Cell therapy is the practice of using cells as tiny factories to deliver a therapeutic agent of choice to a wound or tissue. Such therapies have been used to effect bone formation, wound healing, and to control glucose levels in diabetics. The largest hurdle to overcome is rejection of donor cells. By microencapsulating cells within polyethylene glycol (PEG) hydrogels, we have been able to immunoisolate these cells. In the image to the left, we encapsulated insulin secreting cells and used them to effect rapid wound healing. The cells are entrapped within PEG hydrogel microspheres between 100 - 300 micrometers in size (about the width of 1-3 human hairs). The image shows fluorescent staining of viable cells (live glows green, dead glows red).