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A simple synthetic method for preparing aragonite whiskers has been developed. A suspension of CaC1,-MgC1,-Mg(OH), with pH -9 has been prepared by adding Ca(OH), to MgCI, aqueous solution. CaCO, whiskers (aragonite phase) have been prepared easily by blowing C0,-containing gas into the suspension. The whiskers have high aspect ratios ranging from 20 to 80 with diameters of 0.5-1 pm.

A novel method for preparing calcium hydroxyapatite (Ca10(PO4)6(OH)2: HAp) fibers has been developed. HAp fibers can be prepared successfully by heating a compact consisting of calcium metaphosphate (ß‐Ca(PO3)2) fibers with Ca(OH)2 particles in air at 1000°C and subsequently treating the resultant compact with dilute aqueous HCl solution. The ß‐Ca(PO3)2 fibers and the Ca(OH)2 in the compact were converted into fibrous HAp and CaO phases by the heating, and the CaO phase was removed by acid‐leaching. HAp fibers obtained in the present work were 40‐150 µm in length and 2‐10 µm in diameter. The fibers had almost the same dimensions as those of the ß‐Ca(PO3)2 fibers.

Poly(lactic acid) composites containing a mixture of calcium carbonates (vaterite, aragonite, and calcite) were prepared by a carbonation process in methanol. Soaking of the composites for 3 h in simulated body fluid (SBF) at 37°C resulted in the deposition of bonelike apatite particles on the composite surface. After soaking the composites, vaterite phase in the composites was forward to dissolve rapidly, resulting in increase the supersaturation of the apatite in SBF. 13 C cross-polarization magic angle spinning nuclear magnetic resonance ( 13 C CP/MAS-NMR) spectra of the composites suggested the formation of a bond between Ca 2+ ion and the COO − group, which induces the apatite nucleation. These results may elucidate the mechanism of means to reduce the induction period for apatite formation.Artificial materials are generally encapsulated by a fibrous tissue to be isolated from the surrounding bones when implanted into the bone defects. However, a kind of ceramics and glasses such as hydroxyapatite ceramics or Bioglass bond directly to living bone without forming the fibrous tissue and they are often called bioactive materials. They form a carbonate-containing hydroxyapatite layer on their surface in the living body and bond to living bone through apatite layers. 1,3 This layer is very similar to the apatite in the bone in its composition and structure (bonelike apatite). 4 The apatite can be formed biomimetically on bioactive materials even in simulated body fluid (SBF), which is a buffer solution with inorganic ion concentrations nearly equal to those of human blood plasma. 5 Two indispensable conditions needed for the formation of bonelike apatite on materials are (i) the existence of the surface functional groups that induce nucleation of the apatite and (ii) the supersaturation of the apatite in body fluid or SBF should be increased. [5][6][7] Materials having a high bioactivity or biodegradability play an important role in the recovery of the part of bone defects. In this work, highly bioactive bone-filler materials were prepared for bone substitution at an early stage after clinical operation. Biodegradable poly(lactic acid) (PLA), because of many carboxy groups, is one of the promising candidates for supplying inducers for the bonelike apatite nucleation. A carboxy group is known to induce apatite nucleation 6 and can be formed by hydrolyzation of PLA. To increase the supersaturation of apatite in body fluid or SBF, a large amount of Ca 2+ ions should be dissolved from the materials. Formation of apatite having lattice constant and Ca/P atomic ratio close to those of natural bone has been reported to influence carbonate ions in the solution. 8 From this point of view, calcium carbonate is expected to supply both Ca 2+ and carbonate ions simultaneously into body fluid or SBF resulting in increase in the supersaturation of the apatite.It is well-known that calcium carbonate has three polymorphs, viz., calcite, aragonite, and vaterite. Solubility of vaterite is higher than that of calcite or aragonite. 9...