Self-healing capacity of damage tolerant calcium phosphate biocements

矿物生物水泥机械性能的一个主要问题与其固有的脆性和缺乏延展性有关，这阻碍了它们在承重应用中的使用。该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，这些纤维通过活性氧等离子体处理进行表面改性，以允许与水泥基体发生化学相互作用并诱导再矿化过程。在机械载荷下，引发的裂纹被聚合物纤维桥接，裂纹扩展能量通过纤维、界面和基体之间的摩擦过程以及聚合物的塑性变形而消散。此后，纤维表面的羧酸基团将由于其 Ca2+ 结合能力而诱导再矿化，从而导致内在的裂纹愈合。另一种方法利用通过添加基于聚甲基丙烯酸甲酯的含磷酸盐的微胶囊而实现的外在愈合能力。在最初的水泥开裂过程中，珠子打开，释放出高反应性的酸性磷酸盐，导致裂缝中快速（< 1 分钟）形成二次磷酸盐（透钙磷石）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）的无机成分（HPO42-、Ca2-、CO32-）发生反应，并转化为成分与骨矿物相相似的磷灰石。该项目将涵盖材料合成方面（水泥合成；通过等离子体处理对聚合物纤维进行表面改性；磷酸盐负载微胶囊的制造）、纤维-水泥界面的机械化学表征以及模拟体液中裂缝的再矿化行为和自修复。

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.