Gelatin-Based Matrices as a Tunable Platform To Study in Vitro and in Vivo 3D Cell Invasion

Hydrogels have been used as synthetic mimics of 3D extracellular matrices (ECM) and their physical properties like stiffness, degradability, and porosity have been known to influence the behavior of encapsulated cells. However, to understand the role of individual properties, the influence of biophysical cues should be decoupled from biochemical ones. In this study, we have used hydrogels as a tunable model matrix to develop a 3D cell culture platform for studying cell invasion. Inert polyethylene (glycol) diacrylate (PEGDA) and cell adhesive gelatin methacryloyl (GELMA) were blended in varying compositions, followed by UV-mediated photo polymerization to obtain hydrogels with varying stiffness, degradation, and cell adhesive properties. We developed two hydrogel matrix systems, namely, PEGDA-GELMA (containing a larger proportion of PEGDA) and GELMA-PEGDA (containing predominantly GELMA), and characterized them for differences in pore size, swelling ratio, storage modulus, degradability, and biocompatibility of the matrix. Both hydrogel systems had similar pore dimensions and swelling behavior, but PEGDA-GELMA was found to be stiffer and nondegradable, while GELMA-PEGDA was softer and degradable. Accordingly, MDA-MB-231 breast cancer cells encapsulated in these matrices showed a spheroidal morphology in PEGDA-GELMA hydrogels and were more spindle-shaped in GELMA-PEGDA hydrogels, confirming that size and extent of spreading of cells were influenced by the type of these hydrogels. The softer GELMA-PEGDA matrices readily allowed invasion of MDA-MB-231 cells in 3D and showed differences in epithelial-mesenchymal transition (EMT) gene expression of these cells. We further demonstrated the invasion and sprouting of endothelial cells using a chick aortic arch assay, exhibiting the utility of softer matrices to study 3D cell invasion for multiple applications. We also implanted these matrices in mice and showed that soft gelatin-based hydrogels allow cell infiltration in vivo. Results from our study highlight the tunability of this matrix system and the role of matrix constitution in influencing cell invasion in a 3D microenvironment.