Effects of zinc-containing diamond-like carbon coated splints on the healing of fractures in mice: A pilot study

Abstract Diamond-like carbon (DLC) coatings are highly biocompatible. They have been attracting attention because they can be used in the surface treatment of body-implanted devices. Zinc (Zn) promotes the metabolism of skin and bones. For these reasons, we developed Zn-doped DLC (Zn-DLC), a highly biocompatible DLC, as a coating material to promote bone formation. In our previous study, in vitro tests using osteoblast cells revealed that Zn-DLC promoted calcification associated with osteogenesis. Therefore, in the present study, the ability of Zn-DLC to promote osteogenesis was assessed in vivo using a Zn-deficient mouse model. We compared the healing stages of the bone fractures between Zn-DLC splints group and DLC splints group (N = 7 mice in each group), using computed tomography (CT)-created 3D models of the fractured parts. The number of mice that were fully healed by 4 weeks when fixed with DLC and Zn-DLC splints was two and four, respectively. Then, we investigated the bone features (the bone volume, bending strength, twisting strength, cortical bone thickness, cortical bone area ratio, and spongiosa bone density) after the in vivo test. These results suggested that Zn-DLC had tendencies to improve these parameters compared with DLC, though these differences were not significant statistically. Moreover, we confirmed Zn elution from Zn-DLC, using XPS analysis. These results suggested that Zn-DLC can supply Zn in vivo condition and may improve the therapeutic effect of conventional implants used in the treatment of fractures.