Engineering Hybrid-Hydrogels Comprised of Healthy or Diseased Decellularized Extracellular Matrix to Study Pulmonary Fibrosis

Idiopathic pulmonary fibrosis is a chronic disease characterized by progressive lung scarring that inhibits gas exchange. Evidence suggests fibroblast-matrix interactions are a prominent driver of disease. However, available preclinical models limit our ability to study these interactions. We present a technique for synthesizing phototunable poly(ethylene glycol) (PEG)-based hybrid-hydrogels comprising healthy or fibrotic decellularized extracellular matrix (dECM) to decouple mechanical properties from composition and elucidate their roles in fibroblast activation. Here, we engineered and characterized phototunable hybrid-hydrogels using molecular techniques such as ninhydrin and Ellman's assays to assess dECM functionalization, and parallel-plate rheology to measure hydrogel mechanical properties. These biomaterials were employed to investigate the activation of fibroblasts from dual-transgenic Col1a1-GFP and alpha SMA-RFP reporter mice in response to changes in composition and mechanical properties. We show that reacting functionalized dECM from healthy or bleomycin-injured mouse lungs with PEG alpha-methacrylate (alpha MA) in an off-stoichiometry Michael-addition reaction created soft hydrogels mimicking a healthy lung elastic modulus (4.99 +/- 0.98 kPa). Photoinitiated stiffening increased the material modulus to fibrotic values (11.48 +/- 1.80 kPa). Percent activation of primary murine fibroblasts expressing Col1a1 and alpha SMA increased by approximately 40% following dynamic stiffening of both healthy and bleomycin hybrid-hydrogels. There were no significant differences between fibroblast activation on stiffened healthy versus stiffened bleomycin-injured hybrid-hydrogels. Phototunable hybrid-hydrogels provide an important platform for probing cell-matrix interactions and developing a deeper understanding of fibrotic activation in pulmonary fibrosis. Our results suggest that mechanical properties are a more significant contributor to fibroblast activation than biochemical composition within the scope of the hybrid-hydrogel platform evaluated in this study.

Automated summary

This article presents a new technique for studying cell-matrix interactions and fibroblast activation in pulmonary fibrosis. By synthesizing phototunable hydrogels, researchers are able to decouple the mechanical properties and composition of the materials to gain a deeper understanding of their roles in fibroblast activation.