What he doesn't know is how living tissue responds to injury over the longer term and whether the injury responds more favorably to different kinds of wavelength exposures.
"We're also trying to find out if wounds treated with the FEL heal at the same or different rates, and we're looking at the quality of the healing by observing the histology of the organization of the tissue as the energy enters a site," says Davidson, associate director for research at the FEL Center and a research career scientist at the Veterans Administration Medical Center, adjacent to Vanderbilt Medical Center.
Another question to be answered is whether the FEL offers a superior method for debridement - clearing away of dead or contaminated tissue from a wound - after chemical or thermal burns. Healing cannot begin until dead tissue left after an injury is removed.
When caustic chemicals are left on the skin after industrial accidents or chemical warfare, they continue to irritate tissue causing erosion or failure to heal. In the clinic, accidental spillage onto skin as the highly potent chemotherapy drug adriamycin is being introduced intravenously causes a nasty chemical burn. With the help of the FEL, Davidson is observing the response of the body's healing powers after it is exposed to adriamycin.
The question is how to remove the dead, contaminated tissue. Can we do it more accurately with a laser than a surgical knife? Will laser use result in more rapid repair at the site?
"We've embarked on a project using the FEL to remove all necrotic tissue, and we will compare the rate and quality of healing of these excised wounds using the surgical knife as opposed to the FEL operating at different wavelengths," says Davidson, whose wound healing research is funded by the National Institute on Aging; the National Institute of Arthritis, Musculoskeletal and Skin Diseases and the Department of Veterans Affairs.
"It's our hypothesis that we can have a device that selectively cuts only dead tissue and non-vascularized tissue using the FEL." Davidson also hypothesizes that laser surgery, in general and with the FEL, can reduce the ability of infectious agents to colonize a wound.
Davidson has shown that gene therapy can accelerate wound repair. To introduce genes into skin, scientists have been using the gene gun. Calling it a "rather novel method," Davidson uses a little shotgun that shoots hard, small gold pellets coated with plasmid DNA that encodes various growth factors into skin cells. Once the DNA gets into the cell, it begins the healing process of making new cells and connective tissue.
"We've used this to introduce growth factors and have shown that we can get increased wound strength in a variety of animal models," he says.
But Davidson believes, like scientists at Harvard, that the FEL can be used to introduce DNA into cells. The theory is that "the pulse of the laser beam as it hits a target causes photoacoustic energy (an intense burst of energy) to generate a shock wave which seems to open up channels in membranes of cells long enough for big molecules of DNA outside the cell to move inside."
In the near future Davidson's group is proposing to look at how the FEL alters collagen, the principal structural component of connective tissue.
"Collagen holds our body together. When you heat it up, first it shrinks, then melts, then it cooks and develops new chemical bonds between collagen molecules.
"Depending on how energy is delivered, you will have a balance of all these processes. This is the basis of tissue welding, reshaping of the cornea and reshaping of skin with the new generation of lasers."
-Ellen Bourne