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Gold plating of brain computer interface and flexible neural electrode interface scheme
Brain computer interface (BCI) is accelerating from the laboratory to clinical practice. In September 2025, the team of Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, published NeuroWorm results in the journal Nature - a flexible and driveable nerve fiber electrode with a diameter of only 196 microns, which can "wander" in the brain and actively change the monitoring target. On May 18, 2026, China's first multi center clinical trial of a 128 channel fully implantable brain computer interface system was officially launched. It consists of two modules: cortical implantable flexible electrodes and highly integrated fully implantable signal collectors. The flexible electrodes are made of ultra-thin biocompatible materials, which can significantly reduce the immune response after implantation.
But before this, a problem that has plagued the neuroscience community for decades has always existed: after traditional rigid electrodes are implanted in the brain, the signal continues to decay for weeks to months and eventually disappears completely.
The root of the problem lies not in the electronic design of the electrode, but in the electrode tissue interface. The Young's modulus of silicon is about 190GPa, while the modulus of brain tissue is only 1-10kPa - a mechanical mismatch of more than 6 orders of magnitude, causing micro motion damage at the interface for every tiny brain movement. Damage triggers an immune response, and astrocytes and microglia form a fibrous envelope around the electrode, physically isolating the electrode from neurons. After 13 months of implantation of traditional stainless steel wire electrodes, the thickness of the coating exceeded 451 microns and was accompanied by significant cell apoptosis reactions.
Core proposition:The core engineering proposition of brain computer interface electrodes is clear: how to make an "electronic probe" learn to "coexist peacefully" with the soft brain while maintaining high-density neural recording ability?
Gold (Au) has become the core interface material for brain computer interface electrodes due to its unique physical and chemical properties.
There is no corrosion or toxic ion precipitation in the physiological environment, and there is almost no rejection reaction. The design service life requirement is more than 10 years, and the chemical stability of gold ensures that the electrode maintains long-term signal acquisition capability.
Ensure low loss transmission of microvolt level neural electrical signals in the brain. Research in 2025 shows that the electrochemical performance of biocompatible gold transparent µ ECoG arrays is 0.73 Ω· cm ², with a signal-to-noise ratio of 43.28dB. After 50000 bending cycles, the resistance change is only 0.05%.
It can be perfectly combined with flexible polymer substrates such as PI, PEEK, LCP, etc. The Young's modulus is about 100-300GPa, which effectively alleviates mechanical mismatch through flexible substrate structure design.
It is precisely these intrinsic properties of gold that establish its irreplaceable position as the core material of brain computer interface electrodes.
The performance of gold plating on brain computer interfaces depends not only on the gold material itself, but also on the collaborative design between the gold coating and the flexible substrate.
Has demonstrated unique advantages in the field of flexible neural electrodes. PEEK has excellent biocompatibility, chemical stability, and mechanical properties. The microstructured PEEK film can achieve directional and ordered arrangement in the topological structure, and has irreplaceable value in the design of composite neural electrodes. However, PEEK has low surface energy, strong chemical inertness, and a large difference in thermal expansion coefficient compared to metals (PEEK is about 45-55 × 10 ⁻⁶/℃, while gold is about 14 × 10 ⁻⁶/℃), which leads to poor adhesion, easy peeling, and cracking of the gold plating layer.
It is becoming an ideal substrate material for brain computer interface flexible electrodes and implantable neural electrodes. LCP has an extremely low water absorption rate (<0.1%) and can maintain stable electrical performance in humid environments and long-term use. The cytotoxicity test showed that the cell survival rate was>95%. Research has shown that thin film electrode arrays based on LCP substrates can achieve 25 times higher electrode density and 20 times higher channel count, while the stiffness is only 1/11 of traditional clinical electrodes. The LCP based neural electrode array is prepared by sputtering and depositing a palladium seed layer, followed by electroplating a layer of approximately 5 μ m thick gold.
It is one of the most widely used substrates in flexible electrodes. The PI gold-plated film substrate of Advanced Institute Technology can be as thin as 5 μ m. The ultra-thin gold micro electrode array exhibits excellent electrochemical performance of 0.73 Ω· cm ².
| Base material | Key Features | Typical Applications |
|---|---|---|
| PEEK | Excellent biocompatibility, chemical stability, and mechanical properties | Flexible neural electrodes, long-term implantable electrodes |
| LCP | Water absorption rate<0.1%, cell survival rate>95%, stiffness only 1/11 of traditional electrodes | Brain computer interface flexible electrode, high-density neural probe |
| PI | Can be as thin as 5 μ m and processed maturely | Ultra thin flexible neural electrode, cortical electrode |
Flexible substrates provide a "skeleton" for mechanical adaptation, but the collection of neural signals ultimately depends on the conductive layer - the coating process is the key link in transforming flexible polymers from "insulating films" to "functional electrodes". Advanced Institute Technology provides a one-stop coating solution for brain computer interface electrodes from materials to processes, using core processes such as magnetron sputtering, vacuum evaporation, and pulse electroplating as the starting point.
Plasma pretreatment activation improves the bonding strength between the substrate and the metal layer. The gradient coating design achieves stress transition from the substrate to the metal layer, avoiding interface delamination. The adhesion strength of the hundred grid reaches 5B level, and the peel strength is greater than 0.8N/mm.
Pulse electroplating technology effectively reduces the porosity of the coating, improves density and uniformity by precisely controlling the current switching time and frequency.
Adopting cyanide free gold plating technology to reduce environmental pollution while improving operational safety.
Advanced Institute of Technology:The independently built roll to roll vacuum coating production line can achieve continuous deposition of metal layers on flexible polymer film substrates such as PI, PET, FEP, LCP, PEEK, etc. It has the advantages of uniform coating, strong adhesion, and support for large-scale supply. PEEK gold plating film has a measured gold layer purity of ≥ 99.99%, adjustable thickness range of 0.1-5 μ m, uniformity of ± 0.05 μ m, and no blistering or peeling after 48 hours of salt spray.
The precise control of the process directly translates into a leap in electrode performance.
The average impedance of the gold nanosheet modified electrode decreased from 4.5k Ω to 0.85k Ω at 1kHz, a decrease of 81%. The electrochemical performance of the ultra-thin gold micro electrode array is 0.73 Ω· cm ², with a signal-to-noise ratio of 43.28dB.
The ion beam assisted deposition and gradient coating design form an atomic level bond between the gold coating and the substrate, with a 5B level adhesion that ensures repeated bending, implantation, and long-term service without detachment.
The chemical inertness of gold endows it with excellent corrosion resistance. After 13 months of implantation of NeuroWorm fiber electrodes, the average thickness of the fiber coating was less than 23 μ m, and the cell apoptosis rate was comparable to that of normal tissue.
The brain computer interface electrode technology is undergoing a paradigm shift from "static" to "dynamic". Traditional implantable electrodes can only collect signals at fixed positions after implantation, which can result in passive stimulation and even conduction failure in immune responses. NeuroWorm breaks this tradition - it can "wander" in the brain and actively switch monitoring targets.
This paradigm shift places higher demands on electrode materials: electrodes need to have ultra-thin flexibility (to reduce mechanical interference to tissues), high conductivity (to capture high-quality neural signals), and long-term chemical stability (to serve in body fluids for a long time). The gold plating process - from PEEK/LCP substrate selection to plasma pretreatment, from gold layer deposition to pulse electroplating densification - has always been the core variable determining the upper limit of electrode performance.
Advanced Institute of Technology:The product has passed ISO9001 quality management system certification and complies with GJB 773A aerospace related standards and RoHS environmental requirements. The company owns the independently registered trademark "Research Platinum" and has dual production bases in Shenzhen and Dongguan. With precious metal coating and flexible substrate surface modification as the core, it provides a solid technical foundation for the research and industrialization of brain computer interface electrodes.
The essence of gold plating on brain computer interfaces is to establish a stable, low-noise, and biologically friendly signal channel between rigid electronic devices and soft neural tissue. Gold provides a material foundation that is chemically inert, highly conductive, and biocompatible; The precision coating process converts these intrinsic properties of gold into reliable electrode performance - low impedance ensures signal quality, 5B level adhesion ensures long-term reliability, and cyanide free process balances safety and environmental protection.
From PEEK to LCP, from 5 μ m PI film to stretchable elastomers, from static implantation to dynamic "migration" - the technological form of brain computer interface electrodes is constantly evolving, but the position of gold plating as the core interface engineering has remained unchanged. Understanding the material logic of "why gold" and the process logic of "why plating" is a prerequisite for making correct engineering decisions in this technological leap from laboratory to clinical.
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