Tunable collagen hydrogels are modified by the therapeutic agents they are designed to deliver.

Injectable hydrogels are increasingly being developed for biomedical applications due to their ability to be delivered in a minimally invasive manner. One potential use for such materials is in cell delivery for cardiac regeneration. While the materials' properties are often characterized, how these properties (and in particular gelation) are affected by the addition of the therapeutic agent(s) they are designed to deliver is often overlooked. The aim of this study was to examine the interactive effects between collagen-based hydrogels and different additives (cells and microspheres). The results demonstrated that the incorporation of either cells or microspheres to a collagen hydrogel decreased its gelation time and increased its viscosity. Increased concentrations of the EDC/NHS cross-linker resulted in greater loss of cell viability. However, it was found that this cell loss could be minimized by delivering cells with the cross-linker scavenger glycine. A better understanding of how materials and cells (and other additives) respond to each other will help towards the goal of improving scaffolds being developed for regenerative therapy.