Enhanced osteogenesis of titanium with nano-Mg(OH)2 film and a mechanism study via whole genome expression analysis

Titanium (Ti) has been the most widely used orthopedic implant in the past decades. However, their inert surface often leads to insufficient osteointegration of Ti implant. To solve this issue, two bioactive Mg(OH)2 films were developed on Ti surfaces using hydrothermal treatment (Ti-M1# and Ti-M2#). The Mg(OH)2 films showed nano-flake structures: sheets on Ti-M1# with a thickness of 14.7 ± 0.7 nm and a length of 131.5 ± 2.9 nm, and on Ti-M2# with a thickness of 13.4 ± 2.2 nm and a length of 56.9 ± 5.6 nm. Both films worked as Mg ions releasing platforms. With the gradual degradation of Mg(OH)2 films, weakly alkaline microenvironments will be established surrounding the modified implants. Benefiting from the sustained release of Mg ions, nanostructures, and weakly alkaline microenvironments, the as-prepared nano-Mg(OH)2 coated Ti showed better in vitro and in vivo osteogenesis. Notably, Ti-M2# showed better osteogenesis than Ti-M1#, which can be ascribed to its smaller nanostructure. Moreover, whole genome expression analysis was applied to study the osteogenic mechanism of nano-Mg(OH)2 films. For both coated samples, most of the genes related to ECM-receptor interaction, focal adhesion, and TGF-β pathways were upregulated, indicating that these signaling pathways were activated, leading to better osteogenesis. Furthermore, cells cultured on Ti-M2# showed markedly upregulated BMP-4 gene expression, suggesting that the nanostructure with Mg ion release ability can better activate BMP-4 related signaling pathways, resulting in better osteogenesis. Nano-Mg(OH)2 films demonstrated a superior osteogenesis and are promising surface modification strategy for orthopedic applications.