Stimuli-responsive components typically include responsive molecular units that couple an external trigger to a defined macroscale response. Ongoing efforts to enhance the versatility and complexity of those responses increasingly focus on multi-stimuli-responsive molecular units and crosslinkers, as these bear the possible to impart self-regulatory behaviors creating on cooperative effects and feedback mechanisms. Herein, we study a stimuli-responsive platform consisting of polyacrylamide-based hydrogels with well-known multi-responsive spiropyrans covalently bound as pendant groups or 麓non-innocent麓 crosslinkers. Surprisingly, as compared to their appended counterparts, spiropyran crosslinkers trigger up to two-fold bigger hydrogel swelling in methylenebisacrylamide-crosslinked poly(acrylamide-co-acrylic acid) hydrogels, despite their elevated relative crosslinking density. We seek the origin of this unexpected behavior by employing nanoindentation, swelling research, and UV-vis spectroscopy to study alterations in mechanical properties and in spiropyran isomer distribution as a function of answer pH, co-monomer chemistry, and swelling-induced polymer strain. We then estimate the osmotic counterion pressures as a function of spiropyran isomer distribution but obtain that such pressures alone are insufficient to explain the observed behavior. Charge complexation, cooperative effects involving the hydrogel麓s mechanics and chemistry, and aggregate formation might all be invoked to explain capabilities on the observed 麓non-innocence麓 of spiropyran crosslinkers. Taken collectively, these insights will aid rational implementation of such responsive crosslinkers in components design and extend the functionality of existing polymeric materials towards far more complicated and superior tunable behaviors. 2-Bromo-3,4-difluorobenzonitrile site 2-(4-Hydroxy-1H-indol-3-yl)acetic acid Chemical name PMID:24507727