A REVIEW : NANOFIBERS APPLICATION
ANIL KUMAR M.PHIL./PH.D. NANOSCIENCE 2012-13
CENTRE FOR NANOSCIENCE, CUG, GANDHINAGAR SEC-30, GUJARAT
Nanotechnology
• The study of control of matter on an atomic and molecular scale.
• Deals with structures the size of 100 nanometers or smaller (1 nm = 1/1,000,000,000 m or 10-9 m).
• Involves engineering on a small scale to create smaller, cheaper, lighter, and faster devices that can do more things with less raw materials.
NANOFIBERS - INTRODUCTION
ECM fibers ~ 50-500 nm in diameterCell ~ several-10 umFibers 1-2 orders of magnitude < cellsingle cell contacts thousands of fibers
three techniques to achieve Nano-fibers scale - Self Assembly-Phase Separation-Electro-spinning
Techniques To Achieve Nano-fibers For TE
Self-assembly
Phase separation
Electrospinning
Collagen FibersFormed Of Parallel FibrilsHigh Modulus Of Elasticity
300 nanometers long;
1.5 nanometers in diameter
20 collagen types that exist in animal tissue
Assembly Of Collagen Fibers
Elastin Fibers• An amorphous protein
• Much lower modulus of elasticity than collagen
• Primary constituent of many ligaments
• Crosslinked tropoelastin
NANOFIBERS: SELF-ASSEMBLY
Definition: spontaneous organization into stable structure without covalent bonds
Biologically relevant processes- Cellulose,Lipids, DNA, RNA, protein organization- can achieve small diameter
Example: peptide-amphipathics- hydrophobic tail- cysteine residues disulfide bonds
Self-assembly
• Relies on non-covalent interactions to achieve spontaneously assembled 3D structure.
• Biopolymers such as peptides and nucleic acids are used. Example is peptide-amphiphile (PA)
• (A) Chemical structure of (PA)
• (B) Molecular model of the PA showing the narrow hydrophobic tail to the bulkier peptide region
• (C) Schematic of PA molecules into a cylindrical micelle.5 Nanofiber
peptide-amphiphile
Phase Separation
• This process involves dissolving of a polymer in a solvent at a high temperature followed by a liquid–liquid or solid–liquid phase separation induced by lowering the solution temperature
• Capable of wide range of geometry and dimensions include pits, islands, fibers, and irregular pore structures
• Simpler than self-assembly
a) powder, b) scaffolds with continuous network, c) foam with closed pores.4
Definition: thermodynamic separation of polymer solution into polymer-rich and polymer-poor layers
Elastin Is An “Entropic Spring”
• ΔG = ΔH – TΔS
• ΔH = enthalpy changes, which don’t normally happen in solvents.
• ΔS = entropy changes…changes in the degree oforder
• Stretching a polymerincreases it’s order, andmakes ΔS negative.
• ΔG is then positive, and unfavorable.
NANOFIBERS: ELECTROSPINNING
Definition: electric field used to draw polymer stream out of solution
D- electric field overcomes solution surface tension; polymer stream generated
E- fibers 1) collected and 2) patterned on plate
A- polymer solution in syringeB- metal needleC- high voltage applied to need
NANOFIBERS: ELECTROSPINNING
- multiple polymers can be combined at1) monomer level2) fiber level3) scaffold level
- control over fiber diameteralter concentration/viscosity
- fiber length unlimited- control over scaffold architecture
target plate geometrytarget plate rotational speed
Current approaches combined techniques- usually electrospinning + phase separation- fibers woven over pores
NANOFIBERS: OVERVIEW
ELECTROSPINNING POLYMERS
Chemical Synthetics- Polyglycolic acid (PGA)- Polylactic acid (PLA)- PGA-PLA- Polydioxanone (PDO)- Polycaprolactone- PGA-polycaprolactone- PLA-polycaprolactone- Polydioxanone-polycaprolactoneNatural- Elastin- Gelatin collagen- Fibrillar collagen- Collagen blends- Fibrinogen- Heamoglobine
POLYGLYCOLIC ACID (PGA)
Properties Parameters- surface area to volume ratio- biocompatible- consistent mechanical properties
hydrophilicpredictable bioabsorption
- electrospinning yields diameters ~ 200 nm
Model of Surface-to-volume Comparisons…
• Neglecting spaces between the smaller boxes, the volumes of the box on the left and the boxes on the right are the same but the surface area of the smaller boxes added together is much greater than the single box.
Single Box Ratio6 m2
1 m3 = 6 m2/m3
Smaller Boxes Ratio12 m2
1 m3 = 12 m2/m3
POLYGLYCOLIC ACID (PGA)
Random fiber collection (L), aligned collection (R)
POLYLACTIC ACID (PLA) – 200 nm
- aliphatic polyester- L optical isomer used
by-product of L isomer degradation = lactic acid
- methyl group decreases hydrophilicity- half-life ideal for drug delivery
Compare to PGA- low degradation rate - less pH change
Parameters (similar to PGA)- surface area to volume ratio- spinning orientation affects scaffold elastic modulus
POLYLACTIC ACID (PLA) – 200 nm
Thickness controlled by electrospin solvent
Chloroform solvent (L) ~ 10 um, HFP (alcohol) solvent (R) ~ 780 nm
Both fibers randomly collected
PGA+PLA = PLGA
- tested composition at 25-75, 50-50, 75-25 ratios- degradation rate proportional to composition- hydrophilicity proportional to composition
Recent Study- delivered PLGA scaffold cardiac tissue in mice- individual cardiomyocytes at seeding- full tissue (no scaffold) 35 weeks later- scaffold loaded with antibiotics for wound healing
POLYDIOXANONE (PDO)
- crystalline (55%)- degradation rate between PGA/PLA ,close to 40-60 ratio- shape memory- modulus – 46 MPa; compare: collagen – 100 Mpa, elastin –
4 MPa
Advantages- PDO ½ way between collagen/elastin, vascular ECM components- cardiac tissue replacement (like PLGA)- thin fibers (180nm)
POLYCAPROLACTONE (PCL)
- highly elastic- slow degradation rate (1-2 yrs)- > 1 um- similar stress capacity to PDO, higher elasticity
Applications Loaded with:- collagen cardiac tissue replacement- calcium carbonate bone tissue strengthening- growth factors mesenchymal stem cell differentation
POLYCAPROLACTONE + PLA
Clinical Applications- several planned- all vasculature tissue- high PLA tensile strength react (constrict) to sudden
pressure increase- increased elasticity with PCL passively accommodate large
fluid flow
ELASTIN
- highly elastic biosolid (benchmark for PDO)- hydrophobic- present in: vascular walls, skin
Synthesis of Biosolid?- 81 kDa recombinant protein (normal ~ 64 kDa)- repeated regions were involved in binding- 300 nm (not as small as PDO ~ 180 nm)- formed ribbons, not fibers – diameter varies
COLLAGENS: GELATIN
- highly soluble, biodegradable (very rapid)- current emphasis on increasing lifespan
Type I- 100 nm (not consistent)- almost identical to native collagen (TEM)- present is most tissues
COLLAGENS: FIBRIL FORMING
Type II- 100-120 nm (consistent)- found in cartilage- pore size and fiber diameter easily controlled by dilution
COLLAGENS BLENDS
In context: vasculature- intima – collagen + elastin- media – thickest+ elastin+collagen - adventia – collagen
RECONSTRUCTING THE MEDIA
- SMC seeded into tube- average fiber ~ 450 nm
slightly larger ECM fibers- incorporation of GAG
carbohydrate ECMcollagen crosslinkermediate signalling
- cross section of tube wall- 5 day culture
complete scaffold infiltration
FIBRINOGEN
- smallest diameter (both synthetic and bio)80, 310, 700 nm fibers possible
- high surface area to volume ratioincrease surface interactionused in clot formation
Stress capacity comparable to collagen (80%)
HEMOGLOBIN
- hemoglobin mats- clinical applications:
drug deliveryhemostatic bandages
- fiber sizes 2-3 um- spun with fibrinogen for clotting/healing- high porosity = high oxygenation
Application of Nano-fibers
• NanoFibers in Tissue Engineering • NanoFibers in Industrial
composite • NanoFibers in Medicals • NanoFibers in Filtration
Cell and Tissue Engineering, Nanotechnology
Tissue Engineering
Cells Scaffolds
Bioreactors Signals
Tissue Engineering (TE)• Scaffolds
Biomaterials, which may be natural or artificially derived, providing a platform for cell function, adhesion and transplantation
• CellsAny class of cell, such as stem or mesenchymal cell
• SignalsProteins and growth factors driving the cellular functions of interest
• Bioreactor System that supports a biologically active environment (ex. Cell culture)
Image sourse: Stke.sciencemag.org, Nature.com
Cosmetic Application (Nanocellulose Pack)
Fibers use in FilterFibers use in Filter
Nanofibre Non-Nanofibre Non-WovensWovens
Filtration System
Air Cleaning
Water depuration: especially removal of ultrafine particles and
heavy metals adsorption
Keratin from Keratin from WoolWool
Properties of regenerated wool keratin
Heavy metals absorption [1] Formaldeyde absorption [2]
Nanofibre non-wovens properties
High surface/volume ratio High porosity
Nanofibrous Scaffold
COOH
NH2
NH2
NH2
NH2
COOH
COOH
Functionalized Nanofiber
Adhesive Proteins
Cells
• Physical, Chemical and Biological mimicking enable various tissue engineering application.
• Tissue engineering holds the promise to develop powerful new therapies "biological substitutes" for structural and functional disorders of human health that have proven difficult or impossible to address successfully with the existing tools of medicine.
Conclusion
Functional Tissue
Thank You so much
Dean’s :-Prof. M.H. Fullekar & Prof. Mansingh
Chair Persons:-Dr. P. Jha
Dr. B. PathakDr. D. Mandal
Friend's :-M.Phil./Ph.D. Students