195 An in vitro model of fibrosis using crosslinked native extracellular matrix-derived hydrogels to modulate biomechanics without changing composition modelled with 3 Maxwell elements while Ru-LdECM hydrogels needed 4 Maxwell elements. Next to the difference in the number of Maxwell elements required to explain the relaxation profiles, the time constants of the elements differed between the two groups: the first element was significantly faster in the LdECM hydrogels (p = 0.002, paired t-test) while the third element took longer in the LdECM hydrogels (p = 0.002, paired t-test) compared to the Ru-LdECM (Figure 4A). The relative importance of the Maxwell elements was used to assess the individual contribution of each element to the total stress relaxation over the 100 seconds (Figure 4B). In both types of hydrogels, the first element made the greatest contribution to the stress relaxation profile, although the percentage contribution was significantly lower in the Ru-LdECM hydrogels compared with the LdECM hydrogels (p = 0.002, paired t-test). The contribution of the second Maxwell element was the second largest in both groups while the relaxation profile of the Ru-LdECM hydrogels had a significant increase in the contribution of this element compared to uncrosslinked hydrogels (p = 0.0002, paired t-test). The third element had the lowest percentage contribution in LdECM hydrogels, with this contribution being lower than this element in its ruthenium-crosslinked counterpart (p = 0.002, paired t-test). Figure 4: Analysis of the stress relaxation behaviour through the generalized Maxwell model system. The relaxation profiles of the both types of hydrogels over 100 s period was mathematically modelled using a Maxwell model system and the relative importance values of the Maxwell Elements were determined. A) Time constants for each Maxwell element for LdECM and Ru-LdECM hydrogels. B) Relative importance (%) of the each Maxwell element for LdECM and Ru-LdECM hydrogels. Each dot represents the mean of three independent measurements on the same hydrogel (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 8
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