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

4. 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

5. Polymer Devices Advantages: Disadvantages: Examples:
Some joint replacement articulating surfaces
Spinal cages
Biodegradable bone plates for low load regions
Biodegradable sutures
See Table 1.1 of Park
Hip joint
Spinal cage for spine fusion
Bone plates

6. 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
____________

8. 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

9. Polymers Structure
Linear
Branched
Crosslinked

11. Synthetic Polymers Biostable Polymers Biodegradable Synthetic 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

12. Polymers
Bioinert
Biodegradable
Polymers
Natural
Synthetic

17. 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

21. 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

22. 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.

23. Artificial Hip Joints (UHMWPE)

24. 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

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

26. 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

27. 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

28. 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

29. 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

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

31. 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.

32. Synthetic vascular grafts from W.L.Gore
Often the surgery will be 4 – 5 grafts, or as many as 9!!
Synthetic not good for small diam. because they get clogged.
Many people who need vascular grafts have pre-existing vascular conditions,
can’t take another graft or not healthy, so need a substitute sdVG.

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

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

35. 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.

36. 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

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

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

39. 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.

40. 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

41. 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)

42. 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

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

44. 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

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

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

47. 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)

48. 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

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

50. Environment controls mechanisms of swelling:
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

51. 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).

52. 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.

54. 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.

58. فصل 10 و 11 کتاب زیستمواد، اندامهای مصنوعی و مهندسی بافت