Self-binding polymers as antibacterial coatings for metallic and ceramic implants

摘要

Introduction: Formation of bacterial biofilms is a severe problem for many prosthetic medical devices. Such biofilms are difficult to treat by systemic antibiotics and therefore often make a revision surgery necessary. The risk of biofilm formation can be reduced using coatings which minimize microbial colonization, while simultaneously foster a stable tissue adhesion on the implant surface. The aim of the project is to develop such a coating for titanium combining the two conflictive properties: antimicrobial effect and compatibility with the body tissue. Experimental Methods: Copolymers were synthesized by free radical copolymerization of Vinylbenzylphosphonate (VBP) or Dimethyl(2-methacryloyl-oxyethyl) phosphonate (DMMEP) for binding to the surface and a second monomer which introduces an antibacterial effect to the coating like e.g. quartemized vinylpyridine or dimethylaminoethyl methacrylate DMAEMA(s. Figure 1). Figure 1: Poly(VBP-co-hexVP) left, poly(DMMEP-co-hexVP) midlle and poly(DMMEP-co-hexDMAEMA) right The copolymers were characterized by 1H-NMR- and IR-spectroscopy and coated on titanium disks by spin or spray coating from solution. After drying the layers the unbound copolymer is washed away by solvent. The layers were characterized by ellipsometry, contact angle measurements and XPS. Antibacterial activity is assessed by investigation of adherence of S. mutans. Biocompatibility is rated based on human gingival fibroblast adhesion and proliferation as evaluated employing a modified LDH activity assay. Results and Discussion: Copolymers combining the antibacterial effect of quarternary ammonium groups with biocompatible phosphonate groups have been synthesized in different compositions. The phosphonate groups bind the copolymer covalently to the surface. The thickness of the layers is ca. 6-8 nm. The coatings on titanium disks were checked for antibacterial activity and biocompatibility. Most of the copolymers show a clear reduction in the number of adherent bacteria. As well as the antibacterial effect, also the biocompatibility strongly depends on the exact composition of the copolymers. There are some compositions which show significant antibacterial effect and simultaneously good biocompatibility. Conclusion: Copolymers of bearing quarternary ammonium groups and phosphonate containing monomers were prepared. The copolymers can be applied in an easy coating, drying, washing process onto titanium implants and form ultrathin polycationic layers. Some copolymer compositions show a significant antimicrobial effect and are sufficiently biocompatible at the same time.