Inspired by a desire to help wounded soldiers, an international, multidisciplinary team of researchers at the Wellman Center for Photomedicine of Senors and Harvard Medical School, Boston, MA, has created a paint-on, transparent “SMART” bandage that can protect severe wounds and burns while also measuring oxygen levels in the tissue. Instant access to oxygen concentration, which shows up as a phosphorescent glow on a smartphone-based color oxygen map, can provide critical healing information and can significantly improve the success of surgeries to restore limbs and physical functions.
Because oxygen plays a critical role in healing, understanding and mapping oxygen levels in severe wounds and burns is clinically important, but often inaccessible due to a lack of methods to accurately measure those levels.
A SMART bandage (for Sensing, Monitoring And Release of Therapeutics) developed by the team, provides noninvasive measurement of tissue oxygenation by combining three simple, compact, and inexpensive components: a bright sensor molecule with a long phosphorescence lifetime and appropriate dynamic range; a bandage material compatible with the sensor molecule that conforms to the skin’s surface to form an airtight seal; and an imaging device capable of capturing the oxygen-dependent signals from the bandage with high signal-to-noise ratio.
How It Works
The bandage’s key ingredient is phosphors, molecules that absorb light and then emit it by phosphorescence. As the concentration of oxygen is reduced, the phosphors glow both longer and more brightly, they explain. To make the bandage simple to interpret, the team also incorporated a green oxygen-insensitive reference dye, so that changes in tissue oxygenation are displayed as a green-to-red colormap. (See Figure 1)
The bandage is painted onto the skin’s surface as a viscous liquid, and dries to a solid thin film within a minute. Once the first layer has dried, a transparent barrier layer is then applied atop it to protect the film and slow the rate of oxygen exchange between the bandage and room air, making the bandage sensitive to the oxygen within tissue.
A camera-based readout device performs two functions: it provides a burst of excitation light that triggers the emission of the phosphors inside the bandage, and it records the phosphors’ emission. Depending on the camera’s configuration, the researchers say that they can measure either the brightness or color of the emitted light across the bandage or the change in brightness over time; both of which can be used to create an oxygenation map.
Since the light emitted by the bandage is bright enough that it can be acquired using a regular camera or smartphone, this may lead to a portable, field-ready device.
The team explains that they are developing brighter sensor molecules to improve the bandage’s oxygen sensing efficiency. And, they say that their laboratory research will focus on expanding the sensing capability of the bandage to other treatment-related parameters — such as pH, bacterial load, oxidative states and specific disease markers—and incorporating an on-demand drug release capacity.
Their goal for the bandage is to allow for the visual assessment of the wound, and to incorporate therapeutic release capabilities that allow for on-demand drug administration at a desired location without the need for bandage removal.