Hydrogel/enzyme oscillator

A comprehensive model of the hydrogel/enzyme oscillator will be complex, since it must take into account the presence and transport of several chemical species, and the distributed mechanical response of the hydrogel membrane. In an earlier analysis of the present system (21,22), a highly simplified, electromechanical relay-like model of the hydrogel was considered. This simple, heuristic model, lacked any elements of hydrogel physical chemistry or transport processes between the hyArogel and the reaction compartment (Cell II). 

There is not always a clear distinction between Type I and Type II systems. Section II of this volume addresses several works with gels. In some cases the nonlinearities of the gel also play a role. The extreme case is the system developed by Siegel. He and his colleagues utilized the hysteresis in a hydrogel s permeability to create autonomous chemomechanical oscillations in a hydrogel/enzyme system driven by glucose 49,50), This is also addressed in chapter 4. 

In this chapter, we provide a brief survey of membrane-based chemical and biochemical oscillators. A comprehensive review of such systems was written by barter in 1990 [6]. The purpose of the present survey is to summarize some key systems already described by barter, and to describe a few developments since her review. We will focus on the single-periodicity oscillations. More complex behaviors such as period doubling, multiple periodicity, chaos, and dissipative spatial structures will not be covered. Following the survey, we present results on our glucose-driven hydrogel/enzyme system. This system rehes on hydrogel properties, in particular the volume phase transition, which were not available in the previous membrane systems. 

The survey is not essential for the material regarding the glucose-driven hydrogel/enzyme system it can be skipped at the reader s discretion. Other oscillating hydrogel systems, developed in Japan and France, are described in Chapters 7-9 of this book. 

Changes in membrane resistance and electro-osmotic properties as salt redistributes play a critical role in the Teorell oscillator, so the membrane is an active player in the oscillation mechanism. Changes in membrane permeabihties to various species (including solvent and current carriers) also play a role in most of the nonen2ymatic oscillators discussed. We also showed that the membrane can act simply to limit transport into and out of a reactor, with the membrane s own properties remaining constant - the PFK system is exemplary of this limit Here, the membrane s selectivity to different reactants contributes to oscillatory behavior. In the discussion of the hydrogel-enzyme system in the next section, the membrane and enzyme behaviors are seen to be mutually coupled, and the most significant transitions occur inside the membrane. 

Dhanarajan, A.P., Misra, G.P., and Siegel, R.A. (2002) Autonomous chemomechanical oscillations in a hydrogel/enzyme system driven by glucose./. Rhys. Chem., 106, 8835-8838. 

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