3D-printed calcium phosphate scaffolds for bone regeneration: impact of geometry and treatment an in vivo study

The combination of the direct ink writing (DIW) manufacturing technique, also named robocasting, with the use of self-setting calcium phosphate inks based on α-tricalcium phosphate opens new possibilities in the field of bone regeneration: i) On one hand, the DIW fabrication process allows a precise control on the external shape and internal porosity of the scaffold. The porosity allows the colonization of the bone tissue and the shape control opens new perspectives in personalised medicine; ii) On the other hand, the use of self-setting α-TCP inks provide a micro/nano porosity and a high specific surface area (SSA) to the bone graft. Both factors have been identified as crucial for the bioactivity of the material. Since the fabrication time is a crucial factor for the successful translation of these technologies to the clinical field, and the hardening reaction of conventional self-setting inks is slow, recent investigations have developedan alternative setting procedure (hydrothermal) that considerably reduces the hardening step from 7 days to 30 minutes. Regarding the role of scaffold architecture in bone regeneration, it has been recently proved that the presence of concave surfaces enhances osteogenesis. However, since DIW is based on the extrusion of a paste through a needle, conventional DIW scaffolds are composed of extruded filaments with convex surfaces. Hence the interest in developing scaffolds with non-cylindrical strands, which have concave surfaces. The aim of this study was to assess the in-vivo performance of calcium phosphate scaffolds, analysing on one side the effect of the setting treatment, i.e., comparing the biomimetic setting with the hydrothermal setting treatment, and on the other side comparing cylindrical vs.non-cylindrical strands. The characterization of the scaffolds obtained with the two different treatments revealed that whereas the biomimetic treatment resulted in calcium deficient hydroxiapatatite (CDHA), the hydrothermal treatmen
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