1. Lecture 3 Polymeric Biomaterials
BIOMATERIALS ENT 311/4
Lecture 3
Polymeric Biomaterials

2. POLYMERIC BIOMATERIALS
Teaching Plan
POLYMERIC BIOMATERIALS
Review structures and properties of biopolymers.
Define & Describe the biomedical application of polymeric biomaterials
DELIVERY
MODE
Lecture
Laboratory
experiments
LEVEL OF COMPLEXITY
Knowledge
Repetition
COURSE OUTCOME
COVERED
Ability to describe the concept of biocompatibility & basic concepts of materials used in medical application
Ability to select biomaterials that can be used for different medical applications and explain the criteria that will lead to a successful implants

3. 1.0 Introduction Application of synthetic polymers
medical disposable supply
prosthetic materials,
dental materials
implants
dressings
extracorporeal devices
encapsulants
polymeric drug delivery systems
tissue engineered products
orthodoses
References: J.S Temenoff, page: 132

4. 1.0 Introduction Main Advantages
Ease of manufacturability to produce various shapes
Ease of secondary processability
reasonable cost
Availability with desired mechanical and physical properties.
Stiff –kukuh/kaku

5. 1.0 Introduction
Stiff –kukuh/kaku

6. 2.0 Basic Structure
Polymers have very long chain molecules which are formed by covalent bonding along the backbone chain.
The long chains are held together by:
primary covalent bonding forces thru crosslinks between chains
2ndary bonding forces such as van derWaals & hydrogen bonds
Each chain can have side groups, branches & copolymeric, chains or blocks

7. 2.0 Basic Structure
As the molecular chains become longer, their relative mobility decreases
The higher the molecular weight, the less the mobility of chains which results in higher strength & greater thermal stability
Polymer chains can be arranged in 4 ways:
Linear
Branched,
Cross-linked
Three-dimensional network

8. 2.0 Basic Structure

9. 2.0 Basic Structure ~Linear Polymers
*The mer units are joined together end to end in single chains represents as a mass of spaghetti
*May have extensive van der Waals & hydrogen bonding between chains
~ Branched Polymers
*Side branch chains are connected to the backbone.
*The branches resulted from side reactions that occur during the polymer synthesis
*The chain packing efficiency is reduced by the formation of side branches which lowers the polymer density

10. 2.0 Basic Structure Cross-linked Polymers
Crosslinking process is achieved either by synthesis or nonreversible chemical reaction carried out at elevated temperature
Is accomplished by additive atoms or molecules covalently bonded to the chains
Network Polymers
Trifunctional mer units, having 3 active covalent bonds to form 3-D networks
A polymer that is highly crosslinked maybe classified as a network polymer

11. 2.0 Basic Structure Molecular Configuration ISOTACTIC CONFIGURATION
All the side groups are situated on the same side of the chain

12. 2.0 Basic Structure Syndiotactic Configuration Atactic Configuration
The side groups alternate sides of the chain
Atactic Configuration
Random positioning of side groups
Conversion of one stereoisomer to another will involve severing of bonds reformation after appropriate rotation

13. 2.0 Basic Structure Copolymers
a)Random copolymer-two different units are randomly dispersed along the chain
b)Alternating copolymer-the 2 mer units alternate chain positions
c) Block copolymer-the identical mers are clustered in blocks along the chain
d) Graft copolymer-homopolymer side branches of one type maybe grafted to homopolymer main chains that are composed of a different mer

14. 2.0 Basic Structure Revision (Molecular Weight Calculation)
The no. average molecular weight
Mn=ΣxiMi
The weight average molecular weight
Mw=ΣwiMi

15. 3.0 Crystal & Amorphous Structure in Bioplymer
Crystallization is easier for polymer with shorter chain
Branched polymer in which side chains are attached to the main backbone chain at positions will not crystallize easily
Linear polymers are much easier to crystallize
Partially crystallized structure (semicrystalline) is commonly occur in linear polymers
The cross-linked or 3-D network polymers cannot be crystallized at all & they become amorphous polymers.

16. 3.0 Crystal & Amorphous Structure in Bioplymer
Polymer with small side group are easy to crystallize
Isotactic & syndiotactic polymers usually crystallize even when the side groups are larger
Copolymerization always disrupts the regularity of polymer chains thus it is more amorphous
Plasticizers can prevent crystallization by keeping the chains separated from one another

17. 3.0 Crystal & Amorphous Structure in Bioplymer
Classical “fringed-micelle” model which shows the amorphous and crystalline regions coexist

18. 4.0 Biopolymers Properties
Thermoplastic Polymers
Usually have linear & branched structures, they soften when heated & harden when cooled.
The process reversible & can be repeated
The reheating and reforming process did not have significant change on the polymer properties
Mostly consist of a very long main chain of carbon atoms covalently bonded together

19. 4.0 Biopolymers Properties
Thermoplastic Polymers

20. 4.0 Biopolymers Properties
Thermosetting Polymers
The term implies that heat is required to permanently set the plastic
Thermosets polymer, once having hardened, will not soften upon heating, their structures are cross-linked & network.
They could be degrade or decompose if heated at very high temperature
Thermoset polymers are harder & stronger than thermoplastics

21. 4.0 Biopolymers Properties
Thermosetting Polymers

22. 5.0 Polymeric Biomaterials
Only ten to twenty polymers are mainly used in medical device fabrications from disposable to long-term implants

23. 5.0 Polymeric Biomaterials
Polyethylene (PE)
Available commercially as
high density (HDPE)
low density (LDPE)
linear low density (LLDPE)
very low density (VLDPE)
ultra high molecular weight (UHMWPE)
Clear to whitish translucent thermoplastic

24. 5.0 Polymeric Biomaterials
Polyethylene (PE)…(continue)
Low density
High Density
Linear low density

25. 5.0 Polymeric Biomaterials
Polyethylene (PE)…(continue)

26. 5.0 Polymeric Biomaterials
Polyethylene (PE)…(continue)
HDPE -pharmaceutical bottles, nonwoven fabrics, & caps
LDPE - flexible container applications, nonwoven-disposable & laminated (or coextruded with paper) foil & polymers for packaging.
LLDPE - pouches & bags due to its excellent puncture resistance
VLDPE - extruded tubes.

27. 5.0 Polymeric Biomaterials
Polyethylene (PE)…(continue)
UHMWPE (MW >2×106 g/mol) has been used for orthopedic implant fabrications.
This orthopedic implant fabrications include load-bearing applications:
Acetabular cup of total hip
Tibial plateau &
Patellar surfaces of knee joints.
Specific Properties: Low cost, easy to process, excellent electrical insulator, excellent chemical resistance, tough & flexible even at low temperature

28. 5.0 Polymeric Biomaterials
Polyvinylchloride (PVC)
PVC is amorphous, does not recrystallize due to the large side group (Cl, chloride)
It has a high melt viscosity hence it is difficult to process.
PVC homopolymer has high strength (7.5 to 9 psi) & brittle
PVC sheets & films – blood, solution storage bags & surgical packaging

29. 5.0 Polymeric Biomaterials
Polyvinylchloride (PVC)…continue
PVC tubing-commonly used in intravenous (IV) administration, dialysis devices, catheters, & cannulae
Specific Properties: Excellent resistance to abrasion, good dimensional stability, high chemical resistance
Note:
To prevent the thermal degradation of the polymer (HCl could be released), thermal stabilizers -metallic soaps/salts are incorporated
Di-2-ethylhexylphthalate (DEHP or DOP) is used in medical PVC formulation.

30. 5.0 Polymeric Biomaterials
Polypropylene (PP)
High melting ( C) & heat deflection temperature
Additives for PP such as antioxidants, light stabilizer, nucleating agents, lubricants, mold release agents, antiblock, & slip agents are formulated to improve the physical properties & processability
PP has an exceptionally high flex life & excellent environment stress-cracking resistance, hence it had been tried for finger joint prostheses with an integrally molded hinge design [Park, 1984]

31. 5.0 Polymeric Biomaterials
Polypropylene (PP)…continue
PP is used to make disposable hypothermic syringes, blood oxygenator membrane, packaging for devices, solutions, and drugs, suture, artificial vascular grafts, nonwoven fabrics, etc.
Specific Properties: Low density, good chemical resistance, moisture resistance & heat resistance
Good surface hardness & dimensional stability

32. 5.0 Polymeric Biomaterials
Polymethylmetacrylate (PMMA)
Commercial PMMA-amorphous material with good resistance to dilute alkalis & other inorganic solutions
Best known for exceptional light transparency (92% transmission), high refractive index (1.49), good weathering properties & as one of the most biocompatible polymers
Used broadly in medical applications:
blood pump & reservoir,
IV system,
membranes for blood dialyzer
in vitro diagnostics.

33. 5.0 Biomedical Applications of Polymeric Biomaterials
Polymethylmetacrylate (PMMA )…continue
It is also found in contact lenses & implantable ocular lenses due to excellent optical properties
Dentures, & maxillofacial prostheses due to good physical & coloring properties
Bone cement for joint prostheses fixation

34. 5.0 Biomedical Applications of Polymeric Biomaterials
Polystyrene (PS) and Its Copolymers
PS has good transparency, lack of color, ease of fabrication, thermal stability, low specific gravity & relatively high modulus
Commonly used in tissue culture flasks, roller bottles, vacuum canisters & filterware
Acrylonitrile–butadiene–styrene (ABS) copolymers are produced by 3 monomers: acrylonitrile, butadiene & styrene
Resistant to common inorganic solutions, have good surface properties, and dimensional stability
For IV sets, clamps, blood dialyzers, diagnostic test kits

35. 5.0 Polymeric Biomaterials
Polyesters
Frequently found in medical applications due to their unique chemical & physical properties
PET (polyethyleneterephthalate) is so far the most important
Biomedical applications-as artificial vascular graft, sutures & meshes.
It is highly crystalline with high melting temperature, hydrophobic & resistant to hydrolysis in dilute acids
Polycaprolactone is crystalline & has a low melting temperature.
Soft matrix or coating for conventional polyester fibers. Tissue engineering

36. 5.0 Polymeric Biomaterials
Polyamides (Nylon)
Flexibility of carbon chain contributes to molecular flexibility, low melt viscosity and high lubricity
Nylons are hygroscopic and lose their strength in vivo when implanted
Poly (p-phenylene terephthalate) commonly known as Kevlar®
Very good mechanical properties, good thermal properties, good chemical resistance, permeable to gases
Tubes for intracardiac catheters,surgical sutures, dialysis devices components,heart mitral valves, sutures

37. 5.0 Polymeric Biomaterials
Polytetrafluoroethylene (PTFE)
Commonly known as Teflon®
The polymer is highly crystalline, high density, low modulus of elasticity & tensile strength
It also has a very low surface tension & friction coefficient (0.1)
Specific Properties: Chemical inertness, exceptional weathering & heat resistance, nonadhesive, very low coefficient of friction
Application: Vascular & auditory prostheses, catheters, tubes

38. 5.0 Polymeric Biomaterials
Rubbers
Rubbers have been used for the fabrication of implants
Natural rubber is compatible with blood in pure form
Crosslinking by x-ray & organic peroxides produces rubber with superior blood compatibility
Silicone rubber developed for medical use
Good thermal stability, resistance to atmospheric & oxidative agents, physiological inertness
Burn treatment, shunt, mammary prostheses, maxillofacial implants

39. 5.0 Polymeric Biomaterials
Polyurethanes
Polyurethanes are usually thermosetting polymers: they are widely used to coat implants
polyurethane rubber is quite strong and has good resistance to oil and chemicals
Exceptional resistance to abrasion, resistance to breaking, very high elasticity modulus at compression traction & sheering remarkable
Adhesives, dental materials, blood pumps, artificial heart & skin

40. 5.0 Polymeric Biomaterials
Polyacetal, Polysulfone & Polycarbonate
Polyacetals & polysulfones are being tested as implant materials
Polycarbonates have found their applications in the heart/lung assist devices & food packaging
Polyacetals have reasonably high molecular weight & excellent mechanical properties
Excellent resistance to most chemicals & to water over wide temperature ranges
Hard tissue replacement

41. 5.0 Polymeric Biomaterials
Polyacetal, Polysulfone & Polycarbonate
Polysulfones have a high thermal stability due to the bulky side groups (therefore, they are amorphous) & rigid main backbone chains
Polycarbonates are tough, amorphous, & transparent polymers
Excellent mechanical & thermal properties, hydrophobicity & antioxidative properties

42. 5.0 Polymeric Biomaterials
Biodegradable Polymers…(continue)
Hydrolysis of PLA yields lactic acid which is a normal byproduct of anaerobic metabolism in the human body & is incorporated in the tricarboxylic acid (TCA) cycle to be finally excreted by the body as CO2 & water
PGA biodegrades by a combination of hydrolytic scission & enzymatic (esterase) action producing glycolic acid either enter the TCA cycle or is excreted in urine and can be eliminated as CO2 & water
PLGA can be controlled from weeks to over a year by varying the ratio of monomers & the processing conditions

43. 5.0 Polymeric Biomaterials
Biodegradable Polymers…(continue)
PLA-high tensile strength & low elongation resulting in a high modulus. Application:bone fracture fixation
PLGA-tissue engineered repair systems where cells are implanted within PLGA films or scaffolds
PLGA-drug delivery systems in which drugs are loaded within PLGA microspheres
Other-Poly-p-dioxanon:bioabsorbable polymer which can be fabricated into flexible monofilament surgical sutures

44. 5.0 Polymeric Biomaterials
Summary

45. Extra: Biopolymers Polymers are used in biomedical applications
Cardiovascular, Opthalmic and Orthopaedic implants
Dental implants, dental cements and denture bases
Low density, easily formed
and can be made biocompatible.
Recent development – biodegradable polymers.

46. Extra: Cardiovascular Applications
Heart valves can be stenotic or incompetent
Polymers are used to make artificial heart valves
Leaflets are made from biometals
Sewing ring made from PTFE or
PET
Connected to heart tissue
Blood clogging is side effect
PTFE is used as vascular graft to bypass clogged arteries.
Blood oxygenators : Hydrophobic polymer membranes used to oxygenate blood during bypass surgery
Air flows on one side and blood on the other side and oxygen diffuses into blood.

47. Extra: Opthalmic Applications
Eye glasses, contact lenses and Intraocular implants are made of polymers.
Hydrogel is used to make soft contact lenses
Absorbs water and allows snug fit
Oxygen permeable
Made of poly-HEMA
Hard lenses made from PMMA
Not oxygen permeable
Mixed with Siloxanylalkyl
Metacrylate and metacrylic
acid to make permeable and hydrophilic.
Intraocular implants are made of PMMA
Poly-HEMA-Poly(hydroxyethyl methacrylic) acid
Properties:water-content like living tissue, inertness to biological processes, resistance to degradation, permeability to metabolites, resistance to absorbtion by the body

48. Extra: Orthopedic Applications
Bone cement: Fills space between implant and bone – PMMA
Centrifuging and vacuum techniques minimize porosity
Used in joint prosthesis (Knee and Hip replacements)
Other applications:
Drug delivery systems: Polymer matrix with drug implanted inside the body
Struture materials: High tensile and knot pull strength.
Non-absorbable: Polypropylene, Nylon
Absorbable : Polyglycolic acid.

49. Extra: Tissue Engineering
Polymers can be synthesized and blend to suite the applications
Biodegradable polymers are used as scaffolding for generation of new tissues
In future, tissues can be generated in vivo or in vitro for repair or replacement.