Biomaterials for Medical Applications

1. Biomaterials for Medical Applications Reporter: AGNESPurwidyantri Student ID no: D0228005 Biomedical Engineering Dept.

2. What is a Biomaterial? A material intented to interface with biological systems to evaluate, treat, augment or replace any tissue, organ or function of the body.

3. Biomaterials cover all classes of materials – metals, ceramics, polymers

4. Medical Devices Values (Biomaterials Science: An Introduction to Materials in Medicine, 2nd ed., B.D. Ratner et al., eds., Elsevier, NY 2004)

5. Structural Hierarchy

6. 10 nm Polymer Crystallinity Adapted from Fig. 14.10, Callister 7e. Ex: polyethylene unit cell • Crystals must contain the polymer chains in some way • Chain folded structure Adapted from Fig. 14.12, Callister 7e.

7. Polymer Crystallinity Polymers rarely 100% crystalline • Too difficult to get all those chains aligned crystalline region • % Crystallinity: % of material that is crystalline. -- TS and E often increase with % crystallinity. -- Annealing causes crystalline regions to grow. % crystallinity increases. amorphous region Adapted from Fig. 14.11, Callister 6e. (Fig. 14.11 is from H.W. Hayden, W.G. Moffatt, and J. Wulff, The Structure and Properties of Materials, Vol. III, Mechanical Behavior, John Wiley and Sons, Inc., 1965.)

8. Polymer Crystal Forms Single crystals – only if slow careful growth Adapted from Fig. 14.11, Callister 7e.

9. Spherulites – crossed polarizers Maltese cross Adapted from Fig. 14.14, Callister 7e.

10. Mechanical Properties i.e. stress-strain behavior of polymers brittle polymer FS of polymer ca. 10% that of metals plastic elastomer elastic modulus – less than metal Adapted from Fig. 15.1, Callister 7e. Strains – deformations > 1000% possible (for metals, maximum strainca. 10% or less)

11. fibrillar structure Near Failure near failure Initial aligned, networked crystalline cross- case regions linked slide case semi- amorphous crystalline crystalline regions case regions align elongate Tensile Response: Brittle & Plastic s (MPa) brittle failure x onset of necking plastic failure x unload/reload e Stress-strain curves adapted from Fig. 15.1, Callister 7e. Inset figures along plastic response curve adapted from Figs. 15.12 & 15.13, Callister 7e. (Figs. 15.12 & 15.13 are from J.M. Schultz, Polymer Materials Science, Prentice-Hall, Inc., 1974, pp. 500-501.)

12. Predeformation by Drawing • Drawing…(ex: monofilament fishline) -- stretches the polymer prior to use -- aligns chains in the stretching direction • Results of drawing: -- increases the elastic modulus (E) in the stretching direction -- increases the tensile strength (TS) in the stretching direction -- decreases ductility (%EL) • Annealing after drawing... -- decreases alignment -- reverses effects of drawing. • Compare to cold working in metals! Adapted from Fig. 15.13, Callister 7e. (Fig. 15.13 is from J.M. Schultz, Polymer Materials Science, Prentice-Hall, Inc., 1974, pp. 500-501.)

13. Tensile Response: Elastomer Case final: chains are straight, still cross-linked Deformation initial: amorphous chains are is reversible! kinked, cross-linked. s (MPa) brittle failure x Stress-strain curves adapted from Fig. 15.1, Callister 7e. Inset figures along elastomer curve (green) adapted from Fig. 15.15, Callister 7e. (Fig. 15.15 is from Z.D. Jastrzebski, The Nature and Properties of Engineering Materials, 3rd ed., John Wiley and Sons, 1987.) plastic failure x x elastomer e • Compare to responses of other polymers: -- brittle response (aligned, crosslinked & networked polymer) -- plastic response (semi-crystalline polymers)

14. Thermoplastics vs. Thermosets T Callister, rubber viscous Fig. 16.9 mobile Tm liquid tough liquid plastic Tg partially crystalline crystalline solid solid Molecular weight • Thermoplastics: -- little crosslinking -- ductile -- soften w/heating -- polyethylene polypropylene polycarbonate polystyrene • Thermosets: -- large crosslinking (10 to 50% of mers) -- hard and brittle -- do NOT soften w/heating -- vulcanized rubber, epoxies, polyester resin, phenolic resin Adapted from Fig. 15.19, Callister 7e. (Fig. 15.19 is from F.W. Billmeyer, Jr., Textbook of Polymer Science, 3rd ed., John Wiley and Sons, Inc., 1984.)

15. T and Strain Rate: Thermoplastics 8 0 6 0 4 0 20 s (MPa) • Decreasing T... -- increases E -- increases TS -- decreases %EL • Increasing strain rate... -- same effects as decreasing T. Data for the 4°C semicrystalline polymer: PMMA 20°C (Plexiglas) 40°C to 1.3 60°C 0 e 0 0.1 0.2 0.3 Adapted from Fig. 15.3, Callister 7e. (Fig. 15.3 is from T.S. Carswell and J.K. Nason, 'Effect of Environmental Conditions on the Mechanical Properties of Organic Plastics", Symposium on Plastics, American Society for Testing and Materials, Philadelphia, PA, 1944.)

16. Melting vs. Glass Transition Temp. What factors affect Tm and Tg? • Both Tm and Tg increase with increasing chain stiffness • Chain stiffness increased by • Bulky sidegroups • Polar groups or sidegroups • Double bonds or aromatic chain groups • Regularity – effects Tm only Adapted from Fig. 15.18, Callister 7e.

17. Time Dependent Deformation • Data: Large drop in Er for T > Tg. (amorphous polystyrene) 5 10 rigid solid Er(10s) (small relax) Adapted from Fig. 15.7, Callister 7e. (Fig. 15.7 is from A.V. Tobolsky, Properties and Structures of Polymers, John Wiley and Sons, Inc., 1960.) 3 10 in MPa transition tensile test 1 10 region eo strain -1 10 viscous liquid -3 s(t) (large relax) 10 60 100 140 180 T(°C) time Tg • Sample Tg(C) values: • Relaxation modulus: PE (low density) PE (high density) PVC PS PC -110 - 90 + 87 +100 +150 Selected values from Table 15.2, Callister 7e. • Stress relaxation test: -- strain to eo and hold. -- observe decrease in stress with time.

18. alligned chains microvoids fibrillar bridges crack Polymer Fracture Crazing Griffith cracks in metals – spherulites plastically deform to fibrillar structure – microvoids and fibrillar bridges form Adapted from Fig. 15.9, Callister 7e.

19. Propagation • Termination Addition (Chain) Polymerization • Initiation

20. Condensation (Step) Polymerization

21. Polymer Types • Coatings – thin film on surface – i.e. paint, varnish • To protect item • Improve appearance • Electrical insulation • Adhesives – produce bond between two adherands • Usually bonded by: • Secondary bonds • Mechanical bonding • Films – blown film extrusion • Foams – gas bubbles in plastic

22. Advanced Polymers • Ultrahigh molecular weight polyethylene (UHMWPE) • Molecular weight ca. 4x106 g/mol • Excellent properties for variety of applications • bullet-proof vest, golf ball covers, hip joints, etc. UHMWPE Adapted from chapter-opening photograph, Chapter 22, Callister 7e.

23. Polymeric Biomaterials: Advantages Disadvantages Easy to make complicated items Tailorable physical & mechanical properties Surface modification Immobilize cell etc. Biodegradable Leachable compounds Absorb water & proteins etc. Surface contamination Wear & breakdown Biodegradation Difficult to sterilize

24. General Criteria for materials selection • Mechanical and chemicals properties • No undersirable biological effects carcinogenic, toxic, allergenic or immunogenic • Possible to process, fabricate and sterilize with a godd reproducibility • Acceptable cost/benefit ratio

25. Material Properties Compresssive strength Tensile strength Bending strength E-Modulus Coefficient of thermal expansion Coefficient of thermal coductivity Surface tension Hardness and density Hydrophobic/philic Water sorption/solubility Surface friction Creep Bonding properties

26. Thank You!