Abstract
<jats:p>The ability to reconfigure microfluidic architectures on demand, without rebuilding the device, would enable adaptive control over transport,mixing,and separation. Here we introduce fully aqueous photoacid-fueled peptide hydrogels and use them as a light-written, self-erasing material for on-the-fly microfluidic reconfiguration. We elucidate design criteria for selecting photoacids and demonstrate that blue-light irradiation of a highly water-soluble spiropyran photoacid transiently lowers the pH and drives self-assembly of the dipeptide Fmoc-Leu-Gly into a fibrous hydrogel. When illumination ceases, spontaneous pH recovery triggers complete network disassembly, causing the material to erase autonomously. Gel lifetimes can be tuned from minutes to hours through the initial pH, illumination dose, buffer conditions, and feature size, while selective post-print irradiation locally prolongs persistence of individual structures. Using digital light projection, we write, erase and rewrite hydrogel walls, separators, mixers, and flow-guiding elements directly inside microfluidic devices, thereby reconfiguring fluid pathways on-the-fly during operation. This work establishes photoacid-driven peptide gelation as a design framework for light-driven transient soft matter and introduces programmable, rewritable hydrogels as adaptive soft hardware for dynamic microfluidics.</jats:p>