Figure 3. Photodegradation of chain and step polymerized hydrogels.
(a) and (b) The o-nitrobenzyl ether moieties (orange ring structures) in PEGdiPDA undergo an irreversible cleavage in response to irradiation (one-photon: λ ~ 320–436 nm, two-photon: λ ~ 740 nm), breaking elastically active network strands in the hydrogel backbone. In this manner, light can be employed to degrade and, ultimately, erode the CP and SP hydrogels. (c) Owing to the inclusion of the same photolabile monomer into the network backbone, the initial effective cleavage kinetic constant, defined as the negative slope of ln(G/G0) as a function of irradiation time divided by the incident irradiation intensity, was similar for the CP (black, formulation b) and SP (grey, formulation d) gels.