Currently, 3D printing has emerged in the biomedical implants in fracture fixations as well as artificial organs. Interestingly, 4D bioprinting is a recently developed method or concept that intends to logically create 3D patterned biological matrices from synthetic hydrogel-based inks with the potential to change form upon stimulation. However, the static and fixed structure of 3D printing unable to mimic the complex structures of human tissue which involves contract and relax. In addressing this issue, the additive manufacturing (AM) of four dimensional (4D printing) has taken a place in biomedical application in fabricating highly printable shapes.

A biomedical implant is a man-made transplanted device used to replace missing life structures and support damaged biological hard tissue. The primary goal of these structures is to preserve the anatomical fixation of the human body. Currently, advanced titanium alloys occupy almost half of the market share of implant products however, they still pose concerns such as decreasing osteogenesis during application. This paper presents a review of the role of additive manufacturing (AM) in providing innovative methods for fabricating metallic alloys toward Industrial Revolution 4.0. Initially, an overview of biomedical implants is discussed, followed by an examination of the ability of titanium alloys produced using AM methods. Mechanical properties and other issues relating to the functional application of these biomedical implants are promptly discovered. Further, the effect of bone-implant contact between implants and tissues, which can lead to failure, while advanced methods to improve osteointegration through surface modification of the AM fabricated titanium alloys are also scrutinised.

Recently, additive manufacturing (AM), being part of IR4.0, received great attention for the fabrication of customized implants with outstanding quality, which are used in hard tissue replacement. For an orthopedic application, the titanium alloy implants, especially those that use Ti-6Al-4V manufactured by selective laser melting (SLM), should facilitate maximum osteointegration between the implant and corresponding bone. However, the superior mechanical characteristics, poor surface integration, antibacterial performance, and readiness of SLM Ti6Al-4V for use in advanced implants are still not comparable to those of anatomical bone. This review focused on the current issue of stress-shielding limitations in SLM Ti-6Al-4V owing to failures in load-bearing applications. The surface treatment and modification strategy that might improve the osseointegration of the implant were discussed. The corrosion resistance of SLM Ti-6Al-4V which could significantly affect antibacterial capability, improve cell adherence and apatite formation on the bone remodeling surface was also addressed. Finally, the current challenges, prospects and applications for SLM Ti-6Al-4V development were presented.

Magnesium (Mg) has attracted great attention as a possible biomedical implant due to its appropriate mechanical property, good biocompatibility, and lightweight. However, fast and uneven degradation has been a significant problem of pure Mg. The goal of this review was to investigate the current state of the art in the corrosion resistance and load-bearing capacities of osteopromotive biomaterials created by altering Mg surface coating with Hydroxyapatite (HA) ceramics. Initially, the osteopromotive characteristics of magnesium and also the magnesium corrosion behaviour in the human body’s microenvironment were discussed. Following that, the different HA sol-gel coating methods in modifying the surface and corrosion behaviour of Mg were established. It was proposed that the optimal HA coating is about 5 to 6 µm as a corrosion barrier, which may also be improved by heat treatment at temperatures ranging from 300°C to 450°C. Finally, the strategies of HA sol-gel surface modification to improve the apatite formed and their degradation issue to promote healing in orthopaedic high load-bearing skeletal sites were elucidated.