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Process engineering, characterization and self-healing assessment ot toughened calcium phosphate silicate composite bone cements Goudarzi, Azadeh


Self-healing, the ability to repair defects without external assistance, is one of the most magnificent characteristics of natural tissues. Achieving similar characteristics in biomaterials substituting natural tissues is highly desirable. As ceramic bone cements are designed to substitute bone tissues, the knowledge of their self-healing processes and characteristics is of vital importance for the advancement of bioceramics in orthopedic applications. In this work we have studied self-healing mechanisms of polyvinyl alcohol (PVA) fiber toughened Tri-Calcium Silicate (C₃S) cements, with and without calcium phosphate additions. The C₃S-PVA samples were partially fractured in three-point-bending, and then soaked in Simulated Body Fluid (SBF) for 7 days at 37°C. The variations in the morphology and width of the healed cracks were tracked by optical and electron microscopy. Chemical composition and phase analysis were determined using EDX, XRD and FTIR. The energy absorbed before the failure of C₃S-PVA samples, determined through the area under load-displacement curves, was nearly two orders of magnitudes higher than the pure C₃S samples. Most of the cracks in the previously fractured C₃S-PVA samples soaked in SBF were visually eliminated in 7 days, also resulting in partial restoration of their load-carrying capacity. Based on the EDX, XRD and FTIR results, a healing mechanism was proposed, including preferential precipitation of calcium phosphates and calcium carbonate phases within the cracks. The same healing treatment was applied to the new composite cement, wherein the C₃S matrix included 10wt% of Mono Calcium Phosphate (MCP) for improved cement biocompatibility and bioactivity. The toughness of C₃S-10MCP-PVA samples was also almost two orders of magnitudes higher than the pure C₃S-10MCP. C₃S- 10MCP-PVA samples had higher damage tolerance (deflection at maximum load) than C₃S-PVA samples. Self-healing studies of the C₃S-10MCP-PVA showed better restoration of the load_carrying capacity than C₃S-PVA. Such evidence emphasizes the effective role of calcium phosphate in the healing process of the toughened bioceramic cements. While such successful SBF-induced healing does not guarantee similar mechanisms operating in vivo, this pioneering research opens up avenues for further improvements of the cementitious ceramic composites in medical applications, as well as in broader engineering applications, e.g. in construction industry.

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