Cyclic mechanical loading of photopolymerized methacrylated hydrogels for probing interdependent effects of strain, stiffness, and substrate composition in pulmonary fibrogenesis

Pulmonary fibrosis is characterized by excessive deposition of extracellular matrix (ECM), stiffening of the lung tissue, and impaired gas exchange. Our current understanding of fibrogenesis generally focuses on the individual roles of mechanical and biochemical stimuli in driving disease progression. However, many mechano-chemical pathways are interrelated, so dissecting the interactive effects of mechanical and biochemical signals is an important knowledge gap. To address this gap, we investigated lung fibroblast behavior on static and cyclically strained photopolymerizable hydrogels consisting of different ratios of methacrylated gelatin, methacrylated hyaluronan, and non-methacrylated gelatin to create substrates with tunable stiffness and chemistry, representative of both healthy and fibrotic lung ECM properties. We observed that higher stiffness gels amplified the impact of strain, resulting in distinct differences in expression of MMP1, CTGF, Rho/ROCK, and ECM deposition genes. Substrates with hyaluronan demonstrated a capacity to modulate strain-induced fibrogenic responses, suggesting a buffering effect of hyaluronan on fibrotic disease progression. Overall, our results highlight mechanotransductive changes in gene expression in response to substrate composition, stiffness, and cyclic mechanical strain. Through the controlled study of mechanical and biochemical cues, our findings contribute to a deeper understanding of the pathogenesis of pulmonary fibrosis.