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POLYMERIC IMPLANTS

Wound dressing. Biodegradable suture. Intraocular Lens. POLYMERIC IMPLANTS. Contact Lens. Some Commonly Used Polymers. Material Applications Silicone rubber Catheters, tubing Dacron Vascular grafts

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POLYMERIC IMPLANTS

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  1. Wound dressing Biodegradable suture Intraocular Lens POLYMERIC IMPLANTS Contact Lens

  2. Some Commonly Used Polymers MaterialApplications 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

  3. 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

  4. 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 ____________

  5. 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

  6. Polymers Structure Linear Branched Crosslinked

  7. 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

  8. Polymers Bioinert Biodegradable Polymers Natural Synthetic

  9. 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

  10. Polymers: Biomedical Applications (C2H4)nH2 • 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

  11. 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.

  12. Artificial Hip Joints (UHMWPE) http://www.totaljoints.info/Hip.jpg

  13. 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

  14. Intraocular Lens 3 basic materials - PMMA, acrylic, silicone

  15. 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

  16. 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

  17. 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

  18. 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

  19. Polymers: Biomedical Applications • Polyurethanes • block copolymer structure • good mechanical properties • good biocompatibility • tubing, vascular grafts, pacemaker lead insulation, heart assist balloon pumps

  20. 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.

  21. Synthetic vascular grafts from W.L.Gore

  22. Useful Definitions Biodegradable Undergoes degradation in the body - Degradation: _____________________________ - Degradation products are harmless and can be secreted naturally water Lactic acid PLLA bone plates

  23. Polymers: Biomedical Applications • Rubbers • latex, silicone • good biocompatibility • Used as maxillofacial prosthetics

  24. Table The clinical uses of some of the most common biomedical polymers relate to their chemical structure and physical properties.

  25. 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

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

  27. 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

  28. 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 كووالانت به يكديگر متصل شده‌اند. در اين فرآيند، روش‌هايي نظير تابش، افزودن اتصال‌دهنده‌هاي عرضي شيميايي و تركيبات واكنش‌گر چند منظوره به كار مي‌روند.

  29. 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

  30. 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)

  31. 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

  32. Properties of Hydrogels • Pore Size • Fabrication techniques • Shape and surface/volume ratio • H2O content • Strength • Swelling activation

  33. 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

  34. Disadvantages of Hydrogels • Low mechanical strength • Hard to handle • Difficult to load • Sterilization

  35. Why Hydrogels ?: Tissue Engineering • Biocompatible • H2O content • Sterilizibilty • Ease of use • High mechanical Strength • Surface to volume ratio • Good cell adhesion • High nutrient transport

  36. 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)

  37. 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

  38. Why Hydrogels?: Drug Delivery • Safe degradation products • Biocompatible • High loading with ensured molecule efficacy • High encapsulation • Variable release profile • Stable • Inexpensive • High quality

  39. 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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