Development of a 3D printed dynamic lung tissue model. Given the promising results obtained for 3T3 fibroblasts subjected to cyclic stretch, we focused on developing a dynamic lung tissue model. To this end, dog-bone shape constructs were 3D printed using 3%GelMA-0.5%CBP-0.5%LAP inks. The crosslinked structures made from the 3% GelMA ink had mechanical properties that recapitulated the storage and compression moduli (G' and E) of porcine lung tissue, making it the best candidate to mimic the lung tissue (Figures ). Primary human lung fibroblasts (hLFs) were seeded on top of the dog-bone structures and cultured for five days under static conditions before starting the cyclic stretching. The stretching amplitude and frequency were chosen to mimic the normal human breathing process. hLFs grown under static or stretching conditions showed the expected spread out and narrow elongated morphologies typical of lung fibroblasts (Figures ). Additionally, the cyclic stretching induced a statistically significant increase in αSMA expression, indicating a fibroblast-to-myofibroblast transition, which is seen during the genesis of lung fibrosis (Figure ).