193 An in vitro model of fibrosis using crosslinked native extracellular matrix-derived hydrogels to modulate biomechanics without changing composition Figure 2: Comparison of stiffness of control and ruthenium-crosslinked hydrogels. LdECM and Ru-LdECM hydrogels were mechanically tested using Low Load Compression Tester (LLCT) with a fixed 20% strain ratio. A) Representative stress-strain curve for LdECM and Ru-LdECM hydrogels. B) Comparison of stiffness of LdECM and Ru-LdECM hydrogels. Each dot represents the mean of three independent measurements on the same hydrogel for each sample (n = 5). Applied test: Paired t-test to compare the LdECM and Ru-LdECM hydrogels that were generated in the same experimental batch (as indicated by the connecting lines in the graph). LdECM: Lung-derived ECM Hydrogels, Ru-LdECM: Ruthenium-crosslinked Lung-derived ECM Hydrogels Decreased stress relaxation rate in ruthenium-crosslinked ECM hydrogels The stress relaxation behaviour of both the LdECM and RU-LdECM hydrogels were measured after applying 20% strain using LLCT measurement. The average stress relaxation profiles of both groups over 100 s are visualized in Figure 3A. RuLdECM hydrogels did not reach 100% stress relaxation during the 100 s monitored, while some LdECM hydrogels achieved 100% stress relaxation. In addition to the decreased total stress relaxation percentage (in 100s) in the Ru-LdECM hydrogels, the relaxation profile was different. The rate of stress relaxation slowed down earlier in the crosslinked hydrogels. To assess the dynamic differences in the initial stress relaxation behaviour patterns in both groups the time to reach 50% total stress relaxation was compared. LdECM hydrogels reached 50% stress relaxation in significantly shorter time compared to the Ru-LdECM hydrogels. (p = 0.0054, paired t-test) (Figure 3B). 8
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