Battery-Free Implants: Powering Bioelectronics By Ultrasound
(Posted on Tuesday, January 23, 2024)
This article was originally published on Forbes on 1/23/24.
This story is part of a series on the current progression in Regenerative Medicine. This piece discusses advances in bioelectronic devices.
In 1999, I defined regenerative medicine as the collection of interventions that restore normal function to tissues and organs damaged by disease, injured by trauma, or worn by time. I include a full spectrum of chemical, gene, and protein-based medicines, cell-based therapies, and biomechanical interventions that achieve that goal.
A new implant powered not by batteries but by ultrasonic electricity may revolutionize our approach to bioelectronics. In Advanced Materials, Dr. Young-Jun Kim and colleagues from Sungkyunkwan University in Korea describe an approach to implantable bioelectronics that is semipermanent, energy efficient, and compact, a trifecta that is difficult to achieve despite today’s technology.
The two most common questions with bioelectronic devices are ‘how is it powered?’ and ‘is it comfortable to use?’
For most bioelectronics, batteries are the typical power source, requiring the user to carry a bag or pouch attached to the system—adding to the system’s total weight and fatigue on the user.
Most of these devices are intended for daily use, and many are installed semi-permanently to the user, meaning they do not come off entirely without medical assistance. Depending on the device’s intended use, some bioelectronic interventions may be small, and others may be much larger. They must be comfortable, as well as functional.
For implants, the device is often connected to a battery patch attached somewhere on the chest. While not invasive, this could become intrusive after months or years of use.
Kim and colleagues took a different approach to the battery-powered design, opting instead for ultrasound technology. We typically think of ultrasound as an imaging technology, often for pregnant women or people with internal damage. However, Kim and colleagues are using ultrasound in another way: low-amperage electric transfers.
The transfer of electrons from one material to another when the two materials have differing polarities is known as triboelectricity. The ultrasound probe has a negative charge, and the implant has a positive charge. When the ultrasonic probe comes close, there is a wireless energy transfer.
Kim and colleagues’ implanted device is called a triboelectric nanogenerator, directly stimulating nerves using low-amperage electricity. Rather than pulling power from a battery pack, a compact ultrasound device delivers low-intensity power through the extradermal portion of the implant.
FIGURE 1: Battery-free, wireless, and Ti-packaged electroceuticals design.
This kind of system is often used for organ therapy, stimulating a failing organ to improve function. For instance, Kim and colleagues implanted the triboelectric system in a live rat model with an overactive bladder to test their device.
FIGURE 2: Schematic illustrating in vivo experiment of the nerve stimulation system implanted in a rat.
They found that compared to an inactive control implant of similar size and location, the device reduced urinary regularity and improved bladder capacity while not impacting healthy bladder function.
FIGURE 3: Traces of bladder pressure and cumulative voiding volume collected before (black), and after (red), stimulation (blue circles: occurrence of urination).
While the system has yet to be applied in human subjects, such studies are impending as this technology advances.
There are a few notable advantages to ultrasonic electricity over batteries. Notably, Ultrasound waves can penetrate through materials, such as metals, reducing device size and discomfort for patients. Further, reducing the need for batteries creates a more energy-efficient and environmentally friendly device. Finally, the low intensity of the electrical current of ultrasounds are much less damaging to the body and nerves than higher intensity systems found in other designs.
Though, in my view, the more interesting takeaway is the triboelectric energy transfer itself. Power is the limiting factor in most ergonomic bioelectronic designs. With triboelectricity, the need for battery-enabled design is completely eliminated.
The drawback is that the ultrasonic probe has to be used every time to activate the implant. This limits the current viability of the system for more common everyday uses. While applications for ultrasound-driven triboelectric design may be limited as portable ultrasound devices also continue to advance, the idea and blueprint are astonishing, at the least.
I would not be surprised if, in the coming months and years, a similar technology were applied to the wider field of regenerative medicine, for instance, in prosthetics, insulin delivery, motor rehabilitation, and so on. I eagerly anticipate such advances.