Decoupled control of stiffness and permeability with a cell-encapsulating poly(ethylene glycol) dimethacrylate hydrogel

Hydrogels are increasingly used as a cell encapsulation and transplantation device. The successful use of a hydrogel greatly relies on an ability to control hydrogel stiffness which affects structural integrity and regulates cellular phenotypes. However, conventional strategies to increase the gel stiffness lead to decrease in the gel permeability and subsequently deteriorate the viability of cells encapsulated in a gel matrix. This study presents a strategy to decouple the inversed dependency of permeability on the stiffness of a hydrogel by chemically cross-linking methacrylic alginate with poly(ethylene glycol) dimethacrylate (PEGDA). As expected, gel stiffness represented by elastic modulus was tuned over one order of magnitude with the concentration of methacrylic alginate and the degree of substitution of methacrylic groups. In contrast, swelling ratio of the hydrogel indicative of gel permeability was minimally changed because of multiple hydrophilic groups of alginate, similar to function of proteoglycans in a natural extracellular matrix. Furthermore, viability of neural cells encapsulated in a hydrogel of PEGDA and methacrylic alginate rather increased with hydrogel stiffness. Overall, the results of this study demonstrate an advanced biomaterial design paradigm which allows one to culture cells in a 3D matrix of varying rigidity. This study will therefore greatly expedite the use of a hydrogel system in both fundamental studies and clinical settings of cell therapies.