A team at the Wireless Bioelectronics Lab at the National University of Singapore led by [Dr John Ho] announced the results of their new Wireless Sensing (WiSe) smart sutures program last month. Their system consists of a specially prepared patch of polymer gel (the sensor) which is sewn into the wound using a silk suture coated with a conductive polymer. An external reader scans the sensor to monitor the status of the wound.
The concept is not unlike a NFC public transportation card, although with simplified electronics. There is no microcontroller or digital data being transferred. Rather, the sensor behaves like a tuned tank. The gel on the sensor was designed to degrade if the wound becomes infected, changing capacitance of the sensor structure and thus shifting its resonant frequency.
If you’ve ever had the misfortune to experience surgery, no doubt the surgeon and nurses drove home the importance of diligent monitoring of the wound for early signs of infection. These smart sutures allow detection of wound infection even before symptoms can seen or felt. They can be used on internal stitches up to 50 mm inside the body. More details can be read in this paper, and we covered another type of smart sensor back in 2016.
If you’ve ever had surgery, you know firsthand how important it is to keep the wound from getting infected. There are special conductive sutures that sense changes in wound status via electrical signal and relay the information to a computer or smart phone. As awesome as those sound, they’re a first-world solution that is far too pricey for places that need it most — developing countries. And surgical wounds in developing countries are about four times more likely to get infected than those in the US.
Iowa high-school student [Dasia Taylor] found a much simpler solution that could drive down the infection rate. She used beets to develop color-changing sutures that turn from bright red to purple within five minutes if an infection is present.
Beets, and other fruits and vegetables like blackberries, plums, and blueberries are natural indicators of pH. They have a compound called anthocyanin that gives them both their pigment and this cool property. Beets are perfect because they change color at a pH of nine — the same pH level of infected human skin, which is normally around five.
[Dasia] experimented with several types of suture thread to see which ones would absorb the beet juice in the first place. She settled on a cotton-polyester blend that is braided. While it probably helps absorb the beet juice, it would also give bacteria several places to hide. Another problem is that many surgeries involve cutting muscle, too, and by the time a deeper infection would show up on the sutures, it would be pretty late in the game. But if these color-changing sutures can be made to be cost-effective, safe for skin, and of course, keep wounds together, this solution is way better than nothing at all and definitely worth producing. You can see [Dasia] talk about her project in the video below.
Want to know more about natural pH indicators? Sure you do.
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Researchers at Tufts University are experimenting with smart thread sutures that could provide electronic feedback to recovering patients. The paper, entitled “A toolkit of thread-based microfluidics, sensors, and electronics for 3D tissue embedding for medical diagnosis”, is fairly academic, but does describe how threads can work as pH sensors, strain gauges, blood sugar monitors, temperature monitors, and more.
Conductive thread is nothing new but usually thought of as part of a smart garment. In this case, the threads close up wounds and are thus directly in the patient’s body. In many cases, the threads talked to an XBee LilyPad or a Bluetooth Low Energy module so that an ordinary cell phone can collect the data.
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