Nanostructured titanium regulates osseointegration via influencing macrophage polarization in the osteogenic environment

Abstract

Introduction

Fabricating nanostructured surface topography represents the mainstream approach to induce osteogenesis for the next-generation bone implant. In the past, the bone implant was designed to minimize host repulsive reactions in order to acquire biocompatibility. However, increasing reports indicate that the absence of an appropriate immune response cannot acquire adequate osseointegration after implantation in vivo.

Materials and methods

We prepared different topographies on the surface of titanium (Ti) specimens by grinding, etching and anodizing, and they were marked as polished specimen (P), specimen with nanotubes (NTs) in small diameters (NT-30) and specimen with NTs in large diameters (NT-100). We evaluated the ability of different topographies of the specimen to induce osteogenic differentiation of mice bone marrow mesenchymal stem cells (BMSCs) in vitro and to induce osseointegration in vivo. Furthermore, we investigated the effect of different topographies on the polarization and secretion of macrophages, and the effect of macrophage polarization on topography-induced osteogenic differentiation of mice BMSCs. Finally, we verified the effect of macrophage polarization on topography-induced osseointegration in vivo by using Cre*RBP-J^fl/fl mice in which classically activated macrophage was restrained.

Results

The osteogenic differentiation of mice BMSCs induced by specimen with different topographies was NT-100>NT-30>P, while the osseointegration induced by specimen with different topographies in vivo was NT-30>NT-100>P. In addition, specimen of NT-30 could induce more macrophages to M2 polarization, while specimen of P and NT-100 could induce more macrophages to M1 polarization. When co-culture mice BMSCs and macrophages on specimen with different topographies, the osteogenic differentiation of mice BMSCs was NT-30>NT-100≥P. The osseointegration induced by NT-100 in Cre*RBP-J^fl/fl mice was much better than that of wild type mice.

Conclusion

It is suggested that the intrinsic immunomodulatory effects of nanomaterials are not only crucial to evaluate the in vivo biocompatibility but also required to determine the final osseointegration. To clarify the immune response and osseointegration may be beneficial for the designation and optimization of the bone implant.

Keywords:

• nanomaterials
• topography
• immunomodulatory effects
• macrophage polarization
• osseointegration

Acknowledgments

We appreciate technical support from Dr Tao Zhou in Xi’an Jiaotong University for micro-CT scanning and analysis. We also appreciate technical support from Professor Hua Han and Hongyan Qin of the Department of Cell Biology and Medical Genetics at The Fourth Military Medical University for the bestowal of Cre*RBP-J^fl/fl mice. The study is supported by the National Natural Science Foundation of China (Nos. 81530051, 81771069, 31670966 and 81571531). We acknowledge Professors Yumei Zhang, Qintao Wang and Lihua Chen who provided theoretical guidance, technical support and critical financial support for the successful completion of this study and made great contributions to the paper. In particular, Professor Lihua Chen has provided much guidance and support from the immunology perspective.

Disclosure

The authors report no conflicts of interest in this work.