Self-healing capacity of damage tolerant calcium phosphate biocements

关于矿物生物水泥的机械性能的一个主要问题与它们固有的脆性和缺乏延展性有关，这妨碍了它们在承重应用中的使用。本项目的目的是制造耐损伤磷酸钙水泥。这将通过将延展性聚乙烯纤维整合到水泥基体中来实现，水泥基体通过活性氧等离子体处理进行表面改性，从而允许与水泥基体发生化学相互作用，并诱导再矿化过程。在机械载荷作用下，裂纹的扩展能量通过纤维、界面和基体之间的摩擦和聚合物的塑性变形来耗散。在此之后，纤维表面的羧酸基团将诱导再矿化，因为它们的Ca2+结合能力导致固有的裂缝愈合。另一种方法是利用在聚甲基丙烯酸甲酯的基础上添加含有磷酸盐的微胶囊来实现外部愈合能力。微珠在水泥初始开裂时被打开，高活性酸性磷酸盐的释放导致裂缝中快速（< 1分钟）形成二次磷酸盐（刷石）或无定形磷酸盐。随后，这些磷酸盐与模拟细胞外生理电解质的模拟体液（SBF）中的无机成分（HPO42-, Ca2+, CO32-）反应，转化为磷灰石，其组成类似于骨的矿物相。该项目将涵盖两个材料合成方面（水泥合成；等离子体处理对聚合纤维的表面改性；装载磷酸盐的微胶囊的制造），纤维-水泥界面的机械化学特征，以及模拟体液中裂缝的再矿化行为和自愈。

A major problem concerning the mechanical properties of mineral biocements is related to their inherent brittleness and absence of ductility, which prevents their use in load-bearing applications. Aim of this project is the fabrication of damage tolerant calcium phosphate cements. This will be realised by the integration of ductile polyethylene fibres into the cement matrix, which are surface modified by a reactive oxygen plasma treatment to allow chemical interactions with the cement matrix and to induce remineralization processes. Under mechanical load, the initiated cracks are bridged by the polymeric fibres and the crack growth energy is dissipated by friction processes between fibre, interface and matrix and the plastic deformation of the polymer. Following this, carboxylic acid groups at the fibre surface will induce remineralization due to their Ca2+ binding capacity leading to an intrinsic crack-healing. A further approach utilizes the extrinsic healing capacity achieved by the addition of phosphate containing microcapsules on the basis of polymethylmethacrylate. The beads are opened during initial cement cracking and the release of highly reactive acidic phosphates leads to the fast (< 1 min) formation of a secondary phosphate (brushite) or amorphous phosphates in the crack. Subsequently, these phosphates react with the inorganic components (HPO42-, Ca2+, CO32-) of a simulated body fluid (SBF) mimicking the extracellular physiological electrolyte and are transformed into apatite with a composition similar to the mineral phase of bone. The project will cover both material synthesis aspects (cement synthesis; surface modification of polymeric fibres by plasma treatment; the fabrication of phosphate loaded microcapsules), the mechano-chemical characterisation of the fibre-cement interface and the remineralisation behaviour and self-healing of cracks in simulated body fluid.