POLYMERIC IMPLANTS

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POLYMERIC IMPLANTS
Contact Lens
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Some Commonly Used Polymers

• Material Applications
• Silicone rubber Catheters,
  tubing
• Dacron
  Vascular grafts
• Cellulose
  Dialysis membranes
• Poly(methyl methacrylate) Intraocular lenses,
  bone cement
• Polyurethanes Catheters,
  pacemaker leads
• Hydogels
  Opthalmological devices, Drug Delivery
• Collagen (reprocessed) Opthalmologic
  applications, wound
  dressings

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Polymer Devices
Disadvantages
Advantages
Examples Some joint replacement articulating
surfaces Spinal cages Biodegradable bone plates
for low load regions Biodegradable sutures
Bone plates
Hip joint
Spinal cage for spine fusion
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Mechanical Properties Why is important to study
for all biomaterials?
Determines how well it will work (or not work)
for a given device. One major factor is the
modulus of the material.
metal
polymer
polymer
Toe implant
______________
hydrogel
____________
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Polymers

• Terminology
• copolymer polymers of two mer types
• random -B-A-B-A-B-B-A-
• alternating -A-B-A-B-A-B-A-
• block -A-A-A-A-B-B-B-
• heteropolymer polymers of many mer types

COPOLYMER
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Polymers Structure
Linear
Branched
Crosslinked
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Synthetic Polymers

• Biostable Polymers
• Polyamides
• Polyurethanes
• Polyethylene
• Poly(vinylchloride)
• Poly(hydroxyethylmethacrylate)
• Poly(methylmethacrylate)
• Poly(tetrafluoroethylene)
• Poly(dimethyl siloxane)
• Poly(vinylalcohol)
• Poly(ethylenglycol)

• Biodegradable Synthetic Polymers
• Poly(alkylene ester)s
• PLA, PCL, PLGA
• Poly(aromatic/aliphatic ester)s
• Poly(amide-ester)s
• Poly(ester-urethane)s
• Polyanhydrides
• Polyphosphazenes

• Stimuli Responsive
• Poly(ethylene oxide-co-propilene oxide)
• Poly(methylvinylether)
• Poly(N-alkyl acrylamide)s
• Poly(phosphazone)s

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Polymers Bioinert Biodegradable
Polymers Natural Synthetic
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Synthetic Biomaterials

• POLYMERS Silicones, Gore-tex (ePTFE),
  Polyethylenes (LDPE,HDPE,UHMWPE,) Polyurethanes,
  Polymethylmethacrylate, Polysulfone, Delrin
• Uses Orthopedics, artificial tendons,
  catheters, vascular grafts, facial and soft
  tissue reconstruction
• COMPOSITES CFRC, self reinforced, hybrids
• Uses Orthopedics, scaffolds
• HYDROGELS Cellulose, Acrylic co-polymers
• Uses Drug delivery, vitreous implants, wound
  healing
• RESORBABLES Polyglycolic Acid, Polylactic acid,
  polyesters
• Uses sutures, drug delivery, in-growth, tissue
  engineering

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Polymers Biomedical Applications

• Polyethylene (PE)
• five density grades ultrahigh, high, low, linear
  low and very low density
• UHMWPE and HDPE more crystalline
• UHMWPE has better mechanical properties,
  stability and lower cost
• UHMWPE can be sterilized

(C2H4)nH2
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Polymers Biomedical Applications

• UHMWPE Acetabular caps in hip implants and
  patellar surface of knee joints.
• HDPE used as pharmaceutical bottles, fabrics.
• Others used as bags, pouches, tubes etc.

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Artificial Hip Joints (UHMWPE)
http//www.totaljoints.info/Hip.jpg
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Polymers Biomedical Applications

• Polymethylmethacrylate (PMMA, lucite, acrylic,
  plexiglas)
• (C5O2H8)n
• acrylics
• transparency
• tough
• biocompatible
• Used in dental restorations, membrane for
  dialysis, ocular lenses, contact lenses, bone
  cements

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Intraocular Lens
3 basic materials - PMMA, acrylic, silicone
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Polymers Biomedical Applications

• Polyamides (PA, nylon)
• PA 6  NH-(CH2)5-COn made from e-Caprolactam
• high degree of crystallinity
• interchain hydrogen bonds provide superior
  mechanical strength (Kevlar fibers stronger than
  metals)
• plasticized by water, not good in physiological
  environment
• Used as sutures

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Polymers Biomedical Applications

• Polyvinylchloride (PVC) (monomer residue must be
  very low)
• Cl side chains
• amorphous, hard and brittle due to Cl
• metallic additives prevent thermal degradation
• Used as blood and solution bags, packaging, IV
  sets, dialysis devices, catheter, bottles,
  cannulae

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Polymers Biomedical Applications

• Polypropylene (PP) (C3H6)n
• properties similar to HDPE
• good fatigue resistance
• Used as syringes, oxygenator membranes, sutures,
  fabrics, vascular grafts
• Polyesters (polymers which contain the ester
  functional group in their main chain)
• PET (C10H8O4)n
• hydrophobic (beverage container PET)
• molded into complex shapes
• Used as vascular grafts, sutures, heart valves,
  catheter housings

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Polymers Biomedical Applications

• Polytetrafluoroethylene (PTFE, teflon) (C2F4)n
• low coefficient of friction (low interfacial
  forces between its surface and another material)
• very low surface energy
• high crystallinity
• low modulus and strength
• difficult to process
• catheters, artificial vascular grafts

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Polymers Biomedical Applications

• Polyurethanes
• block copolymer structure
• good mechanical properties
• good biocompatibility
• tubing, vascular grafts, pacemaker lead
  insulation, heart assist balloon pumps

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Polyurethanes A urethane has an ester group and
amide group bonded to the same carbon. Urethanes
can be prepare by treating an isocyanate with an
alcohol.
Polyurethanes are polymers that contain urethane
groups.
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Synthetic vascular grafts from W.L.Gore
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Useful Definitions
Biodegradable Undergoes degradation in the
body - Degradation ___________________________
__ - Degradation products are harmless and can
be secreted naturally
water
Lactic acid
PLLA bone plates
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Polymers Biomedical Applications

• Rubbers
• latex, silicone
• good biocompatibility
• Used as maxillofacial prosthetics

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Biomedical polymer Application
Poly(ethylene) (PE) Low density (LDPE) High density (HDPE) Ultra high molecular weight (UHMWPE) Bags, tubing Nonwoven fabric, catheter   Orthopedic and facial implants
Poly(methyl methacrylate) (PMMA) Intraocular lens, dentures, bone cement
Poly(vinyl chloride) (PVC) Blood bags, catheters, cannulae
Poly(ethylene terephthalate) (PET) Artificial vascular graft, sutures, heart valves
Poly(esters) Bioresorbable sutures, surgical products, controlled drug release
Poly(amides) (Nylons) Catheters, sutures
Poly(urethanes) (PU) Coat implants, film, tubing
Table The clinical uses of some of the most
common biomedical polymers relate to their
chemical structure and physical properties.
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Hydrogels

• Water-swollen, crosslinked polymeric structure
  produced by reactions of monomers or by hydrogen
  bonding
• Hydrophilic polymers that can absorb up to
  thousands of times their dry weight in H2O
• Three-dimensional insoluble polymer networks

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Applications of Hydrogels

• Soft contact lenses
• Pills/capsules
• Bioadhesive carriers
• Implant coatings
• Transdermal drug delivery
• Electrophoresis gels
• Wound healing
• Chromatographic packaging material

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Types of Hydrogels

• Classification
• Method of preparation
• Homo-polymer, Copolymer, Multi-polymer,
  Interpenetrating polymeric
• Ionic charge
• Neutral, Catatonic, Anionic, Ampholytic
• Physical structure
• Amorphous, Semi-crystalline, Hydrogen-bonded

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Types of Gelation

• Physical , Chemical
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Types of Hydrogels

• Natural Polymers
• Dextran, Chitosan, Collagen, Alginate, Dextran
  Sulfate, . . .
• Advantages
• Generally have high biocompatibility
• Intrinsic cellular interactions
• Biodegradable
• Cell controlled degradability
• Low toxicity byproducts
• Disadvantages
• Mechanical Strength
• Batch variation
• Animal derived materials may pass on viruses

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Types of Hydrogels

• Synthetic Polymers
• PEG-PLA-PEG, Poly (vinyl alcohol)
• Advantages
• Precise control and mass produced
• Can be tailored to give a wide range of
  properties (can be designed to meet specific
  needs)
• Low immunogenecity
• Minimize risk of biological pathogens or
  contaminants
• Disadvantages
• Low biodegradability
• Can include toxic substances
• Combination of natural and synthetic
• Collagen-acrylate, P (PEG-co-peptides)

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Properties of Hydrogels

• Swelling properties influenced by changes in the
  environment
• pH, temperature, ionic strength, solvent
  composition, pressure, and electrical potential
• Can be biodegradable, bioerodible, and
  bioabsorbable
• Can degrade in controlled fashion

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Properties of Hydrogels

• Pore Size
• Fabrication techniques
• Shape and surface/volume ratio
• H2O content
• Strength
• Swelling activation

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Advantages of Hydrogels

• Environment can protect cells and other
  substances (i.e. drugs, proteins, and peptides)
• Timed release of growth factors and other
  nutrients to ensure proper tissue growth
• Good transport properties
• Biocompatible
• Can be injected
• Easy to modify

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Disadvantages of Hydrogels

• Low mechanical strength
• Hard to handle
• Difficult to load
• Sterilization

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Why Hydrogels ? Tissue Engineering

• Biocompatible
• H2O content
• Sterilizibilty
• Ease of use
• High mechanical Strength
• Surface to volume ratio
• Good cell adhesion
• High nutrient transport

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Why Hydrogels? Cell Culture Systems

• Biocompatible substrate
• Non-toxic and have no immunological responses
• Cytoarchitecture which favors cell growth
• Flexibility for cells to rearrange in 3-D
  orientation
• Seeded with appropriate growth and adhesion
  factors
• Porosity (i.e. channels for nutrients to be
  delivered)

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Why Hydrogels? Cell Culture Systems

• Mimic cytomechanical situations
• 3-D space provides balanced cytoskeleton forces
• Dynamic loading to promote cell growth
• Flexibility
• Provide scaffold for various cells
• Consistent, reproducible and easy to construct

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Why Hydrogels? Drug Delivery

• Safe degradation products
• Biocompatible
• High loading with ensured molecule efficacy
• High encapsulation
• Variable release profile
• Stable
• Inexpensive
• High quality

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• Hydrogels are network polymers that swell through
  a variety of mechanisms in an aqueous environment
  
• Environment controls mechanisms of swelling
• pH, ionic strength, solvent composition, pressure
  and even electric fields
• Applications in medicine, engineering, and
  biology

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Chitosan

• Chitosan (2-amino-2deoxy-(1?4)-ß-D-glucopyranan),
  a polyaminosaccharide,
• obtained by alkaline deacetylation of chitin
  (the principal component of living organisms such
  as fungi and crustacea).

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Chitosans key properties

• 1) biocompatibility
• 2) nonantigenicity
• 3) nontoxicity (its degradation products are
  known natural metabolites)
• 4) the ability to improve wound healing/or clot
  blood
• 5) the ability to absorb liquids and to form
  protective films and coatings, and
• 6) selective binding of acidic liquids, thereby
  lowering serum cholesterol levels.

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Alginate
Mannuronic acid
Guluronic acid
These products are produced from naturally
occurring calcium and sodium salts of alginic
acid found in a family of brown
seaweed. Alginates are rich in either mannuronic
acid or guluronic acid, the relative amount of
each influence the amount of exudate absorbed and
the shape the dressing will retain.
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