Microstructure, shape memory properties, and in vitro biocompatibility of porous NiTi scaffolds fabricated via selective laser melting

In this study, three porous NiTi scaffolds with the same porosity but different pore sizes (900, 835, and 618 μm) were fabricated via selective laser melting (SLM). The microstructure, mechanical properties, shape memory properties, and in vitro biocompatibility of the different porous NiTi scaffolds were studied systematically by scanning electron microscopy, micro-computed tomography, differential scanning calorimetry, compressive testing, and in vitro cell culture experiments. The pore sizes of the SLM porous NiTi scaffolds were smaller than those of computer-aided design models owing to the existence of spatter powders, whereas the strut diameters showed the opposite tendency. Furthermore, the elastic modulus of the three NiTi scaffolds was close to that of human bones and lower than that of most previously reported porous NiTi and Ti alloys with similar porosities. Moreover, the scaffolds demonstrated better compressive strength than that of most of the reported porous NiTi alloys with similar porosities as well as better strength and fracture strain than those of human bones, particularly for scaffolds with larger pore sizes. Moreover, the best recoverable strain of 5.10% and recovery rate of 91.4% were obtained for porous NiTi scaffolds with a pore size of 900 μm owing to their minimal stress concentration during loading. The in vitro study further demonstrated that a relatively small pore size could promote the bridging growth of cells in pores, and the in vitro biocompatibility of the porous NiTi scaffolds was equivalent to that of bulk SLM NiTi. The results obtained in this study can provide guidance for the application of porous NiTi scaffolds in biological implants.