Mechanical behavior of a NiTi superelastic bone plate obtained by investment casting assisted by additive manufacturing

Abstract

The mechanical behavior of nickel-titanium shape memory alloys (NiTi SMA) presents unique features that benefit the bone fracture healing process: matching elastic modulus ranges, the ability to recover large deformations, and mechanical dissipation capacity. In this sense, this work proposes a new manufacturing process for NiTi SMA bone implants, particularly bone plates: additive manufacturing assisted investment casting (IC). This process delivers near-net NiTi SMA parts with either simple or complex shapes, also allowing a high degree of customization. Four identical NiTi SMA bone plates were manufactured through IC and characterized. Four-point bending tests were performed on the bone plate prototypes to verify their mechanical and fatigue behaviors. The NiTi bone plates have an elastic modulus of the order of 49 GPa at 37 °C and recovered all deformations upon unloading when submitted to four-point bending deflections up to 4 mm. The fatigue life was between 103 and >105, depending on the deflection amplitude. Our next work with this technology will address aspects of cytotoxicity and implantation of the part in animals.