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

为了开发出能够检测疲劳裂纹扩展并阻止疲劳裂纹扩展的人工骨，设计了由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系统。提出了复合材料的智能功能机理如下。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，然后在裂缝中析出羟基磷灰石晶体。由于磷酸四钙的溶解和羟基磷灰石在裂纹中的沉淀，通过降低裂纹尖端实际经历的有效裂纹驱动力来抑制疲劳裂纹的扩展，这是基于裂纹尖端的钝化和裂纹表面之间产生的楔形、桥接或滑移力。在本研究中，为了评估由羟基磷灰石和磷酸四钙压实的粉末的致密化行为，在空气和CaO粉末中，在1150ﾟC到1350ﾟC下烧结3小时。用阿基米德浸渍技术测定了复合材料的体积密度，并用X射线衍射法对其晶相进行了鉴定。在1250ﾟC下加热3h，复合材料的理论密度可达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，在空气和CaO粉末中，在1350ﾟC下烧成3h的复合材料，从烧结体表面到500微米深处都有磷酸四钙与羟基磷灰石共存。

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.