Structural Characterization of Cross-linked Pluronic Hydrogels via Small Angle X-ray Scattering

Abstract

Engineered living materials (ELMs) are a new technology within Synthetic Biology (SynBio) that incorporates living microbial organisms within hydrogel matrices. Unlike traditional liquid cultures of living cells, both components in engineered living hydrogels can be programmed to meet specific goals. The living cells can be engineered to fulfill a multitude of functions, ranging from sensing to chemical production, and even generation of electricity. Hydrogels are a popular construct for these materials for a number of reasons. Most hydrogels offer a high degree of biocompatibility and chemical permeability that make it ideal for sustaining living microbes. There are a number of design criteria that must be met to determine if the hydrogel platform is a good candidate for manufacturing chemical intermediates. They must be able to provide compartmentalization of living cells, prevent cell leakage, maintain mechanical integrity, allow substrates and products to flow in and out of the hydrogel matrix, and sustain long shelf life. The primary motivation behind the research presented in this thesis is to contribute to the collaborative effort amongst an interdisciplinary team of researchers funded by the National Science Foundation (NSF). This group is interested in expanding the potential of SynBio and ELMS by developing next-generation bioreactors capable of converting cheap raw materials (such as sugars and amino acids) into high-value products such as pharmaceuticals and chemical intermediates using yeast and bacteria as the biocatalysts. Current manufacturing processes for these chemicals of interest require sourcing materials that rely on unsustainable farming practices. The development of these microbe-laden hydrogels could introduce a more sustainable approach to manufacturing these products. Pluronic F127 was selected as the polymer for this hydrogel due to its relatively high solubility in water and its ability to self-assemble in aqueous media without additives. Pluronic F127 as it exists off the shelf does not fulfill the required design criteria. Although it is capable of gelling, it cannot maintain this mechanical integrity when exposed to solution. Therefore, a new functionalized form of F127, known was F127-BUM, was developed by the Nelson Research Group. The work presented in this thesis focuses on using small angle X-ray scattering to characterize the progression of F127 through functionalization with bisurethane methacrylate to form F127-BUM, polymerization into cured hydrogels to prevent dissolution in water, and lyophilization/rehydration for extended shelf life.