A comparative analysis of antibacterial properties and inflammatory responses for the KR-12 peptide on titanium and PEGylated titanium surfaces

Covalent immobilisation of antimicrobial peptides on titanium (Ti) surfaces has been widely performed to inhibit bacterial adhesion and biofilm formation, however, it is unclear whether a spacer is necessary in this process for anti-bacteria adhesion, while still exhibiting good biocompatibility. We investigated the antibacterial properties and inflammatory response of Ti and PEGylated Ti with covalently immobilized KR-12 peptide on the surfaces. The KR-12 peptide was derived from LL-37, which is bactericidal and bacteriostatic in solution. Successful covalent immobilisation was determined by X-ray photoelectron spectrometry, contact angle measurements, and atomic force microscopy. KR-12 incorporation significantly decreased the bacterial adhesion to the Ti surface. Compared to the Ti-KR-12, the KR-12 immobilisation via a PEG spacer increased anti-microbial efficiency and reduced in vitro adhesion and biofilm formation of Staphylococcus epidermidis. Activated macrophages deprived from THP-1 cells with long filopodia were observed on the titanium surface, which was in agreement with increased TNF-α and IL-1β secretion. The KR-12-modified Ti surface and PEGylated Ti surface significantly decreased TNF-α and IL-1β secretion and macrophages remained in inactivated round states. The grafting of a PEG spacer prior to KR-12 immobilisation on the Ti surface improved the antibacterial properties and reduced macrophage activation, and may also decrease overall inflammatory responses. Thus, this approach showed the potential to biofunctionalize Ti for anti-bacteria adhesion and reducing macrophage inflammation.