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Materials


mesh material’s permeability yields superior results in high-intensity exercise conditions. The participant had the traditional ECG electrodes applied to the skin, by way of a PDMS film device, alongside the e-ECM. Both were secured with medical tape and ECG signals were recorded. The participant then undertook high-intensity, vigorous exercise for 20 minutes on a bicycle, while hooked up to both devices. ECG signals were then recorded after the exercise period.


The results were an impressive demonstration of the superiority of e-ECM devices over traditional PDMS films. Throughout the exercise period, they “remained conformally laminated to the subject’s skin” and the waveform signal produced after exercise was comparable to that recorded prior to exercise, even showing a slight increase in signal to noise ratio. “We assume the signal increase after exercising was due to increased conformality and sweat evaporation through the fibrous e-ECM device, allowing for a more conformal skin to electrode interface than prior to the experiment,” notes the paper.


By contrast, the PDMS film electrodes were not capable of remaining laminated on the skin during exercise and presented a significant decrease in the signal to noise ratio after sweating. The wave forms were “almost unidentifiable”. “Thus,” concludes the paper, “after high sweating conditions, the e-ECM device demonstrated its ability to allow for passive fluid diffusivity, validating its application in long-term fitness monitoring.”


Going inside The Binghamton team’s study offers a snapshot of how electrospun PDMS could be developed to advance bioelectronics, with promising potential for applications in medicine and health. The permeable structure of the material allows biofluids, gases and small molecules to pass through, so it could be successfully integrated not just with skin, but with other biological tissue too – like neural and cardiac tissue – where, importantly, it could be used to limit inflammation and promote healing. “That work is very preliminary, but it’s our future direction,” Brown says. “Right now, we’re looking into in-vitro studies creating soft bioelectronics on PDMS nanofibres. We believe the fibrous architecture of the PDMS will create a more hospitable environment for cells to integrate, and with soft bioelectronics on that fibrous PDMS, we can get better accuracy and performance in our electronic measurements in-vitro, with cardiac tissue specifically.” However, more work is needed before these visions can become reality, as Koh points out. “For


Medical Device Developments / www.nsmedicaldevices.com


Customised silicone heart valves


The work on electrospun PDMS is far from the only novel use of silicone that is improving the biocompatibility of medical devices. In 2019, researchers working at ETH Zurich and the South African company Strait Access Technologies developed an artificial heart valve made of silicone and produced through 3D printing.


The poor biocompatibility of conventional heart valves, which consist either of hard polymers or animal tissue combined with metal frames, means patients that receive the implants have to take immunosuppressants or anticoagulants, with all their undesirable side effects, for the rest of their lives. However, the silicone models produced by ETH and SAT are compatible with the human body without the need for medication and achieve the same blood flow. Moreover, they can be precisely tailored to individual patients using computer tomography or magnetic resonance imaging. The researchers use the images to create a digital model and a computer simulation to calculate in advance the forces acting on the implant and its potential deformation. Pre-existing heart valves, on the other hand, have a rigid geometric shape, making it challenging for surgeons to ensure a tight seal between the new valves and the cardiac tissue. It also takes several working days to make an artificial heart valve by hand from bovine material, as opposed to the 90 minutes it takes to print a silicone equivalent. It will still take up to a decade before silicone heart valves are cleared for clinical use, and there remain technological and commercialisation hurdles, but researchers believe they can extend the life of silicone valves to match the ten to 15 years current models last in patients. “It would be marvellous if we could one day produce heart valves that last an entire lifetime and possibly even grow along with the patient, so that they could also be implanted in young people as well,” said Manuel Schaffner, one of the valve study’s lead authors.


real-life applications, we need to solve other problems: not only integrating cells and growing them on top of electronics, but also making the electronics capable of functioning wirelessly, on top of or inside the body,” she says. “Researchers in this area are working on those kinds of interactions, so we hope we will see that milestone very soon.” In addition – and building on the experimental testing Brown, Koh and colleagues conducted on e-ECMs under high-intensity, vigorous sweating conditions – work is under way to incorporate the new platform into biosensors for athlete monitoring systems. Notwithstanding Brown and Koh’s modesty, their work could pave the way for exciting research and developments in the field of wearable biosensors and implantable bioelectronics. ●


Biosensors using e-ECM devices remain laminated to the skin after high-intensity exercise, and offer a slight improvement in signal to noise ratio when the wearer is sweating.


99


Matthew Brown, Binghamton University


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