Collagen–Poly(<i>N</i>‑isopropylacrylamide) Hydrogels with Tunable Properties

There is a lack of hydrogel materials whose properties can be tuned at the point of use. Biological hydrogels, such as collagen, gelate at physiological temperatures; however, they are not always ideal as scaffolds because of their low mechanical strength. Their mechanics can be improved through cross-linking and chemical modification, but these methods still require further synthesis. We have demonstrated that by combining collagen with a thermoresponsive polymer, poly­(<i>N</i>-isopropylacrylamide) (PNIPAM), the mechanical properties can be improved while maintaining cytocompatibility. Furthermore, different concentrations of this polymer led to a range of hydrogels with shear moduli ranging from 10⁵ Pa down to less than 10² Pa, similar to the soft tissues in the body. In addition to variable mechanical properties, the hydrogel blends have a range of micron-scale structures and porosities, which caused adipose-derived stromal cells (ADSCs) to adopt different morphologies when encapsulated within and may therefore be able to direct cell fate