Mechanics-Switchable\nand Antiswelling Colloidal Hydrogels\nInspired by the Cononsolvency Effect

Stiffness switching hydrogels have been in high demand\nfor intelligent\ndevices, adhesion science, soft robotics, and flexible electronics.\nHowever, it is challenging to post-tune the mechanical properties\nof a hydrogel once the polymer network structure is formed. Inspired\nby the cononsolvency effect, we prepared a mechanics-switching colloidal\nhydrogel through the precipitation polymerization of methacrylamide\nin mixed dimethyl sulfoxide and water solvents. The colloidal network\nenables the hydrogels to simultaneously strengthen, stiffen, and toughen.\nThe colloidal hydrogels not only display a broad spectrum of adjustable\nmechanical properties (ranging from 0.08 to 57.1 MPa) via solvent\nresponse but also accomplish reversible stiffness conversion through\nthe solvent-tuned conformational adjustment of colloidal polymer networks,\nwith the maximum modulus conversion reaching 1427, and exhibit solvent-responsive\nshape memory. Based on the stable and tight colloidal network, the\nhydrogels exhibit antiswelling properties in various aqueous solutions\nand solvents. The colloidal hydrogel would provide more possibilities\nin various applications, such as antiimpact protection, shape memory,\nelectronic switches, and intelligent engineering materials. It is\nenvisioned that this work will provide key opportunities in developing\nmechanics-switching and on-demand tuning of soft materials for tissue\nengineering, flexible electronics, and biomedical science.