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

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Metallic Biomaterials

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Metallic Biomaterials

CHEE 340


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


Metal Bonding

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

CHEE 340


Crystals

Grain Boundary

Grain or Crystalline Structure

Crystals and Grain Formation

CHEE 340


Product Manufacture

  • There are 4 main methods of metal product manufacture:

  • machining

  • melt casting

  • forming

  • hot isostatic pressing (sintering)

CHEE 340


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


Metallic Biomaterials

  • There are 3 main groups of metals used as biomaterials:

    • stainless steels

    • Co-based alloys

    • titanium-based alloys

CHEE 340


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


Mechanical Properties

CHEE 340


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


Corrosion

CHEE 340


Mechanisms of Corrosion

  • Crevice Corrosion

  • Pitting Corrosion

  • Intergranular Corrosion

CHEE 340


Mechanisms of Corrosion

  • Fretting CorrosionStress Corrosion Cracking

CHEE 340


Mechanisms of Corrosion

Contribution of biological environment

From : S.H. Teoh, International Journal of Fatigue 22 (2000) 825–837

CHEE 340


Wear

  • The effects of wear are most predominant in joint prostheses.

  • There are two types of wear :

  • Interfacial Wear: Occurs when bearing surfaces come into contact with no lubricant fluid between them.

  • Fatigue Wear:Progressive failure due to application of cyclical stresses.

CHEE 340


Fatigue

CHEE 340


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