Project Number: MQP TAC-FR08 Alginate Polymers for Drug Delivery A Major Qualifying Project Report submitted to the Faculty of WORCESTER POLYTECHNIC INSTITUTE in fulfillment of the requirements for the Degree of Bachelor of Science by Michael Brunetti Anne St. Martin Date: April 27, 2006 Approved: ______________________________________ Professor Terri A. Camesano, Advisor ______________________________________ Professor W. Grant McGimpsey, Co-Advisor
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5/12/2018 Modified Alginate Polymers for Drug Delivery 2006 - slidepdf.com
Acknowledgements........................................................................................................ i
Abstract.......................................................................................................................... ii
Table of Contents ......................................................................................................... iii Table of Figures............................................................................................................. v
Alginate Chemistry......................................................................................................................................................4 Sources of Alginate...................................................................................................................................................4 Chemical Structure ...................................................................................................................................................5
Gel Formation..............................................................................................................................................................6 Large Bead Preparation.............................................................................................................................................7 Matrix Gels, Fibers, and In Situ Gelling Systems.....................................................................................................7 Microbead Preparation..............................................................................................................................................8 Alginate as Surfactant in Emulsion Bead Formation ........... .......... ........... .......... ........... .......... ........... .......... ........... .9 Emulsion Formation .................................................................................................................................................9 Polymeric Surfactants .............................................................................................................................................10 Dry Emulsions ........................................................................................................................................................10
Physical Properties of Alginate Beads .....................................................................................................................11 Chemical Reactivity................................................................................................................................................11 Release of Matrix Encapsulated Particles...............................................................................................................12 Release of Emulsion Encapsulated Particles...........................................................................................................12
Biological Properties of Alginate..............................................................................................................................15 Immunogenicity......................................................................................................................................................15 Bioadhesion ............................................................................................................................................................16
Possible Applications of Alginate Polymer Controlled Drug Release Systems ....................................................16
Analysis of Chemical Properties of Lidocaine.........................................................................................................20 Extinction Coefficient Determination.....................................................................................................................21 Solubility of Lidocaine ...........................................................................................................................................22 Partition Coefficient (Kp) ........................................................................................................................................22 Oil Purity ................................................................................................................................................................23
Appendix B: Data ........................................................................................................ 58
B.1. Particle Sizer Data .............................................................................................................................................58
Table of FiguresFigure 1. Blood Circulation Drug Level With Oral Drug Delivery (a) and Controlled Drug Delivery (b) ........... ......2 Figure 2. The chemical structure of alginate with β -D-mannuronic (M) acid blocks and α -L-gluronic (G) acid
blocks ..........................................................................................................................................................6 Figure 3. Egg-Box association of poly-L-guluronate sequences of alginate and conversion of random coils to
ribbon structures when cross-linked with calcium ions...............................................................................7 Figure 4. (A) Two immiscible liquids not emulsified (B) An emulsion of phase B dispersed in Phase A (C) The
In the field of medicinal chemistry a substantial challenge lies in developing drugs that
can be administered by the traditional oral methods. During drug research and development,
molecules that are not suitable for these classic delivery systems are typically discarded due to
the high costs of developing corresponding delivery systems. A drug delivery system capable of
releasing drugs with poor oral bioavailability would greatly increase the development rate of
novel medications.
Recent investigations in the area of controlled drug delivery have the potential to solve
the problem of poor bioavailability through polymer-drug combinations that are able to release
the active drug in a pre-designed manor. This release can be either cyclic or over a long period
of time, and it may be triggered by external environmental events. In either case, the exact
mechanism is studied and developed to ensure the successful delivery of drug therapies while
preventing the problems of both over and under dosing. In addition, controlled drug delivery
allows for the maintenance of a desired range of drug levels, requires fewer administrations, and
optimizes the therapeutic use of the drug. Specifically these delivery systems are ideal for the
slow release of water soluble drugs, the fast release of low-solubility drugs, drug delivery to
specific sites, drug delivery using nanoparticulate systems, delivery of two or more agents with
the same formulation, and systems based on carriers that can dissolve or degrade and be readilyeliminated. An ideal system should be mechanically strong, inert, comfortable to administer,
biocompatible, safe from accidental release, easy to fabricate and sterilize, and capable of
loading high levels of the desired drug (Brannon-Peppas, 1997).
The ultimate goal within controlled drug delivery investigations is to yield an optimally
high blood level of the drug over an extended period of time. With traditional oral and injection
methods, the blood drug level follows a pattern as illustrated in Figure 1(a) as the specific level
rises after each administration and decreases quickly until the next administration (Brannon-Peppas, 1997).
The aim of drug administration is to maintain a steady blood level of the specific drug
over an extended time period that does not go below a minimum concentration of effectiveness,
or above a maximum level of possible toxicity. With controlled drug delivery, the drug level
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ability to encapsulate protein (Tanaka, Matsumara et al.), 1984, and DNA (Smith, 1994) while
maintaining biological activities and have illustrated very strong bioadhesive abilities making
alginate a promising candidate for site-specific mucosal delivery (Mestecky, 1987).
An area of controlled drug delivery currently under investigation at ENSIC is the use of polymer surfactants in oil-water emulsions. While research has been focused on the use of
dextran polymer as surfactant in these emulsions, the researchers are also interested in the
possibility of using modified alginate polymer. Alginate-protein matrices are currently under
investigation by ENSIC researchers (Léonard, Rastello de Boissen et al., 2004), and the idea of
using the alginate polymer as a surfactant in the emulsion drug delivery investigations was
identified as a promising research avenue.
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matrix where it constitutes up to 40% of the dry weight. The alginate forms mixed slats with
various cations naturally found in sea water including Mg2+
, Ca2+
, Sr2+
, Ba2+
, and Na+, and the
native species is usually found as an insoluble Ca2+
cross-linked gel (Sutherland, 1991).
When alginate is harvested, the algae is mechanically collected and dried, then thematerial is milled and treated with dilute acid to remove and dissociate neutral
homopolysaccharides and exchange the alkaline earth cations with H+ before the alginate in
extracted. With the addition of sodium carbonate below pH 10, the alginate is then converted to
the soluble sodium salt from the insoluble protonated form and can be further purified and sold
in salt or acid form (Sutherland, 1991).
Due to the natural extraction process used to obtain alginate, there are many impurities
that may potentially contaminate the product. These impurities include heavy metals, endotoxin,proteins, other carbohydrates, and polyphenals contained in the kelp (Smidsrod and Skjak-Braek,
1973). When harvested alginate is used in food and drug industries small traces of theses
impurities are acceptable, but when it comes to medicinal applications they must be removed.
New methods of harvesting and purification have been developed to address the problem of
contamination, and now pharmaceutical grade alginate is available from numerous chemical
manufactures.
Chemical StructureAlginate polymers are linear unbranched polysaccharides consisting of 1,4’-linked-β-D-
mannuronic acid and α-L-gluronic acid residues as represented in Figure 2. The pattern held by
these residues varies greatly and are arranged in a block pattern along the length of the chain
backbone.
The homopolymeric regions of β-D-mannuronic acid blocks and α-L-gluronic acid
blocks are interdispersed with alternating regions of 1,4’-linked-β-D-mannuronic-acid-α-L-
gluronic acid blocks as seen in Figure 2 (Haug, Larsen et al., 1967). The distribution of
monomers along the polymer chain is random and therefore alginates do not have a repeating
unit. However, the molecular variability of the polymer is reflective of the organism from which
the polymer is extracted. For instance, alginates isolated from L. hyperboea kelp have a high
number of α-L-gluronic acid residues, while alginates isolated from A. nodosum and L. japonica
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Another method of microbead preparation involves the use of alginate polymer as a
surfactant stabilizer in oil-water emulsions. Alginate surfactants serve to lower the interfacial
energy between the phases, thereby increasing the stability and lifetime of the emulsion.
Emulsion Formation
Emulsions are formed when two immiscible substances are combined, with one substance
being dispersed in the continuous phase substance as can be observed in Figure 4. Emulsions
fall into a greater class of two-phase systems known as colloids, with the special characteristic
that both the dispersed and continuous phases are liquid. Depending on the volume fraction of
the phases, both water-in-oil and oil-in-water emulsions can be formed. There is a rule which
governs the emulsion formation, known as the Bancroft Rule: emulsifiers and emulsifyingparticles tend to promote dispersion of the phase in which they do not dissolve well; for example,
proteins dissolve better in water than in oil and therefore tend to form oil-in-water emulsions,
promoting the dispersion of oil droplets throughout a continuous phase of water
(www.wikipedia.org). Emulsions often have a cloudy appearance due to the scattering of light
as it passes through the many interfaces contained within the emulsion.
Emulsions can be prepared through various methods of agitation, as the two phases are
immiscible and droplets will not form spontaneously. Methods for emulsion preparation include
sonication, which can produce droplets of 100 to 400nm. When investigating emulsions for drug
release experiments, the desired drug is dissolved into the oil, and then combined with the
A B
C D
Figure 4. (A) Two immiscible liquids not emulsified (B) An emulsion of phase B dispersed in Phase A (C) The
unstable emulsion (D) The purple surfactant as an emulsion stabilizer
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alginate and aqueous phase and agitated to form polymer stabilized oil-in-water emulsions
containing the desired drug.
Polymeric Surfactants
When emulsions are formed, they are thermodynamically unstable, the result of the
degree of mechanical energy needed to form the emulsion droplets in compensation for the
increasing of interface area between the two (Sadtler, Imbert et al. 2002). Polymeric surfactants
on these emulsions have been used to solve this problem of instability by lowering the surface
tension between the liquid phases. Polymeric surfactants are widely used as emulsions
stabilizers in biotechnology and drug delivery processes, and are commonly referred to as
emulsifiers, detergents, or dispersants.
As amphiphilic molecules, polymers have two main regions, a soluble lyophilic region,
and an insoluble lyophobic region. The polymer chain coils itself around the oil droplets, with
the hydrophobic regions anchoring into the oil and the hydrophilic regions branch out to the
aqueous phase. The anchoring of hydrophilic branches provides stability against washing, while
increasing steric stability and overall emulsion stability (Tadros, Vandamme et al., 2004). As
well, these surfactants provide steric repulsion between oil droplets, and help protect against
aggregation. Polymer surfactants are highly researched because of their strong ability to lower
surface tension and thicken the aqueous phase of emulsions. Moreover, their biocompatibility
makes them prime candidates for biological applications.
Dry Emulsions
Once emulsions are formed, they can be dried to increase stability for drug delivery and
ensure a longer shelf life. Liquid state emulsions are physically unstable, and the stability of the
emulsion beads is greatly increased upon removal of the solvent (Dollo, Corre et al., 2004). This
can be accomplished through freeze-drying, where the aqueous phase is frozen and then removed
with a vacuum through sublimation. Freeze-drying, also known as lyophilization, furtherstabilizes the emulsion because it is a very unobtrusive method and avoids higher temperatures
usually involved with solvent removal. Once the emulsions are dried, they can them be
compressed into pill form for easier administration, or they can be stored in solid state for an
extended period of time. Dried emulsions can be easily reconstituted by adding a specific
amount of the continuous phase as was previously removed, and using light vortex and
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shown that the impurities found in commercial alginate are responsible for the side affects
observed, including cytokine release and inflammatory reactions (Zimmerman, Klock et al.,
1995). However it is also proven that pure alginate does not contain these impurities and
therefore does not induce any side effects. In addition, researchers have proven that there is a
correlation between the level of mannuronic acid blocks and cytokine production (Otterlei,
Ostgaard et al., 1991), therefore it is recommended that pure alginate rich in α-L-gluronic acid is
used for in vivo research to avoid inflammatory reactions (Spargo, Rudolph et al., 1994).
Further research into the use of alginate as surgical gauzes and films reports full
biodegradability of the polymer in animal tissues with very little reaction (Blaine, 1947). As
well, when used as implants, alginate high in α-L-gluronic acid has proven to produce less of an
immunological response then polyvinyl alcohol and agarose gels (Spargo, Rudolph et al., 1994).
Moreover, investigations involving implantation of high α-L-gluronic acid alginate into the
upper nasophrynx of mice produced little or no inflammatory response, making alginate a very
promising drug delivery agent for mucosal delivery (Schuh, Fanslow et al., 1996).
Bioadhesion
Alginate polymer has a very strong bioadhesive property, which again makes it a viable
candidate for mucosal delivery. With carboxyl end groups, alginate is classified as an anionic
mucoadhesive polymer. Research has shown that polymers with charge density are strongmucoadhesive agents (Chickering, Jacob et al., 1995). It is believed that penetration of the
polymer chain across a polymer-mucosa interface is responsible for the great adhesion (Jabari,
Wisniewski et al., 1993). Alginate has proven to have the greatest mucoadhesive strength when
compared with other polymers including polystyrene, chitosan, carboxy-methylcellulose, and
poly (lactic acid). Alginate’s strong bioadhesive properties will serve to localize the drug upon
release, and therefore would potentially improve the overall drug effectiveness with mucosal
delivery.
Possible Applications of Alginate Polymer Controlled Drug Release Systems
There are numerous possible applications of alginate polymer drug delivery systems
using both encapsulation with matrices and encapsulation with alginate surfactant oil in water
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miglyol. Three trials were performed using different volume ratios of oil to aqueous and
different total volumes.
1) 3:5 (oil:aqueous), 4 mL total
2) 3:5 (oil:aqueous), 10 mL total
3) 1:1 (oil:aqueous), 10 mL total
In each case, the samples were mixed well overnight and allowed to settle until the
phases were visually separated. In the second trials, the lidocaine was dissolved in oil (6
mg/mL) and mixed with the pure NaOH solution at a ratio of 1:1 (oil:aqueous), 10 mL total.
Like in the previous trials, the samples were shaken overnight, and then allowed to settle.
In each case, the aqueous phase was analyzed using UV spectroscopy and the previously
determined extinction coefficient in order to determine the resulting concentration of lidocaine in
that phase. Since the initial concentrations were known, the equilibrium lidocaine concentration
in the oil could be calculated.
It was very important that the lidocaine was given adequate time to dissolve in the
primary solvent before the second solvent was added to the solution. In addition, it was
necessary to thoroughly disturb the oil and water mixture with a stir bar to ensure that the drug
had adequate time to move between phases. Likewise, it was equally important to let the two
phases separate afterwards to ensure that only the aqueous phase was removed for UV analysis.
Oil Purity
There were four oils available for drug encapsulation studies and it was necessary to
investigate the purity of the oils in addition to the partition coefficients to determine the oil most
suitable for emulsification. The purity of the oils has a strong affect on emulsion preparation and
stability, so the cleaner the oil the better the emulsification procedures and analysis will run. In
order to determine the purity of the oils, small amounts of each oil (5ml) was washed three timeswith the dilute NaOH solution, then on the third washing samples of the aqueous solution were
tested with UV to determine purity. The pure oils would reveal clean NaOH solutions, while the
aqueous from the still impure oils would give unwanted peaks against the baseline NaOH. The
four oils under investigation were dicaprylyl carbonate, caprylic/capric triglyceride,
octyldodecanol, and miglyol. The miglyol and the caprylic/capric triglyceride proved to be the
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anticipated reaction, and the sonication procedure was started. The sonicator was adjusted for a
time of 3 minutes with a 50% active cycle and a power level of 5, or approximately 100 W.
These settings were kept constant through the remaining emulsification experiments.
The intensive shock waves as applied during emulsification speed up the reaction rate of the oil/polymer solution, producing one homogeneous emulsified solution. The solution
produced was then ready to be investigated for particle size and stability.
Particle Size Analysis
Once the emulsions were prepared it was necessary to determine the size of the emulsion
particles, as the aim was to optimize the emulsion procedure to produce the smallest and most
stable emulsion particles possible. The particle sizes were investigated using a Malvern
Instrument High Performance Particle Sizer produced by Spectris Co. This HPPS contains a
Neon-Helium laser with a high sensitivity that overcomes the multiple angle scattering produced
by the particles. HPPS analytical equipment is capable of measuring particle sizes from 0.6 to
6000 nm, and is able to minimize error from sources such as dust particles and occasional large
emulsion droplets by taking readings at different angles within the cuvette.
The emulsions samples were prepared by adding a drop of emulsion to approximately
3ml of prepared NaCl (10-3
M) solution, and mixed thoroughly with a pipette. The vial was then
inserted in the particle sizer and data was gathered as described in the results section of this
report. In accordance with the observed particle sizes, sizes for various emulsion were explored
from 0.1 to 4.0mg/ml alginate concentration in both NaOH solution and 10-2 M NaCl solution,
and in both 10% and 20% octyldodecanol mixtures. The cuvette with the diluted emulsion
samples was introduced into the HPPS after a warm up period of ten minutes, allowing the
particle sizer to adjust to 25°C. Once the proper temperature was reached the parameter settings
were adjusted as outlined in Appendix A1. Once the settings were optimized, the cuvette
samples were run 3 times, with each run involving between 8 and 20 various sub-measurements.
These measurements were then averaged out and the average particle size and polydispersity
values, or the range of particle size in solution, for each sample were obtained. The emulsions
prepared which retained relatively small particle sizes and decent polydispersity values over a
period of a couple days were then tested for stability.
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The stability of the emulsions was investigated through both lyophilization and
centrifugation, and the sizes of the emulsions were re-measured after disturbance. Primarily,
lyophilization allows for the drying of a specific sample without changing the structure. A small
amount of the emulsion (1 ml) was placed in a 5 ml plastic tube, and a collection of these plastic
tubes were bound together and immersed in liquid nitrogen. When the emulsions inside the
tubes were completely frozen, the bundle was then put into a larger flask that was then connected
to the lyophilizer and allowed to freeze-dry for 48hrs. Lyophilization itself involves the
vacuuming of the solvent at a low temperature, entirely avoiding high temperatures that might
interfere with chemical structure. This method is used often in organic chemistry as it
successfully removes solvent, leaving only the desired chemical compound that can then be
processed and stored as desired. However, with our investigations the lyophilized emulsions
were then reconstituted in 1 ml MilliQ water, and sonicated to ensure complete dissolution
before they were tested again for particle size.
In addition, centrifugation was also used a method to test particle stability. Samples of
promising emulsions were placed in centrifuge tubes and centrifuged at 110 g for 10 min. These
samples were then investigated for oil/water separation, but fortunately no separation was
observed. The centrifuged samples were then also tested for particle size, and all data was
recorded.
The methods of lyophilization and centrifugation were both used to test against
coalescence of the emulsion particles, and emulsion which were able to retain their former
particle size after freeze drying and centrifugation were identified as promising, while only the
optimal emulsions were chosen for drug release experimentation.
Lidocaine Encapsulation
After the conditions for emulsion preparation were optimized the experimentation withlidocaine encapsulation and release was started. It had been determined that emulsions prepared
with 1.4mg/ml alginate in NaCl (10-2 M) were the most stable, so three emulsions were prepared
at the same concentration with the addition of 25mg/ml lidocaine in the octyldodecanol. The
emulsions were tested for particle size reproducibility, and then combined for lidocaine release
analyses.
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are combined. Some reasons for this variation could be that the smaller volume used (4 mL
total) may have affected the UV readings, as there was only 2.5 mL of aqueous phase available
to use in the sample cuvettes. This small sample size could have made a big difference if some
of the oil was retained on the pipette and was mixed with the UV sample. Another possibility is
that different stock solutions were used for the saturated lidocaine in the dilute NaOH solution
for different cases. This could have been a problem, as obtaining a consistent reading for the
saturation concentration of lidocaine proved to be difficult, and was highly temperature and pH
dependant.
Emulsion Stability
As mentioned previously, we tested many types of emulsions for stability by measuring
particle sizes over time using the HPPS. Unlike with other polymers such as modified dextran,researchers at ENSIC did not have a great deal of experience with creating modified alginate
emulsions. For this reason, we varied the properties of the emulsions greatly, from 0.1 to
4.0mg/ml alginate in the aqueous and from 10% to 30% octyldodecanol by volume. The goal
was to find an emulsion that exhibited both stability over time and an ideal average particle size.
The first step was to determine the best fraction of oil to be used in emulsions.
Emulsions were created of 10, 20, 25, and 30% oil, at a variety of alginate concentrations. The
initial average particle sizes for each of these emulsions is shown in Figure 16. From the plot, it
0
200
400
600
800
1000
1200
1400
1600
1800
2000
4 m g / m l
3 m g / m l
2 m g / m l
1 m g / m l
2 . 5 m
g / m l
2 . 0 m
g / m l
1 . 4 m
g / m l
2 . 0 m
g / m l
1 . 4 m
g / m l
0 . 7 5
m g / m l
0 . 1 m
g / m l
Alginate Concentrations
A
v e r a g e S i z e ( n m )
10% oil
20% oil25% oil
30% oil
Figure 16. Initial particles sizes of various emulsions
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the largest particle size of the three samples. This indicates that the 1.4 mg/mL emulsion may
not be the most stable over time, however any decisive conclusion would not be possible, since
only one emulsion was made of each type, limiting the availability of experimental error data.
Because the 1.4 mg/mL emulsion (in 10-4
M NaOH, 10-2
M NaCl), with 10% octyldodecanol,
consistently showed the smallest initial particle size, and the best stability over time, it was
chosen as the best emulsion to continue ahead with drug encapsulation.
The conditions for determining the best alginate emulsion to proceed with were not ideal.
Both a lack of time and equipment availability made a complete and detailed investigation of
emulsion stability impossible. While we believe the best attempts were made to find what
emulsion parameters would create the smallest and most stable emulsion, we are not certain that
the 1.4 mg/mL, 10% oil emulsion is the best. Even with the best particle size being achieved at
517 nm, this is still too large for use in the body. Ultimately, we would like to create a stable
emulsion at about 300 nm or smaller to avoid problems with getting through capillaries.
Lidocaine Encapsulation
The creation of an emulsion containing lidocaine for use in release kinetics tests was
done using 1.4 mg/mL alginate in dilute NaOH and NaCl. The oil, once again octyldodecanol at
10% total emulsion volume, contained the lidocaine at 25 mg/mL. Three emulsions of 10mL
each were created and tested for size. Surprisingly, these emulsions encapsulating the lidocaine
yielded the best particle sizes out of all emulsions created, with an average initial particle size of
466 nm and a standard deviation of 13 nm.
Lidocaine Release Experiments
We performed release experiments to understand how the rate of lidocaine release from a
polymer stabilized emulsion compared to a solution of lidocaine and a solution of lidocaine and
modified alginate (no emulsion). This testing showed how an alginate stabilized emulsion could
be used to provide controlled drug delivery in an intravenous application. The model we usedassumed that the main mechanism for drug release was molecular diffusion. We took the results
of concentration of lidocaine in the bath and plotted them versus time as seen in Figure 18.
The lidocaine release experiments proved to give very interesting and compelling results.
With the exception of a few scattered data points, the release curves for just lidocaine and for
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Christensen, K.L., Pedersen, G.P., Kristensen, H.G. Preparation of Redispersable Dry Emulsionsby Spray-Drying J. of Pharmaceutical Sciences 212; (2001) 187-194
Clark, A.H., Ross-Murphy, S.B., Structural and Mechanical Properties of Biopolymer Gels, Adv.
Polym. Sci. 83 (1987) 57-192.
Correia, R.C., McEleaney, K.S., Pinzon, P.A., Dextran C6 As Surfacant For Oil In WaterEmulsions. MQP, Worcester Polytechnic Institute (2005)
Daly, M.M., Knorr, D., Chitosan-alginate Complex Coacertive Capsules: Effects of Calcium,Plasticizers, and Polyelectrolytes on Mechanical Stability, Biotech. Prog. 4 (1998) 76-81.
Dollo, G., Le Corre, P., Chevanne, F., Le Verge, R.,. Bupivacaine Containing Dry Emulsion Can
Prolong Epidural Anesthetic Effects in Rabbits. European Journal of Pharmaceutical Sciences 22(2004) 63-70.
Durand, A., Marie, E., Rotureau, E., Léonard, M., Dellacherie, E., Amphiphilic Polysaccharides:Useful Tools for the Preparation of Nanoparticles with Controlled Surface Characteristics.
Gray, C.J., Dowsett, J.,Retention of Insulin in Alginate Gel Beads, Biotech. Bioenf. 31 (1988)
607-612.
Gombotz, W.R., Wee, S.F., Protein Release From Algiante Matrices, Adv. Drug. Reviews 31
(1998) 267-285.
Haug, A., Larsen, B., Smidsrod, O., Studies on the Sequence of Uronic Acid residues in Alginic
Acid, Acta Chem. Scand. 21 (1967) 691-704
Huguet, M.L., Neufeld, R.J., Dellacherie, E., Calcium-Alginate Beads Coated With PolycationicPolymers: comparison of Chitosan and DEAE-Dextran. Process Biochemistry Vol. 31, No, 4.
(1996) 347-353.
Igari, Y., Kibat, P.G., Langer, R., Optimization of a Microencapsulated Liposome System for
Enzymatically Controlled Release of Macromolecules. J. Control. Release 14 (1990) 263-267.
5/12/2018 Modified Alginate Polymers for Drug Delivery 2006 - slidepdf.com
Imbert, P., Satdler, V.M., Dellacherie, E. Phenoxy-Substituted Dextrans as Emulsifying Agent:
Role of the Substitution Ratio on O/W Emulsion Stability and Interfacial Activity J. of Colloidsand Surfaces A: Physicochem. Engineering Aspects 211; (2002) 157-164
Jabari, E., Wisniewski, N., Peppas, A., Evidence of Mucoadhesion by Chain Interpretation at a
Poly(acrylic acid)/mucin Interface Using ATR-FTIR Spectroscopy, J. Control. Release 26 (1993)99-108.
Kwok, K.K., Groves, M.J., Burgess, D.J., Production of 5-15µm Diameter Alginate-polylisineMicrocapsules by an Air Atomization Technique, Pharm. Res. 8 (1991) 341-344.
Liu, L.S., Liu, S.Q., Ng, S.Y., Froix, M., Ohno, T., Heller, J., Controlled Release of Interleukin-2for Tumor Immunotherapy Using Alginate/Chitosan Porous Microspheres, J. Control. Release 43
(1997) 65-74.
Martinsen, A., Skjak-Braek, G., Smidsrod, O., Zanetti, F., Paoletti, S., Comparison of DifferentMethods for Determination of Molecular Weight and Molecular Weight Distribution of
Alginates, Carbohydr. Polym. 15 (1991) 171-193.
Mestecky, J., The Common Mucosal Immune System and Current Strategies for Induction of
Immune Responses in External Secretions, J. Clin. Immunol. 7 (1987) 265-276.
Mestecky, J., McGhee, J.R., Immunoglobulin A (IgA): Molecular and Cellular Interactions
Involved in IgA Biosynthesis and Immune Response, Adv. Immunol. 40 (1987) 153-189.
Murnper, R.J., Hoffman, A.S., Puolakkainen, P., Bouchard, L.S., Gombotz, W.R., Calcium-Alginate Beads For The Oral Delivery of Transforming Growth Factor-β1: Stabilization of TGF-
β1 by The Addition of Polyacrylic Acid Within Acid-Treated Beads, J. Control. Release 30(1994) 241-251.
Otterlei, M., Ostgaard, K., Skjak-Brack, G., Smidsrod, O., Soon-Shiong, P., Espevik, T.,
Induction of Cytokine Production From Human Monocytes Stimulated With Alginate, J.
Immunother. 10 (1991) 286-291.
5/12/2018 Modified Alginate Polymers for Drug Delivery 2006 - slidepdf.com
Rastello de Boissen, M., Léonard, M., Hubert, P., Marchal, P., Stequert, P., Castel, C., Favre, E.,Dellacherie, E., Physical Alginate Hydrogels Based on Hydrophobic or Dual Hydrophobic/Ionic
Interactions, Bead Formation, Structure and Stability. J. Colloid Interface Science 273(1) (2004)
134-139.
Rees, D.A., Polysaccharide Shapes and Their Interactions – Some Recent Advances, Pure Appl.
Chem. 53 (1981) 1-14.
Rees, D.A., Welsh, E.J., Secondary and Tertiary Structure of Polysaccharides in Solution and
Rotureau, E., Léonard, M., Dellacherie, E., Durand, A., Amphiphilic Derivatives of Dextran:
Adsorption at Air/Water and Oil/Water Interfaces. Journal of Colloid and Interface Science 279
(2004) 68-77.
Rouzes, C., Durand, A., Léonard, M., Dellacherie, E., Surface Activity and EmulsificationProperties of Hydrophobically Modified Dextrans. Journal of Controlled and Interface Science253 (2002) 217-223.
Rouzes, C., Léonard, M., Durand, A., Dellacherie, E., Influence of Polymeric Surficants on theProperties of Drug-Loaded PLA Nanospheres. Colloids and Surfaces B: Biointerfaces 32 (2003)
125-135.
Sadtler, V., Imbert, P., Dellacherie, E. Ostwald Ripening of Oil-in-Water Emulsions Stabilizedby Phenoxy-Substituted Dextrans. J. of Colloid and Interface Science 254; (2002) 355-361
Schuh, J., Fanslow, W., Gombotz, W., Wee, S.F., Intransal Localization and Response toPolycation-Coated Ovaencapsulated Algiante Microbeads, Vet. Pathol. 33(5) (1996) 581.
Segi, N., Yotsuyangi, T., Ikeda, K., Interaction of Calcium Induced Alginate Gel Beads WithPropranolol, Chem. Pharm. Bull. 37 (1989) 3092-3095.
Smidsrod, O., The Relative Extension of Alginates Having Different Chemical Composition,
Carbohyd. Res. 27 (1973) 107-118.
Smidsrod, O., Skjak-Braek, G., Alginate As Immobilization Matrix for Cells, TIBTECH 8
(1990) 71-78.
Smith, T.J., Calcium Algiante Hydrogel As a Matrix For Enteric Delivery of Nucleic Acids,
Biopharm. 4 (1994) 54-55.
Spargo, B.J., Rudolph, A.S., Rollwagen, F.M., Recruitment of Tissue Resident Cells to Hydrogel
Composites: in Vivo Response to Implant Materials, Biomaterials 15 (1994) 853-858.
5/12/2018 Modified Alginate Polymers for Drug Delivery 2006 - slidepdf.com
Steenson, L.R., Klaenhammer, T.R., Conjugal Transfer of Plasmid DNA Between Streptococci
Imobilized in Calcium Alginate Gel Beads. Applied and Environmental Microbiology. (1987)898-900.
Sutherland, I.W., Alginates, in: D. Byrom (Ed.), Biomaterials; Novel Materials from Biological
Sources, Stockton, New York, 1991, pp. 309-331.
Tadros, T.F., Vandamme, A., Booten, K., Levecke, B., Stevens, C.V. Stabilisation of emulsionsusing hydrophobically modified inulin (polyfructose). J. of Colloids and Surfaces A:
Tanaka, H., Matsumara, M., Veliky, I.A., Diffusion Characteristics of Substrates in Ca-Alginate
Gel Beads, Biotech. Bioeng. 26 (1984) 53-58.
Vandenberg, G.W., Drolet, C., Scott, S.L., de la Noüe, J., Factors Affecting Protein ReleaseFrom Alginate-Chitosan Coacertive Microcapsules During Production and Gastric/Intestinal
Simulation. Journal of Controlled Release 77 (2001) 297-307.
Wan, L.S., Heng, P.W., Chan, L.W., Drug Encapsulation in Alginate Microspheres by
Emulsification, J. Microencapsulation 9 (1992) 309-316.