Biodegradable suture
Wound dressing
POLYMERIC IMPLANTS
Contact Lens
Intraocular Lens
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
Polymer Devices
Advantages:
Disadvantages:
Examples:
Some joint replacement articulating surfaces
Spinal cages
Biodegradable bone plates for low load regions
Biodegradable sutures
Hip joint
Spinal cage for spine fusion
Bone plates
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
____________
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
Polymers Structure
Linear
Branched
Crosslinked
Synthetic Polymers
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
Biostable Polymers
• Polyamides
• Polyurethanes
• Polyethylene
• Poly(vinylchloride)
• Poly(hydroxyethylmethacrylate)
• Poly(methylmethacrylate)
• Poly(tetrafluoroethylene)
• Poly(dimethyl siloxane)
• Poly(vinylalcohol)
• Poly(ethylenglycol)
Stimuli Responsive
 Poly(ethylene oxide-co-propilene oxide)
 Poly(methylvinylether)
 Poly(N-alkyl acrylamide)s
 Poly(phosphazone)s
Polymers
Bioinert
Biodegradable
Polymers
Natural
Synthetic
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
Polymers: Biomedical Applications
• Polyethylene (PE) (C2H4)nH2
– 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
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.
Artificial Hip Joints (UHMWPE)
http://www.totaljoints.info/Hip.jpg
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
Intraocular Lens
3 basic materials - PMMA, acrylic, silicone
Polymers: Biomedical Applications
• Polyamides (PA, nylon)
•
PA 6 : [NH−(CH2)5−CO]n made from ε-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
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
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
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
Polymers: Biomedical Applications
• Polyurethanes
– block copolymer structure
– good mechanical properties
– good biocompatibility
• tubing, vascular grafts, pacemaker lead insulation, heart
assist balloon pumps
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.
O
RN C O
an isocyanate
+ ROH
RNH C OR
an alcohol
a urethane
Polyurethanes are polymers that contain urethane groups.
CH3
O C N
N C O
+
HOCH2CH2OH
ethylene glycol
toluene-2,6-diisocyanate
O
C NH
CH3
O
O
CH3
NH C OCH2CH2O C NH
O
O
NH C OCH2CH2O C
n
a polyurethane
Synthetic vascular grafts from W.L.Gore
Useful Definitions
Biodegradable
Undergoes degradation in the body
- Degradation: _____________________________
- Degradation products are harmless and can be
secreted naturally
water
Lactic acid
PLLA bone plates
Polymers: Biomedical Applications
• Rubbers
– latex, silicone
– good biocompatibility
• Used as maxillofacial prosthetics
Biomedical polymer
Poly(ethylene) (PE)
Low density (LDPE)
High density (HDPE)
Ultra high molecular weight
(UHMWPE)
Application
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.
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
Applications of Hydrogels
•
•
•
•
•
•
•
•
Soft contact lenses
Pills/capsules
Bioadhesive carriers
Implant coatings
Transdermal drug delivery
Electrophoresis gels
Wound healing
Chromatographic packaging material
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
‫‪Types of Gelation‬‬
‫• ‪Physical , Chemical‬‬
‫ژله‌اي شدن فيزيكي‪ :‬زنجيرهاي پليمر از طريق‬
‫واكنش‌هاي يوني‪ ،‬پيوند هيدروژني‪ ،‬درهم‬
‫گره خوردن مولكولي يا از راه طبيعت‬
‫آب‌گريزي ماده اتصال مي‌يابند‪.‬‬
‫ژله‌اي شدن شيميايي‪ :‬زنجيرهاي هيدروژل با‬
‫پيوند كوواالنت به يكديگر متصل شده‌اند‪.‬‬
‫در اين فرآيند‪ ،‬روش‌هايي نظير تابش‪،‬‬
‫افزودن اتصال‌دهنده‌هاي عرض ي شيميايي و‬
‫كار‬
‫تركيبات واكنش‌گر چند منظوره به ‌‬
‫مي‌روند‪.‬‬
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
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)
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
Properties of Hydrogels
• Pore Size
• Fabrication techniques
• Shape and surface/volume ratio
• H2O content
• Strength
• Swelling activation
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
Disadvantages of Hydrogels
• Low mechanical strength
• Hard to handle
• Difficult to load
• Sterilization
Why Hydrogels ?: Tissue Engineering
•
•
•
•
•
Biocompatible
H2O content
Sterilizibilty
Ease of use
High mechanical
Strength
• Surface to volume ratio
• Good cell adhesion
• High nutrient transport
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)
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
Why Hydrogels?: Drug Delivery
•
•
•
•
•
•
•
•
Safe degradation products
Biocompatible
High loading with ensured molecule efficacy
High encapsulation
Variable release profile
Stable
Inexpensive
High quality
• 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
Chitosan
• Chitosan (2-amino-2deoxy(1→4)-β-D-glucopyranan), a
polyaminosaccharide,
• obtained by alkaline
deacetylation of chitin (the principal
component of living organisms such as
fungi and crustacea).
Chitosan’s 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.
Alginate
Guluronic acid
Mannuronic 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.
‫• فصل ‪ 10‬و ‪ 11‬کتاب زیستمواد‪ ،‬اندامهای مصنوعی و مهندس ی بافت‬