Chlorhexidine adsorption to anatase and rutile titanium dioxide

Many dental and biomedical implants are composed primarily of titanium. Titanium metal is coated with a layer of titanium dioxide under ambient conditions. Crystalline titanium dioxide most commonly occurs in one of two crystal structures: anatase and rutile. Recently, there has been interest in functionalisation of implant surfaces with antimicrobials, to reduce the likelihood of bacterial infestation and colonisation of the surrounding tissues. In this study, the adsorption and subsequent desorption of a common antimicrobial, chlorhexidine digluconate, to anatase and rutile titanium dioxide was investigated in two different buffers (MES, PBS). Chlorhexidine in MES buffer adsorbed rapidly (<60 s) to both anatase and rutile titanium dioxide and exhibited Langmuir-type adsorption isotherms. Approximately 50% less chlorhexidine adsorbed to rutile than anatase titanium dioxide after normalising for surface area. In PBS buffer, more CHX adsorbed to rutile than anatase, although precipitation of chlorhexidine phosphate limited the range of concentrations over which this could be investigated. Chlorhexidine appeared to desorb slowly over a period of several days, and desorbed more rapidly from anatase than rutile. These results suggest that a pre-implantation treatment with chlorhexidine solution might provide post-operative antimicrobial action at the implant site. The difference between adsorption to anatase and rutile titanium dioxide is interesting and cannot be readily explained using surface chemistry. The implications for biofilm formation on titanium implants are the subject of further investigation.