Diffusion of interleukin-2 from cells overlaid with cytocompatible enzyme-crosslinked gelatin hydrogels

In designing an implantable cell encapsulation construct to continuously deliver therapeutic proteins to a patient, it is critical that the biomaterial be compatible with the encapsulated cells, as well as conducive to the diffusion of desired molecules. As a continuation of our previous work, which demonstrated the cytocompatibility of gelatin hydrogels enzymatically crosslinked by microbial transglutaminase (mTG-gels), this work seeks to elucidate the diffusion properties that are needed for sustained release of therapeutic proteins produced by the engineered cells. HEK293 cells genetically engineered to secrete an anticancer drug, interleukin-2 (hIL2), through 4% mTG-gels used as a 1D diffusion model. Under steady-state conditions, cells secrete hIL2 at a therapeutic rate of 5.0-5.7 ng/cm(2)/h/10(6) cells. The diffusion coefficient of hIL2 through the hydrogels is D(m) = 4.0 x 10(-7) cm(2)/s. This value is comparable with similarly sized proteins through hydrogels and is further verified by modeling nonsteady-state diffusion through various thicknesses of the hydrogels, as well as by acellular diffusion chamber experiments. These findings demonstrate that the enzymatically crosslinked hydrogels are not only cytocompatible but also have suitable transport properties that will facilitate the design of sustained drug release devices.