Titanium and its alloys are widely used as orthopedic and dental implant materials due to their excellent mechanical properties, corrosion resistance, and biocompatibility. However, their inherently bioinert surface is unfavorable for cell adhesion, proliferation, and differentiation. Furthermore, the smooth substrate surface has a limited drug-loading capacity, which restricts their efficacy as drug carriers. This study fabricates a pH-responsive composite coating on a titanium substrate and preliminarily evaluates its effects on the biological behavior of human gingival fibroblast (HGF-1) cells. This work provides a novel strategy for achieving smart drug release triggered by the acidic microenvironment around implants. With smooth titanium sheets as the substrate, a porous TiO2 ceramic layer is first prepared via micro-arc oxidation (MAO) technology. Subsequently, a pH-responsive composite coating, designated MT(TP/LL-37)10, is fabricated on the titanium surface by alternately depositing 10 layers each of a homogeneous tannic acid-polyacrylic (TA-PAA) mixture and the antimicrobial peptide LL-37, based on the principle of electrostatic layer-by-layer self-assembly (LbL). The morphology, chemical composition, hydrophilicity, and pH responsiveness of the composite coating are analyzed by SEM & EDS, XPS, and contact angle measurements. The in vitro release of LL-37 is detected by enzyme-linked immunosorbent assay (ELISA), and the effects of various sample groups on the adhesion, spreading, viability, and proliferation of HGF-1 cells are evaluated through in vitro cell experiments. SEM, XPS, and contact angle analyses collectively confirm the successful preparation of sample MT(TP/LL-37)10, which exhibits a porous morphology and is loaded with LL-37. Its water contact angle is measured at (43.5±2.1)°, indicating significantly superior hydrophilicity compared with smooth titanium sheets. After immersion in PBS at pH 7.4 and pH 5.5 for seven days, the atomic percentage of nitrogen on MT(TP/LL-37)10 decreases to (10.5±0.8) and (7.1±0.5), respectively, from an initial (12.1±0.7). This demonstrates a significantly higher release rate under acidic conditions than that under neutral conditions, confirming its excellent and superior pH responsiveness compared with the control group. In vitro release experiments show that the cumulative release of LL-37 from the coating reaches (15.4±0.7) μg at 240 h, which is significantly higher than that of the control group. In vitro cell experiments indicate that the coating possesses good cytocompatibility and effectively promotes the early adhesion and proliferation of HGF-1 cells. In summary, the pH-responsive MT(TP/LL-37)10 composite coating developed in this study is constructed by first preparing a porous TiO2 ceramic layer via MAO to address the issues of poor hydrophilicity and low drug-loading capacity of smooth titanium surfaces. Subsequently, the LbL technique is used to deposit multiple layers of pH-responsive TA-PAA and LL-37, further enhancing the drug-loading performance and effectively mitigating the initial burst release of the drug. Moreover, the coating exhibits favorable pH-responsive sensitivity in an acidic environment, providing a novel strategy for achieving intelligent and sustained release triggered by the acidic microenvironment around implants. In vitro cell experiments demonstrates that the coating possesses good cytocompatibility and facilitates the early adhesion, spreading, and proliferation of HGF-1 cells. Future research will focus on evaluating the long-term biosafety of this coating in vivo and assessing its ability to promote soft tissue integration in large animal models. Additionally, exploring its combined application with other growth factors or drugs represents an important direction for further enhancing its performance.
Key words
pH-responsive /
layer-by-layer self-assembly /
micro-arc oxidation /
LL-37 /
polyacrylic acid /
composite coating
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Funding
Basic Research Program of Shaanxi Provincial Department of Science and Technology (2024JC-YBQN-0966); Key Scientific Research Program of Shaanxi Provincial Department of Education (24JR146); Science and Technology Program of Weiyang District, Xi'an City (202331); Xi'an Medical University Scientific and Technological Capacity Improvement Special Program (2024NLTS070); Innovation Team of Digital Occlusal Prosthodontic Reconstruction (2021TDPT01)
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