Development of bioresorbable sintered apatites

采用热分析、X射线衍射和红外光谱等方法研究了在10 0ﾟC、pH 9.0条件下烧结3d的碳酸盐磷灰石的烧结性能。等静压后试件的线性热收缩急剧增加的烧结温度与磷灰石中最初存在的碳酸盐的量成比例地降低。例如，碳酸盐含量超过8wt%的样品可以在比不含碳酸盐样品的烧结温度低近400ﾟC的温度(650ﾟC)下烧结。通过化学和红外光谱估计，烧结结束时碳酸盐的损失量与热重估计的样品重量损失大致相同。研究了烧结型碳酸盐磷灰石在37ﾟC、pH值为5.0的10 mM/L醋酸溶液中的溶解行为，并与烧结型羟基磷灰石和骨磷灰石进行了比较，以建立磷灰石生物材料体外化学溶解与体内破骨细胞吸收能力之间的相似性。烧结的碳酸盐磷灰石和骨磷灰石都有相当程度的溶解。它们的溶液组成以几乎相同的方式变化，直到反应接近尾声。烧结型碳酸盐磷灰石在30s时的溶液组成与烧结型羟基磷灰石在3.8d时的过饱和度相当，说明前者的溶解度远高于后者。破骨细胞取自1日龄新生兔的长骨，可吸收骨和烧结型碳酸盐磷灰石，但不能吸收烧结型羟基磷灰石。这些发现表明，烧结碳酸盐磷灰石具有可与骨相比的特性，特别是在对酸性介质的反应方面，将是一种有用的可生物吸收骨替代品。

Sintering of carbonate apatite, prepared at 100ﾟC and pH 9.0 for 3 days, was studied by therma analysis, x-ray diffraction and infrared spectroscopy. The sintering temperature, at which the linear thermal shrinkage of isostatically compacted specimens increased sharply, decreased in proportion to the amount of carbonate initially present in the apatite. For example, specimens with over 8 wt% carbonate could be sintered at a temperature (650ﾟC) which was nearly 400ﾟC lower than that needed for sintering a specimen with no carbonate. Amounts of carbonate lost at the end of sintering, estimated chemically and by infrared specroscopy, were approximately equal to sample weight losses estimatd thermogravimetrically. Dissolution behavior of sintered carbonate apatite was also investigated in a 10mM/L acetic acid solution adjusted to pH 5.0 at 37ﾟC and compared to that of sintered hydroxyapatite and bone apatite for the purpose of establishing some similarities between pysicochemical dissolution of apatite biomaterials in vitro and their ability to be resorbed by osteoclasts in vivo. Both the sintered carbonate apatite and the bone apatite dissolved to an appreciable extent. Their solution compositions changed in an almost identical manner until toward the end of the reaction. The solution compositions for sintered carbonate apatite at 30 seconds was comparable with that for sintered hydroxyapatite at 3.8 days with respect to the degree of supersaturation, indicating that the former specimen is much more soluble than the latter specimen. Osteoclasts, which were obtained from the long bones of 1-day-old neonatal rabbits, resorbed bone and sintered carbonate apatite, but they did not resorb sintered hydroxyapatite. These findings suggest that sintered carbonate apatites, which have characteristics that can be favorably compared with those of bone, especially with respect to its reactivity to acid media, would be useful as bioresorbable bone substitutes.