Elastic spinal sensor: New hydrogel technology can change nerve monitoring

Scientists have developed a flexible conductive hydrogel that could greatly improve researchers’ monitoring of spinal cord activity during exercise, potentially changing future spinal injury research and treatments.

The research team, led by Siyuan Rao, assistant professor at the Thomas J. Watson School of Engineering and Applied Sciences at Binghamton University, created a novel electrode design that addresses a key challenge in neural interfaces: maintaining electrical connections while accommodating the natural movement of tissue.

The new approach creates a motor adaptive soft neural interface that minimizes tissue damage during animal movement while still capturing high-quality physiological signals. As Rao explained in the press release: “If you have rigid materials in your soft tissue, especially during movement, it will cause a lot of damage. Our technology solves this fundamental problem, so we can get the activity of a single unit from the spinal cord and keep the device functional for a long time.”

What the researchers call train technology (tension enhancement in the anisotropic nanodirection) uses carbon nanotubes embedded in polyvinyl alcohol hydrogels. These microcarbon structures form conductive pathways in the gel, allowing neural signals to propagate while maintaining the flexibility of the material.

The difference between this approach is how the team manipulates the internal structure of the material. By repeatedly stretching the hydrogels in a specific direction, they cause embedded carbon nanotubes to be self-align, resulting in directional conductivity, such as training muscle fibers to enhance in a specific direction.

The cyclic stretching process systematically readjusts the nanotubes along the stretching direction. This creates a preferred circuit, thereby improving conductivity precisely in the desired direction while the material remains soft and compatible.

In laboratory tests, the hydrogel electrodes exhibited significant durability, although stretching up to 20,000 stretch cycles under 20% of the strains – sure to simulate repeated exercise tissues that may be experienced during daily activities. When implanted in mice, the electrode successfully recorded muscle activity and spinal neuron signals over a prolonged period.

A notable achievement is the function of the electrodes eight months after ventral spinal cord implantation in mice – a significant improvement to conventional techniques, which often fail due to mechanical stress or tissue repulsion.

The researchers were able to record individual neuronal activity deep in the spinal cord over this extended timeframe. This is especially valuable because it is extremely challenging to use traditional surface electrodes to access these deeper ventral structures that control motor functions.

The composition of the hydrogel is similar to a specialized sponge that contains water, and almost invisible carbon nanotubes are distributed in its three-dimensional network. As Huang described: “You can imagine it being a sponge with a lot of water and conductive material, which are nano-carbon tubes that are invisible to the naked eye because they are small.”

The structure closely mimics the mechanical properties of the actual neural tissue, with an elasticity of about 16 MPa, which is softer than conventional metal or silicon electrodes.

Importantly, there was no significant difference in the motion patterns of mice implanted with electrodes compared to control animals, suggesting that the technique integrates well with natural biological functions.

This study is based on an increasing interest in “soft electronics” in biomedical applications where traditional rigid materials often trigger inflammation, scars and signals over time – problems that limit the long-term viability of neural interfaces.

The team used advanced imaging techniques to verify the alignment of carbon nanotubes in hydrogels. Using stimulated Raman scattering microscopes, they can directly visualize how carbon nanotubes recombinate carbon nanotubes after the stretching process, confirming their hypothesis about the mechanisms behind improving directional conductivity.

These implications go beyond basic research tools. Although this clinical application will require years of additional development and safety testing, similar hydrogel techniques can eventually be adapted to therapeutic applications in humans with spinal cord injury or neurological disease.

Rao’s team is now focused on augmenting the capabilities of the technology. They are particularly interested in combining it with optogenetic approaches that may inhibit pain signals or stimulate recovery of motor function. As Rao points out, “We especially want to look at the ventral horn motor neurons that control voluntary movement.”

This study reflects the growth of trends in interdisciplinary collaboration in neurotechnology, from contributors to multiple institutions including the University of Massachusetts, the University of Texas, Michigan State University, MIT and Boston Children’s Hospital.

For Huang (Huang), who oversees several students during the project, the study provides valuable leadership experience. “Just like we were in the car,” he said. “I was in the driver’s seat, and all the masters’ students were my passengers – but they weren’t just sitting in the car. They also contributed, like one of them, please note that the map tells me the instructions, or I tell them the instructions. That’s how we work.”

As neural interface technology continues to advance, this hydrogel approach represents a promising direction for establishing a lasting connection between electronic devices and living tissue, one of the most enduring challenges in bioelectronics.

The spinal cord undergoes complex mechanical dynamics during natural movement. The new technology adapts to these conditions rather than fighting them, which explains how researchers can maintain stable recordings over such a long period of time.