Mostafalu et al/Microsystems & Nanoengineering 2016
This is one in a series presenting news on technology and innovation, made possible with generous support from the Lemelson Foundation.
After a doctor stitches up a gash or other cut, the wound usually gets a bandage. But that covering blocks the view of the wound as it heals. And that can be a problem if the gash gets infected. The problem may not signal when treatment is needed. Now, researchers have developed “smart” sutures that can alert caregivers when problems emerge. Future versions might even be able to deliver drugs to help a stitched-up wound heal.
Sutures are the threads used to close up a wound. They are pretty low tech. In many cases, they’re made of natural materials such as cotton or silk. In others, they’re made from a form of plastic. Some are even made of materials that dissolve in the body over time. (Those don’t require a return visit to have the doctor take them out.) Regardless of what they’re made from, however, their purpose is the same. They hold large wounds or incisions together so that they can heal.
But sometimes wounds don’t heal properly. Tissues can swell and bulge, causing the sutures to tighten. That can create an ugly scar. Or, the wound may become infected. That causes the tissue to redden and heat up. If these things don’t cause pain, the infection may hide out as it builds to a dangerous degree beneath a bulky bandage, says Sameer Sonkusale. He’s an electrical engineer at Tufts University in Medford, Mass. So he and his teammates figured out a way to transform sutures into sensors. These special stitches can report what’s going on beneath a bandage. They even can send out health dispatches from inside the body.
The key to making a suture "smart," says Sonkusale, is allowing it to conduct electricity. Thread alone won’t normally do that. So, the researchers coated a cotton thread with a conducting material. Some coatings can sense the stretching of tissue. This might indicate swelling. In other cases, the coatings can measure the pH, or acidity, of the tissue they pass through. Changes in pH might indicate an infection is developing. The team sometimes added small sensors in the thread to measure body temperature. They detect when a wound warms, signaling a brewing infection.
As any of these traits change — stretch, temperature or pH — there will be a slight change in the electrical resistance of the suture. That, in turn, will affect how much electrical current the suture can carry, Sonkusale explains. Any changes in resistance can be monitored by a watch-like device. The device sends a tiny electrical current into the suture. It might be worn on the arm or attached to clothing. The device can then send data on what it learns from the wound wirelessly to a nearby smartphone or computer for recording and analysis.
The researchers described their smart sutures online July 18 in Microsystems & Nanoengineering.
The team has developed an interesting way to embed sensors directly into a patient's skin, says John Rogers. He's a materials scientist at Northwestern University in Evanston, Ill. (A materials scientist can design new materials or analyze existing ones.) Such bio-integrated — or built-into-the-body — electronics can collect data more accurately than wearable devices such as fitness trackers, he notes.
One day, says Sonkusale, smart sutures might be tailored to monitor blood proteins that indicate healing is underway. Or they might monitor blood sugar levels in people with diabetes, he adds.
Doctors might even take advantage of the suture’s capillary action, Sonkusale explains. That’s its ability to wick fluids from one place to another. (This is the principle by which melted wax gets pulled up a candle’s wick, toward its flame.) By using that wicking, sutures could carry drug-laced fluids from outside the body into a wound. Such drugs might fight an infection or otherwise aid a wound to heal more quickly.
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blood sugar The body circulates glucose, a type of simple sugar, in blood to tissues of the body where it is used as a fuel. The body extracts this simple sugar from breakdown of sugars and starches. However, some diseases, most notably diabetes, can allow an unhealthy concentration of this sugar to build up in blood.
capillary action This is the force that governs the movement of a liquid along the surface of a solid. Because molecules of the liquid are attracted to the surface and to each other, they can pull each other along. Capillary action explains how sponges wick up liquids.
diabetes A disease where the body either makes too little of the hormone insulin (known as type 1 disease) or ignores the presence of too much insulin when it is present (known as type 2 diabetes).
electrical resistance The tendency of an electricity-conducting material to oppose the passage of a current through it. That resistance (usually measured in units known as ohms) will convert some of the electric energy into heat.
electric current A flow of charge, called electricity, usually from the movement of negatively charged particles, called electrons.
electrical engineer An engineer who designs, builds or analyzes electrical equipment.
electricity A flow of charge, usually from the movement of negatively charged particles, called electrons.
electronics Devices that are powered by electricity but whose properties are controlled by the semiconductors or other circuitry that channel or gate the movement of electric charges.
engineer A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need.
incision (v. to incise) A cut with some blade-like object or marking that has been cut into some material. Surgeons, for instance, use scalpels to make incisions through the skin and muscle to reach internal organs.
infection A disease that can spread from one organism to another.
materials science The study of how the atomic and molecular structure of a material is related to its overall properties. Materials scientists can design new materials or analyze existing ones. Their analyses of a material’s overall properties (such as density, strength and melting point) can help engineers and other researchers select materials that are best suited to a new application.
pH A measure of a solution’s acidity. A pH of 7 is perfectly neutral. Acids have a pH lower than 7; the farther from 7, the stronger the acid. Alkaline solutions, called bases, have a pH higher than 7; again, the farther above 7, the stronger the base.
proteins Compounds made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. The hemoglobin in blood and the antibodies that attempt to fight infections are among the better-known, stand-alone proteins. Medicines frequently work by latching onto proteins.
sensor A device that picks up information on physical or chemical conditions — such as temperature, barometric pressure, salinity, humidity, pH, light intensity or radiation — and stores or broadcasts that information. Scientists and engineers often rely on sensors to inform them of conditions that may change over time or that exist far from where a researcher can measure them directly.
silk A fine, strong, soft fiber spun by a range of animals, such as silkworms and many other caterpillars, weaver ants, caddis flies and — the real artists — spiders.
smartphone A cell (or mobile) phone that can perform a host of functions, including search for information on the Internet.
suture A stitch or row of stitches holding together the edges of a wound or surgical incision.
tissue Any of the distinct types of material, comprised of cells, which make up animals, plants or fungi. Cells within a tissue work as a unit to perform a particular function in living organisms. Different organs of the human body, for instance, often are made from many different types of tissues. And brain tissue will be very different from bone or heart tissue.
trait A characteristic feature of something. (in genetics) A quality or characteristic that can be inherited.
JOURNAL: P. Mostafalu et al. A toolkit of thread-based microfluidics, sensors, and electronics for 3D tissue embedding for medical diagnostics. Microsystems and Nanoengineering. Published online July 18, 2016. doi: 10.1038/micronano.2016.39.