Fig. 3. (a) In the course of swelling in PBS, 8arm-d,l-HCys 100 hydrogel disks lost their shape by turning into spherical caps before finally dissolving within a few days. (b) A possible reason for this behavior is that unreacted thiols can undergo thiol-disulfide metathesis with crosslinks leading to relaxation of internal stress and resulting in expansion of the network. The network could be stabilized by (c) a non-cleavable background network or (d) capping of free thiols by maleimide or an excess of linker.