Surface engineering of titanium alloy using metal-polyphenol network coating with magnesium ions for improved osseointegration

Although titanium-based implants are widely used in orthopedic and dental clinics, improved osseointegration at the bone-implant interface is still required. In this study, we developed a titanium alloy (Ti-6Al-4V, Ti) coated with epigallocatechin gallate (EGCG) and magnesium ions (Mg²⁺) in a metal-polyphenol network (MPN) formation. Specifically, Ti discs were coated with EGCG in MgCl₂ by controlling their concentrations and pH, with the amount of coating increasing with the coating time. An in vitro culture of human adipose-derived stem cells (hADSCs) on the EGCG-Mg²⁺-coated Ti showed significantly enhanced ALP activity and mRNA expression of osteogenic markers. In addition, the EGCG-Mg²⁺-coated Ti enhanced the mineralization of hADSCs, significantly increasing the calcium content (22.2 ± 5.0 μg) compared with cells grown on Ti (13.5 ± 0.3 μg). Treatment with 2-APB, an inhibitor of Mg²⁺ signaling, confirmed that the enhancement of osteogenic differentiation in the hADSCs was caused by the synergistic influence of EGCG and Mg²⁺. The EGCG-Mg²⁺ coating significantly reduced the osteoclastic maturation of Raw264.7 cells, reducing tartrate-resistant acid phosphatase activity (5.4 ± 0.4) compared with that of cells grown on Ti (1.0 ± 0.5). When we placed Ti implants onto rabbit tibias, the bone-implant contact (%) was greater on the EGCG-Mg²⁺-coated Ti implants (8.1 ± 4.3) than on the uncoated implants (4.4 ± 2.0). Therefore, our MPN coating could be a reliable surface modification for orthopedic implants to enable the delivery of an osteoinductive metal ion (Mg²⁺) with the synergistic benefits of a polyphenol (EGCG).