PHOTOCHEMICAL TISSUE BONDING: A skin excision two weeks after surgery. Deep sutures were used to bring the sides of the five-centimeter wound together. Then the upper layer of closure was done with sutures on the right side and with light activated technology on the left side. The redness on the right side is caused by the sutures and leads to scarring. Image: IMAGE COURTESY OF WELLMAN CENTER FOR PHOTOMEDICINE
When accidents happen, doctors typically rely on sutures, staples or adhesives to fix the damage. These approaches work, of course, but they tend to cause inflammation in the surrounding tissue and leave scars long after a wound has healed. Researchers at Harvard Medical School and the Massachusetts General Hospital Wellman Center for Photomedicine have recently completed a study they hope will shine some light on this problem—laser light, that is.
Through a process called photochemical tissue bonding, a green laser interacts with pink dye placed on a wound to stimulate healing. The researchers are studying the use of this technique to reconnect severed peripheral nerves, blood vessels, tendons and incisions in the cornea. "We set out to develop a technology for tissue repair that would lead to much less scarring and could be done on small structures such as a nerve or blood vessel," says Irene Kochevar, a Harvard Medical School dermatology professor and Wellman Center researcher. "If you don't have to use sutures, you don't stimulate inflammation, which leads to fibrosis and collagen deposits [that create scar tissue]."
Kochevar and Robert Redmond, an associate professor of dermatology and associate chemist at the Wellman Center, began a U.S. Defense Department–sponsored study in early 2008 with Massachusetts General Hospital dermatologist Sandy Tsao, who was removing skin lesions from patients. After an elliptical incision was made to remove the lesion, part of the wound was repaired using sutures, while the rest was treated with photochemical tissue bonding. Months after the incision was made, the researchers found no scarring on the portion of the cut treated by the dye and laser, she says.
The key lies in stimulating the body's own repair mechanisms. When a pink dye known as "rose bengal" is placed on tissue and struck with a green laser beam for three minutes, the dye absorbs the light, causing collagen molecules in the tissue to cross-link and close a wound in a way that more resembles the coming together of Velcro than the zipper-like markings left by sutures.
More recently, Kochevar and Redmond have been applying the technique to repair damaged nerves in animals. "We take a piece of amniotic membrane, which is from the innermost part of the placenta, put the pink dye on that membrane, wrap it around the pieces of the severed nerve and irradiate the membrane," Kochevar explains. "It's like putting a shrink wrap on the pieces that holds them together." In some ways this is a better way to repair nerves than using sutures because nerve material can sometimes sneak out into the surrounding muscle when stitched together. Also, without sutures there's a lower chance of creating inflammation that could retard nerve growth.
Looking forward, Kochevar says she would like to be able to reduce the amount of time the laser needs to be trained on the dye in order for the bonding process to begin—from a few minutes required today to only a few seconds in the future. Kochevar also wants to develop a way increase the number of nano-sized bonds created in the treated area of tissue, strengthening the cross-linking process so that photochemical tissue bonding can be used on parts of the body—such as elbows and knees—that require a lot of flexibility.