Rat scan

CT scan of a rat shows a small implanted device that uses light signals from tiny LEDs to activate nerve cells in the bladder and control urinary problems. [Image: Gereau Lab, Washington University in St. Louis]

Urinary problems, from overactive bladder to incontinence, can be painful and embarrassing to the patient, and continuous nerve-stimulation remedies often confuse other parts of the nervous system. Researchers at several U.S. universities have created a small implantable device that uses thin inorganic LEDs and a strain gauge to stimulate the bladder to empty only when it is necessary (Nature, doi: 10.1038/s41586-018-0823-6).

The optogenetic bladder-control device designed at Washington University School of Medicine, Missouri, and Northwestern University, Illinois, has been implanted only in a rat so far, but team members hope to develop it into a medical device for humans.

A normal bladder consists of smooth muscle tissue that lets the organ expand to hold its contents, then contracts to expel the urine once it is full. For various reasons, some patients have more difficulty controlling this cycle, especially as they age. The Washington–Northwestern team wanted to build a sensor-actuator system that would switch on and off the way that normal urinary-tract nerves work with the muscle tissue.

Detecting nature's call

To sense the bladder's fullness or emptiness, the researchers encircled the rat's bladder with a 15-μm-thick, stretchable strain gauge made of silicone doped with carbon black. As the bladder fills up, the strain changes the resistance of the material and eventually activates micro-LEDs mounted on a flexible, 25-μm-thick substrate.

Normal bladders don't respond to light, so the scientists introduced light-sensitive proteins known as opsins into the muscle tissue, and a virus bound the opsins to the tissue. When the bladder filled up, the micro-LEDs emitted a small amount of visible light—roughly 44 μW at 540 nm—to stimulate the opsins and cause the bladder muscle to contract.

Other components of the device included wireless communications and power subsystems and—outside of the rat—data collection and visualization software installed on a handheld device. Together, the components formed a “closed-loop” optogenetic control system that activated itself only when it sensed the need to void the animal's bladder.

The scientists noted that the implants did not seem to cause any distress to the animal, but more safety and efficacy studies—particularly on the long-term viral bonding of opsins to muscle tissue—would be needed before any clinical studies on humans. In particular, humans have much thicker bladder walls than rats, so the light-delivery subsystem would have to take that into account.

The research team included representatives from the University of Illinois at Urbana-Champaign, USA, University of Central Florida, USA, Texas A&M University, USA, and Beihang University, China.