Photodegradable Macromers and Hydrogels for Live Cell Encapsulation and Release

Hydrogel scaffolds are commonly used as 3D carriers for cells because their properties can be tailored to match natural extracellular matrix. Hydrogels may be used in tissue engineering and regenerative medicine to deliver therapeutic cells to injured or diseased tissue through controlled degradation. Hydrolysis and enzymolysis are the two most common mechanisms employed for hydrogel degradation, but neither allows sequential or staged release of cells. In contrast, photodegradation allows external real-time spatial and temporal control over hydrogel degradation, and allows for staged and sequential release of cells. We synthesized and characterized a series of macromers incorporating photodegradbale ortho-nitrobenzyl (o-NB) groups in the macromer backbone. We formed hydrogels from these macromers via redox polymerization and quantified the apparent rate constants of degradation (kapp) of each via photorheology at 370 nm, 10 mW/cm(2). Decreasing the number of aryl ethers on the o-NB group increases kapp, and changing the functionality from primary to seconday at the benzylic site dramatically increases kapp. Human mesenchymal stem cells (hMSCs) survive encapsulation in the hydrogels (90% viability postencapsulation). By exploiting the differences in reactivity of two different o-NB linkers, we quantitatively demonstrate the biased release of one stem cell population (green-fluoroescent protein expressing hMSCs) over another (red-fluorescent protein expressing hMSCs).