Regenerating blood vessels is important for combating the aftereffects of a heart attack or peripheral arterial disease, and for ensuring that transplanted organs receive a sufficient supply of blood. Now researchers at Northwestern University have created a nanomaterial that could help the body to grow new blood vessels.
Capillary action: The transparent circle in the center of this image is a nanomaterial designed to mimic the protein VEGF. Here, it has enhanced the growth of blood vessels in the membrane from a chicken egg after three days.
Samuel Stupp and his colleagues developed a liquid that, when injected into patients, forms a matrix of loosely tangled nanofibers. Each of these fibers is covered in microscopic protuberances that mimic vascular endothelial growth factor, or VEGF—a protein that occurs naturally in the body and causes chemical reactions that result in the growth of new blood vessels. By mimicking VEGF, the nanofiber has the same biological effect.
Jeff Karp, director of the Laboratory for Advanced Biomaterials and Stem-Cell-Based Therapeutics at Brigham & Women's Hospital, says, "this is an elegant approach to rationally design engineered materials to stimulate specific biological pathways." Karp was not involved with the project.
Ali Khademhosseini, an associate professor at the Harvard-MIT Division of Health Sciences and Technology, adds that "the ability to induce blood vessel formation is one of the major problems in tissue engineering."
Tissue engineers have tried using VEGF itself to stimulate the growth of blood vessels, but clinical trials with the protein were unsuccessful, says Stupp, director of the Institute for BioNanotechnology in Medicine at Northwestern. This is because VEGF tends to diffuse out of the target tissue before it can do its job. Maintaining a therapeutic concentration in the target tissue would require a series of expensive, invasive injections.
The new nanomaterial has a similar effect, but it lasts much longer, and is completely biodegradable once its job is finished. Stem cells could be used to regenerate blood vessels, but their use is expensive and controversial.
The researchers tested their material in mice. The blood supply to the animals' hind legs was restricted. Left untreated, these limbs would die. The nanofiber treatment rescued the limbs, and resulted in better motor function and blood circulation than the other treatments, including a treatment with VEGF.
Stupp says there could be more uses for nanofibers that mimic proteins from the body. For example, they could be used to stimulate the formation of connective tissues such as bone and cartilage, or to regenerate neurons in the brain.
"The next step is to proceed with extensive toxicological testing," says Stupp. "The long view would be to produce a cell-free, growth-factor-free therapy for the treatment of ischemic disease and heart attacks."
Khademhosseini also sees a lot of potential in nanomaterials that mimic natural proteins. "Such materials could have a great future application in regenerative medicine, as they will enable the body's own regenerative response to heal," he says.
By Kenrick Vezina
From Technology Review