Key points are not available for this paper at this time.
A glucose-responsive polymer gel bead with a diameter in the range of several hundred micrometers, bearing a phenylborate derivative (3-acrylamidophenylboronic acid) as a glucose-sensing moiety, was successfully prepared by inverse phase suspension polymerization. The kinetics of the glucose responsive swelling and shrinking process of the gel bead was studied by monitoring changes in the size and shape of the gel under a microscope. The equilibrium swelling volumes of the gel determined under various temperatures and glucose concentrations revealed the presence of critical temperatures and glucose concentrations to induce discontinuous volume phase transitions of the gel. The glucose-induced swelling process was accompanied by the appearance of a marked swelling boundary (swelling front) intervening between the core collapsed phase and the outer swollen layer of the gel, and the swelling curve as a function of the square root of the time exhibited a sigmoidal (nonlinear) feature, both indicating that the process is essentially rate determined by the relaxation process of the polymer chains due to the hydration. The swelling rate was significantly affected by the bead size and the terminal glucose concentration. An accelerated disappearance of the swelling front was observed immediately before the gel reaches the equilibrium swelling, which was highlighted by an increased bead size, implying that increasing elastic and osmotic pressures generating from the swollen layer affect the swelling kinetics. The glucose-induced shrinking process involved the formation of a skin layer on the gel surface followed by a radical structural change. The observed, appreciably long-termed preservation of a quasi-swollen state on a sub-millimeter scale gel bead with a distinctive skin layer may propose the potential applicability of the gel to chemical valve systems discretely switching for solute release.
Matsumoto et al. (Wed,) studied this question.