Bone formation following implantation of fibrous calcium compounds (beta-Ca(PO3)2, CaCO3(aragonite)) into bone marrow.

Bone formation around three types of fibrous calcium-containing crystals has been examined histologically using rats. The implanted materials are (i) calcium metaphosphate (beta-Ca(PO(3))(2)) fibers having aspect ratios of 15-80 with 2-20 microm in diameter, (ii) beta-Ca(PO(3))(2)) fibers surface-modified using dilute NaOH and (iii) calcium carbonate (CaCO(3); aragonite phase) whiskers having aspect ratios of 15-40 with 0.5-3 microm in diameter. Beta-Ca(PO(3))(2) fibers show a mechanically high strength with a low modulus of elasticity, and the surface-modified fibers have a thin layer consisting of a calcium orthophosphate phase. CaCO(3) whiskers were used for comparison reasons. The materials were implanted for 4, 8, and 12 weeks into bone defects created in the bone marrow of rat tibiae. Cancellous bone formation was observed around beta-Ca(PO3)2 fibers, the surface-modified fibers and CaCO(3) whiskers after implantation for 12, 4 and 4 weeks, respectively. CaCO(3) whiskers were scarcely observed after 12 weeks for resorbing. The calcium phosphate fibrous materials show combined advantages of mechanically high strength for toughening a matrix phase and biological activities; thus, these materials may prove to be useful for novel applications in the biomedical field.