The researchers — who are based at Stanford University, the Georgia Institute of Technology, Emory University, and Michigan State University — first prepared sensors and electrodes on a thermoplastic film and then rolled the film into a spiral. The use of thermoplastic elastomers facilitated spontaneous bonding between layers, eliminating the need for adhesives. With the approach, a 230-μm-diameter soft fibre was fabricated containing 1,280 electrode channels. This fibre was used to perform motility sensing, electrical stimulation and electrochemical sensing of serotonin in the small intestine of awake pigs. The team also showed that a 32-channel brain probe could provide continuous single-neuron recording in awake and moving mice for up to 4 months.
Meanwhile, another rolled-up implantable sensor has been reported that can detect electrophysiological and mechanical signals, and can move. Ruijie Xie et al. — who are based at various institutions in China — fabricated a stretchable fibre containing segmented electrodes and strain sensors. A patterned gold film was first deposited on a 400-nm-thick thermoplastic film. This was then rolled up into a fibre shape and the detection sites and wire bonding points exposed, while other areas were self-encapsulated. To guide the fibre to the desired internal location, a small magnetic bead was placed at the head of the fibre that can be moved by applying an external magnetic field. Up to 60 electrode channels were accommodated along a single fibre with a minimum diameter of 109 μm. The team showed that the fibre could be implanted in a rabbit brain and used for electrocorticography, capturing local field potentials by steering the fibre to different locations. They also showed that it could provide stable bioelectrical monitoring in rats for more than 43 weeks.
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