Abstract
Hydrogels are highly tunable, water-swollen polymer networks with strong potential as biomaterials and surface coatings due to their soft, tissue-like character, controllable physical properties, and capacity to resist biofouling. Among these, polyampholyte hydrogels have emerged as especially promising non-fouling materials because their balanced cationic and anionic character promotes a tightly bound hydration layer that limits nonspecific adsorption, bacterial adhesion, and subsequent biofilm formation. This dissertation explores the design, synthesis, scale-up, and evaluation of peptide-based zwitterionic cross-linkers for incorporation into TMA/CAA polyampholyte hydrogels, with the goal of creating materials with enhanced non-biofouling performance while retaining favorable physical and mechanical properties.A central focus of this work is the peptide-based zwitterionic cross-linker Ser-Ser, a serine-serine dimethacrylate designed to provide uninterrupted charge density throughout the hydrogel network. To enable meaningful hydrogel studies, the previously reported milligram-scale synthesis of Ser-Ser was optimized and scaled to a multigram process through a streamlined six-step linear route requiring only three chromatographic purifications. This synthetic advance provided sufficient material for broad evaluation in both bulk and thin film hydrogel systems and demonstrated the practicality of peptide-based zwitterionic cross-linkers as viable building blocks for non-fouling materials.
Using equimolar TMA/CAA formulations, hydrogels cross-linked with Ser-Ser were compared with those containing the established carboxybetaine cross-linker CBMAX and the PEG-based control DEGDMA. In both bulk hydrogels and thin film coatings, zwitterionic cross-linkers outperformed the uncharged PEG-based cross-linker in resisting Ralstonia pickettii adhesion. Most notably, Ser-Ser demonstrated exceptional long-duration performance against bacterial adhesion. In bulk hydrogels, after four weeks of repeated bacterial exposure, Ser-Ser maintained bacterial surface coverage below 0.005%, outperforming CBMAX, which showed increased adhesion at the same time point, while DEGDMA failed substantially. In thin film coatings on stainless steel, Ser-Ser likewise performed among the best formulations, contributing to marked reductions in bacterial surface coverage under optimized coating conditions. Collectively, these results indicate that subtle differences in cross-linker chemistry exert a major influence on the long-term non-fouling behavior of polyampholyte hydrogels, and that Ser-Ser is a particularly promising zwitterionic cross-linker for long-duration antibacterial applications.
To further diversify peptide-based zwitterionic cross-linker chemistry, this work also introduces DAP-DAP, a dipeptide-based bis(methacrylamide) cross-linker designed to probe the effect of replacing methacrylate functionality with methacrylamide functionality while maintaining similar charge spacing and overall zwitterionic character. When incorporated into TMA/CAA hydrogels, DAP-DAP displayed physical properties comparable to established systems and showed strong resistance to bacterial adhesion over a 31-day R. pickettii exposure, with bacterial surface coverage remaining low and comparable to the other zwitterionic cross-linkers. Although DAP-DAP did not surpass Ser-Ser in bacterial resistance, its performance confirmed that methacrylamide-based peptide cross-linkers are viable non-biofouling additives for polyampholyte hydrogels and represent an important extension of the zwitterionic cross-linker platform.
Overall, this dissertation demonstrates that peptide-based zwitterionic cross-linkers are a versatile and effective strategy for advancing non-fouling polyampholyte hydrogels. Through the successful scale-up of Ser-Ser, the identification of its exceptional resistance to bacterial adhesion relative to CBMAX, and the diversification of the platform to DAP-DAP, this work establishes a foundation for the continued design of tunable peptide-derived cross-linkers for biomaterial and surface coating applications.