Impact Of Laser Powder Bed Fusion Process Defects On Mechanical Properties Of Ti6Al4V Mandible Implants

Abstract

Each year millions of patients’ quality of life is improved through surgical procedures involving medical implanted devices. The need for new implants, treatments and prostheses, as well as prolonging the life span of current implants has increased; the global prosthetics and orthotics market size is expected to reach $11.7 billion by 2025, as indicated in Healthcare Market Report (2020). Additive manufacturing (AM) was implemented in the medical field fairly recently. Despite the enormous contribution medical devices have made to the public health, there is a fear of possible liability exposure in the event of device malfunction or failure. Efficient quality control of implants produced by new AM technologies is an important task for suppliers in order to be in full compliance with existing regulations and certification of such implants. If any defects occur, implant strength will directly influence the part’s mechanical properties and performance, leading to the redistribution of stress and change in displacements affecting attached bone tissue and mineral matrix of the bone, resulting in implant failure. For wide applications in the medical industry, it is crucial that AM implants comply with international standards with regard to their mechanical properties. Three point bending tests (TPB) were carried out in this work on AM Ti6Al4V ELI specimens. TPB is a common tool used to characterize bone material properties and mechanical performance of biomaterials. Powder bed fusion is the unique AM method to produce metal objects with complex geometries and internal structures; it permits the manufacture of complex-shaped functional 3D objects such as customized implants. The benefits of AM in bone reconstruction using metal alloys are unquestionable in terms of customization of implants and production time. Comprehensive analysis of the laser powder bed fusion (LPBF) process together with functional anatomy biomechanics of the human mandible was done in this work. Some case studies on defects found in LPBF implants were evaluated. Based on biomechanics of the human mandible, LPBF Ti6Al4V ELI samples were designed. Experiments and numerical simulations of samples with sizes and placements of artificial pores were done. All samples were tested perpendicular to the vertical building direction and showed no signs of failure at a single loading pattern. Defects were designed and induced in the additive manufacturing of test samples of titanium, with different size and placement. Results indicate that defects of 1000 μm×300 μm×210 μm and 1000 μm×500 μm×420 μm at various depth to the neutral axis had no significant outcome on the mechanical performance of the samples with size of 100 mm 15 mm  2.5 mm when it was tested statically at loading of 800, 900 and 1500 N, representing a maximum biting force. This approach is a promising method of setting up a critical pore size to failure tolerance for AM implants with some defects.