Liquid Electrodes Morph Into Flexible Wires for Neural Stimulation

Taffy-like “injectrodes” could replace expensive, rigid neural implants

3 min read
Kip Ludwig, a professor of biomedical engineering and neurological surgery at the University of Wisconsin–Madison, holds a syringe with 'injectrodes.'
Kip Ludwig, a professor of biomedical engineering and neurological surgery at the University of Wisconsin–Madison, holds a syringe filled with “injectrodes.”
Photo: Renee Meiller/UW-Madison College of Engineering

Our nervous system is specialized to produce and conduct electrical currents, so it’s no surprise that gentle electric stimulation has healing powers. Neural stimulation—also known as neuromodulation, bioelectronic medicine, or electroceuticals—is currently used to treat pain, epilepsy, and migraines, and is being explored as a way to combat paralysis, inflammation, and even hair loss. Muscle stimulation can also bestow superhuman reflexes and improve short-term memory.

But to reach critical areas of the body, such as the brain or the spine, many treatments require surgically implanted devices, such as a cuff that wraps around the spinal cord. Implanting such a device can involve cutting through muscle and nerves (and may require changing a battery every few years).

Now, a team of biomedical engineers has created a type of electrode that can be injected into the body as a liquid, then harden into a stretchy, taffy-like substance. In a paper in the journal Advanced Healthcare Materials, the multi-institutional team used their “injectrodes” to stimulate the nervous systems of rats and pigs, with comparable results to existing implant technologies.

“Instead of cutting down to a nerve, we can just visualize it under ultrasound, inject this around it, and then extrude back a wire to the surface,” says study author Kip Ludwig, a professor of biomedical engineering and neurological surgery at the University of Wisconsin–Madison. That process creates a bypass between the surface of the skin and the deep nerve one wants to stimulate, without damaging tissue in between, he adds.

Researchers have created numerous flexible or stretchy electrodes to mold to the shape of, say, brain tissue, but this technology can be injected into the body and fill in cracks and crevices around nerves.

Working with Andrew Shoffstall at Case Western Reserve University and Manfred Franke of Neuronoff Inc., a California-based biotech company, Ludwig and colleagues developed an electrode consisting of bits of metal and a silicon base—similar to surgical glue—that combine to form a thick liquid. This liquid can be put into a syringe and injected into the space around a nerve, where it hardens into a solid form, with a consistency similar to taffy.

This taffy-like wire is conductive, can move and bend with the nerve or joint, and can be activated to stimulate the nerve with an inexpensive external unit—a transcutaneous electrical nerve stimulation, or TENS, unit—which anyone can buy at a pharmacy or online.

To test their new creation, the researchers injected the material into rats and pigs, and compared the performance to that of silver wires and a clinical electrode implant. The injectrodes worked just as well as both other tools, and even appeared to require a lower current for the same amount of neural activity. It is also possible to tailor the viscosity, or thickness, of the liquid electrodes for different applications, says Ludwig.

Diagram explaning 'injectrodes.' This illustration shows how an “injectrode” consisting of a silicon base (1) and bits of metal (2) can be injected into the body as a liquid and then harden around a nerve to enable electrical stimulation. Illustration: Neuronoff

Still, to remove the wire, one would have to “go in and get it,” says Ludwig—meaning surgically remove it like any other electrical lead. Currently, his team is testing the safety and efficacy of the injectrodes over long periods of time and testing the possibility of having robots inject the material. Ludwig hopes to apply to the FDA and begin safety testing in humans in two years.

Ludwig and his collaborators co-founded Neuronoff to commercialize the technology. The team also recently received a US $2.1 million grant from the National Institutes of Health to test the injectrodes as an alternative to opioids for treating chronic back pain.

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This CAD Program Can Design New Organisms

Genetic engineers have a powerful new tool to write and edit DNA code

11 min read
A photo showing machinery in a lab

Foundries such as the Edinburgh Genome Foundry assemble fragments of synthetic DNA and send them to labs for testing in cells.

Edinburgh Genome Foundry, University of Edinburgh

In the next decade, medical science may finally advance cures for some of the most complex diseases that plague humanity. Many diseases are caused by mutations in the human genome, which can either be inherited from our parents (such as in cystic fibrosis), or acquired during life, such as most types of cancer. For some of these conditions, medical researchers have identified the exact mutations that lead to disease; but in many more, they're still seeking answers. And without understanding the cause of a problem, it's pretty tough to find a cure.

We believe that a key enabling technology in this quest is a computer-aided design (CAD) program for genome editing, which our organization is launching this week at the Genome Project-write (GP-write) conference.

With this CAD program, medical researchers will be able to quickly design hundreds of different genomes with any combination of mutations and send the genetic code to a company that manufactures strings of DNA. Those fragments of synthesized DNA can then be sent to a foundry for assembly, and finally to a lab where the designed genomes can be tested in cells. Based on how the cells grow, researchers can use the CAD program to iterate with a new batch of redesigned genomes, sharing data for collaborative efforts. Enabling fast redesign of thousands of variants can only be achieved through automation; at that scale, researchers just might identify the combinations of mutations that are causing genetic diseases. This is the first critical R&D step toward finding cures.

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