Curcumin-coated anodized titanium surfaces for enhanced in vitro cytocompatibility and early osteogenic activity

To characterize a carrier-free curcumin coating applied by dip-coating to acid-etched and anodized Ti-6Al-4 V (Cur-Ti) and to compare its in vitro cytocompatibility and early osteogenic activity, measured as total alkaline phosphatase (ALP) activity, with those of a sol-gel hydroxyapatite coating (HA-Ti) prepared on the same substrate and of uncoated anodized titanium.

Grade 5 titanium discs were acid-etched, anodized to form a TiO₂ nanotube layer, and coated with curcumin by dip-coating from a dimethyl sulfoxide solution or with HA by a sol-gel process. Coatings were characterized by FESEM, XRD, FTIR, confocal Raman, and UV-Vis reflectance spectroscopy. Cytocompatibility was assessed by the MTT assay in L929 fibroblasts and MG-63 osteoblast-like cells at 24 and 48 h according to ISO 10993-5, and total ALP activity was measured in MG-63 cells cultured on uncoated Ti, HA-Ti, and Cur-Ti for 7 and 14 days (n = 6 discs per group per time point). Coating thickness, curcumin loading and release, and ALP normalized to protein or DNA were not measured.

Characterization confirmed a continuous, conformal, amorphous curcumin layer with intact functional groups on the anodized substrate. Relative to HA-Ti, MTT viability on Cur-Ti was higher by 13.1% and 10.6% in L929 cells and by 13.4% and 11.9% in MG-63 cells at 24 and 48 h, respectively (all p ≤ 0.003; Cohen's d 2.2 to 6.2), and both coatings exceeded the 70% viability threshold of ISO 10993-5. Total ALP activity on Cur-Ti was 164.62 ± 3.71 U/L at day 7 and 229.82 ± 2.51 U/L at day 14, which was 70.2% and 114.9% above uncoated Ti and 24.1% and 28.8% above HA-Ti (Tukey HSD, p < 0.0001).

A carrier-free curcumin coating on anodized Ti-6Al-4 V supported higher cytocompatibility and higher total early osteogenic (ALP) activity than a conventional sol-gel HA coating on the same substrate. Because ALP was not normalized per cell and cell-free MTT controls were not included, these findings indicate an early osteogenic signal at the well level rather than enhanced differentiation per cell. Curcumin loading and release, antibacterial activity, wettability, coating adhesion, and corrosion behavior were not evaluated and are identified as priorities for future work before any multifunctional claim can be made.