polymeric implants biodegradable suture intraocular lens wound dressing contact lens
TRANSCRIPT
POLYMERIC IMPLANTS
Biodegradable suture
Intraocular Lens
Wound dressing
Contact 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 DeliveryCollagen (reprocessed) Opthalmologic applications, wound
dressings
Polymer Devices
Advantages: Disadvantages:
Examples:Some joint replacement articulating surfacesSpinal cagesBiodegradable bone plates for low load regionsBiodegradable sutures
Hip joint Spinal cage for spine fusion Bone plates
Mechanical Properties: Why is important to study for all biomaterials?
Toe implant
polymermetal
polymer
______________ hydrogel ____________
Determines how well it will work (or not work) for a given device.
One major factor is the modulus of the material.
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
PolymersBioinertBiodegradable
PolymersNaturalSynthetic
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)– 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
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 Lens3 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
PolyurethanesA urethane has an ester group and amide group bonded to the same carbon. Urethanes can be prepare by treating an isocyanate with an alcohol.
RN C O ROH RNH C
O
OR+
an isocyanate an alcohol a urethane
Polyurethanes are polymers that contain urethane groups.
O C NCH3
N C O
toluene-2,6-diisocyanate
+ HOCH2CH2OH
ethylene glycol
C
O
NHCH3
NH C
O
OCH2CH2O C
O
NH NH C
O
OCH2CH2O C
OCH3
n
a polyurethane
Synthetic vascular grafts from W.L.Gore
Useful Definitions
BiodegradableUndergoes degradation in the body
- Degradation: _____________________________
- Degradation products are harmless and can be secreted naturally
PLLA bone plates
waterLactic acid
Polymers: Biomedical Applications
• Rubbers
– latex, silicone
– good biocompatibility
• Used as maxillofacial prosthetics
Biomedical polymerBiomedical polymer ApplicationApplication
Poly(ethylene) (PE)Poly(ethylene) (PE)
Low density (LDPE)Low density (LDPE)
High density (HDPE)High density (HDPE)
Ultra high molecular weightUltra high molecular weight
(UHMWPE) (UHMWPE)
Bags, tubingBags, tubing
Nonwoven fabric, catheterNonwoven fabric, catheter
Orthopedic and facial implants Orthopedic and facial implants
Poly(methyl methacrylate) (PMMA) Poly(methyl methacrylate) (PMMA) Intraocular lens, dentures, bone cementIntraocular lens, dentures, bone cement
Poly(vinyl chloride) (PVC) Poly(vinyl chloride) (PVC) Blood bags, catheters, cannulae Blood bags, catheters, cannulae
Poly(ethylene terephthalate) (PET)Poly(ethylene terephthalate) (PET) Artificial vascular graft, sutures,Artificial vascular graft, sutures,
heart valves heart valves
Poly(esters)Poly(esters) Bioresorbable sutures, surgicalBioresorbable sutures, surgical
products, controlled drug releaseproducts, controlled drug release
Poly(amides) (Nylons)Poly(amides) (Nylons) Catheters, suturesCatheters, sutures
Poly(urethanes) (PU) Poly(urethanes) (PU) Coat implants, film, tubing 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
ژله اي شدن فيزيكي: زنجيرهاي پليمر از طريق واكنش هاي يوني،
پيوند هيدروژني، درهم گره خوردن مولكولي يا از راه طبيعت
آب گريزي ماده اتصال مي يابند. ژله اي شدن شيميايي: زنجيرهاي هيدروژل با پيوند كوواالنت به يكديگر متصل شده اند. در اين فرآيند، روش هايي نظير تابش،
افزودن اتصال دهنده هاي عرضي شيميايي و تركيبات واكنش گر چند منظوره به كار مي روند.
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
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.
کتاب زیستمواد، اندامهای 11 و 10فصل •مصنوعی و مهندسی بافت