Biomimetic apatite formation on poly(lactic acid) composites containing calcium carbonates
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Yoshitaka Hibino and Ken-ichiro Hata Department of Tissue Engineering, Nagoya University School of Medicine, Turumai-cho, Showa-ku, Nagoya 466-8550, Japan
Minoru Ueda Department of Oral and Maxillofacial Surgery, Nagoya University Graduate School of Medicine, Turumai-cho, Showa-ku, Nagoya 466-8550, Japan
Yoshio Ota Yabashi Industries Co. Ltd., Akasaka-cho, Ogaki 503-2213, Japan (Received 18 September 2001; accepted 31 January 2002)
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. 13C cross-polarization magic angle spinning nuclear magnetic resonance (13C CP/MAS-NMR) spectra of the composites suggested the formation of a bond between Ca2+ 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威 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.5–7
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Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 17, No. 4, Apr 2002
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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 nucleation6 and can be formed by hydrolyzation of PLA. To increase the supersaturation of apatite in body fluid
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