Immobilization of cationic rifampicin-loaded liposomes on polystyrene for drug-delivery applications

Polymer-associated infections are a major problem in implanted or intravascular devices. Among others, microorganisms of the staphylococcal family have been identified as the most important culprit. Prevention of bacterial adhesion and colonization of polymeric surfaces by release of antimicrobial agents incorporated into the polymers itself are currently under study. We have developed a novel method for the functionalization of a polymeric surface which is based on the deposition of covalently coupled lipid structures from antibiotic loaded vesicles. We have found that such process significantly reduces the bacterial growth on polystyrene material. In this work, lipid coverage obtained from multilamellar (MLVs) and extruded unilamellar (LUVs) vesicles were analyzed with respect to their adhesion efficiency on three types of polystyrene (PS) well-plates. Two methods of lipid deposition were characterized and compared in terms of surface lipid density and time stability: deposition of cationic vesicles on negatively charged surfaces and formation of covalent linkages between functionalized lipids and amines enriched surfaces. In order to study the antibiotic encapsulation efficiency we measured how the rifampicin (RIF) loading was affected by changes of liposome charge upon introduction of various amounts of stearylamine (SA), distearoyl-trimethylammonium propane (DSTAP) or dioleoyloxypropyl-trimethylammonium chloride (DOTAP) into the liposomal formulation. RIF-coated polymeric surfaces were also tested against a Staphylococcus epidermidis strain to evaluate their efficacy in vitro, showing that only approximately 2% of such bacteria inoculated on MLV-treated PS substrate were able to proliferate. Covalently immobilized lipid films showed about a tenfold increase in time stability compared to electrostatically bonded lipid films. Furthermore, substrates covalently modified with RIF-loaded MLVs retained an antibacterial activity for up to 12 days when aged in buffer at 37 degrees C. Such antimicrobial polymer coatings show promise for their use as antibacterial barrier for the prevention of catheter-related infections.