Smart sutures promise new generation of implantable, wearable diagnostics
With his team, associate professor Sameer R. Sonkusale and principal investigator at Tufts’ NanoLab experimented with sewing threads from different materials, coating them with conductive materials such as carbon nanotubes and infusing them with various chemical reagents.
Sewing specific thread combinations and connecting them to reading electronics, the researchers were then able to monitor electrical signals, either signalling strain, temperature, or even sensing in-vivo subcutaneous chemical markers to diagnostic particular patient conditions. In some cases, they also leveraged the wicking property of threads to design three-dimensional multi-reagent microfluidic circuits.
The thread-based diagnostic device (TDD) platform, as they describe it in Nature’s Microsystems & Nanoengineering journal in the paper “A toolkit of thread-based microfluidics, sensors, and electronics for 3D tissue embedding for medical diagnostics” combine nanomaterial-infused conductive threads connected to a flexible surface readout electronic circuitry, for signal conditioning and wireless transmission.
They fabricated strain sensors out of stretchable rubber fibres coated with carbon nanotubes and silicone (monitoring the thread’s electrical resistance), which they suggest, could be used to monitor wound healing or muscle strain experienced due to artificial implants.
Using different coatings and threads, sensing circuits can be sewn as matching electrodes. In one experiment, the researchers were able to monitor the electricity flow between one cotton thread coated with carbon nanotubes and polyaniline nanofibers, and another thread coated with silver and silver chloride. In-vivo, this electricity flow offers an internal measure of the medium’s acidity, which can be a sign of infection in a recently stitched wound.
They also devised an amperometric glucose sensor consisting of carbon/functionalized CNT threads (working electrode), carbon threads (counter electrode), and silver/silver chloride threads as the reference electrodes. They infused the working electrodes with glucose oxidase, an enzyme that reacts with glucose present in the blood to generate an electrical signal. Alternating voltages pulses of 0.5 and 0V, they were able to read out the output current as a response to different glucose concentrations.
pH measurement is another thread-based experiment they carried out successfully.
Of course, the experiments could go on, threads can be functionalized with an endless variety of sensing chemistries, to measure proteins, DNA and other biomarkers directly in the tissues where they are implanted. And complex multi-reagent microfluidic circuits could be devised, splitting threads into distinct channels probing different areas.
Next, the researchers aim to integrate other electronic components on the threads, including capacitors, diodes, and transistors, to create a highly flexible and self-contained implantable diagnostic platform.
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