A novel strategy for secretory leukocyte protease inhibitor (SLPI) immobilization on alkaline-etched titanium via a plasma-polymerized interlayer and covalent coupling to enhance osteoblast activity.

Titanium (Ti) implants are the gold standard for orthopedic and dental applications, but their bioinert surfaces lack the osteoinductive properties. Combining alkaline etching for biomimetic surface topography and biofunctionalization with secretory leukocyte protease inhibitor (SLPI) has potential to promote osteogenic activities. Thus, this study is the aim to develops and characterizes a novel strategy to immobilize recombinant human SLPI (rhSLPI) onto alkaline-etched Ti (TiOH) surfaces via plasma polymerization. The grade 5 Ti and TiOH were polymerized utilizing a plasma-polymerized interlayer, followed by UV-graft polymerization of polyacrylic acid (PAAc) and EDC/NHS-mediated covalent coupling to immobilize 10 µg/mL rhSLPI (TiS and TiOHS, respectively) to immobilize 10 µg/mL rhSLPI (TiS and TiOHS, respectively). The ELISA and XPS confirmed the successful rhSLPI immobilization. Moreover, the SEM revealed the pillar-like morphology on the TIOH and TiOHS groups, whereas the Ti and TiS showed smooth surfaces, which is consistent with the profilometer. Additionally, the TiOH and rhSLPI-immobilized groups showed significantly higher hydrophilicity. Moreover, all sample types showed biocompatible to hFOB 1.19 cell. The TiOHS demonstrated highest cell adhesion, while TiS promoted highest cell proliferation. Alizarin red S (ARS) staining demonstrated TiOHS promoted the highest mineral deposition. In conclusion, the rhSLPI immobilization on alkaline-etched Ti via plasma polymerization, PAAc grafting and EDC/NHS covalent coupling. The combined platform (TiOHS) demonstrated enhanced physicochemical and biofunctional properties, resulting in promoted in vitro human osteoblast cell adhesion and differentiation.