Layer-by-Layer Assembly of TiO₂ Nanoparticles for Stable Hydrophilic Biocompatible Coatings

Stable, super-hydrophilic (water contact angle ≈ 0°) titanium dioxide nanoparticle thin films have been obtained on substrates with different initial wettability such as glass, poly(methyl methacrylate) and poly(dimethyl siloxane) using layer-by-layer nano-assembly method. Titanium dioxide nanoparticles were alternated with poly(styrene sulfonate) to form films of thickness ranging from 11 nm to 220 nm. The hydrophilicity of these thin films increases with increasing number of deposited PSS/TiO₂ bilayers. It was found that 2, 5 and 20 layers were needed to form super-hydrophilic TiO₂ coating on glass, PMMA and PDMS respectively. Oxygen plasma treatment of substrate surfaces enhanced the formation of homogeneous TiO₂ films and accelerated the formation of hydrophilic layers. Super-hydrophilicity has been shown to be unique to PSS/TiO₂ films as compared with other polyelectrolyte/nanoparticle layers, and UV irradiation may restore hydrophilicity even after months of storing of the samples. Biocompatibility of TiO₂ nanoparticle films has been demonstrated by the successful cell culture of human dermal fibroblast.