Peri-implantitis remains the major impediment to the long-term use of dental implants. With increasing concern over the growth in antibiotic resistance, there is considerable interest in the preparation of antimicrobial dental implant coatings that also induce osseointegration. One such potential coating material is fluorapatite (FA). The aim of this study was to relate the antibacterial effectiveness of FA coatings against pathogens implicated in peri-implantitis to the physicochemical properties of the coating. Ordered and disordered FA coatings were produced on the under and upper surfaces of stainless steel (SS) discs, respectively, using a hydrothermal method. Surface charge, surface roughness, wettability, and fluoride release were measured for each coating. Surface chemistry was assessed using X-ray photoelectron spectroscopy and FA crystallinity using X-ray diffraction. Antibacterial activity against periodontopathogens was assessed in vitro using viable counts, confocal microscopy, and scanning electron microscopy (SEM). SEM showed that the hydrothermal method produced FA coatings that were predominately aligned perpendicular to the SS substrate or disordered FA coatings consisting of randomly aligned rodlike crystals. Both FA coatings significantly reduced the growth of all examined bacterial strains in comparison to the control. The FA coatings, especially the disordered ones, presented significantly lower charge, greater roughness, and higher area when compared to the control, enhancing bacteria–material interactions and therefore bacterial deactivation by fluoride ions. The ordered FA layer reduced not only bacterial viability but adhesion too. The ordered FA crystals produced as a potential novel implant coating showed significant antibacterial activity against bacteria implicated in peri-implantitis, which could be explained by a detailed understanding of their physicochemical properties.

Graphical abstract Highlights CT networks were developed with heparin-mimicking monosodium 5-sulfoisophthalate  Tunable degradation profiles were observed in aqueous media up to 30 days  No toxic response was observed with L929 mouse fibroblasts  Native CT antibacterial activity was retained with Porphyromonas gingivalis Abstract Chitosan (CT) is an antibacterial polysaccharide that has been investigated for drug carriers, haemostats and wound dressings. For these applications, customised CT devices can often be obtained with specific experimental conditions, which can irreversibly alter native biopolymer properties and functions and lead to unreliable material behaviour. In order to investigate the structure-function relationships in CT covalent networks, monosodium 5-sulfoisophthalate (PhS) was selected as heparin-mimicking, growth factor-binding crosslinking segment, whilst 1,4-phenylenediacetic acid (4Ph) and poly(ethylene glycol) bis(carboxymethyl) * Corresponding author. Email address: g.tronci@leeds.ac.uk (G. Tronci).2 ether (PEG) were employed as sulfonic acid-free diacids of low and high crosslinker length respectively. Hydrogels based on short crosslinkers (PhS and 4Ph) displayed increased crosslink density, decreased swelling ratio as well as minimal hydrolytic and lysozymic degradation, whilst addition of lysozymes to PEG-based networks resulted in 70 wt.-% mass loss. PhS-crosslinked CT hydrogels displayed the highest loss (40 ± 6 CFU%) of antibacterial activity upon incubation with Porphyromonas gingivalis, whilst respective extracts were tolerated by L929 mouse fibroblasts.