Properties improvement of titanium alloys scaffolds in bone tissue engineering: a literature review

Abstract

Owing to their excellent biocompatibility and corrosion-resistant properties, titanium (Ti) (and its alloy) are essential artificial substitute biomaterials for orthopedics. However, flaws, such as weak osteogenic induction ability and higher Young's modulus, have been observed during clinical application. As a result, short- and long-term postoperative follow-up has found that several complications have occurred. For decades, scientists have exerted efforts to compensate for these deficiencies. Different modification methods have been investigated, including changing alloy contents, surface structure transformation, three-dimensional (3D) structure transformation, coating, and surface functionalization technologies. The cell-surface interaction effect and imitation of the natural 3D bone structure are the two main mechanisms of these improved methods. In recent years, significant progress has been made in materials science research methods, including thorough research of titanium alloys of different compositions, precise surface pattern control technology, controllable 3D structure construction technology, improvement of coating technologies, and novel concepts of surface functionalization. These improvements facilitate the possibility for further research in the field of bone tissue engineering. Although the underlying mechanism is still not fully understood, these studies still have some implications for clinical practice. Therefore, for the direction of further research, it is beneficial to summarize these studies according to the basal method used. This literature review aimed to classify these technologies, thereby providing beginners with a preliminary understanding of the field.

Keywords: 3D structure; Titanium (Ti); biomaterials; orthopedics.

Figure 1

Component change of the titanium alloy. The materials science researchers dedicate to add elements in different proportions into titanium, which could construct different alloy phases and get different physical or bioactive properties.

Figure 2

Nano-scale surface modification (A) and 3D structure formation (B). The main structures of nanoscale surface modification are classified as nano-rod, nano-particle, nano-hemisphere and nano-amorphous structure. It could improve titanium alloy properties by promoting protein absorption, cell differentiation, cell proliferation as well as increasing wettability. 3D structure can simulate natural bone structure thus promoting osseointegration, osteogenesis, angiogenesis and reducing Young’s modulus of titanium alloy.

Figure 3

Coating methods of titanium. By selecting the appropriate coating material, the researchers can almost solve any single problem. The hydroxyapatite improves cell adhesion and promotes bone formation. The coating technology can reduce systemic side effects by creating local-release and slow-release effect. The antibiotics or cytokines coating can inhibit bacterial growth and reduce inflammation.

Figure 4

Functionalization. To improve the properties of titanium alloys, the researchers construct activated surfaces by physical/chemical/biological methods. It could induce apatite formation spontaneously and promote bone formation. The co-culture of exogenous stem cell could stimulate osteogenic differentiation of adjacent somatic cells by secret exosomes.