Hydrogels used for cell-based drug delivery.

Stem cells, progenitor cells, and lineage-committed cells are being considered as a new generation of drug depots for the sustained release of therapeutic biomolecules. Hydrogels are often used in conjunction with the therapeutic secreting cells to provide a physical barrier to protect the cells from hostile extrinsic factors. Although the hydrogels significantly improve the therapeutic efficacy of transplanted cells, there have been no successful products commercialized based on these technologies. Recently, biomaterials are increasingly designed to provide cells with both a physical barrier and an extracellular matrix to further improve the secretion of therapeutic proteins from cells. This review will discuss (1) the cell encapsulation process, (2) the immunogenicity of the encapsulating hydrogel, (3) the transport properties of the hydrogel, (4) the hydrogel mechanical properties, and will propose new strategies to improve the hydrogel and cell interaction for successful cell-based drug delivery strategies. 2008 Wiley Periodicals, Inc.