2.79J/3.96J/BE.441/HST522J MATERIALS: BONDING AND PROPERTIES. M. Spector, Ph.D.

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1 Massachusetts Institute of Technology Harvard Medical School Brigham and Women s/massachusetts General Hosp. VA Boston Healthcare System 2.79J/3.96J/BE.441/HST522J MATERIALS: BONDING AND PROPERTIES M. Spector, Ph.D.

2 CHEMICAL BONDING Primary Metallic 100 kcal/mol Covalent 200 Ionic Secondary van der Waals 1-2 Hydrogen 3-7 Hydrophobic 1-2 Interactions

3 MATERIALS WITH PRIMARY ATOMIC BONDS e - M e _ e - e - e - M e - e - e - e - M e - e - M M _ e - M e - e - Metallic (electron glue or cloud ) -metals -100 kcal/mol Ionic (attraction of positive and negative ions) -ceramics -calcium phosphates kcal/mol H H H H C C C C H H H H Covalent (shared- pair electrons) -polymers -biological macromolec. (e.g. e.g.,, proteins) -200 kcal/mol

4 COMPOSITION OF METALS (%) Stainless Steel Fe Cr (17-20%) Ni (10-17) Mo (2-4) C (0.03) Mn,, P, S, Si (<2.8) Cobalt Chromium Co Cr (27-30) Titanium Ti Al ( ) V ( ) Fe,C,O (0.5) 20%) Cr (27 30) Al (5.5 17) Mo (5-7) V (3.5 4) Ni (2.5) Fe,C,O (0.5) C (0.03) Fe, C, Mn, Si (<3.1)

5 METALS e - e - M M e - e - e - e - e - e - M e - e - e - e - M e - e - M M M e - M e - e - Fracture surface

6 METAL SURFACE e - M e - e - e - e - M e - e - e - M e - e - M M e - M e - e - e - Free surface Electropositive

7 FORMATION OF METALLIC OXIDE e - O = O = e M - M e - e - e - e - M e - e - e - e - M M e - O = M e - e - e - Surface

8 THE METALLIC OXIDE (CERAMIC) SURFACE OF METALS Oxide 10nm-10 10µm Metal

9 ORTHOPAEDIC METALS Stainless Steel Cobalt- Chromium Titanium ADVANTAGES Strength Ease of manuf. Availability Strength Rel.. wear resist. Strength Low modulus Corrosion resist. DISADVANTAGES Potential for corrosion High mod. of elasticity High mod. of elasticity Poor wear resistance

10 METALS FOR TJA: PAST, PRESENT, AND FUTURE Stainless Steel Cobalt-Chromium Chromium Alloy Titanium Oxinium Oxinium (Smith &Nephew Orthopaedics; ; oxidized zirconium) is the first new metal alloy in orthopaedic surgery in 30 years.

11 METALS FOR TJA: PAST, PRESENT, AND FUTURE Stainless Steel Inertness/Biocompatibility Strength Cobalt-Chromium Chromium Alloy Titanium Selection Criteria Lower Modulus Oxinium Scratch-resist. resist. Lubricatious Non-Allergen.

12 ORTHOPAEDIC METALS Stainless Steel Cobalt- Chromium Titanium Oxinium ADVANTAGES DISADVANTAGES Strength Potential for corrosion Ease of manuf. High mod. of elasticity Availability Strength High mod. of elasticity Rel.. wear resist. Strength Poor wear resistance Low modulus Corrosion resist. Scratch-resist. resist.? Low modulus

13 Composition of Orthopaedic Metals Nb (2.5%) Zr Oxinium ASTM B550

14 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 µm thick. Oxygen Diffusion Air Original Surface Oxygen Enriched Metal Ceramic Oxide Oxygen Enriched Metal 500 o C Zirconium metal alloy is heated in air Oxygen diffuses into the metal surface Surface becomes enriched in oxygen Surface transforms to ceramic oxide Metal Substrate G. Hunter, S&N

15 Co-Cr Cr ALLOY VERSUS Zr-Nb ALLOY: THICKNESS OF THE OXIDE Chromium oxide 0.01 µm Co-Cr Cr alloy Ceramic 500 times thicker Zirconium oxide 5 µm Metal Oxinium Zr-Nb alloy

16 Fatigue Testing of Oxinium Femoral Components Fatigue strength the same as for Co-Cr Cr devices. Supports 4.4 kn (1000 lbf) ) in 10 Mcycle fatigue test. Tested worst-case: thin condyle, no bone, full flexion. Image removed due to copyright considerations. *Tsai et al., SFB 2001

17 ADVANTAGES OF OXINIUM 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 less adhesive wear of PE; better patella articulation Much lower modulus than Co-Cr Cr alloy (similar to Ti): lower stiffness and less stress shielding Non-allergenic

18 WEAR PROCESSES Asperity Abrasive plowing wear Metal Adhesive wear particle adherent to metal PE Component Crack propagated by cyclic loading results in fatigue (delamination) wear

19 WEAR PROCESSES Asperity Metal Abrasive wear PE Component Solution is a scratch-resistant metal/ceramic counterface; X-linked PE may not be the solution

20 EFFECT OF A SINGLE SCRATCH ON PE WEAR Profound effect of a single scratch; wear due to the ridge of metal bordering an scratch No PE wear if the metal ridge is removed Image removed due to copyright considerations. 10-fold increase in PE wear when the ridge bordering the scratch exceeded 2µm m in height (This type of scratch is not noticeable by eye.) Dowson, et al., Wear (1987)

21 Scratches on Retrieved Co-Cr Femoral Condyles Scanning Electron Microscopy Ant-post movement Ridge of metal >2µm 50 µm 100 µm Ridge of metal

22 SOURCES OF PARTICLES THAT CAUSE SCRATCHES ON CONDYLES Bone PMMA (bone cement) Wear and corrosion products from modular junctions Prosthetic coatings (viz.( viz.,, plasma sprayed Ti)

23 Is ceramic-on-pe the answer? Alumina or zirconia heads Image removed due to copyright considerations.

24 IF CERAMIC IS THE ANSWER How to obtain the benefit of ceramic-on on-pe articulation in TKA? Bulk ceramics do not have the necessary mechanical properties for TKA. Answer: A new metal alloy, zirconium niobium (Oxinium), the surface of which can be oxidized to form zirconium oxide (zirconia), a durable scratch- resistant ceramic.

25 Oxinium Image removed due to copyright considerations. May be a more innovative a development than cross-linked PE. One of only 2 materials developed principally for TJA (the other is hydroxyapatite).

26 CHARACTERISTICS OF OXIDES THAT AFFECT THEIR PERFORMANCE Thickness Adherence to metal substrate Porosity/density/strength of the oxide Oxide (Ceramic) Metal

27 Co-Cr Cr ALLOY VERSUS Zr-Nb ALLOY THICKNESS OF THE OXIDE Chromium oxide 0.01 µm Co-Cr Cr Ceramic Metal 500 times thicker Zirconium oxide Zr-Nb 5 µm

28 COMPARISON OF THE OXIDE THICKNESSES ON Co-Cr Cr AND Zr-Nb Chromium Oxide layer 2 µm Typical scratch in the Co-Cr Cr surface 0.01 µm thick Co-Cr Alloy Zirconium Oxide layer 5 µm thick Zr-Nb Alloy Thicker oxide layer (500x thicker) to protect against scratches.

29 Transmission Electron Microscopy Interface between oxide and metal: -no voids -no imperfections Prof. L.W. Hobbs, MIT ADHERENCE OF Zr OXIDE TO THE METAL Zirconium oxide Image removed due to copyright considerations. Zr0 2 thickness Cr V Benezra, et al. MRS Symp., 1999 Zirconium metal

30 Transmission Electron Microscopy Brick Wall Tough STRENGTH OF Zr OXIDE Zirconium oxide Rectangular crystals of Zr0 2 Image removed due to copyright considerations. V Benezra, et al. MRS Symp., 1999 Zirconium metal

31 Wear of PE with OxZr versus CoCr Condyles Knee Simulator Study Mean Tibial Wear (mm 3 ) Cast CoCrMo Oxidized Zr Number of Cycles (millions) Smith & Nephew Orthopaedics

32 WEAR PROCESSES Materials Issues Metal Abrasive Adhesive PE Fatigue (delamination) wear

33 WEAR PROCESSES Materials Issues What is missing from this picture? Metal Abrasive Adhesive PE Fatigue (delamination) wear

34 WEAR PROCESSES Materials Issues Metal Joint Fluid* Abrasive Adhesive PE Fatigue (delamination) wear * What role does the joint fluid play in the tribology of TJA?

35 WEAR IN TOTAL JOINT ARTHROPLASTY Lubrication Tribology Depends on amount, composition and mechanical properties of joint fluid Friction Better the lubrication lower the friction Wear Lower the friction, less wear

36 Image removed due to copyright considerations. Wear testing of a total knee replacement prostheses in a knee simulator. Bovine serum; not water Image removed due to copyright considerations. How good a lubricant is the patient s joint fluid?

37 COMPOSITION AND MECHANICAL PROPERTIES OF JOINT FLUID IN PRIMARY AND REVISION TKA Differences in certain compositional features and certain mechanical properties of joint fluid from revision cases when compared to the properties of fluid from patients before TKA. How well can joint fluid lubricate TKA? D. Mazzucco and M. Spector, J. Orthop. Res. 2002;20: D. Mazzucco, et al., Biomat., (In press)

38 COMPOSITION OF JOINT FLUID Metal Joint Fluid z PE Hyaluronic Acid Protein Phospholipid The amount and composition and properties of joint fluid in TKA patients vary widely; this could explain why some pts. have high wear. Solution; Metal with lower friction even in presence of abnormal joint fluid.

39 COMPOSITION OF JOINT FLUID Metal Joint Fluid z PE Two types of Lubrication: Fluid Film Boundary Layer Hyaluronic Acid Protein (Lubricin) Phospholipid

40 WEAR PROCESSES Fluid Film Lubrication Metal Joint Fluid z Fluid Film Lubrication; surfaces separate no friction and no wear; due to viscosity of fluid (HA conc. and MW), topography of counterfaces, and velocity: TKA? PE Hyaluronic Acid, HA

41 WEAR PROCESSES Fluid Film Lubrication Metal Joint Fluid z Fluid Film Lubrication; determine the patient s fluid viscosity (HA conc. and MW); benefit of HA injection? PE Hyaluronic Acid, HA

42 WEAR PROCESSES Boundary Layer Lubrication Metal Joint Fluid z PE Boundary Layer Lubrication; protein and lipid adsorb to the surfaces to decrease friction and reduce adhesive wear; can contribute to reducing abrasive and fatigue wear Protein Lipid

43 WEAR PROCESSES Boundary Layer Lubrication Metal Joint Fluid z PE Boundary Layer Lubrication; Determine the protein and lipid content of the joint fluid; employ a metal counterface that will best adsorb the lipid and protein; Oxinium Protein Lipid

44 ADVANTAGES OF OXINIUM Weds the best of a ceramic with the best of a metal. Scratch resistant: less abrasive wear of PE Better lubricity than Co-Cr Cr alloy: lower friction may result in less adhesive wear of PE; better patella articulation Much lower modulus than Co-Cr Cr alloy (similar to Ti): lower stiffness and less stress shielding Non-allergenic

45 WEAR IN TOTAL JOINT ARTHROPLASTY Lubrication Tribology Depends on amount, composition and mechanical properties of joint fluid Friction Better the lubrication lower the friction Wear Lower the friction, less wear

46 FRICTION APPARATUS Dead Weight Strain Gauge Cantilever Arm PE Pin Ground Metal Disk To Computer Coef.. of friction (µ)=lateral force/normal force

47 Friction of Oxinium with PE versus Co-Cr 0.08 Coefficient of Friction ice-ice AC-AC ± % dec.* 0.054±0.002 Water Serum Co-Cr Alloy * Wear of PE in serum< 1 / 3 wear in water Mazzucco & Spector

48 Friction of Oxinium with PE versus Co-Cr 0.08 Coefficient of Friction ± ± ± % dec.* 15% dec. 0 Water Serum Serum Co-Cr Alloy Oxinium * Wear of PE in serum< 1 / 3 wear in water Mazzucco & Spector

49 Oxinium versus CoCr Alloy for All Lubricants Co-Cr Ox-Zr Dynamic Coef h-prot-high g-prot-low f-phos-high e-phos-low d-ha-high c-ha-low b-serum a-pbs Lubricant 2-factor ANOVA; p<0.0001; power=1 Mazzucco & Spector

50 Dynamic Coefficient of Friction Water 0.06 Serum Mazzucco & Spector Results: Joint Fluid Lubrication TKA OA 3x difference in wear rate Within each group, samples are arranged in the order they were obtained Bars represent standard deviation

51 ADVANTAGES OF OXINIUM 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 less adhesive wear of PE; better patella articulation Much lower modulus than Co-Cr Cr alloy (similar to Ti): lower stiffness and less stress shielding Non-allergenic

52 Decrease in the Stress in the Distal Femur after TKA due to the Stiffness of the Co-Cr Femoral Component: Finite Element Analysis Image removed due to copyright considerations. M. Angelides, et al., Trans. Orthop. Res. Soc., 13:475 (1988)

53 Bone Loss due to Stress Shielding under a Femoral Component: Canine Model Image removed due to copyright considerations. J.D. Bobyn, et al., Clin. Orthop., 166:301 (1982)

54 RADIOGRAPHIC BONE LOSS AFTER TKA* Retrospective radiographic analysis of 147 TKAs. 3 designs Cemented and porous-coated, non-cemented Determination of whether bone loss was evident in the post-op op radiographs. 3 examiners * Mintzer CM, Robertson DD, Rackemann S, Ewald FC, Scott RD, Spector M. Bone loss in the distal anterior femur after total knee arthroplasty. asty. Clin Orthop. 260:135 (1990)

55 Bone Loss After TKA: Radiographic Study A-P Radiograph Lateral Radiograph Sites at which changes in bone density was evaluated. Image removed due to copyright considerations. Image removed due to copyright considerations. C.M. Mintzer, et al., Clin Orthop. 260:135 (1990)

56 Bone Loss Under the Femoral Component of a Total Knee Replacement Prosthesis: Stress Shielding 1 year post-op op Image removed due to copyright considerations. Image removed due to copyright considerations. C.M. Mintzer, et al., Clin Orthop. 260:135 (1990)

57 BONE LOSS UNDER THE FEMORAL COMPONENT OF TKA Bone loss occurred in the majority of cases (68% of patients). Bone loss occurred within the first post- operative year and did not appear to progress. Bone loss was independent of implant design and mode of fixation (i.e( i.e.,., cemented vs. non-cemented). C.M. Mintzer, et al., Clin Orthop. 260:135 (1990)

58 EFFECT OF BONE LOSS ON BONE STRENGTH How much bone loss needs to occur before it is detectable in a radiograph? Radiographic evidence of bone loss in the distal femur = 30% reduction in bone density.* How does bone loss affect bone strength? Bone strength is proportional to density 2. Therefore a 30% decrease in bone density means a 50% decrease in bone strength. *D.D. Robertson et al., J. Bone Jt. Surg.. 76-A:66 (1994)

59 BONE LOSS UNDER THE FEMORAL COMPONENT OF TKA Conclusion Bone loss occurs in the distal anterior femur post-tka due to stress shielding related to the stiffness of the cobalt- chromium alloy component C.M. Mintzer, et al., Clin Orthop. 260:135 (1990)

60 BONE LOSS DUE TO STRESS SHIELDING Potential Problems Complicates revision arthroplasty due to the loss of bone stock. May place the prosthesis at risk for loosening. May place the distal femur at risk of fracture. Solution Oxinium TKA. Oxinium has approximately ½ the stiffness of Co-Cr Cr alloy, therefore there should be less stress shielding and less bone loss.

61 ADVANTAGES OF OXINIUM 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 less adhesive wear of PE; better patella articulation Much lower modulus than Co-Cr Cr alloy (similar to Ti): lower stiffness and less stress shielding Non-allergenic

62 METAL SENSITIVITY IN PATIENTS 10-15% 15% of population have dermal sensitivity to metal (14% to Ni) Metals known as sensitizers: Ni > Co and Cr >>> Ti and V 60% of pts. with failed TJRs were metal sensitive vs. 25% with well-functioning implants Did metal sensitivity cause failure or did the failed implant cause metal sensitivity? Hallab,, Merritt, Jacobs, JBJS 83-A:428 (2001)

63 WHAT ARE CERAMICS? Compounds of metallic and nonmetallic (e.g.( e.g., oxygen) elements. Ceramic materials: Alumina (aluminum oxide) Zirconia (zirconium oxide) Metal oxides on metallic materials: Chromium oxide (on Stainless Steel and Co-Cr Cr alloys) Titanium oxide (on Titanium and Titanium alloy) Zirconium oxide (on Zr-Nb alloy)

64 ADVANTAGES OF CERAMICS Dense/hard (scratch resistant) Related to the character of the ionic bonding Ability to be polished to an ultra smooth finish

65 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

66 POLYMERS H H Polyethylene C C H H H Polymethylmethacrylate C C CH 3 H COOCH 3

67 ORTHOPEDIC POLYMERS ADVANTAGES DISADVANTAGES UHMWPE PMMA Relatively high wear resistance Polymerization in vivo Subject to oxidation Low fatigue strength (for load-bearing applications)

68 MOLECULAR STRUCTURE OF POLYETHYLENE Micrometer Level Fusion defects due to incomplete consolidation are cracks that can be propagated by fatigue (delamination) wear.

69 ULTRAHIGH MOLECULAR WEIGHT POLYETHYLENE H H C C H H 10-30nm Amorphous Region Tie Molecules Crystallites

70 MOLECULAR STRUCTURE OF 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( e.g.,., fibers) added to PE are only effective if PE bonds to them

71 POLYETHYLENE WEAR AND STRENGTH Intrinsic Factors Molecular weight distribution Cross-linking Crystallite size, shape, and orientation Degree of crystallinity Number of tie molecules Crystallites 10-30nm Tie Molecules

72 EFFECT OF GAMMA RADIATION ON H H PE: OXIDATION Gamma Radiation C C O 2 H H H O O 2 O 2 O 2 O 2 O 2 C C H H

73 GAMMA-RADIATION INDUCED MODIFICATION OF POLYETHYLENE Oxidation Aldehyde* O from C-CC cleavage C C Cross-linking C C C Ketone** from C-HC cleavage * Small peak in IR **Large peak in IR O C C C C C C from C-HC cleavage

74 Image removed due to copyright considerations From Sutula, Sperling, Collier, Saum, Williams. Delamination and White Band: Impact of Gamma Sterilization in Air and Material Consolidation AAOS 1995 Orlando

DuraCer. Ceramic Components. The Strong Choice In Ceramics

DuraCer. Ceramic Components. The Strong Choice In Ceramics The Strong Choice In Ceramics is a magnesia-stabilized zirconia (MgPSZ) ceramic material whose combination of physical properties is attractive for use in orthopaedic surgery. Mg-PSZ ceramic often is referred