Additively manufactured composite bone implants

Bone implants are conventionally made of metallic materials such as stainless steel, cobalt-chromium-molybdenum (CoCrMo) alloys, and titanium alloys due to their satisfactory mechanical strength, corrosion resistance, and relatively good biocompatibility, i.e., its ability to perform in conjunction with a living system. However, these materials have much higher elastic moduli than bone tissue. The mismatch in mechanical properties between bone and metallic implant causes severe stress shielding of the surrounding tissue, which can lead to bone resorption and damage, compromising bone integrity. Alternative metallic implant designs have been proposed to minimize this problem, using Topology Optimization (TO) methods to conceive lightweight components with bone-like stiffness. Nevertheless, metallic implants may have problems such as loosening, the release of harmful metallic ions, risk of inflammatory reactions, and incompatibility with magnetic resonance imaging and computed tomography. Composite materials consist of two or more materials combined to produce a new material with desirable properties. In orthopedic applications, fiber-reinforced polymers are the most widely used composite materials as a result of their excellent strength-to-weight ratio and their superior biocompatibility, when compared with metallic materials. Also, their material properties can be easily tailored to match specific design and application requirements. Additive Manufacturing (AM) has provided important opportunities to produce complex, patient-specific implants with customized mechanical properties. Some of its remarkable features are the rapid product development process and the high level of automation. Recent advances have been done in the AM of composite materials. However, there are only a few studies on this research field, and even less discussing additively manufactured bone implants. This work aims to investigate the application of additive manufacturing in the production of composite bone implants, exploring its state of the art, advantages, challenges to be faced and future possibilities. Furthermore, we intend to summarize and discuss some of the most important material properties that should be analyzed during the design process to produce composite bone implants with enhanced biocompatibility, reducing stress shielding and minimizing the patient’s discomfort.