231 Fibroblast remodeling of extracellular matrix is directed by the fibrotic nature of the threedimensional microenvironment Figure 5: Mechanical properties in empty and fibroblast-seeded control and IPF lung ECM-derived hydrogels. Control and IPF primary lung fibroblasts were seeded in control or IPF lung ECM-derived hydrogels and cultured for 7 or 14 days. Fibroblast-seeded hydrogels were mechanically tested using low load compression testing (LLCT) and compared with their corresponding empty hydrogels. A) Schematic representation of the stiffness analysis performed using compression. B) An example stress-strain curve obtained using LLCT, C) Day 7 response analysis for stiffness of the hydrogels (kPa), D) Day 14 response analysis for stiffness of the hydrogels (kPa), E) Schematic representation of the stress relaxation analysis performed using compression. F) An example relaxation profile obtained using LLCT, G) Day 7 response analysis for time to reach 50% stress relaxation (s), H) Day 14 response analysis for time to reach 50% stress relaxation (s). The dotted line shows the intrinsic difference between empty IPF and control hydrogels. The estimate (± 95% confidence interval) shows the difference between the IPF and control hydrogels seeded with control (light blue, triangle) or IPF (dark blue, square) fibroblasts. P values below each fibroblast group represent the differences induced by fibroblasts in IPF versus control hydrogels compared to the intrinsic difference between IPF and control empty hydrogels. P-values above the estimates indicate the differences between the responses of IPF and control fibroblasts in the different hydrogels. Applied statistical test: mixed-model analysis. All measurements were performed at 20% strain rate. Applied statistical test: mixed-model analysis. ns: not significant, IPF: Idiopathic pulmonary fibrosis. n=6 for fibroblast donors, 3 independent locations per sample were measured. 9
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