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3/30/2006 1 HFM Fabrication -Fiber Spinning
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HFM Fabrication-Fiber Spinning
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Phase InversionControlled precipitationSolution--> porous solid that is interconnected and traversed by an interpenetrating pore structure which provides channels across the wall structure
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DryDry--Jet Wet SpinningJet Wet SpinningSpinnerette
Nonsolvent Stream
Polymer Solution Stream
PolymerSolution
Stream
NonsolventStream
Note: Picture notdrawn to scale
OutflowStream
Nonsolvent Bath
Anatomy of a SpinneretAnatomy of a SpinneretSpinneretSpinneret
PolymerSolution
Stream
NonsolventStream
Note: Picture notdrawn to scale
OutflowStream
HFM
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Required ElementsA polymer of sufficient Mw
that is, enough length to provide inter chain entanglement following precipitation and adhesive force to provide the appropriate mechanical properties for a particular application
Polymer & solvent
Miscible non-solvent
Anatomy of a SpinneretAnatomy of a SpinneretSpinneretSpinneret
PolymerSolution
Stream
NonsolventStream
Note: Picture notdrawn to scale
OutflowStream
HFM
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Polymer Solution
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The Addition of Non-solvent
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Precipitation with Chain Entanglement
Anatomy of a SpinneretAnatomy of a SpinneretSpinneretSpinneret
PolymerSolution
Stream
NonsolventStream
Note: Picture notdrawn to scale
OutflowStream
HFM
HFM
Various Various Stages in Stages in the Early the Early Life of a Life of a HFMHFM
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Lumen of Hollow Fiber
Dense Skin
Polymer Rich Zone
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Topography of Selective Skin Layer
PhotodiodePhotodiode
XYZ XYZ piezotranslatorpiezotranslator
Cantilever and Cantilever and Probe TipProbe Tip
LaserLaser
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Inner Skin Ultra-topography
4° C - 100% H20 Quench
54° C - 100% H20 Quench1000 x 1000 nm
54° C - 50/50 DMF/H20 Quench
22° C - 100% H20 Quench
35
nm
0
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Lumen of Hollow Fiber
Dense Skin
Polymer Rich Zone
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Production Spinning Line
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CC
EE
BB
AAGGDD
FF
HHA A PANPAN--PVC Li et al. 1998PVC Li et al. 1998B B PANPAN--PVC Li et al. 1998PVC Li et al. 1998C C Polyimide Chung et al. 1992Polyimide Chung et al. 1992D D PolysulfonePolysulfone ValetteValette et al.1999et al.1999E E Cellulose acetate Cellulose acetate HaoHao et al. 1996et al. 1996F F PAN copolymer PAN copolymer ValetteValette et al.1999et al.1999G G AN69 AN69 ValetteValette et al.1999et al.1999H H PMMA PMMA ValetteValette et al.1999et al.1999
On a Larger Scale Various Structures are Apparent and can On a Larger Scale Various Structures are Apparent and can be controlled by changing Fabrications conditionsbe controlled by changing Fabrications conditions
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Nerve Track Repair: Bridging Substrates
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Nerve Repair-Entubulation
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HydrogelsHydrogels
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Definition-water insoluble, three dimensional network of polymeric
chains that are crosslinked;-polymers capable of swelling substantially in aqueous
conditions (eg hydrophilic)-polymeric network in which water is dispersed throughout
the structure-typically in the swollen state the mass fraction of water is
much higher than the mass fraction of polymer.
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The Cross-links may be physical or chemical:
++
__
__
__
++
++
by reaction of one or more monomers with pendant functional groupsElectrostatic, hydrogen or van der Waalsinteractions (physical), heating creates a solution;Covalent bonds (chemical)
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HydrogelsOne or more highly electronegative atoms which results in charge asymmetry favoring hydrogen bonding with water;hydrophilic nature -dry materials absorb water;By definition, water must constitute at least 10% of the total weight (or volume) for a materials to be a hydrogel;When the content of water exceeds 95% of the total weight (or volume), the hydrogel is said to be superabsorbant;
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Hydrogels: Swelling
Degree of swelling can be quantified by:ratio of sample volume in the dry state to sample volume in the swollen state; weight degree of swelling: ratio of the weight of swollen sample to that of the dry sample
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Hydrogels:
In a chemically cross-linked hydrogel, all of the polymer chains are connected by covalent bonds to form a network; and, thusThe material can be viewed as one molecule of large size or supramacromolecule;The thermodynamically driven swelling force is counterbalanced by the retractive force of the crosslinkedstructure; The unique property of these gels is there ability to maintain their original shape during and after swelling;Two forces become equal at some point and equilibrium is reached
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XerogelsDried hydrogels;Usually clear and swelling in water takes a long time;The swelling behavior is due to slow diffusion of water through the compact polymer chains;A useful property in controlled drug delivery;
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Chitosan
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Hydrogels: Swelling
Why is the degree of swelling important?solute diffusion coefficient through the hydrogelsurface properties and surface mobilityoptical properties (particularly for contact lens applications)mechanical properties
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Hydrogel Forming Polymers
OHO
OH
HO2C
OOHO
NH
HO
O
O
OHO
OH
NaO2C
O
npoly(hyaluronic acid) poly(sodium alginate)
n
Natural
Synthetic
O
O
nNHOn O
n
poly(ethylene glycol)poly(lactic acid) poly(N-isopropyl acrylamide)
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Fibrin Hydrogel (Blood Clot)
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HydrogelsHighly swollen hydrogels:
cellulose derivativespoly(vinyl alcohol)poly(N-vinyl 2-pyrrolidone), PNVPpoly(ethyleneoxide)
Moderately or poorly swollen hydrogels:poly(hydroxyethyl methacrylate), PHEMA and derivatives
One may copolymerize a highly hydrophilic monomer with other less hydrophilic monomers to achieve
desired swelling properties
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Examples of biological hydrogels:
Jello (a collagen gel ~ 97% water)Extracellular matrix componentsPolysaccharidesDNA/RNABlood clotMucin - lining the stomach, bronchial tubes, intestinesGycocalyx - lining epithelial cells of blood vesselsSinus secretions
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Function of a biological hydrogelDecreased permeability to large moleculesStructural strength (for epithelial cell walls)Capture and clearance of foreign substancesDecreased resistance to sliding/glidingHigh internal viscosity (low washout)
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Hylauronic Acid
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Polyelectrolyte Hydrogels
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Polyelectrolyte MultilayersLayer by layer deposition
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Alginate gels
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Alginate gels
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Enzyme Immobilization
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Cell Encapsulation
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Applications Pharmaceutical applications
monomer composition and relative amounts of multi-polymer hydrogels can be varied to alter the diffusion characteristics; and permeability of the gel containing pharmaceutical agents
Deliverydrug gets trapped in the hydrogel during polymerizationdrug introduced during swelling in waterRelease occurs by outflow of drug from the gel and inflow of water to the gel
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Drug delivery
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Applications in Biomaterials and Tissue Engineering
Cell EncapsulationDrug delivery Surface modificationEnzyme Immobilization Biosensors Lab on a chip
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Hydrogels: ApplicationsBiomedical use due to bio- and blood-compatibilityPharmaceutical use due to hydrophilicity (controlled/sustained drug release)Earliest biomedical application contact lenses
good mechanical stabilityfavorable refractive indexhigh oxygen permeabilityneeds hygienic maintenanceunable to correct for astigmatism
lubricating surface coatingused with catheters, drainage tubes and glovesnon-toxic
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Corning® Ultra Low Attachment ProductsUnique hydrogel surface inhibits cell
attachment
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Important features of hydrogelsUsually comprised of highly polyionic polymersOften exhibit large volumetric changes eg. Highly compressed in secretory vessicle and expand rapidly and dramatically on releaseCan undergo volumetric phase transitions in response to ionic concentrations (Ca++, H+), temperature, ..Volume is determined by combination of attractive and repulsive forces:
repulsive electrostatic, hydrophobicattractive, hydrogen binding, cross-linking
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Hydrogel Forming Polymers
OHO
OH
HO2C
OOHO
NH
HO
O
O
OHO
OH
NaO2C
O
OO
O
NHO
npoly(hyaluronic acid) poly(sodium alginate)
n
n
poly(ethylene glycol)
n
poly(lactic acid)
n
poly(N-isopropyl acrylamide)
Natural
Synthetic
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HydrogelsHydrogels //Applications in Applications in OpthamologyOpthamology
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Hydrogels: Applications
Earliest biomedical application contact lensesgood mechanical stabilityfavorable refractive indexhigh oxygen permeabilityneeds hygienic maintenanceunable to correct for astigmatism
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Acrylates
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Methacrylates
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Poly(methyl methacrylate)
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Poly(2-hydroxyethylmethacrylatepHEMA
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Hydrogels: PHEMA
The most widely used hydrogelwater content similar to living tissuesinert to biological processesshows resistance to degradationpermeable to metabolitesnot absorbed by the bodywithstands sterilization by heatprepared in various shaped and forms
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Contact lensPMMAHEMAFabrication methods
Computer assisted cutting (lathe)-PMMA rodsSpin casting-polymerization Molding-polymerization
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Intraocular lensPMMAHEMAPolymer backbone - mixture of PMMA and PHEMAVarying water contentsAdditives such as UV blockers
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Foldable IOL complications/explantations -
Survey Lens Totals2001
9%
8%
14%
16%28%
25%
Multifocal,SiliconeOne Piece (plate),SiliconeOne Piece with Haptics,AcrylicThree Piece,AcrylicThree Piece,HydrogelThree Piece,Silicone
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Reasons for Revision Surgery
Incorrect lens power seen most commonlyGlare/optical aberrationsDislocation/decentrationLate postoperative opacification
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IOL Optic Opacification
Surface opacificationOpacification within the substance of the opticAnalysis of opacifications reveals presence of calciumCalcium stainingScanning electron microscopic analysis
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Total Total diameter: diameter: 9.7 mm9.7 mm
Accommodative IOL: 1CU (HumanOptics)
