Development of intelligent biomaterials with the ability to detect the extension of a fatigue crack and to impede it

为了研制具有检测和阻止疲劳裂纹扩展能力的人工骨，设计了分散在羟基磷灰石多晶中的磷酸四钙颗粒组成的两相复合材料体系。提出了复合材料智能功能的机理。当充满唾液的疲劳裂纹从复合材料表面延伸到磷酸四钙颗粒时，磷酸四钙颗粒溶解在唾液中，羟基磷灰石晶体在裂纹中析出。由于磷酸四钙的溶解和随后在裂纹中羟基磷灰石的沉淀，裂纹尖端实际经历的有效裂纹驱动力（基于裂纹尖端的钝化以及裂纹表面之间产生的楔入力、桥接力或滑动力）的降低，抑制了疲劳裂纹的发展。为了研究由羟基磷灰石和磷酸四钙组成的粉状材料的致密性，将含有30 mol / l磷酸四钙的粉状材料在1150 ~ 1350℃的温度下，在空气和CaO粉末中烧结3小时。用阿基米德法测定了烧结复合材料在甲苯中的堆积密度，并用x射线衍射法鉴定了结晶相。在1250℃的温度下加热3小时，复合材料的密度达到理论密度的96%，但磷酸四钙的加入阻碍了羟基磷灰石的烧结。x射线衍射实验结果表明，在1350°C的温度下，在空气和CaO粉中烧结3 h的复合材料，在复合材料表面至500 μ m深度范围内均存在磷酸四钙和羟基磷灰石。

In order to develop the artificial bone exhibiting the ability to detect the extension of a fatigue crack and to impede it, two-phase composite system consisting of tetracalcium phosphate particles dispersed in hydroxyapatite polycrystals was designed. The mechanism of intelligent functions of the composites proposed was as follows. When a fatigue crack filled with saliva extends from the surface of the composites to tetracalcium phosphate particles , the tetracalcium phosphate particles dissolves in saliva, and then hydroxyapatite crystals have been precipitated in the crack. As a result of dissolution of tetracalcium phosphate and subsequent pricipitation of hydroxyapatite in the crack, the fatigue crack advance is restrained by lowering the effective crack driving force actually experienced at the crack tip, which based on the blunting of the crack tip and on the generation of wedging, bridging, or sliding force between the crack surfaces.In this study, in order to estimate the densification behavior of powder compacts compsed of hydroxyapatite and tetracalcium phosphate, the powder compacts containing 30 mol% tetracalcium phosphate were sintered at 1150ﾟC to 1350ﾟC for 3 hours both in air and in CaO powder. Bulk densities of sintred composites were determined by Archimedes immersion technique in toluene, and crystaline phases were identified using X-ray diffraction technique. Although the maximum density of 96% theoretical was obtained when the composites were heated at 1250ﾟC for 3 hours, it was revealed that the addition of tetracalcium phosphate blocked he sintering of hydroxyapatite. From the results of X-ray diffraction experiments, it was found that tetracalcium phosphate existed with hydroxyapatite within the range from the surface of the sintered composites to the depth of about 500 mu m for the composites sintered at 1350ﾟC for 3 hours both in air and in CaO powder.