Development of PDMS/TiO₂/Ag₃PO₄ antibacterial coating on 316L/PDMS implants: Evaluation of superhydrophobicity, bio-corrosion, mechanical behaviour, surface nanostructure and chemistry.

Abstract

Nanocomposite coatings based on polydimethylsiloxane were developed by adding silver phosphate and titania nanoparticles with a PDMS pre-layer for 316L stainless steel. FTIR spectra and XRD patterns confirmed the synthesis of TiO₂ and Ag₃PO₄ nanoparticles and nanocomposite coating. FESM and AFM images show that with the increase of Ag₃PO₄ nanoparticles, the roughness of coatings increased (Ra and Rq for adding 7 wt% of Ag₃PO₄ coating was 29 and 293 nm). The wettability results demonstrated that the presence of 7 wt% Ag₃PO₄ nanoparticles in the coating has the highest water contact angle (152 °). Nano-scratch results proved that creating a pre-layer of PDMS can increase the scratch resistance of PDMS + TiO₂+Ag₃PO₄ nanocomposite coating (displacement and scratch coefficient were 408 nm and 0.07μΝ^-1/2 with the pre-layer). Corrosion current density of 316lSS with PDMS + TiO₂+Ag₃PO₄ coating was 0.00045 μA/cm², while for 316LSS with pure PDMS coating was 0.00114 μA/cm² at 37 °C in PBS solution. The Nyquist curves showed the diameter of the semicircle for the nanocomposite coating was larger than pure PDMS coating, which indicates the higher corrosion resistance of the nanocomposite coating (5.98 × 10⁷ Ω). By increasing Ag₃PO₄ nanoparticles from 1 to 7 wt%, the number of E. coli bacteria in contact with the nanocomposite decreased significantly from 580000 to 31000 CFU/cm². In the disk diffusion test, the largest inhibition zone was related to the nanocomposite coating with the addition of 7 wt% Ag₃PO₄ (23 mm). Therefore, the PDMS + TiO₂+Ag₃PO₄ nanocomposite coating has improved properties such as superhydrophobicity, advanced mechanical behavior, bio-corrosion resistance, and antibacterial activity.