Mesoporous silica coatings for controlled release of the antibiotic ciprofloxacin from implants

Abstract

To generate bioactive coatings for medical implants, a novel procedure has been developed using a coating of mesoporous silica for controlled drug delivery. Plain glass slides were used as substrates. The mesoporous coatings were then loaded with the antibacterial drug ciprofloxacin. The drug release kinetics were investigated in a physiological buffered solution. The drug loading capacity of the unmodified mesoporous coatings was low but could be increased nearly ten-fold (to about 2 µg cm⁻² of the macroscopic surface) by functionalizing the mesoporous surface with sulfonic acid groups. To achieve a controlled drug release over an extended time period, further coatings were added. Covering the surface of the drug loaded mesoporous silica layer by dip-coating with bis(trimethoxysilyl)hexane resulted in an organosiloxane layer which retarded the release for up to 30 days. By an additional evaporation coating with dioctyltetramethyldisilazane, the release of ciprofloxacin was prolonged for up to 60 days. The biocompatibility of the different coatings was tested in cell culture assays. The presence of the additional silane-derived hydrophobic coatings somewhat reduced the biocompatibility. The antibacterial efficacy of the materials was demonstrated by using clinically relevant biofilm-forming pathogenic bacteria. A test where the sequential release of ciprofloxacin (in 2 days intervals) and the bacterial viability were tested in parallel showed good concordance in the results. The material where a sulfonate-functionalized mesoporous silica layer is loaded with ciprofloxacin and then coated by an organosiloxane layer derived from bis(trimethoxysilyl)hexane showed the best results with regard to antibacterial efficacy and will further be tested in animal experiments.