Rapid and Facile Light-Based Approach to Fabricate Protease-Degradable Poly(ethylene glycol)-norbornene Microgels for Cell Encapsulation

Thiol-norbornene photoclickable poly (ethylene glycol) (PEG)-based (PEG-NB) hydrogels are attractive biomaterials for cell encapsulation, drug delivery, and regenerative medicine applications. Although many crosslinking strategies and chemistries have been developed for PEG-NB bulk hydrogels, fabrication approaches of PEG-NB microgels have not been extensively explored. Here, a fabrication strategy for 4-arm amide-linked PEG-NB (PEG-4aNB) microgels using flow-focusing microfluidics for human mesenchymal stem/stromal cell (hMSCs) encapsulation is presented. PEG-4aNB photochemistry allows high-throughput, ultrafast generation, and cost-effective synthesis of monodispersed microgels (diameter 340 +/- 18, 380 +/- 24, and 420 +/- 15 mu m, for 6, 8, and 10 wt% of PEG-4aNB, respectively) using an in situ crosslinking methodology in a microfluidic device. PEG-4aNB microgels show in vitro degradability due to the incorporation of a protease-degradable peptide during photocrosslinking and encapsulated cells show excellent viability and metabolic activity for at least 13 days of culture. Furthermore, the secretory profile (i.e., MMP-13, ICAM-1, PD-L1, CXCL9, CCL3/MIP-1, IL-6, IL-12, IL-17E, TNF-alpha, CCL2/MCP-1) of encapsulated hMSCs shows increased expression in response to IFN-gamma stimulation. Collectively, this work shows a versatile and facile approach for the fabrication of protease-degradable PEG-4aNB microgels for cell encapsulation.