Ladder-like polysilsesquioxanes with antibacterial chains and durable siloxane networks

Significant progress has been made in endowing biomedical materials with antibacterial properties. However, the commercialization of these systems still poses various practical challenges. In this study, we report a facile technique for the preparation of practical and efficient antibacterial coatings based on well-defined polysilsesquioxane (PSQ) structures containing quaternary ammonium cation and long alkyl chains. PSQ is a hybrid material containing organic groups within a flexible and robust siloxane network, and can be endowed with different functions according to the synthetic conditions employed in the sol-gel process. However, depending on the synthetic precursors, a non-uniform PSQ structure can be formed, which limits the functions and stability of the resulting material. Accordingly, we synthesized PSQs with homogeneously distributed quaternary ammonium cation and long alkyl chains, using optimized synthetic conditions. The PSQs were coated on devices via self-assembly, and the thickness of the coating could be controlled from the nano- to the microscale depending on the deposition time. All coated substrates exhibited more than 60% bacterial reduction rate for three types of bacteria compared to the control groups. The coating inhibited the activity of the membrane adhesins, which prevented the strong adhesion of bacteria to the surfaces. Furthermore, the coated substrates also showed an increased mechanical strength in bulk strength tests. The nanoscale coatings notably increased the hardness of the dental substrates more than twofold compared to that of the control. The easy preparation and efficacy of the PSQs highlight their applicability as antibacterial coatings in various medical devices requiring high durability.