Analytical Expressions of Concentrations inside the Cationic Glucose-Sensitive Membrane

A mathematical model of Wu et al. [J. Membr. Sci 254 (2005) 119-127] of a cationic glucose-sensitive membrane is discussed. The model involves the system of non-linear steady-state reaction-diffusion equations. Analytical expres-sions pertaining to concentration of oxygen, glucose, and gluconic acid for all values of parameters are presented. We have employed Homotopy analysis method to evaluate the approximate analytical solutions of the non-linear boundary value problem. A comparison of the analytical approximation and numerical simulation is also presented. A good agreement between theoretical predictions and numerical results is observed.

Mechanistic insights into the novel glucose-sensitive behavior of P(NIPAM-co-2-AAPBA)

A glucose-sensitive polymer,poly(N-isopropylacrylamide-co-2-acrylamidophenylboronic acid)(P(NIPAM-co-2-AAPBA)),was synthesized by reversible addition fragmentation chain transfer(RAFT)copolymerization.Addition of glucose results in reduced solubility and hence increased turbidity,rather than the normal increase in solubility(decreased turbidity)observed for other PBA-based glucose-sensitive polymers.The novel glucose-sensitive behavior is explained by a new mechanism,in which glucose acts as an additive and depresses the lower critical solution temperature(LCST)of the polymer,instead of increasing solubility by increasing the degree of ionization of the PBA groups.Experimental and theoretic analysis for the influence of glucose on the thermal behavior of P(NIPAM-co-2-AAPBA)reveals that glucose depresses the LCST of P(NIPAM-co-2-AAPBA)copolymers in a two-stage manner,a fast decrease at low glucose concentrations followed by a slow decrease at high glucose concentrations.For low glucose concentrations,the binding of glucose with PBA groups on the polymer chain increases the number of glucose molecules proximal to the polymer which influences the thermal behavior of the polymer,causing a rapid decrease in LCST.Importantly,the transition occurs at a glucose concentration equal to the reciprocal of the binding constant between PBA and glucose,thus providing a novel method to determine the binding constant.Other saccharides,including mannose,galactose and fructose,also depress the LCST of P(NIPAM-co-2-AAPBA)copolymer in the same way.