Porous NiTi SMA superelastic bone staple manufactured by rapid investment casting: Microstructure, in vitro cytotoxicity evaluation, and mechanical behavior

NiTi shape memory alloy (SMA) bone staples are functional devices that have the unique ability to exert continuous and dynamically active compression, aligning with the mechanobiological factors associated with bone healing. In this work, NiTi SMA alloys produced by electron beam melting were reprocessed to test the manufacturing of porous bone staples prototypes using the rapid investment casting (RIC) process. The results showed that the porous NiTi SMA bone staple exhibited superelasticity at body temperature (37 °C), reducing the compression force by up to 18% compared to the dense staple, and thereby reducing the risk of stress shielding at the fracture site. Furthermore, we confirmed the presence of the protective passive TiO 2 layer, ensuring cytocompatibility of the samples produced by the RIC process. Therefore, it was possible to demonstrate that RIC technology can be used to prototype porous NiTi SMA bone staples with thermomechanical strength and cytocompatibility, including the possibility of customization of the implant to a specific patient, and that this technology can be extended to other NiTi SMA implantable medical devices.