Remember those little capsules from when you were a kid that expanded into dinosaurs when they got wet? Harvard bioengineers have taken a cue from this childhood favorite, and have developed uniquely shaped, injectable sponges that could be used to slowly administer drugs or support tissue regrowth. These sponges — which were shaped into pink stars, hearts, and squares for the demonstration — are actually created by freezing a seaweed-based gel. The process, known as cryogelation, depends on the formation of ice crystals, which push back and stiffen the gel. When these crystals melt, they leave behind a network of pores and a solid, sponge-like material.

Once created, a sponge is compressed, filled with medicine or cells, and injected into the body, where it slowly expands to its full size and shape. The sponges can be uniquely tailored to individual medical needs, and could be used to inject transplanted stem cells and act as a tailored scaffold to heal tissue damage without extensive surgery. Doctors could also use the material to gradually release drugs into the body as the sponge decays, or to transplant immune cells. Researchers say the next step is to control how fast the sponge deteriorates, so that the scaffold will break down as it's replaced by new, healthy tissue.