| This thesis reports the synthesis, characterization and swelling properties of a class of glucose-sensitive, phenylboronic acid (PBA)-containing hydrogels, and the application of such hydrogels in microfluidic drug delivery devices. The thesis primarily consists of two parts, the polymers and the microfabrication.; The PBA-containing hydrogels were produced by copolymerizing 3-methacrylamido phenylboronic acid (MPBA) with acrylamide (AAm) and N,N′-methylenebisacrylamide (Bis). Hydrogel swelling increases steadily with increasing pH and fructose concentration. The literature-reported acid-base equilibrium and binding mechanism between fructose and benzeneboronic acid (BB) accounts for these results very well. The swelling behavior of MPBA-co-AAm hydrogel in the presence of glucose depends on whether the pH of the external solution is above or below the pKa of MPBA (PK a = 8.6). When pH < pKa, the gel swells monotonically with increased glucose concentrations. However, when pH > pKa, the gel initially shrinks, and then reswells with increasing glucose level. We propose that glucose binding to MPBA leads to both charging and reversible crosslinking of the hydrogel, causing either swelling or deswelling. The proposed mechanism is confirmed by measurement of compression modulus as a function of glucose concentration and by the swelling of the hydrogels at different glucose levels in the presence of competitive binding by fructose. Theoretical modeling based on Flory-Rehner-Donnan theory, modified to account for the formation of extra crosslinks by divalent complexation of glucose to MPBA, reproduces most of the trends observed in the experiments.; An attempt to tailor the swelling properties of PBA-containing hydrogels was made by decreasing the apparent pKa of the hydrogel. MPBA, Bis and dimethylaminopropyl methacrylamide (DMAPMA) were copolymerized to form MPBA-co-DMAPMA, which has an apparent pK a = 7.1. The same deswelling/reswelling behavior observed at pH = 10 for MPBA-co-AAm was observed at pH = 7.4 for MPBA- co-DMAPMA.; In the microfabrication, stimuli-sensitive hydrogels, poly (N-isopropylacrylamide) (NIPAA gel, temperature-sensitive) and poly(MPBA-co-AAm) (glucose-sensitive), were both incorporated into two different microstructures, a microvalve and a crosscut configuration. In both devices, swelling and shrinking of the incorporated hydrogels modulated the fluid flow through the device. Implications of the hydrogel-incorporated microdevices for controlled drug delivery are discussed. |
