(Above: Printed sensor array on flexible polymer substrate of a type to go under a bandage and track wound healing. Courtesy Michel Maharbiz)
by Gordy Slack
Most scrapes and boo-boos heal quickly and completely with traditional, over-the-counter bandages. However, for deeper cuts or surgical incisions, something more is needed so that physicians can monitor the healing process happening underneath the bandage. “Right now, if you have a bandaged wound, the only way to tell its status is to remove the bandage and look,” says Michel Maharbiz, Associate Professor of Electrical Engineering and Computer Sciences at UC Berkeley. Neglecting to inspect wounds can allow infections and other serious pathology to go undetected and untreated. But removing a bandage may expose a wound to infections, disrupt the healing process, or structurally damage the wound itself.
Maharbiz is working with colleagues to develop a bandage that reads electrical fields naturally emitted by wounds to track the rate and extent of healing. This new tool could potentially be applied to internal surgical sites and sutures, tracking internal healing and then wirelessly sending data out of the body to an external processor. Currently, there is no good way for doctors to track progress of internal wounds so this bandage could be used in numerous situations.
The project, called FRONTS (Flexible Resorbable Organic Nanomaterial Therapeutic Systems) and sponsored by the NSF, employs an interdisciplinary group of researchers from UC Berkeley and UCSF, to develop the bandage device. Maharbiz focuses on the project’s nanosensors, but the group also includes specialists in printed electronics, biocompatible materials, surgical devices and procedures, and the physiology of wound healing.
After an injury, epidermal cells replicate and move into the area of a wound in order to close it up and start the healing process. This causes ionic concentrations to shift, a change that generates subtle but characteristic electrical fields. The fields are detectable by sensor arrays that can be printed onto a flexible substrate that is part of the bandage itself. UC Berkeley EECS Professors Vivek Subramanian and Ana Claudia Arias head the electronic printing efforts and can print circuits, sensors, and batteries on all kinds of flexible materials, including biocompatible ones that are “thin, light, flexible, and disposable,” Subramanian says.
“To get data out of the wounds we need a thin-film battery, we need electrodes to do measurements, and, in the longer term, if we are going to put this inside the body, we need electronics that will dissolve away,” notes Subramanian.
It has long been known that wounds, when healing, create signature electrical fields. “But no one has done a good job of putting all of this information together to build good models of wound healing, and make those models tractable, make them useful in the clinic,” says Maharbiz. The novel step embodied in the FRONTS project is the detection and precise measurement of those fields over time, thereby non-invasively tracking the healing process. Together with Maharbiz, Subramanian is developing ways to automatically interpret and analyze the electrical signals given off by wounds.
For simplicity’s sake, the first application for such bandages would be on damaged tissue on the outside of the body. “For on-skin measurements,” says Subramanian, “the materials do not have to dissolve; they are just thin-film printed systems integrated into bandages.”
The on-skin concept is currently being tested on animals models at the University of California in San Francisco. Shuvo Roy, a UCSF professor in bioengineering, and Michael Harrison, a pediatric surgeon and professor emeritus also at UCSF, are preparing for clinical human trials if the animal models are successful. “We already have a clinic and a practitioner in the plan so we can move quickly to testing the bandages in the clinic,” says Maharbiz.
The group is developing a more complex and challenging version of the bandage as well. It relies on the same principles, but this array of sensors would be left inside the body after surgery in order to track the healing progress of internal lesions created during surgery. In those cases, unless doctors reopen the surgical site, it is impossible to track how fast and well a wound is healing. The sensors themselves could be embedded deep in the abdominal cavity at the site of the wound but have a thin tail-like antenna connecting them to a chip near the skin that sends the data to a receiver outside the body.
The body tends to reject equipment left inside it for very long, though, so the research group is experimenting with non-toxic materials that will biodegrade and be absorbed by the body. Everything from the batteries to the circuit boards must be biocompatible, non-toxic, and resorbable, says Subramanian.
Beyond just tracking the progress of healing wounds, the group is hoping eventually to influence that healing by the introduction and manipulation of electrical fields. This part of the project is “still pretty speculative,” says Maharbiz. However, there is strong evidence, he says, that wounds not only produce electrical fields, but that whole communities of cells—particularly epithelial cells—are also responsive to them. The electrical disturbance to epithelial cells created by a wound is immediate and is thought to trigger a process known as galvanotaxis in which cells proliferate and migrate to the site of injury. By manipulating the electrical fields around a wound, it may be possible to influence how it heals, minimizing harmful scar tissue and maximizing the chances for full and robust recovery, says Maharbiz. “It would help doctors gain control over how the healing takes place, more than just making it go fast.”
Applying electrical fields is a much trickier engineering and clinical problem than just reading them, says Maharbiz, because these fields may cause unintended electro-chemical side effects (in addition to tissue healing) that doctors would first have to understand and control for.
Roy is also investigating additional sensors that could be made part of a bandage system to track more kinds of information emitted by wounds: pressure and oxygen sensors, for example, could help detect the emergence of pressure ulcers, a common problem for hospital patients who remain in one position for a long time. With the population getting older and assistive care becoming ever more prominent, a device that can assist with preventing ulcers in patients would be very useful.