Protótipos de grampos ortopédicos porosos de liga com memória de forma ni-ti: desenvolvimento e caracterização.

Abstract

Shape Memory Alloy (SMA) orthopaedic staples of the Superelastic (SE) binary system Nickel-Titanium (Ni-Ti) are functional metallic fixators that have the unique ability to exert continuous compression during shape recovery and dynamic compression, aligning due to mechanobiological factors associated with bone healing. In this work, two Ni-Ti SMA alloys produced by VIM (Vaccum Induction Melting) and EBM (Electron Beam Melting) processes were used to test the fabrication of porous staple prototypes using investment casting technology aided by additive manufacturing. The obtained results showed that the EBM alloy provided the best castability to obtain such prototypes. Therefore, prototypes produced showed the mechanical behavior of superelasticity at the isotherm of 37 °C, showing a reduction of up to 20% in the maximum force value, generated in the condition of maximum opening of the legs, when compared to dense staple of Ni-Ti SMA. The secant stiffness varied with the temperature and was in the range between 13 N/mm and 27.5 N/mm, showing a reduction of approximately 14.1% at 37 °C, when compared to the dense staple. Finally, the influence of geometric parameters on the mechanical behavior and on the stress distribution and martensite fraction were evaluated. Thus, it was observed that the initial angle of the legs has a greater influence on the generated force and that the pores introduce stress concentrators, thus increasing the stress levels and consequently the martensite fraction. Therefore, it was possible to demonstrate that the technology can be used to obtain such products, including the possibility of customization. And that such technology can be extended to other implantable medical devices, such as bone fixation plates, pins and screws.