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Unformatted text preview: Massachusetts Institute of Technology Harvard Medical School Brigham and Women’s Hospital VA Boston Healthcare System 2.782J/3.961J/BEH.451J/HST524J BIOMATERIALS SURVEY M. Spector, Ph.D. TYPES OF PRIMARY ATOMIC BONDS e-­ e-­ e-­ e-­ M -­ M e-­ e-­ e e-­ M e-­ M ­ e-­ M e + + _ + M e-­ + _ + _ e-­ + _ e-­ Metallic (electron “glue” or “cloud”) -metals -metals Ionic (attraction of positive and negative ions) -ceramics -ceramics -calcium phosphates -calcium Page 1 HHHH CCC C HHHH Covalent (shared- pair electrons) (shared-polymers -polymers -biological macromolec. -biological macromolec. (e.g., proteins) BIOMATERIAL APPLICATIONS • Nonabsorbable materials for the fabrication of permanent implants. • Absorbable materials for the production of scaffolds for tissue engineering and regenerative medicine. COMPOSITION OF METALS (%) Stainless Steel Fe Cr (17-20%) (17-20%) Ni (10-17) (10-17) Mo (2-4) (2-4) C (0.03) Mn, P, S, Si (<2.8) Mn, Cobalt Chromium Co Cr (27-30) (27-30) Mo (5-7) (5-7) Ni (2.5) Fe, C, Mn, Si (<3.1) Mn, Page 2 Titanium Ti Al (5.5-6.5) (5.5-6.5) V (3.5-4.5) (3.5-4.5) Fe,C,O (0.5) Mechanical Prop. Mechanical Elastic Modulus Condition (GPa) Yield Strength (MPa) Ultimate Strength (MPa) Endurance Limit (MPa) ASTM# Stain. steels F55, F56 Annealed 190 331 586 241–276 F138, F139 Cold forged 190 1213 1351 820 Cobalt alloys F75 Cast/anneal 210 448–517 655–889 207–310 HIP* 253 841 1277 725–950 F799 Hot forged 210 896–1200 1399–1586 600–896 F90 Annealed 210 448–648 951–1220 F562 Hot forged 232 965–1000 1206 500 Cold-forged/ aged 232 1500 1795 689–793 Titanium alloy F67 30% Coldworked 110 485 760 300 F136 Forge anneal 116 896 965 620 Forged/heat treated 116 1034 1103 620–689 * HIP = hot isostatically pressed; ASTM = Amer. Soc. for Test. and Matls. ORTHOPAEDIC METALS ADVANTAGES DISADVANTAGES Stainless Steel Strength Ease of manuf. manuf. Availability Potential for corrosion High mod. of elasticity CobaltCobaltChromium Strength Rel. wear resist. Rel. High mod. of elasticity Titanium Strength Low wear resistance Low modulus Corrosion resistance Page 3 WHAT ARE CERAMICS? WHAT • Compounds of metallic and nonmetallic (e.g., oxygen) elements • Ceramic materials: Alumina (aluminum oxide) Zirconia (zirconium oxide) • Metal oxides: Chromium oxide Titanium oxide ADVANTAGES OF CERAMICS • Dense/hard (scratch resistant) Related to the character of the ionic bonding • Ability to be polished to an ultra smooth finish Page 4 THE METALLIC OXIDE (CERAMIC) SURFACE OF METALS 10nm-10m m 10nm-10 Oxide Metal CHARACTERISTICS OF OXIDES THAT AFFECT THEIR PERFORMANCE • Adherence to metal substrate Related to the mismatch in bonding (oxides comprise ionic and covalent bonds in contrast to metallic bonds) • Porosity/density • Thickness Page 5 METALS FOR TJA: PAST, PRESENT, AND FUTURE 1900-1940 1940-1960 1970 1980 1990 2000 2010 1900-1940 1940-1960 � Stainless Steel � Cobalt-Chromium Alloy Cobalt-Chromium � Titanium � Oxinium Oxinium is the first new metal alloy in orthopaedic surgery in 30 years. WHAT IS OXINIUM? Oxinium is a new metal alloy (zirconium­ (zirconiumniobium) that has a ceramic surface produced by a special oxidation process. It has also been referred to as “oxidized zirconium.” Page 6 METALS FOR TJA: PAST, PRESENT, AND FUTURE 1900-1940 1940-1960 1970 1980 1990 2000 2010 1900-1940 1940-1960 Stainless Steel � � Cobalt-Chromium Alloy Cobalt-Chromium � Titanium � Oxinium Selection Criteria � � Inertness/Biocompatibility Strength � Lower Modulus � Scratch-resist. Scratch-resist. � Lubricatious � Non-Allergen. Non-Allergen. ORTHOPAEDIC METALS Stainless Steel CobaltCobaltChromium Titanium Oxinium ADVANTAGES Strength Ease of manuf. manuf. Availability Strength Rel. wear resist. Rel. Strength Low modulus Corrosion resist. Scratch-resist. Scratch-resist. Low modulus Page 7 DISADVANTAGES Potential for corrosion High mod. of elasticity High mod. of elasticity Poor wear resistance ? WEAR PROCESSES Asperity Metal Abrasive plowing wear Adhesive wear particle adherent to metal PE Component Crack propagated by cyclic loading results in fatigue (delamination) wear EFFECT OF A SINGLE SCRATCH ON PE WEAR • Profound effect of a single scratch; wear due to the ridge of metal bordering an scratch 10-fold increase in 10-fold Image removed due to copyright restrictions. PE wear when the Diagram showing scratch profile before lapping ridge bordering the (with ridges) and after lapping (no ridges). scratch exceeded 2m m in height No PE wear if the metal ridge is removed (This type of scratch is not noticeable by eye.) Dowson, et al., Wear (1987) Dowson, et Page 8 Scratches on Retrieved Co-Cr Femoral Condyles Scanning Electron Microscopy Photos removed due to copyright restrictions. 100 m m 50 m m Ridge of metal WEAR PROCESSES WEAR Asperity Metal Abrasive wear PE Component Solution is a scratch-resistant metal/ceramic counterface; X-linked PE may not be the solution Page 9 Composition of Orthopaedic Metals Composition Nb (2.5%) Zr Oxinium ASTM B550 COMPOSITION OF METALS (%) Stainless Steel Fe Cr(17-20%) (17-20%) Ni (10-17) (10-17) Mo (2-4) (2-4) C (0.03) (0.03) Mn, P, S, Mn, Si (<2.8) CobaltCobaltChromium Co Cr (27-30) (27-30) Mo (5-7) (5-7) Ni (2.5) Titanium Alloy Ti Al (5.5-6.5) (5.5-6.5) V (3.5-4.5) (3.5-4.5) Fe,C,O (0.5) Fe, C, Mn, Mn, Si (<3.1) Page 10 ZirconiumZirconiumNiobium* Zr Niobium (2.5) (2.5) * Oxinium How is the Ceramic Surface Produced on Oxinium?: Oxidation Process • Wrought zirconium alloy device is heated in air. • Metal transforms as oxide grows; not a coating. • Zirconium Oxide (Zirconia ceramic) is ~5 mm thick. Air Oxygen Diffusion Air temp.>500oC Zirconium metal alloy is heated in air Oxygen diffuses into the metal surface Original Surface Surface becomes enriched in oxygen Ceramic Oxide Surface transforms to ceramic oxide Oxygen Enriched metal Metal Substrate Figure by MIT OCW. Oxinium Photo removed due to copyright restrictions. • May be a more innovative a development than cross-linked PE. • One of only 2 materials developed principally for TJA (the other is hydroxyapatite). Page 11 Fatigue Testing of Oxinium Femoral Components • Fatigue strength the same as for Co-Cr devices. Co-Cr • Supports 4.4 kN (1000 lbf) in 10 Mcycle fatigue test. lbf) • Tested worst-case: thin condyle, no bone, full flexion. worst-case: Photo removed due to copyright restrictions. *Tsai et al., SFB 2001 Co-Cr ALLOY VERSUS Zr-Nb ALLOY: Co THICKNESS OF THE OXIDE Chromium oxide 0.01 m m Co-Cr alloy Co500 times thicker 500 Ceramic Zirconium oxide Oxinium Metal Zr-Nb alloy Zr- Page 12 5 mm ADVANTAGES OF OXINIUM ADVANTAGES Weds the best of a ceramic with the best of a metal. • Scratch resistant: less abrasive wear of PE • More lubricatious: lower friction may result in lubricatious: less adhesive wear of PE; better patella articulation articulation • Much lower modulus than Co-Cr alloy (similar to CoTi): lower stiffness and less stress shielding • Non-allergenic Non- CHARACTERISTICS OF OXIDES THAT AFFECT THEIR PERFORMANCE • Thickness • Adherence to metal substrate • Porosity/density/strength of the oxide Oxide (Ceramic) Metal Page 13 Co-Cr ALLOY VERSUS Zr-Nb ALLOY THICKNESS OF THE OXIDE Chromium oxide 0.01 m m Co-Cr Co500 times thicker 500 Ceramic Zirconium oxide 5 mm Zr-Nb Zr- Metal COMPARISON OF THE OXIDE THICKNESSES ON Co-Cr AND Zr-Nb Chromium Chromium Oxide layer 2 mm Typical scratch in the Co-Cr Cosurface 0.01 m m thick Co-Cr Alloy Zirconium Oxide layer 5 mm thick Zr-Nb Alloy Thicker oxide layer (500x thicker) to protect against scratches. Page 14 Transmission Electron Microscopy Interface between oxide and metal: -no voids -no imperfections ADHERENCE OF Zr OXIDE TO THE METAL Zirconium oxide Zr02 thickness Prof. L.W. Hobbs, MIT Cr203 Zirconium metal Source: Benezra, V., M. Spector, et al. "Microstructural Investigation of the Oxide Scale on Zr-2.5 Nb and its Interface with the Alloy Substrate." In Biomedical Materials -- Drug Delivery, Implants and Tissue Engineering. Mat. Res. Soc. Symp. Proc. Vol. 550, 1999, pp. 337-342. STRENGTH OF Zr OXIDE Transmission Electron Microscopy Zirconium oxide Rectangular crystals of Zr02 “Brick Wall Tough” Zirconium metal Source: Benezra, V., M. Spector, et al. "Microstructural Investigation of the Oxide Scale on Zr-2.5 Nb and its Interface with the Alloy Substrate." In Biomedical Materials -- Drug Delivery, Implants and Tissue Engineering. Mat. Res. Soc. Symp. Proc. Vol. 550, 1999, pp. 337-342. Page 15 Image removed due to copyright restrictions. Photo of ceramic on PE hip joint.ew Text Hip Simulator Study I.C. Clarke and A. Gustafson Clin. Orthop. 379:34 (2000) Image removed due to copyright restrictions. Graph of wear rate vs. protein content. Page 16 Wear of PE with OxZr versus CoCr Condyles Knee Simulator Study Image removed due to copyright restrictions. Graph of mean tibial wear vs. number of cycles. Smith & Nephew Orthopaedics POLYMERS POLYMERS H C H H Polymethylmethacrylate C H Polyethylene H CH3 C C H Page 17 COOCH3 ORTHOPEDIC POLYMERS ADVANTAGES DISADVANTAGES UHMWPE Relatively high Subject to oxidation wear resistance PMMA Polymerization in vivo in Low fatigue strength (for load-bearing load-bearing applications) MECHANICAL PROPERTIES Stainless steel Co-Cr Alloy CoTi (6AL-4V) (6ALBone PMMA UHMWPE Tensile Strength (psi) psi) 90,000 150,000 150,000 10–15,000 10– 7,000 6,500 Page 18 Modulus of Elasticity (106psi) 28 35 16 2–3 0.2–0.5 0.2– 0.06–0.18 0.06– WEAR PROCESSES WEAR Asperity Metal Abrasive plowing wear Adhesive wear particle adherent to metal PE Component Crack propagated by cyclic loading results in fatigue (delamination) wear POLYETHYLENE SYNTHESIS Hoechst COMPACTION Westlake Poly Hi COMP. MFG. Orthopedic Co. Resin (Powder, Flake) 125 µm Extruded Rod Comp. Molded Plate Machined Molded MW Catalyst Fusion defects Sterilization Page 19 g-Radiation-Induced Oxidation Photos removed due to copyright restrictions. Fusion Defects Radiation-induced x-linking Radiation-induced x-linking Mandy and Walker MOLECULAR STRUCTURE OF POLYETHYLENE Micrometer Level Micrometer Fusion defects due to incomplete consolidation are cracks that can be propagated by fatigue (delamination) wear. Page 20 ULTRAHIGH MOLECULAR ULTRAHIGH WEIGHT POLYETHYLENE HH CC 10-30nm 10- HH Amorphous Region “Tie” Molecules Diagram of PE crystallite structure removed Crystallites due to copyright restrictions. MOLECULAR STRUCTURE OF MOLECULAR POLYETHYLENE • • • • Nanometer Level “Tie” molecules bind PE crystallites Mechanical properties are related to the number of tie molecules (fracture occurs through the amorphous region comprised of tie molecules) Mechanical bonding between PE particles is due to entanglement of molecular chains Reinforcing elements (e.g., fibers) added to PE are only effective if PE bonds to them Page 21 g-Radiation-Induced Oxidation Photos removed due to copyright restrictions. Fusion Defects Radiation-induced x-linking Radiation-induced x-linking Mandy and Walker MOLECULAR STRUCTURE OF POLYETHYLENE Micrometer Level Micrometer Fusion defects due to incomplete consolidation are cracks that can be propagated by fatigue (delamination) wear. Page 20 ULTRAHIGH MOLECULAR ULTRAHIGH WEIGHT POLYETHYLENE HH CC 10-30nm 10- HH Amorphous Region “Tie” Molecules Diagram of PE crystallite structure removed Crystallites due to copyright restrictions. MOLECULAR STRUCTURE OF MOLECULAR POLYETHYLENE • • • • Nanometer Level “Tie” molecules bind PE crystallites Mechanical properties are related to the number of tie molecules (fracture occurs through the amorphous region comprised of tie molecules) Mechanical bonding between PE particles is due to entanglement of molecular chains Reinforcing elements (e.g., fibers) added to PE are only effective if PE bonds to them Page 21 Cross-Linked PE Hip Simulator Studies Oonishi/Japan 100 Mrad Courtesy of the Orthpaedic Research Society. Used with permission. CROSS-LINKED POLYETHYLENE: CROSS TRADE-OFFS What is Sacrificed for Lower Wear? • Reduction in the strain to break with cross-linking; fracture at lower crossstrain; less toughness* • Less resistance to crack propagation * g-radiation cross-linked parts are tougher -radiation cross-linked than e-beam cross-linked components e-beam cross-linked Page 24 Representative Tensile True Strain/True Stress Plot for Control and Radiation Cross-Linked UHMWPEs 350 Control 2.5 MRad 5 MRad 10 MRad 20 MRad True Stress [MPa] 300 250 200 150 100 50 0 0.0 0.5 1.0 1.5 2.0 True Strain [mm/mm] A. Bellare, et al. Crack Growth Parameters for Radiation Cross-linked PE Dose [kGy] 0 25 50 100 200 q [rad] 0.372 0.404 0.376 0.328 0.217 e q [rad] 1.126 0.759 0.594 0.439 0.276 p Rss [mm] 22.7 19.4 16.5 15.2 8.2 Jss/J1c* 55.42 4.25 1.30 0.56 0.22 J1c [kJm-2] 2.1 23.8 76.2 - T 31.3 11.3 2.0 -ve -ve * Energy that it takes to propagate a crack. A. Bellare, et al. Page 25 CROSS-LINKED PE CUPS: CROSS POTENTIAL FOR FRACTURE • Rim loaded cross-linked cups crosshave a 100,000-fold decrease in 100,000their resistance to fatigue their fracture, despite having only a fracture, 10-fold decrease in fracture 10toughness • Cups failed after only 100 cycles *S. Li, Soc. for Biomaterials, May 1, 1999 CROSS-LINKED PE CUPS: POTENTIAL FOR FRACTURE • Will we be seeing more frequent fracture of cups? • Will fracture of cups be design sensitive? • In “solving” wear will we have introduced a new problem? *S. Li, Soc. for Biomaterials, May 1, 1999 Page 26 ROLE OF X-LINKED PE IN TKA XElectron Beam X-Linked and Melted X• Against (C. Rimnac and AS Greenwald) – Highly x-linked PEs have … inferior fracture xproperties” properties” – “raise concerns of gross fracture in knee components” components” – “There are THR designs that utilize conventional PE with contemporary sterilization methods that have been shown to have excellent clinical longlongterm performance.” AAOS Bulletin, June 2002, p. 50-51 50-51 WEAR OF CROSS-LINKED PE H Marrs, et al., Trans. ORS, 1998, p. 100 Abrasive wear Adhesive wear Courtesy of the Orthpaedic Research Society. Used with permission. Page 27 E F F E C T S OF A R O U G H M E T A L C O U N T E R F A C E O N W E A R O F C R O S S -LINKED PE Knee Simulator Image removed due to copyright restrictions. Bar graph of wear rate for clean and abraded cases, CoCr/CPE vs. CoCr/XPE. V. Good and K. Widding, S&N In TKA, X-linked PE wears more than conv. PE (EtO) against a scratched metal counterface. BIOMATERIAL APPLICATIONS BIOMATERIAL • Nonabsorbable materials for the fabrication of permanent implants. • Absorbable materials for the production of scaffolds for tissue engineering and regenerative medicine. Page 28 SCAFFOLD (MATRIX) MATERIALS SCAFFOLD Synthetic • • • • • • • • Polylactic acid and polyglycolic acid Polycarbonates Polydioxanones Polyphosphazenes Poly(anhydrides) Poly(anhydrides) Poly(ortho esters) Poly(propylene fumarate) fumarate) Pluronic (polaxomers) polaxomers) – Poly(ethylene oxide) and poly(propylene oxide) SCAFFOLD (MATRIX) MATERIALS Natural • Collagen –Gelatin and fibrillar sponge –Non-cross-linked and cross-linked Non-crosscross- • Collagen-GAG copolymer Collagen• Albumin • Fibrin • Hyaluronic acid • Cellulose –Most abundant natural polymer –Mechanism of absorbability in vivo? in Page 29 SCAFFOLD (MATRIX) MATERIALS SCAFFOLD Natural (Continued) • Chitosan –Derived from chitin, 2nd most abundant natural polymer –Mechanism of absorbability in vivo? in • Polyhydroxalkanoates –Naturally occurring polyesters produced by fermentation • Alginate (polysaccharide extracted from seaweed) • Agarose • Polyamino acids Page 30 ...
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This note was uploaded on 11/11/2011 for the course BIO 2.797j taught by Professor Matthewlang during the Fall '06 term at MIT.

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