A REVIEW : NANOFIBERS APPLICATION

ANIL KUMAR M.PHIL./PH.D. NANOSCIENCE 2012-13

CENTRE FOR NANOSCIENCE, CUG, GANDHINAGAR SEC-30, GUJARAT

kmr.nano@indiatimes.com

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