In-situ Fabrication and Evaluation of Ti-6Al-4V Meta-Biomechanisms based on Selective Laser Melting

Abstract

Cavitary bone defects are common in orthopedic surgery and may be present after curettage of benign tumors or as tumor-like lesions. Bone graft substitutes, especially from biocompatible materials, can be used as a solution for lling up those defects. However, these cavitary bone defects differ in size and
location. It would, therefore, be convenient to utilize an implant that can change its shape according to its surrounding 3D environment, meaning there is no need to customize the implant for every patient case. In the last decade, additive manufacturing (AM) techniques have been the driving force behind the fabrication of complex three-dimensional objects. The various assets of these procedures enable the production of very complex designs with appropriate material properties. These materials that are engineered to exhibit certain properties are referred to as meta-materials. Functionalizing these materials on a nano-scale, to have certain biological or mass transport properties brings us to a new class of materials better known as meta-biomaterials. In this regard, highly deformable implants with novel properties can be referred to as meta-biomechanisms, consisting of multiple interconnected joints. The current research revolves around the direct fabrication of meta-biomechanisms using Selective Laser Melting (SLM). Subsequently, the general design recommendations and process constraints have been discussed briefly for the fabrication of mechanisms using SLM. In this regard, SLM poses an extra burden on the removal of supports, especially for the vulnerable geometries and within the joints clearance. Implementing a design approach, including both systematic and intuitive methods, was chosen as
the main tool towards the accomplishment of the research aim. Consequently, new designs are proposed to minimize these undesirable events and the supports, with the subsequent challenge to obtain multi-joint mechanisms with increased Degrees of Freedom (DOF) and the least amount of supports. The rst joints have been successfully printed, as well as meshes of multiple joints. Surface Morphing Experiments were nally executed to classify them in terms of motion, taking into account the nal application. According to the results, the majority of the proposed meta- biomechanisms approach well the reference acetabular model, with an absolute difference below 1, reassuring the possibility of the proposed meta-biomechanisms as potential implants in cavitary bone defects. Besides the evaluation in terms of mobility, the structures were mechanically tested to derive their behavior under compression loading. The force needed to induce a sharp break was lower than the average peak force reported in hip joints during daily activities. Subsequently, the experiments revealed that their mechanical strength depends on the tting of the structures inside the acetabulum model. The bigger the gap between the structure and the acetabulum, the weaker the structure under compression loading. Overall, their scale and size should be optimized to sustain the average day-to-day forces joints are subjected to.