effect of substrate stiffness on pulmonary fibroblast activation by tgf-β

peptide crosslinkers containing the sequence c-x-cg (x represents various adhesive peptides) were incorporated into poly(ethylene glycol) (peg) hydrogel networks with different mechanical properties. pulmonary fibroblasts (pfs) exhibit increased adhesion to rigid hydrogels modified with x = rgds, dgea and ikvav (0.5 and/or 5 mm) compared with a scrambled control (x = hrpns). pfs exhibit increased adhesion to softer hydrogels when x = dgea at low (0.5 mm) peptide concentration. pfs seeded onto hydrogels modified with x = rgds produce alpha-smooth muscle actin (α-sma), a myofibroblast marker, and form an extensive cytoskeleton with focal adhesions. decreasing substrate stiffness (achieved through hydrolytic degradation) results in down-regulation of α-sma expression by pfs. substrate stiffness increases the sensitivity of pfs to exogenously applied transforming growth factor beta (tgf-β1); pfs on the most rigid gels (e = 900 kpa) express α-sma when treated with low concentrations of tgf-β1 (1 ng ml⁻¹), while those on less rigid gels (e = 20–60 kpa) do not. these results demonstrate the importance of both mechanical and chemical cues in studying pulmonary fibroblast activation, and establish peg hydrogels as a viable material for further study of ipf etiology.