The
establishment of confluent endothelial cell (EC) monolayers
on implanted materials has been identified as a concept to avoid thrombus
formation but is a continuous challenge in cardiovascular device engineering.
Here, material properties of gelatin-based hydrogels obtained by reacting
gelatin with varying amounts of lysine diisocyanate ethyl ester were
correlated with the functional state of hydrogel contacting venous
EC (HUVEC) and HUVEC’s ability to form a monolayer on these
hydrogels. The density of adherent HUVEC on the softest hydrogel at
37 °C (G’ = 1.02 kPa, E = 1.1 ± 0.3 kPa) was significantly lower (125 mm–1) than on the stiffer hydrogels (920 mm–1; G’ = 2.515 and 5.02 kPa, E = 4.8
± 0.8 and 10.3 ± 1.2 kPa). This was accompanied by increased
matrix metalloprotease activity (9 pmol·min–2 compared to 0.6 pmol·min–2) and stress fiber
formation, while cell-to-cell contacts were comparable. Likewise,
release of eicosanoids (e.g., prostacyclin release of 1.7 vs 0.2 pg·mL–1·cell–1) and the pro-inflammatory
cytokine MCP-1 (8 vs <1.5 pg·mL–1·cell–1) was higher on the softer than on the stiffer hydrogels.
The expressions of pro-inflammatory markers COX-2, COX-1, and RAGE
were slightly increased on all hydrogels on day 2 (up to 200% of the
control), indicating a weak inflammation; however, the levels dropped
to below the control from day 6. 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 discussed gelatin-based hydrogels with higher G’ as biomaterials for implants foreseen for the venous system.