Comparative Study of the Mechanical Properties of New PEGSSDA Hydrogels, and Their Effect on Embedded Stem Cell Secretome
Authors: Azar Tala , Cassimatis Nick , Dragowich Matthew , Hashemiyoon Rameen , Ratliff Brian B. 
Published: November 2023

Hydrogels are hyaluronic acid and collagen‐based polymer networks that mimic the 3D cell microenvironment and can be used as tissue‐engineered scaffolds for therapeutic delivery of embedded stem cells and drugs. Mechanical characteristics determine important features of hydrogels (including rigidity and pore size) and affect their therapeutic efficacy. A key component of hydrogels that dictates many of their mechanical characteristics is the crosslinker used in their construction. Recently, new hydrogel crosslinkers were developed. In this study, we compared hydrogels constructed with different concentrations (2% and 4%) of two different PEG (poly(ethylene glycol)) crosslinkers, including PEGDA (poly(ethylene glycol) diacrylate) and the brand new PEGSSDA (a disulfide‐containing PEGDA). Both crosslinkers have acrylate ends, but PEGSSDA is longer due to the additional disulfide bond. We determined various properties of the hydrogels constructed with each crosslinker, including Young's modulus (measurement of rigidity that can be measured using atomic force microscopy), diffusion efficiency and swelling ratio. In follow up experiments, we examined (using luminex multiplex technology) if the cyto‐/chemokine secretome of endothelial progenitor cells (EPCs) was affected when these cells were embedded in PEGDA and PEGSSDA hydrogels. We hypothesized PEGSSDA hydrogels would have different mechanical properties and rigidities than PEGDA hydrogels, an effect that alters the secretome of embedded stem cells presumably due to the altered tension placed on the embedded cells. There was a significant difference in hydrogel swelling ratios between hydrogels constructed with the different crosslinkers and when different crosslinker concentrations were used. The PEGSSDA hydrogels were 15% more permeable than PEGSSDA hydrogels. The measured Young's modulus for 2% and 4% PEGDA hydrogels were 2204 Pa and 4239 Pa, respectively, whereas those of PEGSSDA were 2069 Pa and 2261 Pa, respectively. In general, the cyto‐/chemokine secretome was lower for hydrogel embedded EPCs, as compared to non‐embedded EPCs. EPCs embedded in PEGDA hydrogels, as compared to PEGSSDA hydrogels, had greater release of LIX, VEGF and IP‐10. Upon increased concentration of either crosslinker, hydrogel embedded EPCs released reduced levels of IL‐10, VEGF, GM‐CSF, MIP‐1b and IP‐10. Our results indicate a difference in hydrogel mechanical properties when crosslinked with PEGDA, as compared to PEGSSDA. PEGDA crosslinker creates hydrogels that are more rigid. Furthermore, PEGDA hydrogels enhance cyto‐/chemokine release from embedded EPCs, as compared to PEGSSDA hydrogels. However, upon increased crosslinker concentration of either PEGDA or PEGSSDA from 2% to 4%, hydrogel rigidity was enhanced while cyto‐/chemokine release from embedded EPCs was reduced.Support or Funding InformationAHA grant 12SDG9080006, ASN grant 010973–101, The New York Community Trust Renal Clinical Fund (B.B.R.)