Minocycline-incorporated multilayers on titanium substrates for simultaneous regulation of MSCs and macrophages

Minocycline (Mino) is a well-established antibiotic, which also has osseointegration and anti-inflammatory functions. In this study, we fabricated a multilayered structure with potential osteoinduction capability on titanium via a spin-assisted layer-by-layer (LBL) assembly technique. Mino was used as the intercalated material, while gelatin and chitosan were used as the polycation and polyanion, respectively. The successful fabrication of the multilayers was validated by scanning electronic microscopy (SEM), atomic force microscopy (AFM) and water contact angle measurements. The release result shows that the sustained release of Mino might be attributed to the synergistic effect of drug diffusion and multilayer degradation. The evaluations of alkaline phosphatase (ALP), mineralization, and osteogenic gene expression consistently demonstrate that the Mino-modified samples (Ti/LBL/Mino) significantly improved the osteogenic differentiation of MSCs compared with the control group (Ti). More importantly, the results of flow cytometry, quantitative real-time polymerase chain reaction (qRT-PCR), and western-blot confirm that Ti/LBL/Mino substrates could indirectly promote osteogenesis through macrophage regulation, such as phenotype transformation from M1 to M2 and regulation of inflammatory/osteogenic genes. The aforementioned properties make Ti/LBL/Mino substrate highly suitable for orthopedic applications.