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Metallic Biomaterials

Metallic Biomaterials. Metals Are Crystalline. Body-Centered Cubic.

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Metallic Biomaterials

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  1. Metallic Biomaterials CHEE 340

  2. Metals Are Crystalline Body-Centered Cubic The body-centered cubic (bcc) crystal structure: (a) hard-ball model; (b) unit cell; and (c) single crystal with many unit cells. Source: W. G. Moffatt, et al., The Structure and Properties of Materials, Vol. 1, John Wiley & Sons, 1976. CHEE 340

  3. Metal Bonding • The electrons in metals are mobile and surround a core of cations. This gives rise to their high electrical conductivity. CHEE 340

  4. Crystals Grain Boundary Grain or Crystalline Structure Crystals and Grain Formation CHEE 340

  5. Product Manufacture • There are 4 main methods of metal product manufacture: • machining • melt casting • forging • hot isostatic pressing CHEE 340

  6. Influence of Manufacturing Process Casting Defect Polished-etched view of a cast ASTM F75 femoral hip stem. Note dendrites and large grains In vivo fracture initiated from an inclusion formed during the casting process From : H. Alexander et al., Chapter 2, Biomaterials Science, BD Ratner et al., Academic Press, 1996. CHEE 340

  7. Metallic Biomaterials • There are 3 main groups of metals used as biomaterials: • stainless steels • Co-based alloys • titanium-based alloys CHEE 340

  8. Design Considerations • typically want to match mechanical properties of tissue with mechanical properties of metal • have to consider how the metal may fail in vivo • corrosion • wear • fatigue • need to consider cost CHEE 340

  9. Mechanical Properties CHEE 340

  10. Corrosion • The extra-cellular environment is a chemically aggressive space. Metallic biomaterials are good conductors in an electrolyte solution, leading to galvanic corrosion. CHEE 340

  11. Corrosion CHEE 340

  12. Mechanisms of Corrosion • Crevice Corrosion • Pitting Corrosion • Intergranular Corrosion CHEE 340

  13. Mechanisms of Corrosion • Fretting Corrosion Stress Corrosion Cracking CHEE 340

  14. Mechanisms of Corrosion Contribution of biological environment From : S.H. Teoh, International Journal of Fatigue 22 (2000) 825–837 CHEE 340

  15. Wear • The effects of wear are most predominant in joint prostheses. • There are two types of wear : • Interfacial Wear • Fatigue Wear CHEE 340

  16. Fatigue • Recall that fatigue is progressive failure of a material due to the application of cyclical stresses below the ultimate stress of the material causing crack propagation. • Crack usually starts at a stress concentrator or stress riser. • Methods for reducing fatigue failure : CHEE 340

  17. Fatigue CHEE 340

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