Figure 9.

Formation and degradation of photodegradable hydrogel networks. a) Idealized structures of chain and step polymerized networks and their photodegradation products. Networks of linear PEG-di(photodegradable acrylate) are formed by radical polymerization, resulting in acrylate kinetic chains (black) connected by PEG spacers (red). PEG-tetra(difluorocyclooctyne) undergoes a spontaneous crosslinking reaction when mixed with a photodegradable di-azide peptide. b) Irradiation of the bulk hydrogel with 365 nm light results in loss of crosslinks that can be tracked with photorheometry. Shuttering the light results in stabilization of the modulus readings. c) Two-photon photodegradation (λ=740 nm) was used to create defined three-dimensional topographies within the hydrogel volume. Scale bar 100 μm. Reprinted from Kloxin et al.¹⁸⁹ copyright (2009) AAAS. d) Orthogonal photochemical strategies are used to pattern RGD (dotted line) and erode the hydrogel network. Fibroblasts migrate through the 3D void space only in the region containing the adhesive ligand. Scale bar 100 μm. Reproduced from DeForest et al.¹⁵⁰ copyright (2011) Nature Publishing Group.