Cononsolvency-Assisted Fabrication of Hydrogels and Microgels With Tunable Porosity, Diffusivity and Stiffness

Porous materials including hydrogels offer high potential for applications requiring controlled mass transport, cell infiltration, and mechanical properties, such as tissue engineering, drug delivery, or soft robotics. We report a facile method for the synthesis of hydrogels and microgels with tunable porosity, offering control over diffusivity and mechanical properties. By exploiting the cononsolvency of polymers based on dimethylacrylamide (DMAAm) and hydroxyethylacrylamide (HEAAm) in water-acetonitrile mixtures, we produce porous networks with adjustable pore sizes up to several micrometers by varying the acetonitrile content in aqueous solution used during synthesis. The adjustment of the pore size by variation of the solvent mixture allows for fine-tuning of the hydrogel and microgel mechanical and diffusion properties with stiffnesses ranging from a few kPa up to more than 100 kPa and diffusion coefficients of 4 kDa FITC-dextran varying from 50 to over 130 µm² s^-1. Detailed analyses using optical microscopy, (cryo-)scanning electron microscopy, rheology, nanoindentation, and fluorescence recovery after photobleaching confirm the dependence of the observed properties on the network morphology and the similarity of the pore size and interconnectivity between hydrogel and microgel samples. The obtained hydrogels and microgels show strong potential for applications in bioengineering, sensing, and responsive materials.