Biomaterials

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

A1.50
B1.33
C1.67

Show answer and explanation

Answer: C. 1.67

The formula contains 10 Ca and 6 P (from the 6 PO₄ groups), so Ca/P = 10/6 ≈ 1.67. Bone apatite contains carbonate ions and other species, and its Ca/P is somewhat lower than this. 1.50 is the ratio 3/2 of tricalcium phosphate (TCP, Ca₃(PO₄)₂). β-TCP is more soluble than hydroxyapatite and is used as a bioresorbable material that is resorbed in the body and replaced by bone. 1.33 is the ratio 8/6 of octacalcium phosphate (Ca₈H₂(PO₄)₆·5H₂O). If the Ca/P ratio of a synthesized powder deviates from 1.67, β-TCP or CaO forms as a by-product on firing, so controlling the composition is important.

Report an error

Practice this topic Back to topic

More Biomaterials questions

Which statement correctly describes osseointegration, as the term is used for pure titanium in dental implants and similar devices?
When a metal with a Young's modulus far higher than that of bone is used for the stem of an artificial hip joint, which statement correctly describes the resulting problem of stress shielding?
A rod of cortical bone (Young's modulus 20 GPa) and a rod of Ti-6Al-4V (Young's modulus 110 GPa) with the same cross-sectional area are joined in parallel and together carry a tensile load along their length. If both have the same strain, which value is closest to the fraction of the total load carried by the bone?
What is the main reason why β titanium alloys such as the Ti-Nb-Ta-Zr system have been developed for implants that fix bone?
Estimate the Young's modulus of porous titanium with open pores using the Gibson–Ashby equation E* = Es(ρ*/ρs)². If the Young's modulus of dense titanium is Es = 110 GPa and the porosity is 60%, which value is closest to E*? ρ*/ρs is the relative density.