Efficient fabrication of stretching hydrogels with programmable strain gradients as cell sheet delivery vehicles.

Fabricating functional cell sheets with excellent mechanical strength for tissue regeneration remains challenging. Therefore, we devised a novel 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide/N-hydroxy-succinimide crosslinked hydrogel carrier composed of gelatin (Ge) and beta-cyclodextrin (β-CD) that promoted the adhesion and proliferation of keratinocytes (Kcs) compared with those cultured on a Ge hydrogel due to significantly higher pore size, porosity, and stiffness, as confirmed using field emission scanning electron microscopy (FE-SEM) and shear wave elastography (SWE). Upon exposure to a programmable gradient microenvironment, cells displayed a stress/strain-dependent spatial-temporal distribution of extended cellular phenotypes and cytoskeletons. The promoted proliferation of Kcs and the increased retention of the undifferentiated cell phenotype on Ge-β-CD composite hydrogels under a 15% strain led to the accelerated detachment of cell sheets with retained cell-cell junctions. Moreover, the stretch-triggered upregulated expression of phosphorylated yes-associated protein (YAP) 1 suggested that this effect might be associated with the mechanical stimulation-induced activation of the YAP pathway.