Response of endothelial cells to gelatin-based hydrogels

Dysfunctional or incomplete endothelium on cardiovascular devices has been identified as key factor of thrombus formation. Therefore, the establishment of confluent endothelial cell (EC) monolayers is a challenge in cardiovascular device engineering. Previous studies revealed that arterial EC were able to endothelialize gelatin-based hydrogels. However, as EC differ markedly in their function dependent from their origin, this study investigated whether venous EC (HUVEC) also form a monolayer on gelatin-based hydrogels obtained by reacting gelatin with different molar ratios of lysine diisocyanate ethyl ester (using a 3-, 5- or 8-fold excess) exhibiting variations in their elastic properties. The density of adherent HUVEC on the soft hydrogel at 37 °C (G’ = 1.02 kPa, E = 1.1±0.3 kPa) was significantly lower than on the stiffer hydrogels (G’ = 2.515 and 5.02 kPa, E = 4.8±0.8 and 10.3±1.2 kPa). This was accompanied by increased matrix metalloproteases and stress fiber formation, while cell-to-cell contacts were comparable. The pattern of eicosanoids and cytokines corresponded to those results. The expression of pro-inflammatory markers COX-2, COX-1, and RAGE were slightly elevated, indicating a weak inflammation. The study revealed that hydrogels with higher moduli approached the status of a functionally-confluent HUVEC monolayer. The results indicate the promising potential especially of the hydrogels with higher G’ as biomaterials for implants foreseen for the venous system.