Engineering Biocatalytic Materials: Encapsulation Systems for Biotechnology

Abstract

My dissertation presents scientific and engineering contributions. Both sol-gel and layer-by-layer technologies were used to study prokaryotic cells under confinement and the role that the encapsulation material plays in affecting these cells. My work focused on the development, synthesis, and use of biologically active materials for water treatment based on silica gel bioencapsulation. Silica gels were developed with improved mechanical properties while ensuring that these materials were cytocompatible. The ratio of the silicon alkoxide crosslinker to silica nanoparticles was crucial in adjusting the maximum stress at failure. I demonstrated a 6-fold improvement in the compressive stress at failure in a silica bioencapsulation matrix containing metabolically active cells. These gels were organically modified to study the effect of encapsulation matrix hydrophobicity on the relative adsorption and biodegradation of organic pollutants. The ratio of biodegradation to adsorption was a strong function of the hydrophobicity of the pollutant. A layer-by-layer approach was used to minimize the diffusion length and protect the encapsulated biocatalyst from environmental stressors. I showed that targeting the cytoplasmic membrane with detergents increased its permeability and enabled a 15-fold enhancement in the rate of biocatalysis. To demonstrate the protective effects of the microbial exoskeleton, the coated cells were exposed to environmental stressors ranging from heat shock and desiccation to enzymatic attack and predation by protozoa. With a minimum of 4 layers, the biocatalytic activity was preserved for all cases examined. The translational application of cyanuric acid hydrolase (CAH) was also studied. By treating the cells with glutaraldehyde to crosslink the membrane-bound proteins, the cell was stabilized and CAH was retained within the whole cell biocatalyst.