Polymer networks, materials comprised of interconnected polymer chains, have been the subject of research interest for decades and have, particularly in recent years, found use cases in a variety of applications. Despite their broad use cases these materials are limited by their inherent tendency toward brittleness. One strategy for increasing the toughness of polymer networks is to introduce mechanochemically reactive groups in the crosslinks of a network instead of in the load-bearing primary polymer chains. Previously reported scissile crosslinkers have typically relied on strained ring structures or unusually weak covalent bonds for selective bond scission, introducing challenges such as difficult synthetic procedures and high design complexity. My collaborators at Johns Hopkins University have developed a novel, synthetically accessible crosslinker design that allows for selective mechanochemical bond scission via the replacement of a single carbon atom with silicon. They demonstrated that this scissile crosslinker doubles the toughness of a polymer network prepared by controlled polymerization. In my project I incorporated this crosslinker into a liquid resin compatible with free radical vat photopolymerization, 3D printed this new material, and mechanically characterized it through tensile testing. My work demonstrated that the same toughening effect occurs on polymer networks that are much less controlled and that this strategy for network toughening is compatible with 3D printing, which allows for the fabrication of more complex constructs. In conjunction with the expedient synthesis of this new crosslinker my project demonstrates that this approach to network toughening has the potential for large-scale applications.

Fat, oil, and grease (FOG) in residential wastewater presents significant environmental challenges, contributing to the formation of fatbergs that disrupt wastewater systems, increase treatment costs, and heighten public health risks. Traditional methods, like commercial enzymes, are only temporarily effective and require constant maintenance. The goal of this research is to develop Engineered Living Materials (ELMs) comprising a yeast strain, Yarrowia lipolytica, within polymeric matrices for sustained FOG degradation. Y. lipolytica is known for its ability to efficiently degrade hydrophobic FOG components due to its diverse lipase enzyme expression. I encapsulated engineered Y. lipolytica strains in UV-cured poly(ethylene glycol) diacrylate (PEGDA) hydrogels. The findings showed sustained lipase activity and robust cell growth, confirmed by enzyme assays and confocal microscopy. However, over 28 days, significant degradation of the PEGDA-based ELMs occurred, likely due to the breakdown of ester bonds by lipolytic enzymes. To address this, I switched to a thiol-ene polymer network composed of tetra-PEG-allyl and PEG-dithiol, which is expected to resist degradation more effectively. I confirmed the viability and lipase production in these thiol-ene ELMs using the same methods. Varying polymer chain lengths in the thiol-ene network influenced Y. lipolytica growth patterns and morphology, including a shift toward hyphal growth—a filamentous form typical of its dimorphic nature. These changes were influenced by the polymer network’s architecture and material stiffness. Moving forward, I will investigate how hyphal growth impacts FOG degradation and assess the long-term mechanical properties of these thiol-ene ELMs. I expect these ELMs to remain stable over time and reduce FOG concentrations in simulated wastewater. Ultimately, this research aims to provide a sustainable solution for wastewater treatment, addressing the environmental, economic, and infrastructural impacts of fatbergs.