A novel bandage is capable of providing alerts to nursing staff as soon as a wound starts healing badly. Sensors integrated into the base material glow with a different intensity if the pH level of the wound changes. This will help in monitoring even chronic wounds at home.
Using a UV lamp, the pH level in the wound can be verified without removing the bandage and the healing process can continue unimpeded. Image: Empa / CSEM
Changing bandages very often is considered to be very unpleasant, even for everyday injuries that are smaller. The bandage pulls and stings, and at times a scab can also start bleeding all over again. It is thus better to wait until the bandage comes off by itself.
However, it is entirely a different story with chronic wounds: generally, nursing staff have to change the dressing on a regular basis. This is essential to examine the wound, remove swabs and clean it and also for hygiene purposes. This process can unnecessarily irritate the skin; bacteria can also get in, the risk of infection soars. It would indeed be a lot better to leave the bandage on for a longer time period and allow the nursing staff to “read” the condition of the wound from outside.
The concept of being able to see via a wound dressing resulted in the project Flusitex (Fluorescence sensing integrated into medical textiles). This project is funded by the Swiss initiative Nano-Tera. Researchers from
Empa collaborated with ETH Zurich, Centre Suisse d’Electronique et de Microtechnique (CSEM) and University Hospital Zurich in order to develop a high-tech system that is expected to provide relevant data about the condition of a wound to nursing staff.
The idea of a smart wound dressing with integrated sensors is to provide continuous information on the state of the healing process without the bandages having to be changed any more frequently than necessary.
Luciano Boesel, Empa’s Laboratory for Biomimetic Membranes and Textiles and Co-ordinator of the project
This would refer to a gentler treatment for patients, along with less work for nursing staff, thus lower costs. Globally, almost $17 billion was spent on treating wounds in 2016.
Upon healing wounds, the body generates certain substances in a complex sequence of biochemical processes, which brings about a major difference in several metabolic parameters. For example, the amount of oxygen and glucose increases and falls based on the phase of the healing process; this is similar to the pH level change. All these differences can be identified with specialized sensors. Keeping this in mind, Empa collaborated with project partner CSEM in order to develop a cheap, portable and easy-to-use device for measuring fluorescence that has the potential of monitoring a number of parameters simultaneously. It should allow nursing staff to keep tabs on the pH and also on oxygen and glucose levels while the wound heals. If these differ, it will be possible to arrive at conclusions about other vital biochemical processes dealing with wound healing.
A high pH signals chronic wounds
The pH level is specifically useful for chronic wounds. The pH rises to 8 before falling to 5 or 6 if the wound heals normally. The pH level fluctuates between 7 and 8 if a wound fails to close and becomes chronic. It would thus be helpful if a signal on the bandage could alert nursing staff that the wound pH is permanently high. If changing of the bandage is not needed for hygiene reasons and low pH levels, then they could afford to wait.
But how do sensors work? “Customized” fluorescent sensor molecules respond with a physical signal if specific substances appear in the wound fluid. They begin to glow and some also change color in the visible or ultra-violet (UV) range. It is possible to detect stronger and weaker changes in color due to a color scale and the quantity of the substance that is emitted can be deduced.
Guido Panzarasa, Empa Chemist from the Laboratory for Biomimetic Membranes and Textiles vividly shows how a sample comprising of sensor molecules starts to fluoresce in the lab. A solution with a pH level of 7.5 is cautiously dripped into a dish. The change is plain to see under a UV light. He adds another solution and the luminescence fades. Just one glance of the little bottle proves it: the pH level of the second solution is observed to be lower.
Luminous molecules under UV
A molecule comprising of pyranine and benzalkonium chloride was designed by the Empa team. While benzalkonium chloride is a substance also used for standard medical soap to combat fungi, bacteria and various other microorganisms, pyranine is a dye found in highlighters that glows under UV light.
“This biomarker works really well,” says Panzarasa; “especially at pH levels between 5.5 and 7.5. The colors can be visualized with simple UV lamps available in electronics stores.” Recently, the Empa team published their results in the journal “Sensors and Actuators”.
Another advantage of the designer molecule refers to its antimicrobial effect, thanks to the benzalkonium chloride. This has been proved by Researchers from Empa’s Laboratory for Biointerfaces for the bacteria strain Staphylococcus aureus. It could also be possible to combat unwelcome bacteria by selecting the ideal bandage material in future. Further investigations, such as on the compatibility of the chemical with tissues and cells, are presently lacking, however, the Researchers are yet to understand how their sensor works in a complex wound.
Keen interest from industry
Boesel places a prototype on the lab bench to illustrate what a smart wound dressing might in fact look like in the future.
You don’t have to cover the entire surface of wound dressings with sensors. It’s enough for a few small areas to be impregnated with the pyranine benzalkonium molecules and integrated into the base material. This means the industrial wound dressings won’t be much pricier than they are now – only up to 20% more expensive.
Boesel , Empa ’s Laboratory for Biomimetic Membranes and Textiles and Co-ordinator of the project
Currently, Empa Scientists are working on this in the follow-up project FlusiTex-Gateway in collaboration with industrial partners Flawa, Kenzen, Schöller and Theranoptics. Panzarasa currently drips different liquids with varying pH levels onto all the small cylinders on the wound pad prototype. The darker and lighter dots are also considered to be clearly discernible as soon as the UV lamp is switched on. These dots are also visible to the naked eye and glow in bright yellow when the liquids with a high pH get in touch with the sensor. The Scientists are certain that this type of wound dressing is just the ticket as a diagnostic tool since the pH level can be effortlessly read and provides exact information about the alkaline or acidic state of the sample. More quantitative, accurate measurements of the pH level can be obtained for medical purposes by using the fluorescence meter produced by CSEM.
Boesel suggests that it could be possible to read the signals with the help of a smartphone camera. Integrated with a simple app, doctors and nursing staff will now be able to possess a tool that allows them to conveniently and effortlessly read the wound status “from outside” even without the need for a UV lamp. Patients will then be able to detect the early onset of a chronic wound at home.