Fig. 14. Spatiotemporal control of biochemical cues in 3D microenvironment. (A) Four-arm PEG functionalized with cyclooctyne was reacted with azide di-functionalized polypeptides via SPAAC reaction to form a hydrogel network via step-growth mechanism. A light-mediated thiol–ene reaction (cytocompatible 490–650 nm or 860 nm pulsed laser light) was used to immobilize cell adhesive thiol-functionalized peptides (RGD) using vinyl functionalities present on hydrogel network. Further, 3-D channels were degraded within the hydrogel using pulsed laser light (740 nm) via irreversible cleavage of nitrobenzyl ether moiety. (B) A cell-laden (3T3 fibroblasts) fibrin clot was encapsulated in the hydrogel (3D microenvironment). Biochemical (channel containing RGD noted by dashed polygon) and biophysical cues (photodegraded channel) were added to control 3T3 cell outgrowth in the presence of encapsulated hMSCs (right, top-down projection; left, 3D rendering). (Scale bar, 100 μm, hydrogel shown in red, F-actin in green and cell nuclei in blue) Image reprinted from DeForest et al. 320 with permission from Nature publishing group. Copyright (2011).
