Development of Charged Polyampholyte Interfaces: Synthesis, Properties, and Antifouling Application

Biocompatible hydroxyapatite (HA) is a biomaterial widely used in the regeneration and replacement of dental and bone tissue. On these HA surfaces, complex multicellular communities known as biofilms are established by pathogenic microorganisms, contributing to 75% of all bacterial infections and presenting a significant public health concern. Among the various charged polymers, zwitterionic polymers are commonly used for antifouling applications due to their ability to form a strong hydration layer. In contrast, charged polymers like polyampholytes with both positively and negatively charged groups remain largely unexplored for this application. Polyampholytes can be modified to be neutral, cationic, or anionic, as they are composed of two monomers with opposite charges. In this study, we aim to investigate the preparation of polyampholytes with different charges through Reversible Addition-Fragmentation chain Transfer (RAFT) polymerization, coating these polymers onto HA discs and evaluating their antifouling capabilities using bacterial adhesion experiments. We synthesized charged polyampholytes using [2-(methacryloyloxy)ethyl]trimethylammonium chloride (MAETMA) and sodium-<i>p</i>-vinylbenzenesulfonate (VBS), which are cationic and anionic monomers, respectively, in a DI water/dioxane medium via RAFT polymerization. Next, HA discs were coated with a series of synthesized charged polymers, resulting in surfaces with systematically tuned net charges ranging from fully positive to fully negative, labeled as HAP1-HAP5. Cytotoxicity assessments using NIH-3T3 fibroblast cells confirmed the biocompatibility of the polymer-coated HA surfaces. To confirm the antifouling property, adherence studies of <i>Streptococcus mutans</i> (<i>S. mutans</i>), a bacterium that causes dental caries (tooth decay) and dental plaque, were analyzed using a scanning electron microscope (SEM). Among all samples, HAP3 exhibited the minimum bacterial adhesion and the most effective resistance to protein adsorption, significantly outperforming the uncoated HA control.