Antimicrobial releasing biomaterial coatings have found application for instance in the fixation of orthopaedic joint prostheses and central venous catheters. Most frequently, the release kinetics is such that antimicrobially-effective concentrations are only reached within the first days to weeks after implantation, leaving no local antimicrobial release available when a biomaterial-associated infection occurs later. Here we compare the ad libitum release of chlorhexidine and silver-sulfadiazine from a central venous catheter with their release from a new, on-demand release coating consisting of a temperature-sensitive copolymer of styrene and n-butyl (meth)acrylate. The copolymer can be loaded with an antimicrobial, which is released when the temperature is raised above its glass transition temperature. Ad libitum release of chlorhexidine and silver-sulfadiazine from a commercially-purchased catheter and associated antimicrobial efficacy against Staphylococcus aureus was confined to 16days. Consecutive temperature-triggers of our on-demand coating yielded little or no antimicrobial efficacy of silver-acetate release, but antimicrobially-effective chlorhexidine concentrations were observed over a time period of 60-80 days. This attests to the clear advantage of on-demand coatings above ad libitum releasing coatings, that may have released their antimicrobial content before it is actually needed. Importantly, glass transition temperature of chlorhexidine loaded copolymers were lower (48°C) than of silver loaded ones (61°C), facilitating their clinical use.
Sjollema, J., Dijkstra, R.J., Abeln, C., van der Mei, H.C., van Asseldonk, D. and Busscher, H.J. (2014) On-demand antimicrobial release from a temperature-sensitive polymer – comparison with ad libitum release from central venous catheters. Journal of Controlled Release. June 17th. (epub ahead of print).