“…However, at 𝜎 𝑐,𝑒𝑞𝑢𝑖𝑙 < 30 Pa (Figure 3aiv-vi), we observe a transition from primarily spherical cellular morphologies just outside the BRSR -PEG-2k, 2.5wt% formulation (𝜎 𝑐,𝑒𝑞𝑢𝑖𝑙 = 27 Pa)to the initial appearance of spindle-like protrusions in PPEGA9-80 formulation just within the BRSR (𝜎 𝑐,𝑒𝑞𝑢𝑖𝑙 = 22 Pa). A similar protrusive phenotype for human adipose-derived stem cells and fibroblasts has been observed within synthetic and natural fibrous hydrogels, which exhibit strain-stiffening within the BRSR [26,33,34] . However, these previous findings are confounded by the propensity of fibrous materials to also stress-relax, making it difficult to definitively determine the impact of strain-stiffening mechanics on cell behavior.…”