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Biomaterials

Which of these is a bioactive ceramic that bonds directly and chemically to bone?

  1. AHydroxyapatite
  2. BHigh-purity alumina
  3. CYttria partially stabilized zirconia
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Answer: A. Hydroxyapatite

Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) is a calcium phosphate with nearly the same composition as the mineral component of bones and teeth; in the body a layer of the same kind of apatite as bone forms on its surface, and it bonds directly to bone. Because of this property it is used as a filler for bone defects and as a surface coating on metal implants. Bioactive glass bonds to bone in the same way. High-purity alumina and partially stabilized zirconia are bioinert ceramics that hardly react in the body; being hard and wear resistant, they are used for the femoral heads of artificial hip joints, but they do not bond chemically to bone. Their surfaces are either covered by a thin fibrous membrane or only interlock mechanically with bone.

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  1. What is the Ca/P molar ratio of hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂?
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