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

为了开发具有检测和阻止疲劳裂纹扩展能力的人工骨，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体系。提出了复合材料智能功能的机理。当填充有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，然后羟基磷灰石晶体已经在裂纹中沉淀。由于磷酸四钙的溶解和随后的羟基磷灰石在裂纹中的析出，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前进，这是基于裂纹尖端的钝化和裂纹表面之间的楔入、桥接或滑动力的产生。为了评价由羟基磷灰石和磷酸四钙压制的粉末压坯的致密化行为，将含有30摩尔%磷酸四钙的粉末压坯在空气和CaO粉末中在1150 ℃至1350 ℃下烧结3小时。烧结复合材料的体积密度测定阿基米德浸渍技术在甲苯中，和晶相鉴定使用X射线衍射技术。虽然当复合材料在1250 ℃加热3小时时获得了96%理论密度的最大值，但发现磷酸四钙的加入阻碍了羟基磷灰石的烧结。从X射线衍射实验的结果，它被发现，磷酸四钙存在的范围内，从烧结复合材料的表面到约500 μ m的深度的复合材料在1350 ℃下烧结3小时，在空气中和CaO粉末。

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.