As a new type of antibacterial material, copper-containing titanium alloys have good biological and mechanical properties and are expected to be widely used in clinical orthopedics and dental implants. Macrophages are the main cells that mediate the immune response after the alloy is implanted into the human body, and they directly affect the stability of the alloy in long-term service. Due to the addition of copper, the copper-containing titanium alloy gives the alloy antibacterial properties. On the one hand, this promotes the phagocytosis of macrophages and kills bacteria. On the other hand, copper promotes the polarization activation of macrophages, which then express a variety of cytokines and trigger inflammation in the body. However, at present, there is no definitive conclusion about the type of copper-containing titanium alloys that regulate the polarization of macrophages, and the mechanism of copper ions regulating the polarization of macrophages is still not fully clear. This article summarizes the published studies on the regulation of macrophage polarization by copper-containing titanium alloys and reviews the relevant literature in terms of material types, surface treatments, processing methods, cell culture methods, and culture density. The application of medical copper-containing titanium alloys has prospects. It is hoped that by changing the properties of copper-containing titanium alloys, such as the processing methods or surface treatments, the polarization direction of macrophages can be adjusted, with a view to the design and clinical application of medical copper-containing titanium alloys.

Biodegradable magnesium-matrix composites (BMMCs) added with bone-like compounds such as hydroxyapatite (HA) have promising orthopedic application potential, but the in vivo results of BMMCs are insufficient, and the difference between in vitro and in vivo are not clarified. In this work, Mg-Zn-Nd-Zr/(10/15/20wt%) HA (Ca₁₀(PO₄)₆OH₂) composites were prepared through friction stirring processing (FSP). It was found that corrosion rate of the composites increased with increase of the HA content, where the corrosion rate from hydrogen evolution of the Mg/10wt% HA was about 0.107 mm/y, showing better corrosion resistance compared with other BMMCs, and the agglomeration of HA powders significantly aggravated the localized corrosion. The ALP specific activity of the MC3T3-E1 cells cultured for 14 days with Mg/10wt% HA (2.12 IU/mg) was higher than that of the matrix (1.85 IU/mg), but there was no difference with the FSP group (2.13 IU/mg). In the early implantation of the rabbit femur, bone volume fraction (BV/TV) of Mg/10wt% HA was 10.69, which was higher than that of the FSP group (6.35). The histological staining showed that the Mg/10wt% HA implant was surrounded by more trabecular bone tissue, exhibiting better osteoinductive regeneration. The Mg-Zn-Nd-Zr/HA composites exhibit higher osteogenic activity in vivo differently from in vitro osteogenic expression.

Magnesium (Mg) alloys have attracted a wealth of attention in orthopedic fields for their superior mechanical properties, degradability, and excellent biocompatibility. Consistently, to resolve the issues on rapid degradation, more studies are dedicated to the researches on the composition design, preparation and processing, surface modification, the degradation modes of Mg alloys. Nevertheless, the mechanisms by which Mg alloys promote bone healing remain elusive. This review gives an account of specific mechanisms on Mg alloys promoting bone healing from four aspects, immunomodulatory, angiogenesis, osteogenesis and regulation of osteoclast function. We highlight the regulation of Mg alloys on the functional status and interactions of numerous cells that are involved in bone healing, including immune cells, osteogenic-related cells, osteoclasts, endothelial cells (ECs), nerve cells, etc., and summarize the signaling pathways involved, with the aim to provide the basis and support on future investigation on mechanisms on Mg alloys driving bone regeneration. More importantly, it provides a rationale and a general new basis for the application of Mg alloys in orthopedic fields.