Compartmentalized architectures that enable programmable cascade reactions: From ungated diffusion to stimuli-regulated molecular transport.

Cascade reactions are chemical processes comprising at least two consecutive reaction steps, in which each subsequent transformation occurs as a direct consequence of the chemical functionality generated in the preceding step. Inspired by biological compartmentalization, a wide range of artificial architectures have been developed to organize cascade reactions within confined environments. This review focuses on vesicle- and hydrogel-based compartmentalized cascade systems operating in aqueous media, with particular emphasis on how spatial organization and diffusion-mediated molecular transport govern cascade performance. By comparing ungated, diffusion-driven systems with stimulus-regulated systems, we examine how molecular transport is controlled through membrane permeability, hydrogel network structure and compartment architectures. Representative examples are discussed across four application contexts: therapeutic and drug delivery systems, multimodal signal transduction and readout systems, artificial cell models for probing cellular organization and function, and environmental remediation and pollutant treatment.