Natural bone is a kind of nanocomposites composed of orientated hydroxyapatite (HAp) along c-axis and fibrous collagen. Therefore, composites exhibiting composition and structure analogous to those of natural bone have been expected to be useful bone substitute materials. Organic polymer-HAp composites have been attracted much attention since they have interesting features such as bone-bonding ability, i.e. bioactivity and flexibility. In the present study, chitosan-HAp nanocomposites were prepared through mechanochemical reaction using conventional ball mill and subsequent aging. The obtained composites contained carbonate-containing HAp, and HAp nanocrystals in the composites aged at 25 C for 24 h showed a needle-like structure. They can form bone-like HAp on their surfaces after soaking in simulated body fluid (SBF), indicating potential for bioactivity in living body. The prepared chitosan-HAp composites are expected to be one of the useful bone substitute materials.

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Organic-inorganic composites, prepared from bone-bonding bioactive ceramics and organic polymers, are useful for novel bone substitutes having mechanical properties analogous to natural bone. We synthesized composites from cellulose and carbonate hydroxyapatite (CHAp) in situ through mechanochemical reaction. They contained B-type CHAp analogous to bone apatite. They showed a bending strengths of 10-13 MPa and Young's modulus of 1.5-2.2 GPa. We predicted their microstructure by comparing the measured density with the theoretical one. Cellulose was assumed to be distributed in the pore of CHAp at low cellulose content, and in grain boundaries of CHAp at high cellulose content. The composites formed calcium phosphate on their surfaces in simulated body fluid, meaning that they have a potential to be bioactive.