The microfluidic threads penetrate several layers to sample tissue fluid and channel it to sensing threads that collect data, such as pH and glucose levels. Electrically conductive threads then deliver the data to a flexible wireless transmitter that can be sited on top of the skin.
Image credit: Tufts University
Writing the journal Microsystems & Nanoengineering, the team - led by engineers from Tufts University in Medford, MA - says the new "smart thread" diagnostic platform could form the basis of a new generation of implantable medical diagnostics and smart wearable devices.
The paper describes the creation of microfluidic threads that can be sutured through several layers of tissue to sample fluid. The network of microfluidic circuits "interface intimately with biological tissues in three dimensions," note the authors.
Having collected the tiny samples of tissue fluid, the microfluidic threads convey them to sensing threads that measure various properties - such as pH and glucose - and send the data along electrically conductive threads to a flexible wireless transmitter that can be sited on top of skin.
Microfluidics is a relatively new technology that applies ideas from physics, chemistry, biochemistry, engineering, nanotechnology, and biotechnology to the control of tiny amounts of fluid along microchannels.
The team showed how the smart thread can collect and transmit medical data - such as pH and glucose levels, plus tissue pressure, stress, strain, and temperature - in live rats, as well as cultured tissue. The data was transmitted to a cell phone and computer.
Being able to measure such properties in three dimensions in live tissue in real time could be useful for a range of medical applications, such as monitoring wound healing, emerging infections, or just whether the body's chemistry is out of balance.
Ability to suture 3-D diagnostics into organs is unique
The 3-D platform can conform to complex tissue structures, such as those found in organs, wounds, and even orthopedic implants.
Corresponding author Sameer Sonkusale, an associate professor and director of the NanoLab in the electrical and computer engineering department at Tufts School of Engineering, says:
"The ability to suture a thread-based diagnostic device intimately in a tissue or organ environment in three dimensions adds a unique feature that is not available with other flexible diagnostic platforms."
The idea of smart devices capable of medical monitoring - and even intervention - is not new. For instance, researchers are developing smart insulin patches that sense high blood sugar and discharge the right amount of insulin, and smart wound dressings that sense bacterial infections.
However, the structure of these and other implantable devices has essentially been 2-D, and while still useful, is limited to flat tissue such as skin, note the authors.
Another drawback is that, in many cases, the materials in the 2-D substrates are expensive and require specialized processing.
In contrast, the material used to make smart thread is thin, flexible, inexpensive, and easy to form into complex shapes.
The authors note that the thread also has natural wicking properties. This could be used to convey analytes - substances that assist with chemical analysis of the tissue.
"We think thread-based devices could potentially be used as smart sutures for surgical implants, smart bandages to monitor wound healing, or integrated with textile or fabric as personalized health monitors and point-of-care diagnostics."
Prof. Sameer Sonkusale
The researchers say while more work needs to be done - for instance, they need to assess the long-term biocompatibility of the smart thread - the results they have achieved so far point to the possibility of optimizing treatments to suit individual patients.