Design of local chemical feedback systems

Feedback mechanisms are fundamental to biological regulation, enabling dynamic behaviors such as bistability, adaptation, and homeostasis. Inspired by these processes, this thesis investigates how chemical feedback can be locally engineered at material interfaces to regulate the behavior of out-of-equilibrium chemical reaction networks (CRNs). Using microfluidic and hydrogel platforms, the work focuses on surface-driven reactions to control molecular information processing at small scales.

The thesis begins by implementing an autocatalytic trypsin network in a continuous-flow stirred tank reactor (CFSTR), demonstrating history-dependent switching and nonlinear behaviors. This motivates the design of passive micromixers that enable surface-localized reactions without mechanical stirring. Using poly-L-lysine coatings and polyelectrolyte complexation, the study shows that competition between surface-bound and mobile species under pH changes can drive dynamic switching behaviors at the liquid–surface interface.

To increase system complexity, oppositely charged polyelectrolytes in solution are introduced, enabling surface-mediated competition and self-assembly. This results in history-dependent polyelectrolyte complexation regulated by sweep rates and local pH. Finally, an enzymatic cascade reaction with immobilized β-galactosidase and glucose oxidase demonstrates a form of chemical homeostasis, where gradual substrate changes and enzyme ratios buffer the output signal.

Together, these studies show that integrating local chemical feedback at surfaces can regulate CRNs in programmable ways. The results contribute new strategies for designing modular, feedback-responsive systems capable of mimicking life-like behaviors. The thesis concludes with an outlook on extending this approach to thiol-based hydrogel platforms, enabling dynamic, reconfigurable materials. This work advances systems chemistry by offering new tools for the rational design of functional chemical systems operating at the interface of molecular reactions and materials.