What percentage of bone ECM is organics?

• A. 23%
• B. 77%
• C. 50%
• D. 30%

Answer: (A)

Bone extracellular matrix is a two-part composite: organic components and mineral (inorganic) components. The organic portion—primarily collagen type I with some non-collagenous proteins—constitutes roughly a quarter to a third of the matrix by weight, while the mineral part (hydroxyapatite) makes up the rest. In many references this organic fraction is given around 23–30%, with 23% being a common exam figure. So the organic portion of bone ECM is about 23%. The remaining ~77% is inorganic mineral, which provides stiffness and compressive strength. This balance helps explain how bone materials interact with implants: the organic part contributes toughness and remodeling ability, while the mineral part provides rigidity.