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Wednesday, November 19, 2008

Healing with Laser Heat

Healing beam: A patient who underwent gall bladder surgery had two incisions healed with the classic suturing technique and two with laser soldering. After 30 days, the laser-bonded scars (bottom) appeared smaller than those done with a needle and thread (top).
Credit: Abraham Katzir

The promise of medical lasers goes beyond clean incisions and eye surgery: Many believe that lasers should be used not just to create wounds but to mend them too. Abraham Katzir, a physicist at Tel Aviv University, has a system that may just do the trick and is proving successful in its first human trials.

In principle, "laser-bonded" healing offers certain advantages over classic needle-and-thread sutures, including faster healing, decreased risk of infection, and less scarring. Researchers have been working toward flesh-welding lasers for more than a decade, and a number of human trials have shown promise. But what was lacking, until now, was consistency. Flesh, blood vessels, and nerves are delicate tissues that can easily be -- for lack of a better word -- overcooked.

To overcome this problem, Katzir and his colleagues developed a laser-based system with a feedback loop that prevents overheating. First, they had to determine the optimal temperature at which flesh melts but can still heal (about 65 degrees Celsius). Then the group created a pen-sized tool that incorporates optic fibers: one that channels a carbon dioxide-powered infrared laser to the wound with pinpoint precision, and another that leads from the pen to an infrared sensor, which measures the temperature and ensures that the heat remains within the ideal range, between 60 and 70 degrees. All a surgeon has to do is move the pen's tip along the cut, strengthening and sealing the weld with a solder of water-soluble protein.

While many scientists have experimented with laser-bonded healing, most have relied on visual feedback to make sure they were not over- or under-heating the wound. Too little heat results in an unclosed wound, while too much heat causes a bond that initially appears strong but that breaks down as the tissue dies off. "Our advantage is that we have developed optical fibers -- we're one of the very, very few groups in the world who have optical fibers that transmit IR radiation," Katzir says. "We measure the infrared emitted from the spot and can know the temperature exactly."

Until recently, the researchers worked to perfect their technique on pigs, whose skin is most similar to that of a person. Those studies told them that their method was sound: the laser-healed wounds were just as strong, mended faster, and resulted in less inflammation and infection than normal sutures, since a cut that's welded closed is better at keeping bacteria out.

Now, the group has finished their first clinical trial on human patients. Ten subjects underwent laparoscopic surgeries for gall bladder removals: each patient had four small incisions, two of which were closed with sutures and two with Katzir's laser technique.

"It seemed that the laser-bonded cuts healed faster and looked better," he says. The researchers are waiting to see how the two types of closures perform 12 months after surgery before publishing their results, but Katzir is optimistic and already planning the next trial, this time on hernia patients.

"It's a fabulous process, with undeniable biological advantages," says Michael Treat, a surgeon at New York Presbyterian Hospital and associate professor at Columbia University Medical Center. But rather than using lasers to replace a surgeon's needle and thread, he believes that such technology might be better used in robotic systems, in which an entire procedure is automated.

"It's cumbersome for a mechanical system to place sutures, but a laser beam is something that a computer would have an easy time controlling," says Treat, who was involved in some of the field's seminal work. And, he notes, another procedure that could benefit from laser-bonding is nerve repair, where sutures can easily leave too much scarring and rapid, ultra-fine control is essential.

One of Katzir's competitors, Irene Kochevar, is a dermatology professor at Massachusetts General Hospital and is working on her own version of laser-bonded welding, but one that takes advantage of light rather than heat. "If I were to predict, I'd say that his technology and ours both lead to decreased scarring," she says. "He's carried the thermal approach to the highest degree of sophistication of anyone in this area."

Katzir is already thinking beyond the next clinical trial, and believes that his method has a wide range of applications: everything from delicate surgeries on blood vessels to procedures such as cornea transplants, in which sutures can cause incredible discomfort and inflammation, and must remain in place for as long as a year or more.

"It's not simply a replacement of what surgeons do well today," he says, "but it will give surgeons a better tool to do better surgery in the future."