Probable phase composition of the mineral in bone

Area of Science:

• Biomineralization
• Bone Histology
• Materials Science

Background:

• Bone mineral composition is complex and not fully understood.
• Existing formulas for bone mineral do not fully account for all detected elements.
• Previous studies often analyzed elements separately, limiting comprehensive compositional analysis.

Purpose of the Study:

• To review proposed formulas for bone mineral composition.
• To analyze existing literature data for conformity with these formulas.
• To identify and characterize the distinct mineral phases within bone.

Main Methods:

• Literature review of bone mineral composition studies.
• Analysis of literature data where Calcium (Ca), Phosphorus (P), Sodium (Na), Magnesium (Mg), and Carbonate (CO3) were determined in the same samples.
• Comparative analysis of experimental data against proposed mineral formulas.

Main Results:

• Magnesium (Mg) is found in a phase consistent with magnesium whitlockite (Ca/P ratio).
• Sodium (Na) and carbonate (CO3) are present in an apatite-structured carbonated calcium phosphate phase.
• A 'rest phase' with a Ca/P ratio of 2, matching the formula Ca8(PO4)4(CO3)(OH)2·XH2O, was identified in 101 bone samples across multiple species.

Conclusions:

• Bone mineral comprises at least three distinct phases: magnesium whitlockite, a Na- and CO3-containing apatite, and a novel carbonated calcium phosphate.
• The novel carbonated calcium phosphate phase, with a Ca/P ratio of 2, is proposed to have a structure similar to octocalcium phosphate and incorporates citrate ions.
• Human bone mineral is estimated to contain approximately 15% magnesium whitlockite, 25% Na/CO3-apatite, and the remainder as the novel carbonated calcium phosphate phase.