Sensors slip into the brain, then dissolve when the job is done

A team of neurosurgeons and engineers has developed wireless brain sensors that monitor intracranial pressure and temperature and then are absorbed by the body, negating the need for surgery to remove the devices.

Such implants, developed by scientists at Washington University School of Medicine in St. Louis and engineers at the University of Illinois at Urbana-Champaign, potentially could be used to monitor patients with traumatic brain injuries, but the researchers believe they can build similar absorbable sensors to monitor activity in organ systems throughout the body. Their findings are published online Jan. 18 in the journal Nature.

"Electronic devices and their biomedical applications are advancing rapidly," said co-first author Rory K. J. Murphy, MD, a neurosurgery resident at Washington University 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 monitoring pressure and temperature in the brains of patients with traumatic brain injury.

About 50,000 people die of such injuries annually in the United States. When patients with such 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 explained. "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."

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-co-glycolic acid (PLGA) and silicone, and they can transmit accurate pressure and temperature readings, as well as other information.

"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 said. "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.

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 co-senior author Wilson Z. Ray, MD, assistant professor of neurological and orthopaedic surgery at Washington University.

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," Murphy said. "And then after the critical period that you actually want to monitor, it will dissolve away and disappear."

Washington University School of Medicine

New 3D printing tech empowers surgeons at a nano scale

A 3D printer that can produce detailed models narrower than a human hair is helping experts in medical robotics at Imperial's Hamlyn Centre.

The technology, utilising the Photonic Professional GT machine by Nanoscribe and funded by EPSRC, is allowing researchers at the Hamlyn Centre to develop previously impossible medical therapies, devices and procedures. 

These include swimming microrobots for targeted drug delivery as well as ultra-small instruments for microsurgery. Thanks to the work of Hamlyn researchers and their collaborators around the world, these techniques could allow oncologists to deliver cancer drugs that operate like targeted missiles rather than affecting a wider part of the body. Eye surgeons could also benefit through the use of new nano tools for delicate operations to the back of the eye, minimising the risk of damage.

The Hamlyn Centre’s Director Professor Guang-Zhong Yangshowcased the work to President Xi Jinping and other senior Chinese and British officials during their visit to the College on 21 October.

The Imperial researchers use a cutting-edge technique known as Two Photon Polymerisation, where a controlled point of pulsed laser is used to polymerise – in other words, joining together molecules – or solidify a liquid photoresist (a light-sensitive material). By moving a laser with great precision, a structure can be built layer-by-layer in the same manner as standard 3D printers, but at a nano scale. 

Great Wall gift

 

The group can build 3D models and structures with advanced features as small as 150 nanometres – about the same size as the almost-invisible pits imprinted on CDs. This could help surgeons develop three-dimensional tools with force-sensing capabilities, giving tactile feedback, for use at a microscopic scale in surgery. When President Xi visited the Hamlyn Centre in October, he and the Duke of York were presented with gifts demonstrating this pioneering technique. 

Maura Power, a PhD student supervised by Professor Yang at the Hamlyn Centre, explains, “A section of the Great Wall of China was printed on to a square of silicon at one millionth of its true scale. The section of wall is just over 100 micrometres long, which is the same as the width of a typical human hair. An image of the printed wall was acquired using a Scanning Electron Microscope.

The length of the letters in this image are approximately the same diameter as that of human red blood cells. This microscope picture was mounted next to the silicon wafer in a frame which was wrapped in red ribbon and presented to President Xi by Professor Guang-Zhong Yang. 

“For Prince Andrew, a panda leaping over a bamboo was printed to the tip of a needle and also presented in a small frame. The height of the panda is approximately 50 micrometres, or half the width of a human hair.”

Imperial College London