Based on a fat absorption spectrum, tissue was exposed to a range of wavelengths of infrared laser light (800-2600 nanometers) using the Free-Electron Laser facility at Jefferson Lab. The researchers measured how selected wavelengths heated the fat and compared the result to a similar experiment conducted with pure water. At most infrared wavelengths, water is more efficiently heated by infrared light; however, the researchers found three wavelengths – 915, 1210 and 1720 nm – where fat was more efficiently heated than water.
The researchers then exposed fresh, intact pig skin-and-fat tissue samples, about two inches thick, to free-electron laser infrared light centered around the two most promising wavelengths, 1210 and 1720 nm. To imitate potential surgical conditions, the pig skin was placed next to a cold window, which mimicked the application of a cold compress to the skin prior to laser exposure. The researchers zapped samples with beams of infrared laser light ranging from eight to 17 mm wide for about 16 seconds. They found that the 1210 nm wavelength preferentially heated pig fat up to 1 cm deep, without damaging the overlying skin. At 1210 nm, laser-induced heating of fat was more than twice that of the overlying skin; at 1720 nm, it was about 1.7 times that of skin.
Rox Anderson, lead author on the study and a practicing dermatologist at Harvard, says the results provide a proof of principle for the use of selective photothermolysis, selectively heating tissues with light, for several potential medical applications. Dr. Anderson is most excited about the potential for using lasers to target sebaceous glands. “The root cause of acne is a lipid-rich gland, the sebaceous gland, which sits a few millimeters below the surface of the skin,” Anderson says, “We want to be able to selectively target the sebaceous gland, and this research shows that if we can build lasers at this region of the spectrum, we may be able to do that.”
