Origami-inspired sensor could continuously monitor our vital signs

A body sensor inspired by origami could one day be implanted through a tiny incision to track our health in real time. In experiments on rats, the minimally invasive device unfolded beneath their skin to continuously monitor their heart and breathing rates, and scientists expect that a similarly sized implant could work in people.

Implantable sensors already exist, but face a trade-off between size and performance. A relatively large size is generally required to integrate the electronics for wireless power delivery and electrical or electrochemical monitoring. But the new sensor, called MiFi, is folded so it compresses during insertion and then expands beneath the skin into a 2.1 centimetre square that is 0.3 millimetres thick.

"Origami design principles were integral for the development of MiFi as it allowed us to solve one of the most critical optimisation problems within implantable design," says Selin Olenik at Imperial College London.

MiFi monitored the rats’ heart and breathing rates and their body temperature at a similar level of accuracy to a wearable monitor made up of sensors on the skin.

The implant is powered wirelessly via near-field communication, the same technology used for contactless payments, says Olenik. It is made up of different sensing devices, such as an accelerometer that detects tiny chest movements to calculate heart and breathing rates, she says. This information is then transmitted wirelessly to a computer. “This is the first foldable bioelectronic minimally invasive sensor,” says team member Fırat Güder, also at Imperial College London.

Although validated against wearable sensors, the implant outperformed them in terms of stability, says Olenik. “The wearable monitor would intermittently falter and produce non-realistic values."

MiFi also gives us access to interstitial fluid, she says, which is found in the spaces around cells. This contains biomarkers that closely correlate with those in the bloodstream but without the addition of blood-clotting coagulation factors, which can affect sensor performance, says Olenik. “For this reason, MiFi could be used in the future to enable real-time monitoring of chemical markers – e.g., metabolites, enzymes, drugs, antibiotics – that cannot reliably be detected from sweat, for example,” she says.

If eventually tested on people, the implant probably wouldn’t need to be made larger because “the scale of the device is not really determined by the size of the subject, but more by the capabilities of the device itself”, says Olenik.

"The novelty lies in the [device’s] folding and integration," says Ravinder Dahiya at Northeastern University in Massachusetts. It could one day be used to continuously track our health, without being scaled up, but we first need to be sure it works long-term and doesn’t cause harm in people, he says.

Olenik says the next step is longer-term animal studies. The rats in the current study had the device implanted for only about an hour, and while the procedure caused some inflammation, the negative effects of this were “minimal”, she says.

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