Functional polymers and proteins at interfaces

Graduation date: 2010Functional polymers and proteins at interfaces and surfaces are of fundamental importance for biomaterials, biocatalysis and microreactor applications. Candida antarctica lipase B immobilized on poly-DL-tryptophan tethers showed 30x higher\ud specific activity in aqueous and non-aqueous media than the same enzyme adsorbed or covalently bound directly to the surface. An excess of enzyme vs. tethers was observed, indicating multilayer binding. This was attributed to covalent binding of the enzyme to the surface, as well as to the ends of the tethers, and adsorption of the lipophilic enzyme to the hydrophobic polymers.\ud Aspergillus oryzae ß-galactosidase was immobilized on a novel silicon oxide nanospring mat in a microreactor by covalent disulfide bonds. Nanosprings offer high accessible surface area with very low flow resistance and excellent mechanical\ud properties, and can be patterned onto existing devices. Continuous reactions were performed at different flowrates and substrate concentrations. The enzyme activity was stable for over 26 days, and high steady-state conversions (X > 0.7) were achieved\ud with average residence times of less than one minute. The catalyst was regenerated in situ by reduction of the disulfide bonds and subsequent immobilization of fresh enzyme. Numerical simulation and sensitivity analysis indicate that the characteristic high permeability of the nanosprings is critical to reactor performance.\ud In another study, a method was developed to directly image the surface distribution of small polyethylene oxide-polybutadiene-polyethylene oxide (PEO-PBD-PEO) triblock copolymer surfactants using atomic force microscopy (AFM). Triblocks with cleavable ester bonds of various PEO:PBD ratios and molecular weights were\ud synthesized. The triblocks were self-assembled onto hydrophobic silicon wafers, and the adsorbed vinyl-containing PBD blocks immobilized by γ-irradiation. Acid hydrolysis of the cleavable linker released the PEO side-chains. The remaining immobilized PBD was labeled with β-cyclodextrins, and imaged using standard AFM "tapping mode" techniques. Triblocks deposited from dilute (1 mg/mL) solutions formed very sparse, non-uniform layers. At 10 mg/mL, regular patterns consistent with deposition of worm-like or cylindrical micelles were observed. Long PEO chains produced sparse layers, presumably by facilitating desorption of the triblocks.\ud These studies demonstrate novel methods for solid-supported enzymatic reactions and production and characterization of surface coatings, with diverse applications in bioengineering and biomaterials