| The first part of this work describes the ultrasonic degradation of a link-functionalized polymer. In this experiment, a 40 kDa polyethylene glycol polymer containing an azo functionality at its midpoint (PEG-AZO-PEG) was subjected to ultrasound and studied under a variety of conditions. The PEG-AZO-PEG system exhibited site-specific degradation at the azo link, resulting in two 20 kDa polymer fragments, and experienced faster degradation kinetics than the control polymers without a weak link in the center of their backbones. The PEG-AZO-PEG system demonstrated faster degradation kinetics with increasing ultrasound intensities, and slower degradation kinetics with increasing temperature and increasing polymer concentration. In addition, the system was found to have a limiting molecular weight for degradation between 20 and 40 kDa at 8.9 W/cm2. Solvent had a significant impact on the degradation of PEG-AZO-PEG. Although 0.75 mg/mL solutions of PEG-AZO-PEG in acetonitrile, benzene, and methanol, had similar degradation kinetics, a solution of PEG-AZO-PEG in water degraded into 20 kDa fragments at a considerably faster rate, and a solution of PEG-AZO-PEG in chlorobenzene appeared to have a competing, random degradation reaction. The ultrasonic degradation of PEG-AZO-PEG is a mechanical process with an easily controlled rate that can potentially be used to initiate small molecule reactions.;The second part of this work describes the construction of a peptide crosslinked hydrogel that degrades upon exposure to alpha-chymotrypsin. The peptide, Ac-Cys-Tyr-Lys-Cys-NH2, was conjugated to two polymerizable moieties through disulfide exchange with N-[2-(2pyridyldithio)] ethyl methacrylamide. A prepolymer solution containing the peptide crosslinker, a 15% (w/w) solution of acrylamide in water, and photoinitiator was injected into a microchannel and polymerized via photolithography into a hydrogel. The protease, alpha-chymotrypsin, was flowed through the microchannel and hydrogel degradation was observed.;The third part of this work describes a simple laboratory experiment for junior high or high school students that promotes understanding of photolithography, crosslinking density, and the process of photopolymerization, while demonstrating the power of rapid prototyping used to fabricate microscale devices. The versatility of photolithography for microchip construction is exemplified by allowing each student to fabricate polymers in virtually any shape imaginable, including his or her silhouette. |
