Nanoporous silica coatings on implant surfaces: characterization, stability, biocompatibility and drug release properties

Nanoporous silica coatings for drug release purposes were prepared on medical implants. As substrate, we chose Bioverit® II, which is a commercial available glass-mica ceramic implant material. The coating was prepared by a dip-coating technique in which long-chain organic molecules act as placeholders for the pores. Characterization of the coatings by scanning transmission electron microscopy and X-ray diffraction showed a disordered nanoporous system with a layer thickness of 30–150 nm. The nanoporous structure was stable for about 12 h in a typical cell culture medium and rearranged to a packing of silica nanoparticles. The coating allowed cell attachment and showed excellent biocompatibility in cell culture tests independently of the particular cell type examined. In vivo, implant-tissue interactions were examined in the middle ear in a novel mouse model. Whole genome expression profiling showed no persisting inflammatory response in the presence of the implants. Release profiles of the antibiotic ciprofloxacin demonstrated that the coating is suitable for a local drug delivery. The drug loading capacity could be drastically increased after sulfonic acid modification of the Bioverit® II surface