On-demand manipulation of protein release to alter cellular phenotypes in real time is of great interest to the fields of drug delivery, tissue engineering and regenerative medicine.[1-3] For such therapeutic and research ventures, hydrogels, due to their high water content and mechanical stability, have emerged as suitable polymeric materials not only to localize proteins but also to control their release rate on-site.[4, 5] Protein release from hydrogels is typically achieved either through diffusion or by stimuli. Diffusion controlled mechanisms rely upon control of the hydrogel mesh size, which needs to be preprogrammed during synthesis; as a result, limited regulation of release is only possible afterward. To complement this strategy, stimuli (eg, temperature, pH, light and proteins)[6, 7] sensitive materials have evolved and become attractive protein delivery systems, as they offer opportunities to regulate molecular release using a specific stimulus. Stimuli controlled mechanisms applied to hydrogels are typically based on the degradation/swelling of hydrogel networks, in which non-covalently sequestered proteins are released in response to increased pore size/decrosslinking of networks. Such noncovalent approaches do not require chemical modification of proteins and have the potential to precisely control the release of single protein molecules. However, applying such approaches to control the release of multiple proteins is quite complex and often requires either multiple gels or microspheres for encapsulation.[8-12] Thus, a number of studies aimed at directing cellular processes or disease regulation would benefit from the delivery of more than one protein and often necessitates their delivery in varied doses at different time points [8-11]. Herein, we present an approach that allows precise control over the release of multiple proteins from a single hydrogel depot using an external light.

Light triggered molecular cleavage has received widespread interest among researchers in recent years, for activation of caged biomolecular entities,[13-15] alteration of material properties,[16, 17] and to control therapeutic release in real-time.[18, 19] Furthermore, userdefined time and spatial location of photocleavage reactions offer unique opportunities to