Long-term recordings of physiological parameters are important for many applications in research, diagnostics, and therapeutics. The rise of machine learning, in particular, is enabling the extraction of insights from the mountains of data collected through continuous recordings. Devices that capture data of this sort are expected to significantly improve patient outcomes in the near future, so it is no surprise that many researchers and clinicians are excited to make use of them. Unfortunately, however, existing devices tend to only be able to record for short time periods because of difficulties with supplying power. Further, there are areas of the body, such as the musculoskeletal system, that are not conducive to long-term device attachment.
In much the same way as skin, the outer layers of bone tissue are continually renewed. As such, a device affixed with a traditional adhesive would become detached within a few months. A team of researchers at the University of Arizona have come up with a slick method to adhere electronics to bones, which they call osseosurface electronics.
Illustration of device in action (📷: L. Cai et al.)
Their adhesive contains calcium particles that are structurally similar to bone cells. Because the adhesive appears to be just another part of the bone, natural bone tissue actually grows around it to form a permanent bond. With any attached sensors staying put for good, long-term data capture is possible.
There is still the problem of supplying long-lasting power to the device to deal with, however. To tackle this issue, the team built a battery-free device that uses near-field communication for both power delivery and external communications. In order to avoid interfering with normal body functions, and to prevent irritation, the device needed to be very small and unintrusive. The final design is about the same thickness as a piece of paper, and is flexible such that it can conform to the shape of the bone that it is affixed to.
Block diagram of device (📷: L. Cai et al.)
The prototype contains sensors such as strain gauges and thermistors to record real-time bone strain and thermography measurements. The devices were successfully deployed in small animals where they captured data related to recovery from injuries. The researchers believe that similar devices could eventually be used in humans, especially in those suffering with osteoporosis, to monitor the recovery of broken bones.
The technique has not yet been approved for use in humans, but in the future it may provide an improved way to diagnose and treat patients. It may also open up new windows into the musculoskeletal system for researchers that are working to unlock its secrets.