CC BY 4.0 UnportedHörner, MaximilianBecker, JanBohnert, RebeccaBaños, MiguelJerez‐Longres, CarolinaMühlhäuser, VanessaHärrer, DanielWong, Tin WangMeier, MatthiasWeber, Wilfried2024-07-022024-07-022023https://oa.tib.eu/renate/handle/123456789/14750https://doi.org/10.34657/13772Hydrogels with adjustable mechanical properties have been engineered as matrices for mammalian cells and allow the dynamic, mechano-responsive manipulation of cell fate and function. Recent research yields hydrogels, where biological photoreceptors translated optical signals into a reversible and adjustable change in hydrogel mechanics. While their initial application provides important insights into mechanobiology, broader implementation is limited by a small dynamic range of addressable stiffness. Herein, this limitation is overcome by developing a photoreceptor-based hydrogel with reversibly adjustable stiffness from ≈800 Pa to the sol state. The hydrogel is based on star-shaped polyethylene glycol, functionalized with the red/far-red light photoreceptor phytochrome B (PhyB), or phytochrome-interacting factor 6 (PIF6). Upon illumination with red light, PhyB heterodimerizes with PIF6, thus crosslinking the polymers and resulting in gelation. However, upon illumination with far-red light, the proteins dissociate and trigger a complete gel-to-sol transition. The hydrogel's light-responsive mechanical properties are comprehensively characterized and it is applied as a reversible extracellular matrix for the spatiotemporally controlled deposition of mammalian cells within a microfluidic chip. It is anticipated that this technology will open new avenues for the site- and time-specific positioning of cells and will contribute to overcome spatial restrictions.enghttps://creativecommons.org/licenses/by/4.0cell depositioncellular matrixhydrogelsmaterialsmicrofluidicsoptogenetics600Article