Hydroxyapatite-“Stand-in” for New Century Bone

Due to the effects of diseases, aging, and frequent traffic accidents, the number of cases of bone injury has increased year by year. According to statistics, there are 3 million orthopedic cases in China every year, so the demand for bone substitute materials is increasing. In recent years, bone substitute materials represented by hydroxyapatite have gradually become the darlings of clinical application.
Hydroxyapatite is the main component of vertebrate bones and teeth, and has good biological activity and biocompatibility. Compared with traditional metal (stainless steel, titanium alloy) and ceramic (alumina, silicon nitride) bone substitute materials, hydroxyapatite not only has strong corrosion resistance and strong osteoinduction, but it also eliminates degradation in the body. The former has hidden dangers. The current research on hydroxyapatite in bone substitute materials has mainly focused on two aspects, hydroxyapatite coating and human bone bionic regeneration material.
Hydroxyapatite coating refers to a hard tissue implant material prepared by coating hydroxyapatite on the surface of titanium alloy using a physical and chemical method as a substrate. After the material is implanted into the human body, the titanium alloy can provide sufficient mechanical strength, and the surface hydroxyapatite coating is easy to combine with human bone, and induce the formation of new bone on the surface of the human bone. Generally, the formation of new bone can be induced within several months . The hydroxyapatite coating prepared by the Shanghai Institute of Ceramics, Chinese Academy of Sciences using plasma spraying technology, has high bonding strength with the substrate and good biological activity. It has been applied to artificial hip joints and other parts. Coated implants have been applied for more than 70,000, with good clinical results, as shown in Figure 1. However, the hydroxyapatite coating has the disadvantage of insufficient binding force, so that the coating peels off after implantation in the body. The solution to this problem is still under continuous exploration.
Some clinical applications of hydroxyapatite-coated bone substitute materials and in vivo osteogenesis experiments. (A) Hydroxyapatite-coated artificial hip joint; (b) One month after implantation, new bone is generated and fills the pores between the coating and bone tissue; (c) Three months after implantation, new bone is matured Replacement of bone tissue.
Human bone bionic regeneration material refers to the simulation of the formation of natural bone in vitro. Nano-hydroxyapatite crystals of the same size as natural bone are obtained through nanotechnology, and are compounded with collagen to achieve on different scales (micro and macro). New composite material with realistic composition, structure and function and human natural bone. From the analysis of high-resolution electron microscope and atomic force magnifier, the human skeleton has a very delicate structure: bundles of collagen and layers of nano-scale hydroxyapatite crystals are extremely uniformly and orderly “inlaid” together, as shown in the figure 2 shown. This multilayer composite self-assembled structure also allows bones to have both rigidity and bending resistance, so this special structural composition that mimics human bone can theoretically achieve biological activity and mechanical compatibility compatible with human bone. In addition, the presence of collagen makes it easy for this biomimetic bone substitute to quickly adhere to autologous bone tissue. At present, research on this aspect is still in progress. Because it is difficult for the outside world to accurately imitate the osteogenic environment in the body, it is still difficult to bionic human bone. Due to the different roles of cortical bone and cancellous bone in bones, their structural composition is still slightly different, which undoubtedly increases the workload and difficulty of bone bionics.
Regardless of whether it is a hydroxyapatite coating or a human bone biomimetic regeneration material, hydroxyapatite is the key to bone replacement materials. It imparts compressive strength to bone and is the main bearer of bone tissue. In addition, its ability to induce new bone formation is unmatched by other materials. Although the research of bone substitute materials is difficult, with the continuous penetration of nanotechnology and biotechnology in the field of medical materials, we believe that patients will definitely see the dawn of “regeneration of broken bones” in the near future.

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