The Future Of Bioelectronic Medicine

A visualization of neurons.

The integration of human biology with futuristic technology has long been a staple of science fiction, but the emergence of Brain-Computer Interfaces (BCIs) has brought us closer to the concept than we could have imagined. This system analyzes neural signals via sensors and translates them into actionable commands. While traditional BCIs have relied on extensive external hardware and invasive wiring, a sleek solution was introduced by UC Berkeley researchers in 2016: Neural Dust. These microsensors, powered and controlled by ultrasound, represent a shift towards an age of “electroceuticals”, a term coined just three years prior to the invention. Though we are seeing new and improved methods of microtechnology, it is important to understand the earlier devices that made advancement possible.

In 2004, Matthew Nagle, a man paralyzed from the neck down, became the first person to use the BrainGate neural BCI system. Implanted by neurosurgeon Gerhard Friehs, Nagle’s device (a 96-electrode ray) was positioned on the surface of his motor cortex. A wire connected it to his skull and then to a computer. Through the transduction of electrical impulses to the computer and its subsequent decoding, Nagle was able to control a computer mouse cursor, play a ping-pong game, draw, and even operate a robotic hand. Essentially, he was able to operate technology with his thoughts alone. Despite the positive outcome of the operation, the surgery was major, invasive, and unfortunately, temporary. Nagle’s implant was removed a year later on his request, but it was a tremendous breakthrough in biotechnology, setting the stage for Neural Dust twelve years later.

The limitations faced by early participants like Matthew Nagle pushed a new generation of engineers to reconsider how BCI could be implemented. Their goal was to eliminate the wires and batteries that earlier devices required. The original Neural Dust device created in 2016 achieved exactly this. Instead of wired arrays, Neural Dust was designed with motes, which are wireless transceivers that could monitor electrical signals from the brain and other organs. By 2018, the research team worked to transform the original mote into what is now known as “StimDust”. While Neural Dust’s primary use was to record, StimDust was intended to actively stimulate the nervous system. Measuring 6.5 cubic millimeters, it is the smallest experimental nerve stimulator created. 

The evolution from wired implants to wireless motes was crucial in protecting the health of patients and the integrity of the devices. Standard medical implants, such as pacemakers or deep-brain stimulators, are too large to be placed directly on a nerve. Because of their size, surgeons are forced to create a separate space in the body—an “anatomic pocket” to house the device’s battery and hardware. The issue here is that leads must then be threaded through the body to connect the power source to a nerve. The lead wires have been shown to migrate and house bacteria, leading to infection. StimDust removes these factors by being small enough to sit directly on the nerve, wrapped in a tiny cuff. Its miniature size makes the procedure less invasive and more reliable.

A photo of Mathew Nagle drawing a circle with the help of BrainGate and researchers from Brown University.

StimDust is regarded as ingenious because it uses ultrasound as both a power source and a communication line. The device operates through these three main parts:

• Piezoceramic Ultrasonic Transducer: This vibrates when hit by ultrasound waves, converting mechanical energy into power for stimulation.

• Capacitor: This stores the energy harvested from the ultrasound.

• Electrode Interface and Cuff: These allow the device to attach to the nerve and record or generate impulses.

Scientists tested Neural Dust in rats by planting a three-millimeter sensor coated in epoxy in their nerve fibers. The piezoelectrical crystal converts external sound waves and vibrations into an electrical signal. Then, according to the researchers, “A voltage spike in the fiber alters the circuit and the vibration of the crystal, which changes the echo detected by the ultrasound receiver.” This allows them to determine the voltage. By reading that “echo” they could visualize the rat’s nerve firing in real time. With the StimDust experiment, scientists had a more proactive goal. They wrapped the cuff around the sciatic nerve of the rat. By using ultrasound at specific frequencies, they induced electrical current in the mote, which then stimulated the nerve. It effectively triggered the rat’s leg to twitch on command. 

StimDust and similar neurostimulation devices have opened vast possibilities within medicine. For individuals with epilepsy, StimDust could detect the abnormal impulses that trigger seizures and correct it. The vagus nerve regulates systemic inflammation so those with immune disorders could benefit from the corrective stimulation. It also holds promise for prosthetics, much like the array did for Matthew Nagle. By attaching to nerve axons, these motes could allow a user to control a robotic limb, restoring the user’s mobility and sense of autonomy.

Despite the promise of StimDust, long-term effects are unclear, especially since experimentation has only been conducted in vivo in rodents. The human body is a highly corrosive environment and it is unknown if these devices can withstand that corrosion over multiple years. There is also the concern of immune issues. The body can and will, most likely, recognize the StimDust mote as a foreign object and begin to reject it. In this case, the immune system will attempt to wall off the device through scar tissue formed after inflammation. Ultimately, this would block the signals and render the device inoperable. Still, StimDust represents a definitive leap into the future of medicine.