Effect of Gradual Demineralization on the Mineral Fraction and Mechanical Properties of Cortical Bone

Abstract

Bone is often regarded as a composite material consisting of hydroxyapatite (HAp-like) mineral particles, organic matrix (mostly Type I collagen) and water phases in microscopic scale. The mechanical properties of bone at macroscopic scale depend on the structural organization and properties of constituents in the microscopic scale. In the attempts of understanding the effect of microscopic constituent on the mechanical properties of bone, the relationship between mechanical properties and mineral content of intact or completely demineralized samples have been studied. Even a slight alteration in the mineral content would have significant effect on the mechanical properties. In this work, the effect of degree of demineralization to the mechanical properties of bovine cortical bone was examined by gradually removing the mineral content and measuring constituents at every step till almost no traces of minerals were observed. Specimens were demineralized in 10% disodium EDTA solutions for 12, 24, 48, 72 hours and 14 days. The volume fraction of each structural constituent in the demineralized specimens was calculated from their X-ray absorption characteristics and quantifying transmitted X-ray intensity. Tensile tests were performed to measure the elastic modulus and ultimate strength of the demineralized specimens. This work shows the strong dependence of elastic modulus and ultimate strength of cortical bone to the mineral content as microscopic constituent. The degree of dependence with mineral loss has been demonstrated precisely so to provide the importance of mineral content and its role on the mechanical functioning of bone.