Growing blood vessels in damaged or engineered tissue could soon be as easy as putting a postage stamp on a letter, thanks to researchers at the University of Illinois, Urbana-Champaign (Adv. Mater., DOI: 10.1002/adma.201103207). The team led by Hyunjoon Kong and Rashid Bashir developed a microchannel-patterned hydrogel stamp that contains living cells. When the stamp is pressed onto tissue, the cells release growth factors that direct the density and spacing of new blood vessels. Although other methods have been devised to grow blood vessels in engineered tissue, Kong says, it has been a challenge to control vessel spacing on a scale that mimics normal tissue. To overcome this problem and optimize stamp performance, the researchers tuned the ratio of polyethylene glycol and methacrylic alginate in their hydrogels, as well as the size of the microchannels. When applied to the outside of a chick embryo, the stamps released vascular endothelial growth factor and other biomolecules into the microchannels, spurring blood vessel growth in designated spots. The group will next try their stamps on skin wounds in animal test subjects and study how well the newly grown vessels handle blood flow.