Treating battlefield injuries with light

Charles T. Troy, charlie.troy@photonics.com

Closing wounds with stitches and staples could one day be a thing of the past, thanks to work being done on treating airmen’s battlefield injuries with a light-activated technology. The technique results from research managed by the US Air Force Office of Scientific Research and supported by funds from the Office of the Secretary of Defense.

The new treatment includes photochemical tissue bonding, a process that could replace conventional sutures, staples and glues in repairing skin wounds and reconnecting severed peripheral nerves, blood vessels, tendons and incisions in the cornea.

Harvard Medical School professor and Massachusetts General Hospital Wellman Center researcher Dr. Irene Kochevar and her colleague at Wellman, associate professor Robert Redmond, are pleased with the initial lab bench experiments that led to a pilot clinical study.

They have demonstrated that this technology is very helpful in medicine for the Air Force because it produces better healing and functional outcomes than those for the same wounds that were treated with conventional materials, Kochevar said.

The process of creating the bonding or nanosutures is accomplished by applying Rose Bengal dye to the wound or damaged tissue and then exposing it briefly to green light from a 532-nm KTP laser. The researchers also have used LED arrays. The dye absorbs most strongly between 510 and 570 nm, helping it to molecularly bond proteins on the tissue surface.

Healing with light is a two-stage process.

“No glues, proteins or other materials are used that might stimulate an inflammatory response,” Kochevar said. “An immediate, watertight seal is formed between the tissue surfaces, leading to reduced inflammation in the near term and better scar formation in the long term.”

The researchers plan to continue to evaluate the effectiveness of the new technology and the ways in which it can be even more effective in theater. They are seeking a shorter treatment time that will yield an even stronger bond. Currently, Kochevar said, “typical radiation times are 1.5 to 5 minutes. For skin closures, the irradiation time is 200 s (100 J/cm²).”

Kochevar said that the researchers have published more than “a dozen studies, mostly in animal models of different types of surgery (reattachment of peripheral nerves, blood vessels), sealing of corneal wounds and transplants, sealing skin incisions and excisions.

She noted that the two basic types of applications involve bonding tissue surfaces together. “One is rejoining tissue – for example, surgical incisions in tissues such as cornea – the other is patching over a tissue site. For rejoining tissue surfaces, an aqueous solution of the dye is applied to the surfaces, which are then brought into contact and the area irradiated.

“For ‘patching,’ a membrane (amniotic is our favorite) is stained with the dye and then placed over the tissue site. For example, to rejoin a severed peripheral nerve, the two ends are held together with one or two stay sutures, and then the joint is wrapped with dye-stained amnion and irradiated to seal the amnion to the epi-neurium. We follow the animals for up to four months and assess the appropriate end points (histology, electrophysiologic measurements, scar formation, et cetera.”

For now, the work has been confined to animals. However, Kochevar said, they have begun to work with humans in a pilot clinical study for sealing skin surgical wounds.

“We are approaching this challenge by identifying the basic molecular mechanisms responsible for light-activated cross linking. We believe that this information will show us how to improve the efficiency and effectiveness of the nanosuturing technology on the battlefield,” Kochevar said.