A multifunctional antibacterial surface with switchable biocidal activity and bacteria-release capability

摘要

Introduction: For both human healthcare and industrial applications, endowing the surfaces of synthetic materials with antibacterial properties is strongly required to prevent bacterial attachment and the subsequent formation of biofilms. An ideal antibacterial surface should switch its functionality repeatedly between strong biocidal activity and bacterial release, not only maintaining long-term antibacterial effects but also keeping the surfaces free of the accumulation of dead bacteria and debris. In this work, we report a smart antibacterial surface based on silicon nanowire arrays (SiNWAs) modified with a pH-responsive polymer, poly(methacrylic acid) (PMAA), which exhibits the on-demand capability of killing and releasing bacteria in response to the change of environmental pH (as shown in Figure 1). Figure 1. Schematic illustration of a smart antibacterial surface with pH-responsive capability of loading biocide, killing bacteria, and releasing bacteria. Materials and Methods: SiNWAs were prepared via the chemical etching method. The SiNWAs surfaces were then immobilized with an initiator, followed by the surface-initiated polymerization of tert-butyl methacrylate (tBMA). Finally, the grafted PtBMA chains were hydrolyzed in acidic solution to obtain PMAA chains. The resulted SiNWAs-PMAA surfaces were then loaded with an antimicrobial lysozyme for further antibacterial test. Results and Discussion: The lysozyme adsorption on the SiNWAs-PMAA surfaces at various pH values (4 and 7) was investigated using the radiolabeling method. We found that the SiNWAs-PMAA surfaces not only exhibited a remarkably high capacity for binding lysozyme at an acidic pH (pH 4) but also could release a majority of the adsorbed lysozyme when the pH was increased to a neutral value (pH 7). The released lysozyme molecules maintained their enzymatic activity and thus served as biocides to kill bacteria both suspended in solution and attached to the surface, based on the results of three different but complementary antibacterial assays. More importantly, after the killing process, the dead bacteria and debris attached to the SiNWAs-PMAA surfaces could be readily removed by further increasing the pH to a basic value (pH 10) to give a "cleaned" surface. This unique pH-induced loading/release of lysozyme and the attachment/detachment of bacteria could be repeated for several cycles, suggesting the reusability. Conclusions: In summary, we exploited the combination of the pH responsivity of grafted PMAA chains and the enhanced local topographic effect of SiNWAs to regulate the interactions of SiNWAs-PMAA surfaces with proteins and bacterial cells. The functionality of the surface could be simply switched via step-wise modification of the environmental pH and could be effectively maintained after several kill-release cycles. This work provides a new methodology for the engineering of multifunctional surfaces for a variety of practical applications in the biomedical and biotechnology fields.