Zhiran Medical's Stretchable Neural Electrode Breakthrough Solves Chronic Signal Dropout in Invasive Brain-Computer Interfaces

Reprinted from: China Science Daily

Invasive brain-computer interface technology is widely recognized as the optimal solution for high-bandwidth human-machine interaction. However, core bottlenecks hindering its long-term stable application include the propensity of flexible electrodes to shift or dislodge within the brain. Encouragingly, a breakthrough by a Chinese research team holds promise for overcoming these challenges.

Recently, the international academic journal Nature Electronics published the latest advances made by the team of Fang Ying, a senior investigator at the Beijing Institute for Brain Disorders and Brain-like Intelligence and the founder and chief scientist of “Zhiran Medical.” Addressing issues such as the easy displacement and dislodgement of flexible electrodes during dynamic brain activity, the team successfully developed a stretchable flexible electrode that combines high-throughput signal acquisition with biomechanical compliance, providing a solution to enhance the long-term stability of invasive brain–computer interface technology.

Common Challenges of Invasive Brain-Computer Interfaces

Neuralink, founded by Elon Musk, is a pioneer in the field of invasive brain-computer interfaces. In early 2024, Neuralink completed the world’s first human implantation of a 1,024-channel invasive brain-computer interface, generating significant public attention. However, few have noted that in the aftermath of this sensational news, the “Neuralink electrode retraction incident” has cast a shadow over this groundbreaking achievement.

According to foreign media reports, just weeks after Neuralink Corp. completed the aforementioned invasive brain-computer interface (BCI) implantation surgery in a human patient, up to 85% of the flexible electrode wires detached from the patient’s brain tissue, sparking deep concerns within the industry regarding the long-term stability of invasive BCI technology. The Wall Street Journal reported: “Although Elon Musk’s company staged a successful demonstration with the patient, the volume of data collected by the device has declined.”

Why Do Neuralink-Implanted Electrodes Detach in Large Numbers? Fang Ying told China Science Daily that this is actually a common challenge for invasive brain-computer interfaces: the linear structural design of traditional flexible electrodes cannot achieve effective mechanical tensile deformation.

“Our brains are not static; they pulsate rhythmically with respiration and heartbeats. During physical movement, the soft brain tissue undergoes displacement and deformation within the cranial cavity,” Fang Ying explained to reporters. In the face of such dynamic brain motion, traditional linear electrodes cannot conform in real time to changes in brain tissue, making them prone to displacement or even dislodgement from the brain tissue.

Fang Ying stated that electrode displacement or even dislodgement not only directly reduces the quantity and decoding accuracy of acquired neural signals but may also trigger inflammatory responses in brain tissue. Therefore, novel flexible electrode technology capable of adapting to dynamic brain movements and achieving long-term stable neural signal acquisition represents a “critical technical challenge urgently requiring breakthrough” for the clinical application of invasive brain-computer interface technology.

Novel Electrodes Can Unfold in the Brain “Like Cut Paper Window Decorations”

Fang Ying has dedicated many years to the field of flexible high-throughput electrodes. More than a decade ago, Fang Ying’s team was the first internationally to demonstrate that invasive flexible electrodes could achieve long-term, high-fidelity neuronal signal acquisition in rodents. However, she clearly recognizes that the ultimate end-users of invasive brain-computer interfaces are humans, and that the physiological pulsations and intracranial displacement amplitudes in the brains of primates (including macaques and humans) are significantly greater than those in rodents.

“Such a magnitude of difference means that achieving long-term stable interaction in the primate brain remains the most challenging scientific problem in the current field of brain-computer interfaces,” said Fang Ying.

In the subsequent research and development process, the team innovatively proposed and designed the “stretchable flexible electrode” architecture.

Fang Ying explained to China Science Daily that traditional linear electrodes rely solely on the tensile deformation of the bulk material when subjected to force, making them highly prone to reaching their strain limits. In contrast, stretchable electrodes employ strain decoupling to convert tensile loads into bending and torsional deformations. Specifically, the team utilized precision micro-nano fabrication techniques to first fabricate the electrodes into two-dimensional spiral arrays. Upon implantation into the brain, the electrodes unfold smoothly under the influence of the cerebrospinal fluid environment, akin to unfurling paper-cut decorations, thereby transitioning from a two-dimensional (2D) planar configuration to a three-dimensional (3D) helical structure to accommodate cerebral pulsations.

Fang Ying explained to reporters that this design leverages the extremely low bending stiffness of thin-film structures in flexible electronics, directing tensile stress into instability deformations with low energy barriers. Thanks to this approach, the electrodes can dynamically conform to brain pulsations and intracranial displacements after implantation, ensuring long-term stability within brain tissue.

“This stretchable electrode is also softer within the brain than traditional linear electrodes,” emphasized Researcher Fang Ying. “Neuralink’s linear electrode requires a force of 4 millinewtons (mN) to stretch by 100 micrometers, whereas this stretchable electrode requires only 37 micronewtons (μN)—just 1/100th of the former.”

Meanwhile, this extreme flexibility also implies reduced mechanical damage to brain tissue, thereby fundamentally avoiding immune responses and glial scarring associated with linear flexible electrodes—wherein glial scarring leads to a decrease in neuronal density around the electrode, ultimately resulting in loss of signal acquisition capability.

Preliminary Validation in Primate Brains

To verify the implantation reliability and long-term stability of stretchable flexible electrodes, the research team conducted systematic validation using macaques as experimental subjects. After more than eight months of experimentation, the results demonstrated that the stretchable flexible electrodes could achieve stable long-term recording in the macaque brain, with no significant reduction in the number of detectable neurons.

Even more encouragingly, after implanting the 256-channel electrode in macaques, the research team successfully recorded signals from 257 single neurons. The neuron yield (the efficiency of capturing valid neuronal signals per channel) exceeded 100%, enabling high-precision decoding of motor intentions in the brain.

“A neuronal yield exceeding 100% holds milestone significance for the clinical translation of invasive brain-computer interface (BCI) technology,” Fang Ying told China Science Daily. Effective acquisition of neuronal signals is a prerequisite for precise decoding, and the quantity of acquired signals directly determines the decoding accuracy of BCI technology, thereby influencing the core efficacy of brain-computer interaction.

To further validate the large-scale signal acquisition capability of this electrode architecture, the team successfully implanted a 1,024-channel high-density stretchable flexible electrode into the primate brain. This scale matches Neuralink’s core specifications, and large-scale, high-quality neuronal signals were successfully recorded. This once again confirms the superior performance of stretchable flexible electrodes.

According to Fang Ying, leveraging the team’s accumulated expertise in related technologies, they have successfully developed a high-throughput wireless invasive brain-computer interface (BCI) system based on stretchable flexible electrodes. By optimizing the biocompatibility of the BCI system and the bandwidth of signal transmission, this system effectively enhances long-term signal stability and decoding accuracy, thereby laying the technical foundation for the large-scale clinical application of invasive BCI products.

“With steady progress in technological iteration and clinical implementation, China is poised to secure a core voice in the global invasive brain-computer interface race.” Fang Ying expressed strong confidence in the future development of related technologies.