Evaluating the suitability of fast sintering techniques for the consolidation of calcium phosphate scaffolds produced by DLP

Porous scaffolds were fabricated via Digital Light Processing (DLP) from β-TCP powder and sintered by conventional sintering in air (CSA), rapid sintering in air (RSA) and pressure-less spark plasma sintering in vacuum (pl-SPS), at four different temperatures: 1200, 1300, 1400 and 1500 ºC. Each sintering strategy resulted in scaffolds with different phase composition, microstructure and mechanical properties. Long dwell times or high temperatures were required to achieve a complete β→α transformation, and rapid cooling rates avoided the reverse transformation. The presence of graphite in the sintering chamber played a crucial role in stabilising the α-TCP phase, phase prevailing in SPS-treated scaffolds, hindered their densification and avoided the generation of transformation-induced cracks. All scaffolds exhibited compressive strengths within the range of cancellous bone, with the highest average value of 22 ± 4 MPa achieved by the RSA scaffolds sintered at 1300 ºC, thanks to their greater densification and fine microstructure.