Microfluidic adhesion-based cell separation systems are of interest in clinical and biological applications where small sample volumes must be processed efficiently and rapidly. While the ability to capture rare cells from complex suspensions such as blood using microfluidic systems has been demonstrated, few methods exist for rapid and nondestructive release of the bound cells. Such detachment is critical for applications in tissue engineering and cell-based therapeutics in contrast with diagnostics wherein immunohistochemical, proteomic, and genomic analyses can be carried out by simply lysing captured cells. This paper demonstrates how the incorporation of four-arm amine-terminated poly(ethylene glycol) (PEG) molecules along with antibodies within alginate hydrogels can enhance the ability of the hydrogels to capture endothelial progenitor cells (EPCs) from whole human blood. The hydrogel coatings are applied conformally onto pillar structures within microfluidic channels and their dissolution with a chelator allows for effective recovery of EPCs following capture.