194 Chapter 8 Figure 3: Stress relaxation in control and ruthenium-crosslinked ECM-derived hydrogels. After compressing the LdECM and Ru-LdECM hydrogels using Low Load Compression Tester (LLCT) with a fixed 20% strain ratio, the stress relaxation behaviour was recorded over 100s period. A) Average stress relaxation behaviour over 100 s duration. B) Time taken to reach 50% stress relaxation. 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 Extracellular Matrix Hydrogels, Ru-LdECM: Ruthenium-crosslinked Lung-derived Extracellular Matrix Hydrogels. Altered relaxation profile in ruthenium-crosslinked ECM hydrogels Since the ECM hydrogels are a viscoelastic material with various elastic (e.g., ECM proteins) and viscous components (e.g., water, bound water), we mathematically modelled this using a generalized Maxwell model. This approach allowed the total relaxation data to be split into Maxwell elements that can theoretically be attributed to physical components in the hydrogels. Each of these Maxwell elements are responsible for a part of the total relaxation (relative importance), as well as occurring within a specific time window during the relaxation process. The distribution of the time constants of these different elements and their respective relative importance are presented in Figure 4. The stress relaxation of the LdECM hydrogels could be
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