A group of researchers have developed a paint-on ‘smart’ bandage that glows as the wound heals. The transparent bandage employs a sensor as well as imaging technology to monitor the tissue oxygenation concentration − important for understanding how well a wound is healing − which could help to improve the success rates of surgeries that follow severe injuries.
The research was carried out by researchers led by assistant professor Conor L Evans at the Wellman Centre for Photomedicine of Massachusetts General Hospital (MGH) and Harvard Medical School (HMS), and was published at the beginning of October in Biomedical Optics Express.
The work has been part of a long-term programme ‘to develop a Sensing, Monitoring And Release of Therapeutics (SMART) bandage for improved care of patients with acute or chronic wounds,’ said Evans, senior author of the paper.
The ‘smart’ bandage provides direct, non-invasive measurement of tissue oxygenation by combining three 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.
Phosphors − molecules that absorb light and then emit it via a process known as phosphorescence − are what cause the bandage to glow. ‘How brightly our phosphorescent molecules emit light depends on how much oxygen is present,’ said Zongxi Li, a HMS research fellow on Evans' team. ‘As the concentration of oxygen is reduced, the phosphors glow both longer and more brightly.’
The bandage is applied onto the skin’s surface as a viscous liquid, which 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.
The final piece involves a camera-based readout device, which performs two functions: it provides a burst of excitation light that triggers the emission of the phosphors inside the bandage, and then it records the phosphors’ emission. ‘Depending on the camera’s configuration, we can measure either the brightness or colour of the emitted light across the bandage or the change in brightness over time,’ Li said. ‘Both of these signals can be used to create an oxygenation map.’
The emitted light from the bandage is bright enough that it can be acquired using a regular camera or smart phone, which opens up the possibility to produce a portable device in the future.
Currently, the team are developing brighter sensor molecules so that the bandage can detect oxygen more efficiently. They are also looking for industry partners to commercialise the device.
Immediate applications for the oxygen-sensing bandage include monitoring patients with a risk of developing ischemic (restricted blood supply) conditions, postoperative monitoring of skin grafts or flaps, and burn-depth determination as a guide for surgical debridement—the removal of dead or damaged tissue from the body.