Bioabsorbable sensors negate need for removal surgery.

A team of neurosurgeons and scientists at Washington University School of Medicine (WUSTL) in St. Louis and engineers at the University of Illinois at Urbana-Champaign has developed a new type of small, thin, wireless brain sensor that can monitor intracranial pressure and temperature and then be absorbed by the body, which would eliminate the need for surgical removal of the devices that are smaller than a pencil tip. (See Figure 1)

Fig. 1 – Wireless brain sensors, smaller than a pencil tip, can monitor intracranial pressure and temperature before being absorbed by the body, negating the need for surgery to remove the devices.
These tiny implants could potentially be used to monitor patients with traumatic brain injuries. But, in addition, the researchers believe they can build similar bioabsorbable sensors to monitor activity in organ systems throughout the body. Their findings were published in the journal, Nature.

“Electronic devices and their biomedical applications are advancing rapidly,” says co-first author Rory K.J. Murphy, MD, a neurosurgery resident at WUSTL School of Medicine and Barnes-Jewish Hospital in St. Louis. “But a major hurdle has been that implants placed in the body often trigger an immune response, which can be problematic for patients. The benefit of these new devices is that they dissolve over time, so you don’t have something in the body for a long time period, increasing the risk of infection, chronic inflammation, and even erosion through the skin or the organ in which it’s placed. Plus, using resorbable devices negates the need for surgery to retrieve them, which further lessens the risk of infection and further complications.”

Murphy is most interested in using the device to monitor pressure and temperature in the brains of patients with traumatic brain injury, since about 50,000 people die of such injuries annually in the US. When patients with these injuries arrive in the hospital, doctors must be able to accurately measure intracranial pressure in the brain and inside the skull because an increase in pressure can lead to further brain injury, and there is no way to reliably estimate pressure levels from brain scans or clinical features in patients.

“However, the devices commonly used today are based on technology from the 1980s,” Murphy explains. “They’re large, they’re unwieldy, and they have wires that connect to monitors in the intensive care unit. They give accurate readings, and they help, but there are ways to make them better.”

How It Works

Murphy collaborated with engineers in the laboratory of John A. Rogers, PhD, a professor of materials science and engineering at the University of Illinois, to build new sensors. The devices are made mainly of polylactic-coglycolic acid (PLGA) and silicone, and they can transmit accurate pressure and temperature readings, as well as other information.

Fig. 2 – This is an artist's rendering of the brain sensor and wireless transmitter monitoring a rat’s brain. (Credit: Julie McMahon, University of Illinois)
“With advanced materials and device designs, we demonstrated that it is possible to create electronic implants that offer high performance and clinically relevant operation in hardware that completely resorbs into the body after the relevant functions are no longer needed,” Rogers explains. “This type of bio-electric medicine has great potential in many areas of clinical care.”

The researchers tested the sensors in baths of saline solution that caused them to dissolve after a few days. Next, they tested the devices in the brains of laboratory rats. (See Figure 2)

Having shown that the sensors are accurate and that they dissolve in the solution and in the brains of rats, the researchers now are planning to test the technology in patients.

“In terms of the major challenges involving size and scale, we’ve already crossed some key bridges,” said cosenior author Wilson Z. Ray, MD, assistant professor of neurological and orthopaedic surgery at WUSTL.

In patients with traumatic brain injuries, neurosurgeons attempt to decrease the pressure inside the skull using medications. If pressure cannot be reduced sufficiently, patients often undergo surgery. The new devices could be placed into the brain at multiple locations during such operations.

“The ultimate strategy is to have a device that you can place in the brain—or in other organs in the body—that is entirely implanted, intimately connected with the organ you want to monitor, and can transmit signals wirelessly to provide information on the health of that organ, allowing doctors to intervene if necessary to prevent bigger problems,” says Murphy. “And, then after the critical period that you actually want to monitor, it will dissolve away and disappear.”

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