SCIENCE & TECHNOLOGY
SPECTRA TRACK WOUND HEALING
collaborators at Drexel University College of Engineering are using near-infrared spectroscopy to do just that. IN A PRELIMINARY TRIAL of 46 patients
FRANCIS ESMONDE-WHITE
with diabetic foot ulcers, Weingarten and his engineering collaborators used diffuse RAMAN AND NEAR-INFRARED methods give doctors near-IR spectroscopy to measure total access to information they can’t otherwise see hemoglobin, oxygenated hemoglobin, and CELIA HENRY ARNAUD, C&EN WASHINGTON deoxygenated hemoglobin (Wound Rep. Reg. 2012, DOI: 10.1111/j.1524-475x.2012.00843.x). The researchers analyzed each wound DOCTORS CAN’T ALWAYS deteronce per week for four weeks. They mine whether a wound is healing just found that the change in these specby looking. By the time they realize a tral data over time, rather than the abwound isn’t healing, it can be too late. solute values, correlated with healing. Drastic measures—possibly amputaThe spectroscopic data weren’t tion—might be required. used for treatment decisions. But Spectroscopic methods such as during the data analysis, the reRaman and infrared could give docsearchers found that the spectroscotors early warning that a wound, such py caught problems that hadn’t been as a diabetic foot ulcer or a burn, visually apparent. “In about three or isn’t healing as it should. These techfour of the patients, I thought they niques could also provide real-time were healing, but the data said no,” information to surgeons as they make Weingarten says. “The data turned decisions in the operating room out to be right, because three or four about what tissue can be saved and weeks later the wounds fell apart.” what tissue should be removed to Spectroscopy could also help prevent long-term complications. doctors catch a type of bacterial “A chronic wound is one that bone infection called osteomyelitis hasn’t healed after eight weeks,” says that’s a common complication of Michael S. Weingarten, a professor of foot wounds in diabetic patients. surgery at Drexel University College Although it can develop in other of Medicine and medical director of circumstances—at the site of an the Hahnemann Hospital Compreorthopedic implant or as a result of hensive Wound Healing Program. bedsores, for example—it’s typically Otherwise healthy people who injure the result of infection in foot ulcers themselves should be able to heal of diabetic patients. In extreme within that time, he says. cases, osteomyelitis can require amKnowing whether a wound is healputation of a toe or foot. ing is important because too slow Morris’s group at Michigan is progress suggests a change in treatusing Raman to analyze biopsied FOOT FORWARD Blake ment strategy is needed. Current guidelines changes related to tissue from patients with suspected Roessler demonstrates from the Wound Healing Society for the changes in proteins’ osteomyelitis. The work is being how a Raman probe treatment of diabetic ulcers, for example, secondary structures, done in collaboration with Blake J. could be used to make call for reevaluating treatment if the ulcer for lipids that don’t Roessler and Crystal M. Holmes of measurements on the does not shrink by 40% or more after four belong there, or the the department of internal medifeet of diabetic patients. weeks of therapy (Wound Rep. Reg. 2006, absence of lipids that cine at the University of Michigan DOI: 10.1111/j.1524-475x.2006.00176.x). should be there,” says Medical School. When they analyzed Doctors typically track wound healing Michael D. Morris, a chemistry professor at bone samples, they found acidic calcium by measuring the length, width, and depth the University of Michigan who is developphosphate minerals, including brashite and of a wound, Weingarten says. But such ing noninvasive Raman methods to assess noncarbonated hydroxyapatite, says Karen methods depend on where and by whom wound healing. “As healing progresses, Esmonde-White, a postdoctoral biomedithe measurements are being made. They’re you’re looking for a return to normal comcal engineer who works with Morris. notoriously variable. position. The changes in trauma are suffiThese minerals “are absolutely not found Spectroscopists hope that their methciently dramatic that you don’t have much under normal in vivo pH conditions,” she ods will reduce that variability. The goal is trouble finding changes of 10% or more.” says, because these unstable minerals rapto identify spectral signatures that indicate Spectroscopic methods could be paridly convert to carbonated apatite. “The fact whether a wound is healing. ticularly helpful in monitoring foot wounds that we observed these minerals in all the “You’re typically looking for spectral in diabetic patients. Weingarten and his patients we got a biopsy from says that the CEN.ACS.ORG
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JONATHAN PETERSON
wound environment is chronically acidic.” Those findings have given them insights into how the bacterial infection works. “Our results suggest that the bacterial biofilm is generating a chronically acidic environment that dissolves some of the bone mineral. Then these acidic calcium phosphate minerals are precipitating on the surface of the bone,” Esmonde-White says. “We have a unique marker for these bone infections. We don’t observe these minerals under normal conditions or in any other disease.” Her team is now trying to determine how early the changes can be detected. “The trend is toward noninvasive, early diagnoses of the ulcer itself. In more than 80% of amputation cases, they’re preceded by an ulcer,” Esmonde-White says. “If we can detect this at the ulcer phase, then we can use less-invasive interventions.” For example, doctors might be able to remove just part of an infected bone rather than amputate. Another type of wound that spectroscopy could help monitor is burns. “The big deal about burns is that you know there’s a burn injury, but you don’t know how bad the burn is just by looking at it,” says Jonathan R. Peterson, a medical student at Michigan who is working with Morris. Burns are classified by their depth. A superficial burn, which is restricted to the outer skin layer, the epidermis, will heal by itself. But a deep burn, which damages all three skin layers—the epidermis, dermis, and subcutaneous tissue—typically won’t heal. Current practice is to replace the dead tissue with a skin graft. Superficial and deep burns are both “pretty easy to identify just by looking at a burn,” Peterson says. The problem is in the middle. So-called partial-thickness burns, which damage the epidermis and part of the dermis, can also be divided into superficial and deep burns, but it’s not visually obvious which is which. “If it’s superficial partial-thickness, it can also heal by itself,” Peterson says. “If it’s deep, at the beginning it might look like a superficial wound, but it’s not going to survive. There’s nothing you can do to save it.
The sooner you get that out and graft it, the much better results you’re going to have.” Raman might be able to distinguish between these types of burns. As with near-IR, Raman can measure hemoglobin concentration, which reveals whether oxygenated blood is reaching a particular area. The researchers are in the early stages of using Raman in mice to differentiate burns created with branding irons. The results so far are encouraging, Morris says. The work is being done in collaboration with Benjamin Levi and Stewart C. Wang, both of whom are in the department of surgery at the University of Michigan Medical School.
tissue is being oxygenated. “Both of those are linked to the ultimate viability of the tissue, but there’s not always a one-to-one relationship between them. In fact, some data suggest in certain circumstances they’re not linked much at all,” Elster says. Blood getting to the tissue isn’t enough. The oxygen has to be released from hemoglobin in the blood and then be taken up by the tissue. “Raman’s nice because it gives you a molecular signature of the tissue itself,” Elster says. “It starts to get at what the tissue is actually doing with the blood and oxygen that’s being delivered.” Elster is also using Raman to detect hetSPECTROSCOPY could also be used to inerotopic ossification, a type of mineralizaform decisions in the operating room. tion in soft tissue that often develops at the Eric Elster, a captain in the Navy and a interface between an amputation stump and prosthesis. About 65% of military personnel with injuries to their limbs develop heterotopic ossification, and 20% of those need surgery to remove it, Elster says. “Raman can give you this vibrational footprint that shows you mineralization,” he says. “It shows you mineralization before you can see evidence of it visually. That’s important because there are potential therapies for heterotopic ossification that you could implement if you knew earlier.” One of the challenges is BURN MARKS Raman is professor and surgeon at the figuring out whether tissue is used to monitor burns Uniformed Services Univiable. Nonviable tissue needs on an anesthetized versity of Health Sciences to be removed so it doesn’t mouse. Measurements in Bethesda, Md., is working cause additional problems. “But are made in the center with Raman spectroscopists how much do I remove?” Elster of each square formed by four black dye spots. asks. “I don’t want to remove to develop methods that surgeons can use to answer so much tissue in a patient with questions before, during, and an amputation that their subafter surgery. For example, does a patient sequent rehab is even more challenging. need surgery? How much tissue should be But I don’t want to leave necrotic tissue removed? Is a particular tissue viable? Is a because that will pose serious issues, both wound ready to be closed? for the tissue locally and for the patient “These types of assessments of the visystemically.” ability of tissue are currently made with All of these technologies need further visual inspection of the tissue,” Elster says. development before they’ll be ready for Spectroscopy allows us “to use informawidespread use. Doctors don’t want to tion that’s in front of us that we can’t see look at spectra; they want something that with our eyes.” interprets those spectra and gives them the Surgeons typically look for whether equivalent of a traffic light. blood reaches the tissue and whether the “Surgeons and medical people are not spectroscopists,” Morris says. “Translating the information from what a spectroscopist sees—changes in band positions, intensities, and so on—into a red light and a green light is going to be a major issue.” ◾
“Surgeons and medical people are not spectroscopists.” CEN.ACS.ORG
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