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Gold plating and flexible neural electrode solution for brain computer interface
In the development and clinical application of Brain Computer Interface (BCI), engineers face a recurring engineering problem: the signal is clear and distinguishable when the electrode is first implanted, but after weeks or months, the signal amplitude gradually decays, the signal-to-noise ratio continues to deteriorate, and ultimately cannot effectively decode neural information.
The root of the problem lies not in the algorithm or amplifier, but inElectrode tissue interface.
Implantable electrodes immersed in cerebrospinal fluid for a long time face multiple challenges such as electrochemical corrosion, immune response, and mechanical fatigue. Traditional rigid electrodes, due to severe mismatch between their mechanical properties and brain tissue, continue to trigger immune rejection reactions after implantation, forming a fibrous coating around the electrode. Research has shown that traditional stainless steel wire electrodes have a coating thickness of over 451 microns after implantation for 13 months, accompanied by significant cell apoptosis reactions.
�� Core proposition:Brain computer interface electrodes need to strike a delicate balance between flexibility, conductivity, biocompatibility, and long-term stability. Butgilding——Deposition of high-purity gold layer on the surface of flexible polymer substrate is the core process to solve this interface engineering problem.
The long-term implantation of brain computer interface electrodes in the cerebrospinal fluid environment requires almost strict material requirements. Gold (Au) stands out due to its unique physical and chemical properties:
It does not corrode or release toxic ions in physiological environment, and has almost no rejection reaction, meeting the requirement of a lifespan of more than 10 years for implantable devices.
Ensure low loss transmission of brain microvolt level neural electrical signals, exhibiting extremely low and stable impedance characteristics in the frequency range of 10Hz-10kHz.
The Young's modulus is about 100-300GPa, and through structural design, it can be perfectly combined with flexible substrates such as PI, PET, FEP, etc., to alleviate mechanical mismatch.
Conclusion:These intrinsic properties of gold 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. Different substrates have their own emphasis:
Excellent biocompatibility, chemical stability, and mechanical properties. Microstructure PEEK film can achieve directional and ordered arrangement, which is irreplaceable in the design of composite neural electrodes. Advanced Institute Technology provides gold plating processing for PEEK substrates.
Water absorption rate<0.1%, cell survival rate>95%, stiffness only 1/11 of traditional electrodes, can achieve 25 times higher electrode density and 20 times higher channel count. Sputtering palladium seed layer on 25 μ m LCP substrate and then plating about 5 μ m gold.
One of the most widely used flexible substrates, the Advanced Institute Technology PI gold-plated film substrate can be as thin as 5 μ m, and the ultra-thin gold micro electrode array has excellent electrochemical performance (0.73 Ω· cm ²).
Transmittance ≥ 90% has unique value in neural interface scenarios that require optical monitoring.
| 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 1/11 | 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 |
| FEP | Transmittance ≥ 90% | Optical electrical joint neural interface |
Transforming the theoretical advantages of gold plating into reliable electrode products relies on precise control of core processes.
Plasma pretreatment improves the bonding strength between polymer substrates and metal layers; Ion beam assisted deposition forms atomic level bonding between the gold coating and PI, with a 5B level adhesion tested on a hundred grid.
Pulse electroplating technology reduces porosity to<0.5>
Cyanide free gold plating technology reduces environmental pollution, improves operational safety, and meets the requirements of green manufacturing.
The 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 reaches 0.73 Ω· cm ².
Ion beam assisted deposition achieves atomic level bonding, and 5B level adhesion ensures that the coating does not peel off during repeated bending, implantation, and long-term service.
The chemical inertness of gold endows the gold-plated electrode with excellent corrosion resistance, and there is no significant attenuation in cerebrospinal fluid immersion; Combined with PEDOT coating, it can further enhance interface contact and reduce impedance.
The brain computer interface electrode technology is undergoing a paradigm shift from "static" to "dynamic".
Breakthrough by 2025:The team of the Chinese Academy of Sciences reported in the journal NatureNeuroWorm——A flexible and drivable nerve fiber electrode with a diameter of only 196 microns can "wander" within the skull and actively change monitoring targets. After 13 months of implantation, the average thickness of the fibrous coating was less than 23 microns, and the apoptosis rate of surrounding tissue cells was comparable to that of normal tissue.
2026 milestone:Our country's first128 channel fully implantable brain computer interface systemThe multi center clinical trial has officially started (with Beijing Temple of Heaven Hospital as the leading unit and 11 medical institutions participating), and flexible neural electrode technology is accelerating from the laboratory to clinical practice.
Core Insights:In this technological evolution, the gold plating process has always been the core variable that determines the upper limit of electrode performance - whether it is high channel density neural probe arrays or stretchable flexible electrodes, they all rely on precision gold plating technology to provide low impedance, high adhesion, and long-term stable conductive interfaces.
Advanced Institute (Shenzhen) Technology Co., Ltd. (referred to as "Advanced Institute Technology") was established in 2016, headquartered in Bao'an District, Shenzhen. It is a national high-tech enterprise specializing in shielding materials, insulation materials, thermal conductivity materials, and precious metal coatings. The company has independently built a magnetron sputtering and vacuum evaporation production line, using roll to roll continuous production technology, which can achieve precise deposition of metal layers on various flexible film surfaces such as PEEK, PI, PET, LCP, FEP, PPS, etc. The substrate width can reach 350mm, and the ultimate vacuum degree can reach 1 × 10 ⁻⁴ Pa.
The company focuses on metal plating technology and has developed three types of flexible substrate coating solutions: silver plating, gold plating, and platinum plating. In response to the specific requirements of brain computer interface electrodes, Advanced Institute Technology provides the following core capabilities:
Various flexible films such as PEEK, LCP, PI, PET, FEP, etc., with thickness adjustable from a few micrometers to several hundred micrometers.
High purity gold coating, supporting gradient coating design to achieve stress transition, meeting low impedance and high adhesion requirements.
Composite processes such as magnetron sputtering, vacuum evaporation, and pulse electroplating are used to achieve precise coating control.
Plasma pretreatment, ion beam assisted deposition, cyanide free gold plating to ensure 5B level adhesion and porosity<0.5
Coating adhesion level 5B, porosity<0.5>
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 gold plating process transforms these intrinsic properties of gold into reliable electrode performance - low impedance ensures signal quality, high 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 revolution.
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