All sewn up

Turning surgical sutures into sensors

WEARABLE and implantable medical gadgets are a promising technology. By continuously collecting information from patients they make it easier to diagnose and treat whatever the problem may be. But most of the sensors in such devices have to lie flat against the body. That limits what they can do.

Now a team of researchers are trying to use one of humanity’s oldest technologies to do better. As they report in Microsystems & Nanoengineering, Sameer Sonkusale at Tufts University, in Massachusetts, and his colleagues, propose to turn threads, of the sort spun to make clothes, into sensors.

Thread has many advantages. It is cheap, flexible and mostly tolerated by human bodies. Most pertinently, doctors have plenty of experience, via the practice of suturing, of sewing it into bodily tissues. Doing that with smart thread would allow a more detailed overview of what is happening than any skin-mounted sensor could.

Turning yarn into sensors requires clever chemistry. Electrodes for recording mechanical or chemical activity can be created by covering the threads with conductive ink. Sensors designed to measure physical strain—useful in monitoring wound healing—can be made by coating stretchy fibres with carbon nanotubes and silicone. The electrical resistance of those fibres changes as they are placed under strain. By running a small electric current through the thread, Dr Sonkusale and his team can, therefore, measure the forces surrounding it. A related technique can be used to make sensors sensitive to acidity.

Another useful property of some fibres is wicking, in which liquids travel along the fibre via a bit of physics called capillary action. The researchers found that specially treated cotton made a good wick for the interstitial fluid that surrounds most tissues. A smart suture could siphon tiny amounts of that fluid to sensors elsewhere, allowing doctors to keep a continuous and unintrusive eye on their patient’s biochemistry.

So far Dr Sonkusale and his team have tested their technology only in rodents. But it seems to work as expected. One possibility for human trials might be in diabetic patients, who must keep a close eye on any wounds they suffer, as they often resist healing. That can lead to amputations. A few choice stitches could save a limb.