Porous bio-click microgel scaffolds control hMSC interactions and promote their secretory properties

Human mesenchymal stem/stromal cells (hMSCs) are known to secrete numerous cytokines that signal to endogenous cells and aid in tissue regeneration. However, the role that biomaterial scaffolds can play in controlling hMSC secretory properties has been less explored. Here, microgels were co-assembled with hMSCs using three different microgel populations, with large (190 +/- 100 mu m), medium (110 +/- 60 mu m), and small (13 +/- 6 mu m) diameters, to create distinct porous environments that influenced hMSC clustering. Cells embedded in large diameter microgel networks resided in large clusters (similar to 40 cells), compared to small clusters (similar to 6 cells) observed in networks using medium diameter microgels and primarily single cells in small diameter microgel networks. Using a cytokine microarray, an overall increase in secretion was observed in scaffolds that promoted hMSC clustering, with over 60% of the measured cytokines most elevated in the large diameter microgel networks. N-cadherin interactions were identified as partially mediating these differences, so the microgel formulations were modified with an N-cadherin epitope, HAVDI, to mimic cell-cell interactions. Results revealed increased secretory properties for hMSCs in HAVDI functionalized scaffolds, even the non-clustered cells in small diameter microgel networks. Together, these results demonstrate opportunities for microgel-based scaffold systems for hMSC delivery and tailoring of porous materials properties to promote their secretory potential.