For bone-anchored implants, such as dental implants and joint replacements, formation of direct anchorage between the prosthetic material and bone tissue is essential for functionality and long-term stability of the implant. Implant integration is dependent on the appropriate immune response towards the foreign material, resulting in cell-adhesion and regeneration of vital bone tissue surrounding the implant. However, implant integration can be jeopardised by the presence of bacteria, which can cause persistent biomaterial-associated infections that are particularly difficult to treat and often require removal of the implant. Current strategies to control and treat such infections are insufficient and their effectiveness is likely to diminish even further in the imminent era of antibiotic resistance.
We have developed and characterised a bioinspired surface modification strategy based on silicic acid (Si)-mediated substrate-independent surface deposition of tannic acid (TA), an antioxidant and antibacterial plant polyphenol, to tackle biomaterial-associated infections. By following the surface deposition reaction in situ using QCD-D and nanoplasmonic spectroscopy, we confirmed a continuous deposition of homogeneous TA coatings of up to 300 nm in thickness was observed even in mildly acidic conditions, where the autocatalytic oxidation of TA is suppressed. Coating formation beyond a TA monolayer was only observed in the presence of Si, which was found to act as a crosslinker between the TA molecules within the deposited coating as confirmed by FTIR, UVvis and NMR spectroscopy.
Regardless of their thickness, TA coatings were found to be non-toxic to human primary osteoblasts (hOBs) and allow cell adhesion to the coated implant surface. Osteogenic differentiation of adherent hOBs was promoted, particularly on coatings formed at short deposition times resulting in thinner and more rigid phenolic coatings. Despite initial contact killing effect, these coatings did not prevent S. epidermidis biofilm formation, whereas the release of phenolic compounds from the coatings was associated with reduced growth of planktonic bacteria. This indicates that the deposited TA nanocoatings can act as a reservoir for biologically active molecules that can elicit antibacterial and anti-inflammatory effect in the peri-implant tissues, while the Si-mediated TA deposition process allows controlled modulation of the physicochemical coating properties.