Page 44 - Academic Press Encyclopedia of Physical Science and Technology 3rd BioTechnology

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Encyclopedia of Physical Science and Technology EN002G-62 May 19, 2001 19:27

184 Biomaterials, Synthetic Synthesis, Fabrication, and Applications

FIGURE 6 Clinical use of metals in the human body.

of the human body. Figure 7 shows many of the clini- They can also be used in polymer ceramic composites
cal applications of ceramics together with the materials (e.g., polyethylene–hydroxyapatite). The specific mate-
used. Most applications relate to the repair of soft and rial form used depends on the application. For example,
hard tissues but ceramics are also used in the formation of single crystal sapphire is used as a dental implant because
replacement heart valves. of its high strength. A/W glass–ceramic is used to replace
Ceramics include inorganic materials such as carbons, vertebrae because it has high strength and bonds to bone.
silica, and metal oxides in crystalline and glassy phases Bioactive glasses have low strength but bond rapidly to
and salts such as calcium hydroxyapatite, found naturally bone and are therefore used in the repair of bony defects.
in bone and enamel. Ceramics are stiff, brittle materials Itshouldbenotedinallapplications,implantsmustremain
that are generally prepared by high temperature methods within the human body for many years and the long-term
and the resulting materials are insoluble in water. The stability of the materials used in the biological aqueous/
materials have high strength and hardness but they are saline environment must be considered.
only able to deform minimally under loading and there-
fore fracture easily. The materials are made in a variety of
1. Conventional Ceramics
physicalformssuchaspowders,coatings,andbulkphases.
They can show a range of crystallinity from single crystals These include oxides and salts of metallic elements and
(e.g., sapphire), polycrystalline materials (e.g., alumina silicon together with carbons. The use of oxide phases in
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and hydroxyapatite), glasses (e.g., Bioglass ), glasses implants eliminates the problem of metallic corrosion in
mixed with other ceramics (e.g., A/W glass–ceramic). a saline environment with high-purity alumina (Al 2 O 3 )