PNIPAM micro-

capsules with hierarchical structures.92 The G-quadruplex–

polymer conjugates also can be assembled onto a template

surface via hybridization with 30-mer cytosine strands using

the LbL approach to form microcapsules. The residual and

functional quadruplex moieties can be used to effectively bind

therapeutic agents.93

Besides the specific base pair interactions, carbohydrate–

protein interaction is another type of important bio-specific

interactions which participates in a wide variety of biological

and pathological events.94–96 These interactions are, in nature,

a combination of multiple hydrogen bonding and hydro-

phobic interactions.95 Although both of them are weak and

reversible, superior strength of the carbohydrate–protein

interactions arises from the numerous binding sites. Therefore,

novel molecular-engineered microcapsules built from these

interactions may simultaneously possess good stability and

responsiveness to external stimulus. Concanavalin A (Con A),

a well-investigated lectin derived from Jack beans, is known to

possess specific binding capacity to glucose, mannose, fructose

and their corresponding polysaccharides such as dextran and

glycogen.97–99 Thus, Con A can form complex with dextran

and be employed to fabricate thin films with glycogen through

lectin–carbohydrate interactions.100–102 These structures show

readily their responses to glucose.99,102 Hence, it is expected

that the hollow capsules fabricated by Con A and glycogen in

the LbL manner remain stable at the physiological pH range

due to the relatively strong multiple hydrogen bonding but

readily respond to glucose due to its competitive-binding with

Con A. This concept has been realized recently and is further

used to create multi-compartmental micelles-loaded micro-carriers

(Fig. 5).103 The sequential multilayer film growth proceeds success-

fully on both planar and curved substrates when the Con A

molecules adopt confirmation of tetramers or more complicated

aggregates. The obtained capsules show layer-number-dependent

shell shrinkage, distortion and densification. Particularly, when

the layer number is smaller than 7, the capsules shrink to different

extents but their wall thickness remain approximately unchanged,

suggesting molecular rearrangement during the template removal

process. The capsules are stable in a medium of pH 6–9 and

survive through 3 M urea treatment for at least 1 h, indicating

good capsule stabilities. These capsules show specific responses to

glucose, mannose, fructose and dextran but not to lactose and

galactose due to the mismatch structure. The responses of these

assemblies to carbohydrates are independent of the external pH

value in the range 6–9. Triggered by these stimuli, polymeric

micelles pre-loaded in the capsules can be released. With the

carbohydrate-responsive properties in the physiological pH range

as well as the possibility of incorporation and subsequent release

of functional nano-objects, these smart capsules are expected

to find important applications in the fields of drug delivery,

bio-sensing as well as bio-reactions.

3. Speed-up the capsule fabrication by LbL-derived

methods

Using the LbL technique, the multilayer capsules with well-

controlled size and shape, finely tuned capsule wall thickness

and compositions, tailored functionalities can be successfully

fabricated. Despite all the attractive advantages, the main

drawbacks of the LbL technique are the tedious and time-

consuming fabrication process and the waste of materials.

Therefore, development of other facile methods with great

Fig. 5 (a) Schematic illustration of the structure of the Con A–glycogen

smart capsule and its response to carbohydrates. Fluorescent images

of Con A–glycogen microcapsules before (b) and after treatments with

(c) 10 mg ml�1 glucose for 20 s. Adapted from ref. 103.

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ease of fabrication and eventually scalable production of

capsules is of both scientific and technical importance. In the

following sections, we will introduce several methods which

may speed up and scale up the capsule fabrication. Most of these

methods are directly derived or inspired by the LbL methods.

3.1 Controlled precipitation (CP)

The CP method can deposit a thick enough layer on a template

surface. For example, PEs,104 nanoparticles (NPs)105 as well as

dextran106 can be precipitated on a template surface in a controll-

able way by gradual change of the solvent quality. Obviously, the

hollow capsules only can be obtained if the shell can survive core

removal, thus stabilization of the shell is often needed, as reported

recently for the BSA mono-component microcapsules.107,108

Desolvation of BSA from its aqueous solution is achieved by

dropwise addition of poor solvent, e.g. ethanol. The desolvated

BSA molecules are captured by MnCO3 microparticles to form a

continuous thin film on the surfaces. After cross-linking of the

films and core removal, hollow and intact microcapsules are

obtained with well dispersion in aqueous solution. In another

case, if the precipitation is induced by specific interactions of two

substances in the same aqueous solution, the formed film on the

template particle will be stable enough in solution and no further

cross-linking is needed. This one-step CP process is demonstrated

by fabrication of Con A and glycogen complex capsules.109 The

shells are formed on polyethyleneimine (PEI)-modified carbonate

particles by dropwise addition of Con A solution into glycogen

solution, resulting in stable hollow capsules in aqueous solution

after core removal. These capsules retain the responsiveness to

glucose and glucose-containing polysaccharides such as dextran.

Employing micelles-adsorbed CaCO3 particles as the templates,

the micelles also can be incorporated into the capsules. These

multi-compartmental carriers still can be destroyed by glucose,

providing the possibility to load and release multiple reagents.

In the above-mentioned CP methods, precipitation of the

wall materials must be induced by addition of external sub-

stances. Very recently, a core-mediated precipitation method is

developed to fabricate CS microcapsules with micron-size wall

and onion-like concentric layered structures.110 The partial

dissolution of CaCO3 particles in a slightly acidic CS solution

induces pH increase, and thereby precipitation of CS on the

templates. Repeat of this process results in CS capsules with an

onion-like concentric layered structure (Fig. 6). The capsules

are stable without cross-linking and can be well dispersed in

aqueous solutions. This pH increase is automatically realized

and self-restricted by the partial dissolution of CaCO3 cores,

and no deliberate adjustment of the pH value is required.

3.2 Core-mediated in situ PE coacervation

Previously we fabricated multilayer microcapsules using

poly(styrene sulfonate) (PSS)-doped CaCO3 particles as

templates.111,112 After core removal, part of the initially doped

PSS molecules in the CaCO3 particles are encapsulated within the

microcapsules and intertwined with the multilayers, enabling the

capsules to effectively sieve charged molecules. A model is sug-

gested to depict the topology of the microcapsules: with a special

complex layer of poly(allylamine hydrochloride) (PAH) and PSS

(B40 nm) under the regular PAH–PSSmultilayer shell (B15 nm).

The question then arises: is it possible to obtain the intact

complex shell only? Clarification of this question is not only

helpful to confirm the deduced model but also may provide a

new simple way to fabricate hollow capsules. By assembling

only one layer of PAH onto PSS-doped CaCO3 microparticles,

followed by dissolution of the CaCO3 particles with disodium

ethylene diamine tetraacetate dihydrate (EDTA), capsules are

obtained via in situ complexation of the oppositely charged

PEs when they encounter during core removal.113 The capsules

have a size of 150% of their templates due to the osmotic-

induced expansion114,115 and plasticity of the primary shells

during core removal. Due to the less regular internal structure

and cross-linking degree, elasticity modulus of the complex

capsule (140MPa) measured by an osmotic pressure method116,117

is only half of their regularly assembled multilayer counterpart.

This drawback can be remedied by GA cross-linking under mild

conditions.118 Moreover, if the adsorbed PAH layer is cross-

linked followed by core removal in a solution of EDTA mixed

with PAH, microcapsules with charge-controlled permeability

can be fabricated by such an in situ coacervation method

(Fig. 7).119 This new technique has the advantages of time and

materials saving, and can be easily scaled-up.

3.3 Polymerization on the surfaces of templates

Polymerization on a sacrificial particle surface is another

method for the speed-up and scale-up fabrication of hollow

capsules. Template polymerization has been proven a useful

method to obtain multi-component materials.120–122 In this

technique, a polymer is used as the template to associate with

monomers by hydrogen bonding, electrostatic force, or other

interactions, followed by polymerization of the monomers in

which propagation of a radical occurs along the template

polymer chain during most of its lifetime. Radical template

polymerization can yield polymer–polymer complexes held by

cooperative interactions of complementary macromolecules.

This method has been applied to forming ultrathin layers on

colloidal particles and further to fabricating hollow capsules either

driven by electrostatic interaction123 or hydrogen bonding.124

Fig. 6 (a) Schematic illustration of the formation process of chitosan

(CS) microcapsules with a micron-size thick wall and onion-like

structure via a core-mediated precipitation method. CLSM image of

microcapsules with 1 (b) and 4 (c) precipitated CS layers. The red and

green layers are tetramethyl rhodamine isothiocyanate (TRITC) and

fluorescein isothiocyanate (FITC) labeled CS, respectively. Adapted

from ref. 110.

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Poly(vinylpyrrolidone) (PVP) and silica particles are adopted

as the molecular template and sacrificing template, respectively.

The silica particles are modified by 3-(trimethoxysilyl)propyl

methacrylate (MPS) to introduce polymerizable CQC bonds.

Then acrylic acid (AA) and PVP are added in the suspension

and the pH is adjusted toB3. The PVP molecules can not only

stabilize the particle suspension but also act as the molecular

template to bind AA monomers through hydrogen bonding.

The PVP–AA complex is subsequently transformed into the

PVP–PAA complex through polymerization. Consequently, the

initially adsorbed PVP–AA conjugates on the particle surfaces

form the original shells, which become thicker and thicker along

with the polymerization proceeding. This is mainly driven by

the ‘‘grafting from’’ mechanism (i.e. radicals in the shells initiate

polymerization of AAmonomers associated with PVP) and also

possibly by the ‘‘grafting to’’ mechanism (i.e. the PVP–PAA

complexes are grafted to the shells by radial coupling termination).

Nevertheless, hollow capsules composed of PVP and PAA

complexes are obtained after etching out the templates. The

wall of the capsule can be further cross-linked, which endows

the microcapsules with better stability against large pH

fluctuations and reversible swelling–shrinking property at high

and low pH values, respectively.

More recently125,126 a strategy has been proposed to fabricate

polydopamine (PDA) capsules through the oxidative polymeri-

zation of dopamine and the spontaneous deposition of PDA on

the template surface, followed by template removal (Fig. 8).

This process only involves a single-step thin film assembly, but

the wall thickness can be well controlled by the polymerization

time125 and cycles126 in a nanometer scale. This method is very

elegant and versatile because the oxidative polymerization of

dopamine takes place under very mild conditions (slightly

alkaline aqueous solution and room temperature) without any

initiator, and PDA can spontaneously deposit virtually on any

surface.127,128 For example, PDA is successfully deposited on

dimethyldiethoxysilane (DMDES) emulsion droplets with a size

Fig. 7 (a) Schematic illustration to show the fabrication process of the in situ coacervated microcapsules with filled PSS, which possess charge-

controlled permeation property. They repel negatively charged fluorescein (b) but attract positively charged rhodamine 6G (c). Adapted from

ref. 119.

Fig. 8 Assembly of a polydopamine (PDA) film onto a particle and subsequent capsule formation. Oxidative polymerization of dopamine

showing two of the possible structures formed. Reprinted with permission from ref. 125. Copyright 2009, American Chemical Society.

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ranging from 400 nm to 2.4 mm.129 The obtained capsules are

very robust due to the cross-linked structure and can be loaded

with low-molecular-weight dyes.126 These capsules composed

of single common and naturally originated compounds exhibit

negligible toxicity,125 which makes PDA capsules ideal candi-

dates for therapeutic delivery and other biomedical applica-

tions. Moreover, dopamine can be used to modify biopolymers

and mediate assembly of biodegradable microcapsules through

its oxidative polymerization too,130 which greatly extends the

application fields of this method.

3.4 Infiltration and cross-linking on porous templates

Besides deposition on the surface of sacrificial templates, the

materials also can infiltrate into the pores of porous templates.

After stabilizing by cross-linking, capsules or spheres can be

obtained. Indeed, porous CaCO3 and SiO2 microparticles have

been used as templates to fabricate microcapsules with PE

complexes inside for biomacromolecule encapsulation.131,132

By simply mixing the capsules and biomacromolecules aqueous

solution, enzymes and proteins are loaded with high efficiency.

For example, by using porous CaCO3 particles multilayer

capsules with a cell-like topology are successfully fabricated.

They are able to spontaneously load various substances in

aqueous and ethanol solutions.133 Fabrication of such a kind

of capsules relies on infiltration of PEs into the pores of the

template to form PE complexes. Alternatively, SiO2 particles

with a solid core (ca. 300 nm) and a mesoporous shell (ca. 60 nm)

are employed as templates too. Macromolecules are infiltrated

into the mesoporous shell by solution adsorption, followed by

covalent cross-linking. Polymeric capsules are obtained after

template removal (Fig. 9).134 This method has significant advan-

tages compared with the previous one. First, formation of

capsules only needs a single macromolecule infiltration step

which makes the fabrication process speed up. Second, in

principle any macromolecule and its corresponding cross-linking

agent which can infiltrate into the pores can be used to fabricate

such capsules (Fig. 10). This advantage makes the method very

powerful for tailoring the properties of capsules. Finally, the

thickness and porosity of the capsule wall can be controlled by

the features of the porous silica shell. In another very recent

work of the same group,135 bacterially synthesized cysteine-

functionalized poly(L-glutamic acid) (PGA) molecules with

variable percentages of cysteine (6–30%) were infiltrated into

and cross-linked. After core removal, single-component porous

peptide microparticles are obtained. The position of the cross-

linking group (cysteine), which can be precisely tuned by the

bioengineering method, has a great impact on the degradation

rate of the assembled carriers. Thus, this method provides new

opportunities for designing delivery systems with a controlled

degradation property and drug release rate.

4. Capsules with subcompartments

The creation of advanced, multi-compartmental micro- and

nanostructures has received tremendous attention in the past

decades due to their ability to load and release multiple reagents

and applications in various fields.136–139 Hollow capsules with sub-

compartments are of extreme interest since they possess a large

inner space separated from the environment and resemble the

structure of cells. Compared with those traditional methods the

LbL technique is much powerful to design highly sophisticated

capsules. By integration of other techniques, so far many types of

capsules with different subcompartments have been fabricated.38

There are two ways to incorporate the sub-compartments, i.e.wall

decoration and interior loading.

Fig. 9 Schematic representation of the preparation of single-component

macromolecular capsules by using solid core and mesoporous shell

(SC–MS) silica particles as templates. Reprinted with permission from

ref. 134. Copyright 2008, American Chemical Society.

Fig. 10 Poly(L-lysine) (PLL) (a and b) and poly(L-glutamic acid)

(PGA) conjugated with doxorubicin (DOX), and (c and d) nanocapsules

formed using SC–MS templates. The cross-linking agents used are GA

(a), dimethyl 3,30-dithiopropionimidate dihydrochloride (DMDTPC)

(b), and cystamine (c and d), respectively. Panels a–c are TEM images,

the insets of panels (a and c) are SEM images, and panel (d) is a

fluorescence microscopy image of the nanocapsules whose fluorescence

signal arises from encapsulated DOX. Reprinted with permission from

ref. 134. Copyright 2008, American Chemical Society.

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Kreft et al. first reported the LbL microcapsules with a shell-

in-shell structure for integrated and spatially confined enzymatic

reactions.140 Spherical ball-in-ball particles consist of two

concentric CaCO3 compartments, which are separated by PE

multilayers and independently loaded with enzymes. By

assembly of multilayers on such templates followed by CaCO3

removal, the obtained shell-in-shell microcapsules contain

enzymes and are separated by semipermeable membranes.

They can mediate coupling bis-enzymatic reactions. Besides

the above-mentioned concentric structure, other complicated

structures such as pericentric, innercentric and acentric ones

can be obtained as well.141,142

De Geest et al. reported the assembly of multilayers on big

hydrogel particles (hundreds of microns) in which tens of

hollow LbL microcapsules or microparticles are loaded.138,143

Upon degradation of the hydrogel particles, the inside osmotic

pressure will increase and may eventually become large enough

to break the multilayers, leading to capsule rupture and thereby

release of the encapsulated subcompartments.

Recently, the Caruso group reported the incorporation of

intact liposomes into LbL capsule walls or inside capsules to

prepare ‘‘capsosomes’’, which can be then employed as enzymatic

reactors and delivery vehicles for hydrophobic cargos.144–148

Cubic mesophase lipid NPs also can be incorporated into capsule

walls through a similar strategy.149 For sure this kind of

‘‘capsosomes’’ is a promising new concept toward the design

of artificial cells in which complicated enzymatic reactions are

performed.150,151

Alternatively, polymeric micelles also can be incorporated

into the walls or interiors of LbL capsules as the subcompart-

ments. The micelles possess advantages of sustained release of

hydrophobic substances. In particular, polymeric micelles

possess a unique core–shell structure and relatively good

stability,152and thereby have found tremendous applications

as drug-delivery vehicles,153 nano-reactors154 and bio-sensors.155

Hence, the micelles-incorporated microcapsules maintain the

advantages of both micro- and nano-structures. Hollow micro-

capsules containing polymeric micelles in their walls are fabri-

cated by alternating assembly of PAH and poly(styrene-b-acrylic

acid) (PS-b-PAA) micelles on MnCO3 microparticles, followed

by removal of the templates in acid solution.156 Due to the high

stability in aqueous solution, the PS-b-PAA micelles retain their

structure during the whole assembly process. It is unexpected,

however, that the as-prepared microcapsules show extra-

ordinary stability against concentrated HCl (37%) and 0.1 M

NaOH solutions. No variation in capsule size or shape is

observed in acidic solution, while slight swelling and distortion

of the capsules takes place in alkaline solution. However, these

capsules completely recover their original size and morphology

after being incubated in acidic solution again. This extraordinary

stability against highly acidic or alkaline conditions is possibly

due to the hydrophobic interaction between PS cores of the

micelles as well as hydrogen bonding of the PAA chains in

adjacent layers and PAH chains. The capsules obtained can serve

as models for multi-compartmental containers which may

encapsulate both hydrophobic and hydrophilic substances. The

extreme stability of the capsules against harsh conditions in an

aqueous environment can greatly broaden their potential

applications, while their responsiveness to external stimuli

turns out at high pH. It might also be possible to tailor the

release of substances in each compartment by proper molecular

design of the micelles and incorporation of various functional

components.

The incorporation of polymeric micelles into LbL capsule

interiors has been presented by Li et al.157 as well as Tong

et al.158 In the latter method,158 LbL assembly is conducted on

CaCO3 microparticles pre-doped with PS-b-PAA micelles,

resulting in encapsulation of micelles after core removal.

Distribution of the micelles in templates and capsules is char-

acterized by transmission electron microscopy and confocal laser

scanning microscopy (CLSM). The micelles inside the capsules

connect with each other to form a chain and network-like

structure with a higher density near the capsule walls. The

hydrophobic multiple compartments can serve as reservoirs for

loading of hydrophobic drugs such as triclosan, while the

negatively charged PAA corona of the micelles are able to

induce spontaneous deposition159–163 of water-soluble and posi-

tively charged drugs such as doxorubicin (DOX). The concen-

trations of hydrophobic and water-soluble drugs are found to be

3 and 28-fold of the feeding values, respectively. Therefore,

capsules with this synergetic feature show their great promise

in loading of drugs with different physicochemical properties.

Furthermore, the wall of such multi-compartmental capsules

also can be engineered to be responsive to external stimuli. Among

various types of external stimuli such as pH,164 temperature165

or laser,166 glucose is a promising candidate for in vivo appli-

cations since it is abundant in human blood. Incorporation of

sub-compartments such as micelles into the glucose-responsive

vehicles results in smart multi-compartmental carriers and

further micelles release under glucose treatment.103

5. Shape transformation of capsules

The smart capsule systems are of high attraction due to their

ability to respond to the alteration of environment conditions.

LbL assembled capsules can change their structure and properties

intelligently in response to various stimuli such as pH,11,40,164,167–171

ionic strength,172–176 temperature,165,173,177–179 light,166,180–184

and redox potential.185 Most of the intelligence of the hollow

structures, however, results from controllable swelling and

shrinking, accompanying with permeability change.186 Less

concern is paid to shape transformation of the hollow structures,

which is only observed in vesicles and hollow silica spheres

previously.187–193 For instance, budded hollow silica spheres

can be constructed by kinetic self-assembly of silica precursors

and continuously budding surfactants,187 while block copoly-

mers can form vesicles of a special morphology with protruding

rods or porous spheres by changing polymer concentration and

solvent property.188–190 More interestingly, vesicles made of

giant hyperbranched polymers exhibit shape transformation

analogous to cellular processes such as birth, budding, fusion,

and fission.191–193 Therefore, not only the transformation

process of the hollow structures but also the underlying physico-

chemical mechanisms, which may give a hint on the biological

and natural processes, are of high interest.194

Recently, single-component microcapsules have been fabri-

cated in our group by an in situ reaction of reactive hydro-

phobic low-molecular-weight molecules with the corresponding

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PE-doped CaCO3 microparticles, followed by core removal.195–196

The first example is the capsules made of ferrocenecarboxaldehyde

(Fc-CHO) and PAH-doped CaCO3 microparticles.195 The

single-component microcapsules are stabilized by hydro-

phobic aggregation of Fc moieties. The microcapsules

have very thick shells, leading to a robust capsule structure

that is less collapsed in a dry state. Because of the excellent

redox properties of Fc, the PAH–Fc microcapsules show

reversible swelling and shrinking in response to oxidation

and reduction, accompanying with reversible permeability

change.

Through a similar procedure, pyrenecarboxaldehyde is

reacted with the doped PAH to fabricate PAH–pyrene (Py)

microcapsules.196 Surprisingly, one-dimensional nanotubes

(1D-NT) or nanorods (1D-NR) are protruded from the

PAH–Py microcapsules when they are incubated in pH 0

and pH 2 solutions, respectively. The 1D-NTs keep growing

with incubation time. Meanwhile, the microcapsules fade

gradually and disappear completely after 144 h (Fig. 11).

Similarly treated micelles, which are assembled from deliber-

ately synthesized PAH–Py polymers, can transform into one-

dimensional structures too, revealing the chemistry-driven

nature of the phenomenon. The one-dimensional nanotubes

consist of only 1-pyrenecarboxaldehyde with ordered p–pstacking, and exhibit a helical structure and anisotropic pro-

perty. The hydrolysis of the Schiff base and its rate at different

pH values (10 times slower at pH 0 than at pH 2) play a key

role in determining the final nanostructures. The linear PAH

directs the regular building up process especially for the

nanotubes. Using this unique feature, hollow capsules budded

with nanotubes or nanorods mimicking the cellular protrusion

of filopodia are successfully prepared when the process is

terminated at an appropriate time (Fig. 11). These results

and the proposed mechanism open new opportunities for

design of novel materials for nanoscience, and biological and

other advanced technologies.

Attempt is then made to control the 1D-NR growth state

from the PAH–Py microcapsules by chemical cross-linking

and surface modification. After GA cross-linking, the micro-

capsules can keep stable even after protrusion of the 1D-NRs.

Hence, the protruded 1D-NRs on the capsule surface are

easily tuned in terms of length and coverage rate by control-

ling the pH value of the incubation solution. For instance, the

1D-NRs are very short at pH 2 with a very high coverage rate;

however, at pH 1 the 1D-NRs grow longer but the coverage

rate becomes smaller. Because of the reversible reactive pro-

perty of the Schiff base, the 1D-NRs can be removed and

re-protruded from the capsules in a cycling manner.

The 1D-NRs also can grow in the LbL assembled capsules

in a controllable manner (Fig. 12).197 For this purpose,

PSS–PAH multilayers are assembled on the surface of CaCO3

(PAH–Py) microparticles, yielding PAH–Py and (PSS–PAH)ndouble-shell capsules. By incubation of the obtained capsules

in pH 2 solution, the 1D-NRs grow within the (PSS–PAH)nmultilayer capsules in three dimension. Their encapsulation

rate is controlled by the layer number and the size of the

(PSS–PAH)n capsules. Finally, the (PSS–PAH)n capsules can

be destroyed by ultrasonication to release the 1D-NRs, which

have exactly the same chemical and fluorescent properties as

their counterpart fabricated in solution. The fluorescence

emission intensity of Py NRs inside the capsules can be tuned

by a charge transfer pair. This novel composite structure with

PAH–Py NRs inside PE multilayer microcapsules provides a

creative strategy for in situ nanomaterials fabrication, illumi-

nating the trend for controllable properties and functions of

smart nanodevices.

Inspired by the above finding, PAH–Py NRs consisting of a

Py–CHO core and a PAH shell are successfully prepared by

surface grafting of PAH onto Py–CHO NRs.198 The Schiff

base reaction between Py–CHO and PAH on the interface of

NRs and solution results in a more curved and flexible

structure as a result of partial loss of Py–CHO from the NRs.

Fig. 11 TEM images showing the process of nanotube protruding from the PAH–Py microcapsules incubated in pH 0 HCl for 0, 24, 48, 96, and

144 h, respectively. (f) Optical images (inset, a higher magnification) showing the protruded nanotubes from the PAH–Py microcapsules incubated

in pH 0 HCl for 30 h. SEM images of a microcapsule with nanotubes after treatment in pH 0 HCl for (g) 30 h and (h) 72 h, respectively. (i) SEM

image of a microcapsule with nanorods after treatment in pH 2 HCl for 1 h. Reprinted with permission from ref. 196. Copyright 2011, American

Chemical Society.

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The hydrophobic Py–CHO NRs are easily precipitated in

water. In sharp contrast, the PAH–Py NRs with a hydrophilic

and charged PAH layer can be suspended stably in water for at

least 3 months. Because of the charge attraction and coordina-

tion effect of amino groups, AuNPs can be either adsorbed or

in situ synthesized on the PAH–Py NRs surface. It is worth

mentioning that the initial fluorescence emission of Py largely

remained due to the excellent isolation effect of PAH, which

avoids direct contact between Py and the Au NPs. Using a

similar process, other hybrid organic–inorganic functional

nanomaterials with controlled physical and chemical struc-

tures can be synthesized. Therefore, this new approach can

effectively modify organic surfaces with NPs, endowing them

with multiple functions.

6. Biomedical applications

6.1 Drug carriers

The unique colloidal structure of LbL assembled capsules

offers a very versatile platform for encapsulation, storage

and delivery of diverse substances, since those established

techniques form a powerful toolbox to effectively and precisely

control or even tailor their permeability, stimuli-responsiveness

as well as multifunctionalities. These features make the LbL

assembled capsules ideal advanced carriers for delivery diverse

drugs and biotherapeutics, as summarized in the recently

published reviews.8,21,27–29,31,33,34,199,200 Especially, experts in

this field have contributed a theme issue on ‘‘Layer-by-

Layer Self-assembled Nanoshells for Drug Delivery’’ in

Adv. Drug Delivery Rev.201 Many important issues such as

fabrication,202 encapsulation and delivery of diverse drugs and

biotherapeutics,203–205 stimuli-responsive properties,206,207

remote control,208 imaging209 as well as targeting of cancer

cells210 have been comprehensively discussed, which shall not

be repeated in this article. The following sections will focus

only on the very recent progress which is important but less

touched previously.

6.1.1 New encapsulation techniques. Many applications of

the multilayer capsules must face a challenge of efficient

loading of the desired substances, as extensively discussed in

previous review papers.19,25,29,34 This is particularly difficult

for loading of low-molecular-weight and water-soluble species,

which can freely diffuse through the semipermeable walls in

aqueous solutions.211 Small molecules can be encapsulated by

preferred precipitation inside the capsules due to the differences

of physicochemical properties such as pH and solvent polarity

across the capsule wall.212–214 Another versatile and effective

strategy is to preload the hollow capsules with materials which

have high affinity with the substances of interest. This is initially

driven by an unexpected interesting phenomenon that positively

charged molecules can largely deposit into microcapsules

templated on melamine formaldehyde (MF) particles (the

so-called ‘‘spontaneous deposition’’ effect).159 The driving

force for the encapsulation is the existence of a negatively

charged complex PSS–MF within the capsule interior.159

Inspired by this finding, PSS-doped CaCO3 particles are

prepared and used as templates for fabrication of PSS-loaded

capsules,111 which show an intriguing ‘‘charge-controlled

attraction and repulsion’’ effect.111,112 The positively charged

and water soluble substances are automatically and very

effectively loaded into the preformed capsules.163,215 Apparent

concentration of the loaded drugs is up to hundred times of

the bulk.161,162 Nonetheless, challenge still remained to seal the

drugs inside the capsules and then control their release profile

although the strong drug–PE interaction prevents undesired

release to some extent. Kohler et al. demonstrated that

poly(diallyldimethylammonium chloride) (PDADMAC)–PSS

capsules with PSS as the outmost layer can shrink dramatically

at elevated temperature.178,179 The capsule wall becomes

simultaneously thicker and denser, resulting in dextran

Fig. 12 (A) Fabrication of PAH–Py–(PSS–PAH)n double-shell microcapsule (MC) and Py–CHO NRs formation inside the (PSS–PAH)n MC.

(B) The chemical structure of Py–CHO, PAH, and PAH–Py, and the Schiff base formation and hydrolysis. (C) CLSM images of the (PSS–PAH)12MCs containing Py–CHO NRs. Adapted from ref. 197.

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(Mw from 10 kDa to 70 kDa) encapsulation with a slightly

higher concentration than the feeding value.194 The loading of

water-soluble small molecular drugs also can be achieved

using this method.216 In our recent work,217 spontaneous

deposition and heat-induced shrinkage were integrated to

fabricate a drug carrier system, showing a high drug loading

efficiency and more controllable release profile (Fig. 13). The

PDADMAC–PSS capsules are assembled by using PSS-doped

CaCO3 microparticles as templates, so that the resultant

capsules are simultaneously loaded with PSS. While shrinkage

does occur upon heat-treatment, high efficient loading of DOX

is also facilely achieved by a simple incubation. The ratio of

interior drug concentration to that in the bulk of capsules

incubated in 0.5 mg ml�1 DOX solution is as high as 1000. The

heat-treatment does not influence obviously the drug encap-

sulation, whereas the release profiles can be effectively tuned.

Mak et al. recently demonstrated a new method named

matrix-assisted colloidosome reverse-phase LbL which can

encapsulate biomacromolecules in hydrogel microcapsules with

extremely high efficiency and retention stability.218 This method

involves two key steps: preparation of stable biomacromolecules-

loaded hydrogel microbeads (the matrix-assisted colloidosome)

using microparticles as surface stabilizers, which can be dispersed

in organic solvents; and assembly of multilayers on the

microbeads in organic solvents using nonionized PEs by the

LbL method, which prevent diffusion of the highly water-

soluble biomolecules. The encapsulation efficiency of this

method is almost 100% and even after 7 days incubation in

water the retention of encapsulated proteins is still nearly

100%. This method is a valuable addition to the family of

encapsulation techniques through the LbL approach and can

significantly contribute to the fields of bioreactors and biosensors.

In the following work of the same group, encapsulation of

biomacromolecules within microcapsules encoded with a

color/thickness scheme is further demonstrated via a similar

method. The encapsulation and encoding can be simulta-

neously achieved through an inward buildup of concentric

colored layers to create a multicolor layered polymeric shell.219

6.1.2 LbL assembly on smaller particles. Most of the LbL

capsules have a diameter of a few micrometers, which are too

large for intravenous injection. One possible solution is to

assemble multilayers on particles with a smaller size. De Koker

et al. have reviewed the progress of LbL assembly on ultra-

small (sub-100 nm) particles, which are mainly gold NPs.34

The following section shall summarize important examples of pre-

paration of stable nanocolloidal suspensions or surface modifica-

tion of polymeric NPs with a size around 200–300 nm using LbL

assembly. The particles with such a size can be injected into blood

vessels and may accumulate in cancerous tissues through the well-

known enhancer permeability and retention (EPR) effect.

The Lvov group recently reported a sonication-assisted LbL

PE coating method for non- or low-water soluble drug

NPs.220–223 Two different strategies are used.222 In the top-

down approach, nanocolloids are prepared by rupturing a

big drug powder under ultrasonication and simultaneously

adsorbed with oppositely charged PEs in a sequential manner.

In the bottom-up approach the drug is first dissolved in good

solvent (ethanol or acetone), which is miscible with water.

Drug nucleation is initiated by addition of aqueous PE

solution under ultrasonication, and the formed particles are

then sequentially coated with multilayers (Fig. 14). The stable

nanocolloids with a size in the range of 60–200 nm and a very high

drug content (up to 90%) have been successfully fabricated.223

The multilayers on the nanocolloids can not only facilitate

their stable dispersion in aqueous solution but also control

Fig. 13 (a) Schematic illustration to show the high efficient loading of low-molecular-weight drugs into polyelectrolyte encapsulated multilayer

capsules through the combination of spontaneous deposition and heat-induced shrinkage. The blue layer refers to the stable complex or adsorbed

layer, which is formed by the first PDADMAC layer and liberated PSS molecules during the core removal process. The pale blue rhombus refers to

the shrunk and reorganized capsule wall. (b) SEM images of PSS–(PDADMAC–PSS)5 capsules and (c) TEM image of a ultrathin section of the

capsules after being incubated at 80 1C for 20 min. (d) CLSM image of PSS–(PDADMAC–PSS)5 capsules loaded with DOX by incubation at 80 1C

for 20 min. The inset shows the corresponding SEM image. Adapted from ref. 217.

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the sustained release pattern. This method is universal for

many low water-soluble substances ranging from anticancer

drugs to anticorrosion agents, dyes and inorganic salts. The

multilayers can be easily further integrated with additional

functions, such as specific targeting ligands. This may

represent a novel approach to conveniently formulate poorly

soluble drugs.

Drug controlled delivery systems based on polymeric bio-

degradable NPs are mostly investigated. Particularly, bio-

degradable and non-toxic polyester-poly(lactide-co-glycolide)

(PLGA) is one of the commonly used polymers for drug

delivery.224,225 Modification of the NPs surface with targeting

molecules can enhance the drug concentration in the targeted

organs or tissues, and reduce the dosage and toxic side effects.

In order to effectively immobilize the ligands, the NPs should

possess enough number of active groups and are required to be

stable enough to allow the chemical reactions. The LbL

assembly can endow the NPs with multi-properties such as

uniform surface charge density, numerous active groups and

excellent stability in various mediums. In this regard, macro-

molecules-coated PLGA NPs with a size of about 300 nm are

fabricated via an O/W emulsion-solvent evaporation method

by adding PEI or BSA in the water phase. PAA/PEI and

CS/alginate (CS/ALG) are then used to build multilayers on

the PLGA NPs for further immobilization of PEG and folic

acid aiming at long time circulation and targeting.226,227

Release property of the dyes preloaded in the NPs is greatly

affected by surface charge and structure of the multilayers

assembled on the NPs.228 A negatively charged or PEGylated

surface can reduce protein adsorption too, whereas surface

decoration with folic acid can enhance the NP uptake by

human hepatoma cells.

The multilayers also can be assembled on the NPs before

drug loading. This strategy allows the loading of different

drugs into the preformed multilayers-coated particles. Shutava

et al. reported the LbL multilayers-coated gelatin NPs with a

size of 200–300 nm as a vehicle for delivery of natural

polyphenols.229 Using the post-loading strategy, diverse natural

polyphenols are encapsulated and their biological activity is

retained. In our recent work,230 BSA NPs with a size of about

200 nm were coated with PAH–PSS multilayers, onto which a

layer of PAH-g-PEG–COOH is further adsorbed. By conden-

sation of carbodiimide chemistry aptamer-AS1411 molecules

which can target over-expressed nucleolin on the cancer cell

membrane231,232 are then immobilized (Fig. 15). The PEGylated

multilayers-coated BSA NPs show good suspension stability in

diverse mediums in particular serum containing medium.233 By

a mechanism of spontaneous deposition, DOX is effectively

loaded into the pre-formed BSA NPs with both good encapsu-

lation efficiency (98.6%) and loading percentage (9%). The

loaded drugs show a pH-dependent release behavior, i.e. faster

at pH 5.5 than at pH 7.4. The multilayers coating does not

bring significant influences on both drug loading and release.

Fig. 14 (a) Schematic representation of ultrasonication-assisted LbL assembly using the top-down approach. Ultrasonication is applied to break

down the paclitaxel powder and re-aggregation is prevented by adsorption of polyelectrolytes. (b) Schematic representation of ultrasonication-

assisted LbL assembly using the bottom-up approach. Nanoparticulation of paclitaxel dissolved in ethanol solvent is initiated by ultrasonication

and with addition of aqueous polycations. Adapted from ref. 222 with permission from the PCCP Owner Societies.

Fig. 15 Schematic illustration to show the preparation process of

BSA nanoparticles coated with PAH–PSS multilayers and coupled

with aptamer AS1411. Reproduced from ref. 230.

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In vitro cell culture demonstrates that the as-prepared BSA

NPs are specifically delivered to liver cancer cells, leading to

higher cellular uptake and cytotoxicity.

6.1.3 Capsules squeeze through a confined capillary. As

mentioned above, most of the LbL capsules have a diameter

of a few microns, which are easier for preparation and

property manipulation compared with their nanometer-sized

counterparts.234 Thus, for application of intravenous injection

smaller capsules are generally designed. However, Nature

takes a different way. A fascinating characteristic of a red

blood cell (RBC) is its extreme reversible deformability under

physiological flow, so that it can easily pass through the

smallest blood capillary vessel (B3 mm). Generally, the size

of multilayer microcapsules is pretty big and is comparable to

that of human RBC (about 7 mm). It is conceivable that the

microcapsules have to face the same challenge of passing

through the blood capillary vessel as the RBCs do, if they

similarly circulate in the blood stream. Therefore, their

deformability and recovery after passing through a thin capillary

channel is of practical importance and highly deserved to

explore. One can imagine that if the capsules have proper

shape and flexibility, they may easily squeeze through narrow

capillary as well. Indeed, the deformability of polymeric

microparticles (mainly hydrogel microparticles) with different

shapes and sizes through a narrow constriction has been

studied under flow conditions. For example, Doshi et al.

fabricated 7 mm RBC-mimicking particles, which are flexible

enough to flow through narrow glass capillaries (5 mm inner

diameter) and able to recover to discoidal shape.235 Hayashi

et al. fabricated 3.5 mm biconcave disk-shaped particles by

electrospraying of cellulose derivative ethylhydroxyethylcellulose

(EHEC), which can maintain RBC-like shape after filtrating

through a membrane with a pore size of 1 mm.236 Haghgooie

et al. synthesized PEG hydrogel particles with different shapes

including disks, rings, crosses, and S-shapes, and demonstrated

the modes of particles’ passage through poly(dimethyl siloxane)

(PDMS) channels.237 Very recently, the mechanical properties

and flow behavior of large capsules (tens of microns) made of

cross-linked ovalbumin have been investigated by the Leclerc

group.238 However, for the multilayer capsules with a size

comparable to that of human RBC, little is known about their

deformation behavior under flow in a microchannel with a

smaller size,239 although the static deformation behavior has

been systematically studied under the press of a colloidal

probe240 or osmotic pressure.116,117 Recently, a first step toward

the multilayer microcapsules’ deformability under flow in a

confined microchannel has been attempted in our group by

using the spherical PAH–PSS microcapsules either pre-filled

with PSS or not (Fig. 16).241 The influences of capsules size, wall

thickness, cross-linking as well as the filling of PSS inside on

the deformation and recovery behavior of the capsules are

systematically investigated. It is the deformation extent but

not mechanical strength that governs the recovery ability of

capsules. The squeezed hollow microcapsules can recover

their original spherical shape when the deformation extent is

smaller than 16% (reversible deformation), whereas per-

manent physical deformation takes place at a larger deforma-

tion extent such as 34%. The capsules with a thicker wall

(or namely stronger mechanical strength) can better resist the

water flow-induced deformation with a slower passing through

rate. In sharp contrast, all the intact capsules pre-filled with

PSS can recover their original shape although the deformation

extent is as large as 47%. The spontaneously deposited dyes

are well retained after the deformation and recovery process.

To the best of our knowledge, it is the first time to disclose the

alteration of drug amounts in multilayer microcapsules after

squeezing through a constriction. Yet this is only the first step

toward the fabrication of RBC-mimicking multilayer capsules.

Nonetheless, the current results are important not only for

understanding of capsule properties but also for their practical

applications as drug delivery carriers. For example, the capsules

for injection application should have a smaller size and soft wall

structure, while those for embolization should have a stiff wall

which can clog the blood vessels with higher efficiency.

6.2 Biosensors

Because of the convenient and diverse protocols for integration of

assay elements, the LbLmicrocapsules and microparticles are one

of the ideal platforms for sensing applications. Another important

advantage is that the analyte-sensitive and reference fluoro-

chromes can be simultaneously incorporated into a same capsule,

allowing precise ratiometric measurements. The examples of

biosensors based on LbL microcapsules have been first demon-

strated by theMcShane group, with a focus on glucose as a model

analyte.35,242–248 More recently, this concept has been extended to

pH, ions as well as nitric oxide sensing.

The pH sensor based on LbL multilayer microcapsules was

first reported by Kreft et al.249 Mobile pH-sensors are developed

for monitoring the local pH inside living cells (Fig. 17). The

pH-sensitive, high molecular weight SNARF-1–dextran conjugate

molecules are doped into CaCO3 particles via a coprecipitation

method.250 Microcapsules are loaded with SNARF-1–dextran

after assembly of multilayers and subsequent core removal.

SNARF-1 exhibits a significant pH-dependent emission shift

from green to red under acidic and basic conditions, respec-

tively. Its unique spectral properties are maintained after

encapsulation as well. Therefore, pH change of the local

Fig. 16 Scheme drawing to show the structure of the microchannel

device by (a) top view and (b) side view. CLSM images of the 6.8 mm(c) and 8.6 mm (d) (PAH–PSS)5 microcapsules after being squeezed

through the microchannel with a height of 5.7 mm. The former can

recover its original spherical shape (c), while the latter keeps its

deformed shape (d). Adapted with permission from ref. 241. Copyright

2012, American Chemical Society.

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environments can be monitored by the SNARF-1-filled capsules

during their transition from alkaline cell culture medium to

acidic endosomal/lysosomal compartments of human breast

cancer cells and fibroblasts. Based on this pH sensor, a flow-

cytometry-based assay has been developed with which the

uptake of multilayer capsules can be quantified.251 Capsules

on the outer cell membrane emit red fluorescence due to the

alkaline pH of medium, whereas capsules internalized by cells

emit green fluorescence due to the acidic pH in the endosomal/

lysosomal/phagosomal compartments in which incorporated

capsules are located. Thus, by recording the fluorescence

intensities in the red and green channels the localization of

capsules associated with cells can be distinguished. More

detailed analysis of particle uptake can be quantitatively

achieved by this method too.251 The pH sensor also can be

used as an intracellular optical reporter for monitoring lyso-

somal pH changes upon stimulation by some agents.252

Other active or reporting agents can be integrated into the

multilayers and cores too, which are useful to follow the

processing of such particles within targeted cells. Recently,

Reibetanz et al. designed an LbL assembled, biopolymer-

based multilayer system by combining a transporter and a

pH sensor for monitoring intracellular degradation and

processing.253–255 For this purpose, calcium carbonate particles

are functionalized with fluorescein isothiocyanate-labeled PAH

(FITC–PAH) which allows identification of particle localization

in cell compartments of different pH.256 Plasmid DNA as a

reporter agent for drug release in the cytoplasm and dye-

labeled protamine (PRM) are integrated into biocompatible

and biodegradable PRM/dextran sulfate multilayers. Uptake

and processing of the particles by cells are investigated via flow

cytometry and CLSM. They found a clear connection between

expression of the fluorescent proteins and the particle localiza-

tion in the cells. The multifunctional LbL system has some

advantages over other available systems, such as monitoring

of the degradation and processing of the carriers in live cells

without the demand of additional cell-staining.

Using the similar encapsulation strategies, other types of

biosensors based on LbL multilayer capsules are fabricated

too. For example, ion sensors are obtained by encapsulation of

ion-sensitive fluorophores-conjugated dextrans into the multi-

layer microcapsules. Since the capsule walls are permeable to

ions, the fluorescence of the capsules is tuned by ion concen-

tration. Furthermore, additional fluorophores with different

emission wavelengths and being independent of ion concen-

tration can be co-encapsulated, allowing for more precise

ratiometric measurements.257 By incorporation of a unique

quantum dot (QD) barcode into their outermost walls as a tag

for identification of individual sensors, this kind of barcoded

sensor capsules can be used for multiplexed analysis of proton,

sodium, and potassium ions in parallel.258

Quantitative, kinetic, and spatial analyses of the extracellular

delivery of nitric oxide (NO) molecules from the endothelial cell

(EC) layer to the smooth muscle cell (SMC) layer of blood

vessels upon drug stimulation are crucial for pharmaceutical and

biomedical evaluations of hypertension and diabetes.259 By

embedding an NO fluorescent probe, 4,5-diaminofluorescein

(DAF-2), into porous silica microparticles followed by LbL

assembly of chitosan and dextran sulfate (DS), biocompatible

particles with high NO sensitivity are fabricated.260 When the

NO sensors are allocated into each cellular layer, they can

spatially and quantitatively analyze NO diffusion from the EC

layer to the SMC layer using a 3D artery model (Fig. 18).261 The

3D artery model is constructed through an in vitro hierarchical

cell manipulation technique by fabrication of a nanometer-sized

extracellular matrix (ECM) through assembly of fibronectin

(FN)–gelatin(G) LbL films on the surface of each cell

layer.262–264 During this process the NO sensors can be

incorporated into each cellular layer. A graded concentration

change of NO from the uppermost human aortic endothelial

cell (HAEC) layer to the underlying human aortic smooth

muscle cell (AoSMC) layer is then elucidated by 3D analysis

using CLSM, demonstrating the effectiveness of this strategy.

6.3 Bioreactors

Inspired by nature cells, capsules and vesicles are ideal model

systems for transportation, catalysis and protection.265 The

LbL multilayer capsules are particularly suitable for such kinds

of investigations due to their precisely controllable structures

and functionalities.25 The LbL microcapsules are first employed

to encapsulate enzymes for bio-mineralization,266,267 enzyme-

catalyzed polymerization,268,269 and bienzyme reaction.270,271

Although most of the reactions take place inside the capsules,

they can be indeed performed in the multilayer walls as well.272

Li and co-works recently constructed a type of bienzyme

microcapsules,273 exemplified by hemoglobin/glucose oxidase

(HB/GOD capsules)274 and catalase/GOD (Cat/GOD capsules)275

Fig. 17 SNARF-loaded capsules change from red to green fluores-

cence upon internalization by MDA-MB435S breast cancer cells.

(A) SNARF-fluorescence after adding the capsules to the cell culture

and 30 min equilibration. Most of the capsules were outside of the cells

and exhibited red fluorescence due to the alkaline pH of the medium.

(B) The same cells after another 30 min of incubation. Capsules

remaining in the cell medium retained their red fluorescence (red arrows).

Capsules that were already incorporated into the acidic endosome in the

first image retained their green fluorescence (green arrows). Some

capsules were incorporated into endosomal/lysosomal compartments

inside cells within the period of 30 min, which is indicated by their

change in fluorescence from red to green (red to green arrows). Both

images comprise an overlay of microscopy images obtained with phase

contrast, a red and a green filter set. (C) Schematic presentation of the

endocytotic capsule uptake. Reproduced from ref. 249.

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through GA-mediated covalent LbL assembly.67 Both of the

systems are glucose-sensitive and can be used to control the

release of encapsulated insulin.

More recently, the individual polymerase chain reaction

(PCR) has been performed in LbL multilayer microcapsules

(‘‘Microcapsule-PCR’’).276 In this method, the first step is to

encapsulate PCR reagents, such as polymerase, primers and

templates, which are all macromolecules. Briefly, the PCR

reaction mixture and a matrix material (agarose) are emulsi-

fied at relatively high temperature to form microdroplets and

then cooled down to form solid agarose microbeads. LbL

assembly of multilayers on the microbeads leads to encapsula-

tion of the PCR reagents. Due to the semi-permeability of the

multilayer wall, during the PCR low-molecular-weight building

blocks, nucleotides (dNTPs) can diffuse freely into the interior,

while the resulting high-molecular-weight PCR products are

trapped inside the microcapsules. This microcapsule–PCR system

has good stability against annealing, and the individual micro-

capsule compartment does not exchange templates or primers

between each other. A similar strategy is also employed to

synthesize RNA in polymer hydrogel microcapsules.277

The encapsulated DNA also can be enzymatically degraded

under external stimuli.278 This reaction can be carried out in

a synthetic micro-reactor constructed by coencapsulating

double-stranded DNA and enzyme DNase I in multilayered

polymeric capsules. The semipermeable nature of the capsule

wall affords control over the reaction with added low-

molecular-weight chemicals, and the reaction is restricted

inside the capsules. This reaction is the first example of a

triggered degradation of DNA within a polymer reaction

vessel, which may mimic the lysosomal degradation of proteins

and nucleic acids within living cells.

The recent advances in fabrication of highly sophisticated

microcapsules with subcompartments offer new opportunities

for manipulation of more complicated reactions inside cap-

sules, which can better mimic cell functions.38,151 The first

example is the LbL microcapsules with a shell-in-shell structure

for integrated and spatially confined enzymatic reactions.140

Such two-compartment capsules exhibit exciting potential for

biomedical reactions in a confined small space. The barriers

between the integrated components can be remotely removed,

enabling mixing and, hence, the start of a reaction by an

external trigger.279 More recently, significant progress in the

bio-reactions in multi-compartmental microcapsules has been

made by the Caruso group.146,147,151,280–282 They developed a

strategy to incorporate intact liposomes into the LbL capsule

walls or inside the capsules to prepare ‘‘capsosomes’’.

Enzymes are loaded into the liposomes with well retained

activity. The enzyme reactions are triggered either by increasing

temperature to the phase transition temperature of the lipo-

somes, resulting in a disordered phase of the lipid membrane and

thereby allowing substrates to cross the membrane,147,281,282

or simply by adding surfactants to destroy the liposomes and

release the enzyme (Fig. 19).144 In the former strategy, the

encapsulated enzymes can be utilized repeatedly in several

subsequent conversions. More sophisticated capsosomes with

triggered cargo release property are also designed by coencap-

sulation of glutathione reductase-loaded liposomes and

disulfide-linked polymer–oligopeptide into capsosomes.281

The unique architecture of the capsosomes enables conversion

of oxidized glutathione to its reduced form by the encapsu-

lated glutathione reductase under elevated temperature. The

reduced glutathione can subsequently induce the release of

encapsulated oligopeptides from the capsosomes by cutting

the disulfide linkages of the conjugates. This study highlights

the potential of capsosomes to perform complicated enzymatic

reactions. Yashchenok et al. also reported a multi-compartmental

colloidal system by decorating a larger CaCO3 microparticle

with smaller liposomes. The CaCO3 microparticle and lipo-

somes are separately loaded with enzyme and the corre-

sponding substrate. Enzymatic reaction can be then triggered

by disruption of liposomes by ultrasonication.283

Adenosine triphosphate (ATP) synthase (ATPase) is called

‘‘molecular motor’’, and plays an essential role in the activities

of cells and regulates specific functions through their stimuli-

responsive mechanical motions.284 Integration of such natural

active proteins into engineered biomimetic microcapsules

results in novel properties and functions. Li and co-workers

Fig. 18 Schematic illustration of the in vitro spatial and quantitative analyses of NO diffusion from the uppermost EC layer to the SMC layer in a

3D artery model. Biocompatible sensor particles with high NO sensitivity are allocated into each layer. Reprinted with permission from ref. 261.

Copyright 2011, Wiley-VCH.

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first demonstrated the integration of chloroplastic ATPase

into the microcapsule wall containing a lipid bilayer and

synthesis of ATP by this composite capsule.285,286 The driving

force for ATP synthesis catalyzed by ATPase is provided by an

acid–base transition between the interiors and exteriors of the

capsules. Later on ATPase is also integrated on lipid-coated

hemoglobin287 or glucose oxidase288capsules. ATP can be

synthesized in protein microcapsules by utilizing proton gradients,

which are produced from oxidation and hydrolysis of glucose

catalyzed either by added or the immobilized GOD. The most

recent advance reported by the same group is the construction of

an active biomimetic system by integrating kinesin, microtubule,

and biomimetic microcapsule. The LbL multilayer capsules are

coated with kinesin, which can drive cargos such as vesicles,

proteins, and organelles along microtubules.289–291 Thus, the

microtubules act as tracks for the kinesins which are attached

on capsules, and guide the capsules to move from minus to plus

end. Both of the hollow and filled capsules as cargos are

transported by kinesin motors along microtubules (Fig. 20).292

In their following work the multilayer microcapsules are

attached to microtubules through biotin–avidin interaction,

which act as shuttles to transport the attached microcapsules.293

These approaches provide the great promise to design complex

hybrid nanodevices by using biological motors for mimicking

efficient intracellular transport.

7. Conclusions and outlooks

The LbL assembly technique has become a highly versatile and

powerful platform for fabrication of capsules with tailored

structures, compositions, properties and functions. The

as-prepared capsules have shown their great promise of appli-

cations in many areas of science and technologies. In parti-

cular, recent efforts have been made on the multilayer capsules

assembled by new driving forces and those with highly

sophisticated structures for biomedical applications, including

but not limited to drug carriers, biosensors and bioreactors, as

highlighted in this critical review.

Fig. 19 (a) Temperature-triggered enzymatic conversion. An increase in temperature to the phase transition temperature (Tm) of the liposomes

results in a disordered liquid phase of the lipid membrane, allowing nitrocefin to cross the membrane to be hydrolyzed while retaining the

b-lactamase inside the compartments. Reprinted with permission from ref. 282. Copyright 2010, American Chemical Society. (b) Surfactant-

triggered enzymatic conversion. The enzyme b-lactamase is preloaded into liposomes and is sandwiched between two cholesterol-modified

polymers, which are then embedded inside a polymer capsule. Upon addition of Triton X, the liposomes are destroyed and the enzyme is released,

thus causing the hydrolysis of nitrocefin. Reprinted with permission from ref. 144. Copyright 2009, Wiley-VCH.

Fig. 20 (a) Schematic illustration of a multilayer capsule as a cargo is driven by kinesin motors along a microtubule. (b) Time-lapse images of a

hollow capsule coated by kinesin motors moving along a microtubule. Adapted with permission from ref. 292. Copyright 2009, Elsevier.

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Although the past decade witnessed the significant advances

in this area, challenges are still remaining. First of all, new

fabrication strategies should be always pursued to obtain

capsules with novel structures and properties, which can fulfill

the requirements of new applications. For example, the recent

advances in multi-compartmental capsules have provided new

opportunities for bio-mimicking of the natural cells, resem-

bling some cellular processes in man-made particulate systems.

Particularly, the methods which combine the advantages of

precisely controllable structures and properties with speed-up

and scale-up production processes are highly welcomed. This

is also crucial for the real applications of LbL capsules.

Considering the applications of LbL capsules in biomedical

fields, drug delivery vehicles may be the most possible one in

the near future. However, to reach this aim many obstacles

should be pierced through besides the more efficient fabrica-

tion methods. For example, the in vivo tests of LbL capsules

have been only performed very recently215,294–296 and their

in vivo behavior such as degradation and toxicity is largely

unexplored. Since intravenous injection is the most convenient

way for the in vivo administration of LbL capsules, they are

required to circulate in the bloodstream and have good hemo-

compatibility. Several recent research studies have shown that

coating of blood-compatible multilayers on the ultra-small

(B20 nm)297,298 and submicron (B500 nm)299 particles is

beneficial to obtain injectable capsule drug delivery systems.

Therefore, particles with a submicron size are attractive for

preparation of LbL capsules, which may accumulate in

cancerous tissues through the EPR effect. But the assembly

of multilayers on nano- or submicron size templates is much

more difficult than on their micron-size counterparts. The

conditions for assembly should be carefully adjusted. In sharp

contrast, Nature takes a different strategy for facile passing

through a capillary vessel. RBCs possess the fascinating

characteristic of extreme reversible deformability under physio-

logical flow, and can easily pass through the smallest blood

capillary vessel (B3 mm). Inspired by this fact, the LbL multi-

layer microcapsules with suitable shape, size and flexibility may

mimic the behavior of RBC. Although the first step toward this

aim is attempted,241 more efforts should still be made. Further-

more, integration of specific functional moieties onto the

capsule surface, for example, targeting delivery, can enhance

the bioavailability and reduce side effects. On the basis of model

systems300,301 and in vitro experiments,230,302–304 the efficacy

should be further verified in vivo.

The newly developed fabrication strategies allow for design of

theranostic and synergistic drug delivery systems as well. The

theranostic carriers contain both drug and imaging agents within

a single system. This structure allows the carrier to selectively

accumulate in diseased tissues and simultaneously report their

biochemical andmorphological characteristics, while the synergistic

carriers which carry chemo-, radio- and gene therapeutics can

enhance the treatment efficacy.305,306 Apparently, the carrier

systems need co-encapsulation of various functional species with

a precise control over their structures and properties, which can

be fulfilled by the combination use of LbL and other techniques.

For example, the newly fabricated capsules with multi-

compartments and/or optical sensing ability are ideal candidates

for multi-drug delivery as well as theranostic systems.

Nowadays knowledge and techniques from more and more

multidisciplinary fields are applied to the research and appli-

cations of LbL multilayer capsules. It is undoubtedly that with

the efforts afforded by the experts from fields of chemistry,

materials science, physics, biology as well as pharmaceutics,

the above-mentioned challenges will be met sooner or later.

Meanwhile, with the diverse opportunities provided by new

fabrication strategies, more achievements in this field can be

expected in the future.

Acknowledgements

This study was financially supported by the Natural Science

Foundation of China (51120135001 and 21174130), theMinistry

of Science and Technology of China for the Indo-China

Cooperation (2010DFA51510), PhD Programs Foundation

of Ministry of Education of China (20090101110049),

Zhejiang Provincial Natural Science Foundation of China

(Z4090177 and Y4110064), and Open Project of State Key

Laboratory of Supramolecular Structure and Materials

(sklssm201224).

References

1 G. B. Sukhorukov, A. L. Rogach, B. Zebli, T. Liedl,A. G. Skirtach, K. Kohler, A. A. Antipov, N. Gaponik,A. S. Susha, M. Winterhalter and W. J. Parak, Small, 2005, 1,194–200.

2 G. B. Sukhorukov, A. L. Rogach, M. Garstka, S. Springer,W. J. Parak, A. Munoz-Javier, O. Kreft, A. G. Skirtach,A. S. Susha, Y. Ramaye, R. Palankar and M. Winterhalter,Small, 2007, 3, 944–955.

3 G. Decher and J. D. Hong, Makromol. Chem., Macromol. Symp.,1991, 46, 321–327.

4 G. Decher, Science, 1997, 277, 1232–1237.5 F. Caruso, R. A. Caruso and H. Mohwald, Science, 1998, 282,

1111–1114.6 E. Donath, G. B. Sukhorukov, F. Caruso, S. A. Davis and

H. Mohwald, Angew. Chem., Int. Ed., 1998, 37, 2202–2205.7 E. Kharlampieva and S. A. Sukhishvili, Polym. Rev., 2006, 46,

377–395.8 G. K. Such, A. P. R. Johnston and F. Caruso, Chem. Soc. Rev.,

2011, 40, 19–29.9 Y. J. Zhang, S. G. Yang, Y. Guan, W. X. Cao and J. Xu,

Macromolecules, 2003, 36, 4238–4240.10 A. P. R. Johnston, E. S. Read and F. Caruso,Nano Lett., 2005, 5,

953–956.11 Z. P. Wang, Z. Q. Feng and C. Y. Gao, Chem. Mater., 2008, 20,

4194–4199.12 T. Kida, M. Mouri and M. Akashi, Angew. Chem., Int. Ed., 2006,

45, 7534–7536.13 J. F. Quinn, A. P. R. Johnston, G. K. Such, A. N. Zelikin and

F. Caruso, Chem. Soc. Rev., 2007, 36, 707–718.14 C. S. Peyratout and L. Dahne, Angew. Chem., Int. Ed., 2004, 43,

3762–3783.15 Y. Wang, A. S. Angelatos and F. Caruso, Chem. Mater., 2008, 20,

848–858.16 Y. J. Wang, A. D. Price and F. Caruso, J. Mater. Chem., 2009, 19,

6451–6464.17 A. A. Antipov and G. B. Sukhorukov, Adv. Colloid Interface Sci.,

2004, 111, 49–61.18 B. G. De Geest, N. N. Sanders, G. B. Sukhorukov, J. Demeester

and S. C. De Smedt, Chem. Soc. Rev., 2007, 36, 636–649.19 W. J. Tong and C. Y. Gao, Chem. J. Chin. Univ., 2008, 29,

1285–1298.20 M. F. Bedard, B. G. De Geest, A. G. Skirtach, H. Mohwald and

G. B. Sukhorukov, Adv. Colloid Interface Sci., 2010, 158, 2–14.21 A. P. R. Johnston, G. K. Such and F. Caruso, Angew. Chem.,

Int. Ed., 2010, 49, 2664–2666.

Dow

nloa

ded

by Z

hejia

ng U

nive

rsity

on

14 J

une

2012

Publ

ishe

d on

13

June

201

2 on

http

://pu

bs.r

sc.o

rg |

doi:1

0.10

39/C

2CS3

5088

B

View Online



22 O. I. Vinogradova, J. Phys.: Condens. Matter, 2004, 16,R1105–R1134.

23 A. Fery and R. Weinkamer, Polymer, 2007, 48, 7221–7235.24 Q. He, Y. Cui and J. B. Li, Chem. Soc. Rev., 2009, 38,

2292–2303.25 W. J. Tong and C. Y. Gao, J. Mater. Chem., 2008, 18, 3799–3812.26 A. P. R. Johnston, C. Cortez, A. S. Angelatos and F. Caruso,

Curr. Opin. Colloid Interface Sci., 2006, 11, 203–209.27 B. G. De Geest, S. De Koker, G. B. Sukhorukov, O. Kreft,

W. J. Parak, A. G. Skirtach, J. Demeester, S. C. De Smedt andW. E. Hennink, Soft Matter, 2009, 5, 282–291.

28 B. G. De Geest, G. B. Sukhorukov and H. Mohwald, ExpertOpin. Drug Delivery, 2009, 6, 613–624.

29 L. J. De Cock, S. De Koker, B. G. De Geest, J. Grooten,C. Vervaet, J. P. Remon, G. B. Sukhorukov and M. N.Antipina, Angew. Chem., Int. Ed., 2010, 49, 6954–6973.

30 L. L. del Mercato, P. Rivera-Gil, A. Z. Abbasi, M. Ochs,C. Ganas, I. Zins, C. Sonnichsen and W. J. Parak, Nanoscale,2010, 2, 458–467.

31 K. Ariga, M. McShane, Y. M. Lvov, Q. M. Ji and J. P. Hill,Expert Opin. Drug Delivery, 2011, 8, 633–644.

32 S. De Koker, L. J. De Cock, P. Rivera-Gil, W. J. Parak,R. A. Velty, C. Vervaet, J. P. Remon, J. Grooten and B. G.De Geest, Adv. Drug Delivery Rev., 2011, 63, 748–761.

33 S. De Koker, B. N. Lambrecht, M. A. Willart, Y. van Kooyk,J. Grooten, C. Vervaet, J. P. Remon and B. G. De Geest, Chem.Soc. Rev., 2011, 40, 320–339.

34 S. De Koker, R. Hoogenboom and B. G. De Geest, Chem. Soc.Rev., 2012, 41, 2867–2884.

35 M. McShane and D. Ritter, J. Mater. Chem., 2010, 20,8189–8193.

36 D. G. Shchukin and G. B. Sukhorukov, Adv. Mater., 2004, 16,671–682.

37 B. Stadler, A. D. Price, R. Chandrawati, L. Hosta-Rigau,A. N. Zelikin and F. Caruso, Nanoscale, 2009, 1, 68–73.

38 M. Delcea, A. Yashchenok, K. Videnova, O. Kreft, H. Mohwaldand A. G. Skirtach, Macromol. Biosci., 2010, 10, 465–474.

39 I. Pastoriza-Santos, B. Scholer and F. Caruso, Adv. Funct.Mater., 2001, 11, 122–128.

40 T. Mauser, C. Dejugnat and G. B. Sukhorukov,Macromol. RapidCommun., 2004, 25, 1781–1785.

41 W. J. Tong and C. Y. Gao, Polym. Adv. Technol., 2005, 16,827–833.

42 W. J. Tong, C. Y. Gao and H. Mohwald, Chem. Mater., 2005, 17,4610–4616.

43 H. G. Zhu and M. J. McShane, Langmuir, 2005, 21, 424–430.44 S. A. Sukhishvili and S. Granick, J. Am. Chem. Soc., 2000, 122,

9550–9551.45 S. A. Sukhishvili and S. Granick, Macromolecules, 2002, 35,

301–310.46 S. Y. Yang and M. F. Rubner, J. Am. Chem. Soc., 2002, 124,

2100–2101.47 S. Y. Yang, D. Lee, R. E. Cohen and M. F. Rubner, Langmuir,

2004, 20, 5978–5981.48 V. Kozlovskaya, S. Ok, A. Sousa, M. Libera and

S. A. Sukhishvili, Macromolecules, 2003, 36, 8590–8592.49 V. Kozlovskaya, E. Kharlampieva, M. L. Mansfield and S. A.

Sukhishvili, Chem. Mater., 2006, 18, 328–336.50 V. Kozlovskaya and S. A. Sukhishvili, Macromolecules, 2006, 39,

5569–5572.51 A. N. Zelikin, J. F. Quinn and F. Caruso, Biomacromolecules,

2006, 7, 27–30.52 A. N. Zelikin, Q. Li and F. Caruso, Chem. Mater., 2008, 20,

2655–2661.53 A. L. Becker, A. N. Zelikin, A. P. R. Johnston and F. Caruso,

Langmuir, 2009, 25, 14079–14085.54 S. F. Chong, J. H. Lee, A. N. Zelikin and F. Caruso, Langmuir,

2011, 27, 1724–1730.55 S. F. Chong, R. Chandrawati, B. Stadler, J. Park, J. H. Cho,

Y. J. Wang, Z. F. Jia, V. Bulmus, T. P. Davis, A. N. Zelikin andF. Caruso, Small, 2009, 5, 2601–2610.

56 A. N. Zelikin, Q. Li and F. Caruso, Angew. Chem., Int. Ed., 2006,45, 7743–7745.

57 S. F. Chong, A. Sexton, R. De Rose, S. J. Kent, A. N. Zelikin andF. Caruso, Biomaterials, 2009, 30, 5178–5186.

58 A. L. Becker, N. I. Orlotti, M. Folini, F. Cavalieri, A. N. Zelikin,A. P. R. Johnston, N. Zaffaroni and F. Caruso, ACS Nano, 2011,5, 1335–1344.

59 L. A. Connal, C. R. Kinnane, A. N. Zelikin and F. Caruso, Chem.Mater., 2009, 21, 576–578.

60 C. R. Kinnane, G. K. Such, G. Antequera-Garcia, Y. Yan, S. J.Dodds, L. M. Liz-Marzan and F. Caruso, Biomacromolecules,2009, 10, 2839–2846.

61 C. J. Ochs, G. K. Such, Y. Yan, M. P. van Koeverden andF. Caruso, ACS Nano, 2010, 4, 1653–1663.

62 M. K. M. Leung, G. K. Such, A. P. R. Johnston, D. P. Biswas,Z. Y. Zhu, Y. Yan, J. F. Lutz and F. Caruso, Small, 2011, 7,1075–1085.

63 S. L. Ng, G. K. Such, A. P. R. Johnston, G. Antequera-Garciaand F. Caruso, Biomaterials, 2011, 32, 6277–6284.

64 C. J. Ochs, G. K. Such and F. Caruso, Langmuir, 2011, 27,1275–1280.

65 K. Liang, G. K. Such, Z. Y. Zhu, Y. Yan, H. Lomas andF. Caruso, Adv. Mater., 2011, 23, H273–H277.

66 Z. Q. Feng, Z. P. Wang, C. Y. Gao and J. C. Shen, Adv. Mater.,2007, 19, 3687–3691.

67 W. J. Tong, C. Y. Gao and H. Mohwald, Macromol. RapidCommun., 2006, 27, 2078–2083.

68 W. J. Tong, C. Y. Gao and H. Mohwald, Polym. Adv. Technol.,2008, 19, 817–823.

69 L. Duan, Q. He, X. H. Yan, Y. Cui, K. W. Wang and J. B. Li,Biochem. Biophys. Res. Commun., 2007, 354, 357–362.

70 G. K. Such, E. Tjipto, A. Postma, A. P. R. Johnston andF. Caruso, Nano Lett., 2007, 7, 1706–1710.

71 C. R. Kinnane, G. K. Such and F. Caruso,Macromolecules, 2011,44, 1194–1202.

72 B. G. De Geest, W. Van Camp, F. E. Du Prez, S. C. De Smedt,J. Demeester and W. E. Hennink, Macromol. Rapid Commun.,2008, 29, 1111–1118.

73 B. G. De Geest, W. Van Camp, F. E. Du Prez, S. C. De Smedt,J. Demeester and W. E. Hennink, Chem. Commun., 2008, 190–192.

74 T. Peters, Adv. Protein Chem., 1985, 37, 161–245.75 D. C. Carter and J. X. Ho, Adv. Protein Chem., 1994, 45, 153–203.76 O. P. Rubino, R. Kowalsky and J. Swarbrick, Pharm. Res., 1993,

10, 1059–1065.77 T. K. Lee, T. D. Sokoloski and G. P. Royer, Science, 1981, 213,

233–235.78 W. J. Tong, C. Y. Gao and H. Moehwald, Colloid Polym. Sci.,

2008, 286, 1103–1109.79 Y. Jia, J. B. Fei, Y. Cui, Y. Yang, L. A. Gao and J. B. Li, Chem.

Commun., 2011, 47, 1175–1177.80 W. Wei, L. Y. Wang, L. Yuan, Q. Wei, X. D. Yang, Z. G. Su and

G. H. Ma, Adv. Funct. Mater., 2007, 17, 3153–3158.81 W. Wei, L. Yuan, G. Hu, L. Y. Wang, H. Wu, X. Hu, Z. G. Su

and G. H. Ma, Adv. Mater., 2008, 20, 2292–2296.82 Z. J. Wang, H. Zhu, D. Li and X. R. Yang, Colloids Surf., A,

2008, 329, 58–66.83 L. Gao, J. Fei, J. Zhao, W. Cui, Y. Cui and J. Li, Chem.–Eur. J.,

2012, 18, 3185–3192.84 A. P. R. Johnston, H. Mitomo, E. S. Read and F. Caruso,

Langmuir, 2006, 22, 3251–3258.85 A. P. R. Johnston and F. Caruso, Angew. Chem., Int. Ed., 2007,

46, 2677–2680.86 L. Lee, A. P. R. Johnston and F. Caruso, Biomacromolecules,

2008, 9, 3070–3078.87 N. Kato, L. Lee, R. Chandrawati, A. P. R. Johnston and

F. Caruso, J. Phys. Chem. C, 2009, 113, 21185–21195.88 A. Singh, S. Snyder, L. Lee, A. P. R. Johnston, F. Caruso and

Y. G. Yingling, Langmuir, 2010, 26, 17339–17347.89 L. Lee, F. Cavalieri, A. P. R. Johnston and F. Caruso, Langmuir,

2010, 26, 3415–3422.90 A. P. R. Johnston and F. Caruso, Small, 2008, 4, 612–618.91 A. P. R. Johnston, L. Lee, Y. J. Wang and F. Caruso, Small,

2009, 5, 1418–1421.92 F. Cavalieri, A. Postma, L. Lee and F. Caruso, ACS Nano, 2009,

3, 234–240.93 F. Cavalieri, S. L. Ng, C. Mazzuca, Z. F. Jia, V. Bulmus,

T. P. Davis and F. Caruso, Small, 2011, 7, 101–111.94 F. A. Quiocho, Annu. Rev. Biochem., 1986, 55, 287–315.95 Y. C. Lee and R. T. Lee, Acc. Chem. Res., 1995, 28, 321–327.

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96 R. M. Nelson, A. Venot, M. P. Bevilacqua, R. J. Linhardt andI. Stamenkovic, Annu. Rev. Cell Dev. Biol., 1995, 11,601–631.

97 H. Lis and N. Sharon, Chem. Rev., 1998, 98, 637–674.98 J. W. Becker, G. N. Reeke, B. A. Cunningham and G. M.

Edelman, Nature, 1976, 259, 406–409.99 I. J. Goldstein, C. E. Hollerman and E. E. Smith, Biochemistry,

1965, 4, 876–883.100 Y. Lvov, K. Ariga, I. Ichinose and T. Kunitake, J. Chem. Soc.,

Chem. Commun., 1995, 2313–2314.101 Y. Lvov, K. Ariga, I. Ichinose and T. Kunitake, Thin Solid Films,

1996, 284, 797–801.102 K. Sato, Y. Imoto, J. Sugama, S. Seki, H. Inoue, T. Odagiri,

T. Hoshi and J. Anzai, Langmuir, 2005, 21, 797–799.103 Y. Zhu, W. J. Tong and C. Y. Gao, Soft Matter, 2011, 7,

5805–5815.104 A. Voigt, E. Donath and H. Mohwald, Macromol. Mater. Eng.,

2000, 282, 13–16.105 I. L. Radtchenko, G. B. Sukhorukov, N. Gaponik,

A. Kornowski, A. L. Rogach and H. Mohwald, Adv. Mater.,2001, 13, 1684–1687.

106 V. Dudnik, G. B. Sukhorukov, I. L. Radtchenko andH. Mohwald, Macromolecules, 2001, 34, 2329–2334.

107 Y. Zhu, W. J. Tong, C. Y. Gao and H. Mohwald, J. Mater.Chem., 2008, 18, 1153–1158.

108 W. J. Tong, Y. Zhu and C. Y. Gao, Chem. J. Chin. Univ., 2008,29, 1694–1697.

109 W. J. Tong, Y. Zhu and C. Y. Gao, Colloid Polym. Sci., 2012,290, 233–240.

110 Y. Han, W. Tong, Y. Zhang and C. Gao, Macromol. RapidCommun., 2012, 33, 326–331.

111 W. J. Tong, W. F. Dong, C. Y. Gao and H. Mohwald, J. Phys.Chem. B, 2005, 109, 13159–13165.

112 W. J. Tong, H. Q. Song, C. Y. Gao and H. Mohwald, J. Phys.Chem. B, 2006, 110, 12905–12909.

113 F. Wang, J. Feng, W. Tong and C. Gao, J. Mater. Chem., 2007,17, 670–676.

114 C. Y. Gao, S. Moya, E. Donath and H. Mohwald, Macromol.Chem. Phys., 2002, 203, 953–960.

115 C. Y. Gao, S. Moya, H. Lichtenfeld, A. Casoli, H. Fiedler,E. Donath and H. Mohwald, Macromol. Mater. Eng., 2001,286, 355–361.

116 C. Gao, E. Donath, S. Moya, V. Dudnik and H. Mohwald,Eur. Phys. J. E: Soft Matter Biol. Phys., 2001, 5, 21–27.

117 C. Y. Gao, S. Leporatti, S. Moya, E. Donath and H. Mohwald,Langmuir, 2001, 17, 3491–3495.

118 F. Wang, J. Feng and C. Y. Gao, Colloid Polym. Sci., 2008, 286,951–957.

119 F. Wang, W. J. Tong, J. Li and C. Y. Gao, Macromol. Chem.Phys., 2008, 209, 957–966.

120 S. Polowinski, Prog. Polym. Sci., 2002, 27, 537–577.121 T. Szumilewicz, Macromol. Symp., 2000, 161, 183–190.122 G. Polacco, M. G. Cascone, L. Petarca, G. Maltinti,

C. Cristallini, N. Barbani and L. Lazzeri, Polym. Int., 1996, 41,443–448.

123 Z. Q. Feng, Z. P. Wang, C. Y. Gao and J. C. Shen, Mater. Lett.,2007, 61, 2560–2564.

124 Z. Q. Feng, Z. P. Wang, C. Y. Gao and J. C. Shen, Chem. Mater.,2007, 19, 4648–4657.

125 A. Postma, Y. Yan, Y. J. Wang, A. N. Zelikin, E. Tjipto andF. Caruso, Chem. Mater., 2009, 21, 3042–3044.

126 B. Yu, D. A. Wang, Q. Ye, F. Zhou and W. M. Liu, Chem.Commun., 2009, 6789–6791.

127 H. Lee, S. M. Dellatore, W. M. Miller and P. B. Messersmith,Science, 2007, 318, 426–430.

128 R. Z. Ouyang, J. P. Lei and H. X. Ju, Chem. Commun., 2008,5761–5763.

129 J. W. Cui, Y. J. Wang, A. Postma, J. C. Hao, L. Hosta-Rigau andF. Caruso, Adv. Funct. Mater., 2010, 20, 1625–1631.

130 C. J. Ochs, T. Hong, G. K. Such, J. W. Cui, A. Postma andF. Caruso, Chem. Mater., 2011, 23, 3141–3143.

131 D. V. Volodkin, A. I. Petrov, M. Prevot and G. B. Sukhorukov,Langmuir, 2004, 20, 3398–3406.

132 Y. J. Wang, A. M. Yu and F. Caruso, Angew. Chem., Int. Ed.,2005, 44, 2888–2892.

133 W. J. Tong, W. F. Dong, C. Y. Gao and H. Mohwald,Macromol.Chem. Phys., 2005, 206, 1784–1790.

134 Y. J. Wang, V. Bansal, A. N. Zelikin and F. Caruso, Nano Lett.,2008, 8, 1741–1745.

135 D. H. C. Chang, A. P. R. Johnston, K. L. Wark, K. Breheney andF. Caruso, Angew. Chem., Int. Ed., 2012, 51, 460–464.

136 S. A. Walker, M. T. Kennedy and J. A. Zasadzinski, Nature,1997, 387, 61–64.

137 J. F. Lutz and A. Laschewsky, Macromol. Chem. Phys., 2005,206, 813–817.

138 B. G. De Geest, S. De Koker, K. Immesoete, J. Demeester,S. C. De Smedt and W. E. Hennink, Adv. Mater., 2008, 20,3687–3691.

139 W. C. R. Y. Zhang and P. R. Leduc, Trends Biotechnol., 2008, 26,14–20.

140 O. Kreft, M. Prevot, H. Mohwald and G. B. Sukhorukov, Angew.Chem., Int. Ed., 2007, 46, 5605–5608.

141 O. Kulygin, A. D. Price, S. F. Chong, B. Stadler, A. N. Zelikinand F. Caruso, Small, 2010, 6, 1558–1564.

142 M. Delcea, N. Madaboosi, A. M. Yashchenok, P. Subedi,D. V. Volodkin, B. G. De Geest, H. Mohwald and A. G.Skirtach, Chem. Commun., 2011, 47, 2098–2100.

143 B. G. De Geest, M. J. McShane, J. Demeester, S. C. De Smedtand W. E. Hennink, J. Am. Chem. Soc., 2008, 130, 14480–14482.

144 B. Stadler, R. Chandrawati, A. D. Price, S. F. Chong,K. Breheney, A. Postma, L. A. Connal, A. N. Zelikin andF. Caruso, Angew. Chem., Int. Ed., 2009, 48, 4359–4362.

145 L. Hosta-Rigau, B. Stadler, Y. Yan, E. C. Nice, J. K. Heath,F. Albericio and F. Caruso, Adv. Funct. Mater., 2010, 20, 59–66.

146 R. Chandrawati, B. Stadler, A. Postma, L. A. Connal,S. F. Chong, A. N. Zelikin and F. Caruso, Biomaterials, 2009,30, 5988–5998.

147 L. Hosta-Rigau, S. F. Chung, A. Postma, R. Chandrawati,B. Stadler and F. Caruso, Adv. Mater., 2011, 23, 4082–4087.

148 B. Stadler, R. Chandrawati, K. Goldie and F. Caruso, Langmuir,2009, 25, 6725–6732.

149 C. D. Driever, X. Mulet, A. P. R. Johnston, L. J. Waddington,H. Thissen, F. Caruso and C. J. Drummond, Soft Matter, 2011, 7,4257–4266.

150 R. Chandrawati, S. F. Chong, A. N. Zelikin, L. Hosta-Rigau,B. Stadler and F. Caruso, Soft Matter, 2011, 7, 9638–9646.

151 R. Chandrawati, M. P. van Koeverden, H. Lomas and F. Caruso,J. Phys. Chem. Lett., 2011, 2, 2639–2649.

152 J. F. Gohy, Block copolymer micelles, Springer-Verlag Berlin,Berlin, 2005, vol. 190, pp. 65–136.

153 K. Kataoka, A. Harada and Y. Nagasaki, Adv. Drug DeliveryRev., 2001, 47, 113–131.

154 M. Antonietti, E. Wenz, L. Bronstein and M. Seregina,Adv. Mater., 1995, 7, 1000–1005.

155 B. Dubertret, P. Skourides, D. J. Norris, V. Noireaux,A. H. Brivanlou and A. Libchaber, Science, 2002, 298,1759–1762.

156 Y. Zhu, W. J. Tong, C. Y. Gao and H. Mohwald, Langmuir,2008, 24, 7810–7816.

157 X. D. Li, T. Lu, J. X. Zhang, J. J. Xu, Q. L. Hu, S. F. Zhao andJ. C. Shen, Acta Biomater., 2009, 5, 2122–2131.

158 W. J. Tong, Y. Zhu, Z. P. Wang, C. Y. Gao and H. Mohwald,Macromol. Rapid Commun., 2010, 31, 1015–1019.

159 C. Y. Gao, E. Donath, H. Mohwald and J. C. Shen, Angew.Chem., Int. Ed., 2002, 41, 3789–3793.

160 C. Y. Gao, X. Y. Liu, J. C. Shen and H. Mohwald, Chem.Commun., 2002, 1928–1929.

161 X. Y. Liu, C. Y. Gao, J. C. Shen and H. Mohwald, Macromol.Biosci., 2005, 5, 1209–1219.

162 Z. W. Mao, L. Ma, C. Y. Gao and J. C. Shen, J. ControlledRelease, 2005, 104, 193–202.

163 Q. H. Zhao, S. A. Zhang, W. J. Tong, C. Y. Gao and J. C. Shen,Eur. Polym. J., 2006, 42, 3341–3351.

164 A. A. Antipov, G. B. Sukhorukov, S. Leporatti, I. L.Radtchenko, E. Donath and H. Mohwald, Colloids Surf., A,2002, 198, 535–541.

165 K. Kohler and G. B. Sukhorukov, Adv. Funct. Mater., 2007, 17,2053–2061.

166 B. Radt, T. A. Smith and F. Caruso, Adv. Mater., 2004, 16,2184–2189.

Dow

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167 G. B. Sukhorukov, A. A. Antipov, A. Voigt, E. Donath andH. Mohwald, Macromol. Rapid Commun., 2001, 22, 44–46.

168 C. Y. Gao, H. Mohwald and J. C. Shen, Adv. Mater., 2003, 15,930–933.

169 Z. H. An, C. Tao, G. Lu, H. Mohwald, S. P. Zheng, Y. Cui andJ. B. Li, Chem. Mater., 2005, 17, 2514–2519.

170 Z. H. An, H. Mohwald and J. B. Li, Biomacromolecules, 2006, 7,580–585.

171 W. J. Tong, C. Y. Gao and H. Mohwald, Macromolecules, 2006,39, 335–340.

172 G. Ibarz, L. Dahne, E. Donath and H. Mohwald, Adv. Mater.,2001, 13, 1324–1327.

173 C. Y. Gao, S. Leporatti, S. Moya, E. Donath and H. Mohwald,Chem.–Eur. J., 2003, 9, 915–920.

174 R. Georgieva, R. Dimova, G. Sukhorukov, G. Ibarz andH. Mohwald, J. Mater. Chem., 2005, 15, 4301–4310.

175 K. Kohler, P. M. Biesheuvel, R. Weinkamer, H. Mohwald andG. B. Sukhorukov, Phys. Rev. Lett., 2006, 97.

176 R. J. Zhang, K. Kohler, O. Kreft, A. Skirtach, H. Mohwaldand G. Sukhorukov, Soft Matter, 2010, 6, 4742–4747.

177 K. Glinel, G. B. Sukhorukov, H. Mohwald, V. Khrenov andK. Tauer, Macromol. Chem. Phys., 2003, 204, 1784–1790.

178 K. Kohler, D. G. Shchukin, H. Mohwald and G. B. Sukhorukov,J. Phys. Chem. B, 2005, 109, 18250–18259.

179 K. Kohler, H. Mohwald and G. B. Sukhorukov, J. Phys. Chem.B, 2006, 110, 24002–24010.

180 A. G. Skirtach, A. A. Antipov, D. G. Shchukin andG. B. Sukhorukov, Langmuir, 2004, 20, 6988–6992.

181 X. Tao, J. B. Li and H. Mohwald, Chem.–Eur. J., 2004, 10,3397–3403.

182 A. S. Angelatos, B. Radt and F. Caruso, J. Phys. Chem. B, 2005,109, 3071–3076.

183 K. Katagiri, A. Matsuda and F. Caruso, Macromolecules, 2006,39, 8067–8074.

184 M. Bedard, A. G. Skirtach and G. B. Sukhorukov, Macromol.Rapid Commun., 2007, 28, 1517–1521.

185 Y. Ma, W.-F. Dong, M. A. Hempenius, H. Mohwald andG. Julius Vancso, Nat. Mater., 2006, 5, 724–729.

186 Q. He, W. X. Song, H. Moehwald and J. B. Li, Langmuir, 2008,24, 5508–5513.

187 J. G. Wang, Q. Xiao, H. J. Zhou, P. C. Sun, Z. Y. Yuan, B. H. Li,D. T. Ding, A. C. Shi and T. H. Chen, Adv. Mater., 2006, 18,3284–3288.

188 K. Yu, L. Zhang and A. Eisenberg, Langmuir, 1996, 12,5980–5984.

189 P. H. Tung, S. W. Kuo, S. C. Chan, C. H. Hsu, C. F. Wang andF. C. Chang, Macromol. Chem. Phys., 2007, 208, 1823–1831.

190 K. Sha, D. Li, Y. Li, B. Zhang and J. Wang, Macromolecules,2007, 41, 361–371.

191 F. M. Menger and V. A. Seredyuk, J. Am. Chem. Soc., 2003, 125,11800–11801.

192 Y. F. Zhou and D. Y. Yan, Angew. Chem., Int. Ed., 2005, 44,3223–3226.

193 Y. F. Zhou and D. Y. Yan, J. Am. Chem. Soc., 2005, 127,10468–10469.

194 S. Sadasivan, K. Kohler and G. B. Sukhorukov, Adv. Funct.Mater., 2006, 16, 2083–2088.

195 Z. P. Wang, H. Mohwald and C. Y. Gao, Langmuir, 2011, 27,1286–1291.

196 Z. P. Wang, H. Mohwald and C. Y. Gao, ACS Nano, 2011, 5,3930–3936.

197 Z. P. Wang, M. Y. Liu, Y. Xie and C. Y. Gao, J. Mater. Chem.,2012, 22, 2855–2858.

198 Z. P. Wang, A. G. Skirtach, Y. Xie, M. Y. Liu, H. Mohwald andC. Y. Gao, Chem. Mater., 2011, 23, 4741–4747.

199 A. P. R. Johnston, G. K. Such, S. L. Ng and F. Caruso, Curr.Opin. Colloid Interface Sci., 2011, 16, 171–181.

200 Y. Yan, G. K. Such, A. P. R. Johnston, H. Lomas and F. Caruso,ACS Nano, 2011, 5, 4252–4257.

201 M. M. de Villiers and Y. M. Lvov, Adv. Drug Delivery Rev., 2011,63, 699–700.

202 M. M. de Villiers, D. P. Otto, S. J. Strydom and Y. M. Lvov, Adv.Drug Delivery Rev., 2011, 63, 701–715.

203 E. M. Shchukina and D. G. Shchukin, Adv. Drug Delivery Rev.,2011, 63, 837–846.

204 S. De Koker, L. J. De Cock, P. Rivera-Gil, W. J. Parak,R. A. Velty, C. Vervaet, J. P. Remon, J. Grooten and B. G.De Geest, Adv. Drug Delivery Rev., 2011, 63, 748–761.

205 K. Ariga, Y. M. Lvov, K. Kawakami, Q. Ji and J. P. Hill, Adv.Drug Delivery Rev., 2011, 63, 762–771.

206 K. Sato, K. Yoshida, S. Takahashi and J.-i. Anzai, Adv. DrugDelivery Rev., 2011, 63, 809–821.

207 M. Delcea, H. Mohwald and A. G. Skirtach, Adv. Drug DeliveryRev., 2011, 63, 730–747.

208 M. N. Antipina and G. B. Sukhorukov, Adv. Drug Delivery Rev.,2011, 63, 716–729.

209 H. Ai, Adv. Drug Delivery Rev., 2011, 63, 772–788.210 V. Vergaro, F. Scarlino, C. Bellomo, R. Rinaldi, D. Vergara,

M. Maffia, F. Baldassarre, G. Giannelli, X. Zhang, Y. M. Lvovand S. Leporatti, Adv. Drug Delivery Rev., 2011, 63, 847–864.

211 G. B. Sukhorukov, M. Brumen, E. Donath and H. Mohwald,J. Phys. Chem. B, 1999, 103, 6434–6440.

212 G. Sukhorukov, L. Dahne, J. Hartmann, E. Donath andH. Mohwald, Adv. Mater., 2000, 12, 112–115.

213 I. L. Radtchenko, M. Giersig and G. B. Sukhorukov, Langmuir,2002, 18, 8204–8208.

214 I. L. Radtchenko, G. B. Sukhorukov and H. Mohwald, Int. J.Pharm., 2002, 242, 219–223.

215 Q. H. Zhao, B. S. Han, Z. H. Wang, C. Y. Gao, C. H. Peng andJ. C. Shen, Nanomed.: Nanotechnol., Biol. Med., 2007, 3, 63–74.

216 W. X. Song, Q. He, H. Mohwald, Y. Yang and J. B. Li,J. Controlled Release, 2009, 139, 160–166.

217 W. J. Tong, S. P. She, L. L. Xie and C. Y. Gao, Soft Matter, 2011,7, 8258–8265.

218 W. C. Mak, J. Bai, X. Y. Chang and D. Trau, Langmuir, 2009, 25,769–775.

219 J. H. Bai, S. Beyer, W. C. Mak, R. Rajagopalan and D. Trau,Angew. Chem., Int. Ed., 2010, 49, 5189–5193.

220 Y. M. Lvov, P. Pattekari, X. C. Zhang and V. Torchilin, Lang-muir, 2011, 27, 1212–1217.

221 A. Agarwal, Y. Lvov, R. Sawant and V. Torchilin, J. ControlledRelease, 2008, 128, 255–260.

222 P. Pattekari, Z. Zheng, X. Zhang, T. Levchenko, V. Torchilin andY. Lvov, Phys. Chem. Chem. Phys., 2011, 13, 9014–9019.

223 Z. G. Zheng, X. C. Zhang, D. Carbo, C. Clark, C. A. Nathan andY. Lvov, Langmuir, 2010, 26, 7679–7681.

224 M. L. Hans and A. M. Lowman, Curr. Opin. Solid State Mater.Sci., 2002, 6, 319–327.

225 K. E. Uhrich, S. M. Cannizzaro, R. S. Langer andK. M. Shakesheff, Chem. Rev., 1999, 99, 3181–3198.

226 J. Zhou, G. Romero, E. Rojas, L. Ma, S. Moya and C. Y. Gao,J. Colloid Interface Sci., 2010, 345, 241–247.

227 J. Zhou, G. Romero, E. Rojas, S. Moya, L. Ma and C. Y. Gao,Macromol. Chem. Phys., 2010, 211, 404–411.

228 J. Zhou, S. Moya, L. Ma, C. Y. Gao and J. C. Shen, Macromol.Biosci., 2009, 9, 326–335.

229 T. G. Shutava, S. S. Balkundi, P. Vangala, J. J. Steffan,R. L. Bigelow, J. A. Cardelli, D. P. O’Neal and Y. M. Lvov,ACS Nano, 2009, 3, 1877–1885.

230 L. Xie, W. Tong, D. Yu, J. Xu, J. Li and C. Gao, J. Mater. Chem.,2012, 22, 6053–6060.

231 J. K. Kim, K. J. Choi, M. Lee, M. H. Jo and S. Kim, Biomaterials,2012, 33, 207–217.

232 H. Iwasaki, K. Nabeshima, J. Nishio, S. Jimi, M. Aoki, K. Koga,M. Hamasaki, H. Hayashi and A. Mogi, Pathol. Int., 2009, 59,501–521.

233 L. L. Xie, W. J. Tong, J. Q. Xu and C. Y. Gao, Chin. J. Polym.Sci., 2012, DOI: 10.1007/s10118-012-1156-9.

234 G. Schneider and G. Decher, Langmuir, 2008, 24, 1778–1789.235 N. Doshi, A. S. Zahr, S. Bhaskar, J. Lahann and S. Mitragotri,

Proc. Natl. Acad. Sci. U. S. A., 2009, 106, 21495–21499.236 K. Hayashi, K. Ono, H. Suzuki, M. Sawada, M. Moriya,

W. Sakamoto and T. Yogo, Small, 2010, 6, 2384–2391.237 R. Haghgooie, M. Toner and P. S. Doyle, Macromol. Rapid

Commun., 2010, 31, 128–134.238 Y. Lefebvre, E. Leclerc, D. Barthes-Biesel, J. Walter and

F. Edwards-Levy, Phys. Fluids, 2008, 20.239 M. Prevot, A. L. Cordeiro, G. B. Sukhorukov, Y. Lvov,

R. S. Besser and H. Mohwald, Macromol. Mater. Eng., 2003,288, 915–919.

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240 F. Dubreuil, N. Elsner and A. Fery, Eur. Phys. J. E: Soft MatterBiol. Phys., 2003, 12, 215–221.

241 S. She, C. Xu, X. Yin, W. Tong and C. Gao, Langmuir, 2012, 28,5010–5016.

242 T. A. Duchesne, J. Q. Brown, K. B. Guice, Y. M. Lvov andM. J. McShane, Sens. Mater., 2002, 14, 293–308.

243 M. J. McShane, J. Q. Brown, K. B. Guice and Y. M. Lvov,J. Nanosci. Nanotechnol., 2002, 2, 411–416.

244 S. Chinnayelka and M. J. McShane, Diabetes Technol. Ther.,2006, 8, 269–278.

245 J. Q. Brown, R. Srivastava and M. J. McShane, Biosens.Bioelectron., 2005, 21, 212–216.

246 R. Srivastava, J. Q. Brown, H. G. Zhu and M. J. McShane,Macromol. Biosci., 2005, 5, 717–727.

247 R. Srivastava, J. Q. Brown, H. G. Zhu and M. J. McShane,Biotechnol. Bioeng., 2005, 91, 124–131.

248 R. Srivastava and M. J. McShane, J. Microencapsulation, 2005,22, 397–411.

249 O. Kreft, A. M. Javier, G. B. Sukhorukov and W. J. Parak,J. Mater. Chem., 2007, 17, 4471–4476.

250 A. I. Petrov, D. V. Volodkin and G. B. Sukhorukov, Biotechnol.Prog., 2005, 21, 918–925.

251 M. Semmling, O. Kreft, A. M. Javier, G. B. Sukhorukov, J. Kasand W. J. Parak, Small, 2008, 4, 1763–1768.

252 P. Rivera_Gil, M. Nazarenus, S. Ashraf and W. J. Parak, Small,2012, 8, 943–948.

253 U. Reibetanz, M. H. Chen, Z. Y. Liaw, H. L. Oh, E. Donath andB. Neu, Cytometry, Part A, 2009, 75, 714–715.

254 U. Reibetanz, M. H. A. Chen, S. Mutukumaraswamy,Z. Y. Liaw, B. H. L. Oh, S. Venkatraman, E. Donath andB. Neu, Biomacromolecules, 2010, 11, 1779–1784.

255 U. Reibetanz, M. H. A. Chen, S. Mutukumaraswamy,Z. Y. Liaw, B. H. L. Oh, E. Donath and B. Neu, J. Biomater.Sci., Polym. Ed., 2011, 22, 1845–1859.

256 D. Halozan, U. Riebentanz, M. Brumen and E. Donath, ColloidsSurf., A, 2009, 342, 115–121.

257 L. L. del Mercato, A. Z. Abbasi and W. J. Parak, Small, 2011, 7,351–363.

258 L. L. del Mercato, A. Z. Abbasi, M. Ochs and W. J. Parak,ACS Nano, 2011, 5, 9668–9674.

259 L. J. Ignarro, G. M. Buga, K. S. Wood, R. E. Byrns andG. Chaudhuri, Proc. Natl. Acad. Sci. U. S. A., 1987, 84, 9265–9269.

260 S. Amemori, M. Matsusaki and M. Akashi, Chem. Lett., 2010,42–43.

261 M. Matsusaki, S. Amemori, K. Kadowaki and M. Akashi,Angew. Chem., Int. Ed., 2011, 50, 7557–7561.

262 M. Matsusaki, K. Kadowaki, Y. Nakahara and M. Akashi,Angew. Chem., Int. Ed., 2007, 46, 4689–4692.

263 K. Kadowaki, M. Matsusaki and M. Akashi, Biochem. Biophys.Res. Commun., 2010, 402, 153–157.

264 K. Kadowaki, M. Matsusaki and M. Akashi, Langmuir, 2010, 26,5670–5678.

265 D. Lensen, D. M. Vriezema and J. C. M. van Hest, Macromol.Biosci., 2008, 8, 991–1005.

266 A. Antipov, D. Shchukin, Y. Fedutik, I. Zanaveskina,V. Klechkovskaya, G. Sukhorukov and H. Mohwald, Macromol.Rapid Commun., 2003, 24, 274–277.

267 A. M. Yu, I. Gentle, G. Q. Lu and F. Caruso, Chem. Commun.,2006, 2150–2152.

268 R. Ghan, T. Shutava, A. Patel, V. T. John and Y. Lvov, Macro-molecules, 2004, 37, 4519–4524.

269 T. Shutava, Z. G. Zheng, V. John and Y. Lvov, Biomacromolecules,2004, 5, 914–921.

270 N. G. Balabushevich, G. B. Sukhorukov and N. I. Larionova,Macromol. Rapid Commun., 2005, 26, 1168–1172.

271 E.W. Stein, D. V. Volodkin,M. J.McShane andG. B. Sukhorukov,Biomacromolecules, 2006, 7, 710–719.

272 P. Pescador, J. L. Toca-Herrera, E. Donath and I. Katakis,Langmuir, 2008, 24, 14108–14114.

273 W. Qi, L. Duan and J. B. Li, Soft Matter, 2011, 7, 1571–1576.274 W. Qi, X. H. Yan, L. Juan, Y. Cui, Y. Yang and J. B. Li,

Biomacromolecules, 2009, 10, 1212–1216.

275 W. Qi, X. H. Yan, J. B. Fei, A. H. Wang, Y. Cui and J. B. Li,Biomaterials, 2009, 30, 2799–2806.

276 W. C. Mak, K. Y. Cheung and D. Trau, Adv. Funct. Mater., 2008,18, 2930–2937.

277 A. D. Price, A. N. Zelikin, K. L. Wark and F. Caruso, Adv.Mater., 2010, 22, 720–723.

278 A. D. Price, A. N. Zelikin, Y. J. Wang and F. Caruso, Angew.Chem., Int. Ed., 2009, 48, 329–332.

279 O. Kreft, A. G. Skirtach, G. B. Sukhorukov and H. Mohwald,Adv. Mater., 2007, 19, 3142–3145.

280 H. Lomas, A. P. R. Johnston, G. K. Such, Z. Y. Zhu, K. Liang,M. P. van Koeverden, S. Alongkornchotikul and F. Caruso,Small, 2011, 7, 2109–2119.

281 R. Chandrawati, P. D. Odermatt, S. F. Chong, A. D. Price,B. Stadler and F. Caruso, Nano Lett., 2011, 11, 4958–4963.

282 R. Chandrawati, L. Hosta-Rigau, D. Vanderstraaten, S. A.Lokuliyana, B. Stadler, F. Albericio and F. Caruso, ACS Nano,2010, 4, 1351–1361.

283 A. M. Yashchenok, M. Delcea, K. Videnova, E. A. Jares-Erijman,T. M. Jovin, M. Konrad, H. Mohwald and A. G. Skirtach, Angew.Chem., Int. Ed., 2010, 49, 8116–8120.

284 M. G. L. van den Heuvel and C. Dekker, Science, 2007, 317,333–336.

285 L. Duan, Q. He, K. W. Wang, X. H. Yan, Y. Cui, H. Moewaldand J. B. Li, Angew. Chem., Int. Ed., 2007, 46, 6996–7000.

286 Q. He, L. Duan, W. Qi, K. W. Wang, Y. Cui, X. H. Yan andJ. B. Li, Adv. Mater., 2008, 20, 2933–2937.

287 W. Qi, L. Duan, K. W. Wang, X. H. Yan, Y. Citi, Q. He andJ. B. Li, Adv. Mater., 2008, 20, 601–605.

288 L. Duan, W. Qi, X. H. Yan, Q. He, Y. Cui, K. W. Wang, D. X. Liand J. B. Li, J. Phys. Chem. B, 2009, 113, 395–399.

289 K. J. Bohm, R. Stracke, P. Muhlig and E. Unger, Nanotechnology,2001, 12, 238–244.

290 R. Stracke, K. J. Bohm, J. Burgold, H. J. Schacht and E. Unger,Nanotechnology, 2000, 11, 52–56.

291 Q. Chen, D. Y. Li and K. Oiwa, Biophys. Chem., 2007, 129,60–69.

292 W. X. Song, Q. He, Y. Cui, H. Mohwald, S. Diez and J. B. Li,Biochem. Biophy. Res. Commun., 2009, 379, 175–178.

293 W. X. Song, H. Mohwald and J. B. Li, Biomaterials, 2010, 31,1287–1292.

294 S. De Koker, B. G. De Geest, C. Cuvelier, L. Ferdinande,W. Deckers, W. E. Hennink, S. De Smedt and N. Mertens,Adv. Funct. Mater., 2007, 17, 3754–3763.

295 A. Sexton, P. G. Whitney, S. F. Chong, A. N. Zelikin, A. P. R.Johnston, R. De Rose, A. G. Brooks, F. Caruso and S. J. Kent,ACS Nano, 2009, 3, 3391–3400.

296 S. Facca, C. Cortez, C. Mendoza-Palomares, N. Messadeq,A. Dierich, A. P. R. Johnston, D. Mainard, J. C. Voegel,F. Caruso and N. Benkirane-Jessel, Proc. Natl. Acad. Sci. U. S. A.,2010, 107, 3406–3411.

297 Z. Poon, D. Chang, X. Y. Zhao and P. T. Hammond, ACS Nano,2011, 5, 4284–4292.

298 Z. Poon, J. B. Lee, S. W. Morton and P. T. Hammond, NanoLett., 2011, 11, 2096–2103.

299 L. Yu, Y. G. Gao, X. L. Yue, S. Q. Liu and Z. F. Dai, Langmuir,2008, 24, 13723–13729.

300 J. Feng, B. Wang, C. Y. Gao and J. C. Shen, Adv. Mater., 2004,16, 1940–1944.

301 B. Wang, Q. H. Zhao, F. Wang and C. Y. Gao, Angew. Chem.,Int. Ed., 2006, 45, 1560–1563.

302 M. Fischlechner, O. Zschornig, J. Hofmann and E. Donath,Angew. Chem., Int. Ed., 2005, 44, 2892–2895.

303 C. Y. Peng, Y. Y. Zhang, W. J. Tong and C. Y. Gao, J. Appl.Polym. Sci., 2011, 121, 3710–3716.

304 C. Cortez, E. Tomaskovic-Crook, A. P. R. Johnston, B. Radt,S. H. Cody, A. M. Scott, E. C. Nice, J. K. Heath and F. Caruso,Adv. Mater., 2006, 18, 1998–2003.

305 X. Chen, S. S. Gambhir and J. Cheon, Acc. Chem. Res., 2011, 44,841–841.

306 T. Lammers, S. Aime, W. E. Hennink, G. Storm and F. Kiessling,Acc. Chem. Res., 2011, 44, 1029–1038.

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