Finite Element Analysis of Programmable Chemical Actuators

Abstract

Spatiotemporal modulation of electrochemical gradients to control enzyme activity in biological systems has been achieved using programmable chemical actuators (PCAs). The electronic-ionic coupling by polypyrrole is the operational physics foundation of PCAs. In a previous study, pH-indicating dyes were used to measure the effects of potential application techniques on the temporal control over the gradient. Also, when PCAs were operated under duplex pulse amperometry, the duty cycle was studied as a control variable over soluble alkaline phosphatase activity. The data were used here to develop numerical models of the ion transport mechanisms in three PCAs differing in size and geometry based on finite element analysis. The models considered electric fields, ion flux, diffusion, and Coulombic repulsion and were implemented and solved with COMSOL Multiphysics using the Secondary Current Distribution and Transport of Diluted Species predefined application modes. The new models were able to accurately predict ion transport patterns induced by PCAs in a 6-well plate and a 10 mL beaker but were less accurate for a PCA in a semi-microcuvette, probably due to the dependence of current density on the surface roughness of the working electrode. Nonetheless, these models provide a good foundation to design PCAs for new applications.