In the 1980s, the invention of the Utah Array and Michigan Array allowed neuroscientists to record the firing activity of hundreds of neurons simultaneously for the first time. These silicon-based microelectrode arrays perform well in acute experiments with high signal-to-noise ratio and precise spatial resolution.

But when electrodes need to be implanted for a long time, a problem gradually emerges: the signal continues to decay for weeks to months and eventually disappears completely.

Researchers have found that the root of the problem lies not in the electronic design of the electrodes, but in the "mechanical war" between the electrodes and the brain. The Young's modulus of silicon is about 190GPa, while the modulus of brain tissue is only 1-10kPa. This mechanical mismatch of over six orders of magnitude causes micro motion damage to every tiny brain movement - breathing, heartbeat, head rotation - at the electrode tissue interface. Injury triggers an immune response, and astrocytes and microglia form a glial scar wrap 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 μ m. Neurons gradually degrade and die, and signals disappear accordingly.

2、 Cortical microelectrode: definition and classification

Implantable cortical microelectrode array is an invasive neural interface device that directly penetrates the cerebral cortex and implants into neural tissue, capable of recording action potentials (spikes) of single or multiple neurons. According to the different electrode structures, they are mainly divided into the following types:

• Utah Array- Three dimensional silicon-based penetrating microelectrode array, traditional 96 channel, new graded electrodes achieve higher density.
• Michigan ArrayA planar silicon-based probe with multiple recording sites linearly distributed along the probe handle.
• Neuropixels probes- High density silicon-based probe, integrated with 960 recording sites on a single handle.
• Flexible polymer based electrodeUsing flexible materials such as PI, Parylene-C, LCP, PEEK, etc. as substrates, conductive patterns were constructed through advanced microfabrication technology. In a 4-week comparative experiment in the deep brain region of the mouse striatum, more stable signal-to-noise ratio and single unit output were observed.

3、 Why is flexibility: from "hard hitting" to "soft contact"

The rise of flexible neural electrodes stems from a simple physical insight: in order for implants to coexist with the brain for a long time, their mechanical properties need to be matched.

4、 Four major families of flexible substrates

To achieve flexible cortical microelectrodes, substrate selection is the first hurdle. The current mainstream flexible substrates include:

Advanced Institute of Technology:The coating process is suitable for substrates such as PI, Parylene, LCP, PEEK, as well as elastic materials such as PET, FEP, PPS, PDMS, TPU, etc.

5、 Coating: The 'last step' in determining electrode performance

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".

6、 Gold plating vs platinum plating: the selection logic of two core solutions

7、 Advanced Institute Technology's Implantable Cortical Microelectrode Coating Solution

Advanced Institute (Shenzhen) Technology Co., Ltd. was established in 2016, headquartered in Bao'an District, Shenzhen. It has an independently registered trademark "Research Platinum" and has dual production bases in Shenzhen and Dongguan. It has passed ISO9001 quality management system certification. The company focuses on metal plating technology and has developed three types of flexible substrate coating solutions: silver plating, gold plating, and platinum plating.

At the core coating process level, Advanced Institute Technology adopts composite physical vapor deposition (PVD) processes such as magnetron sputtering and vacuum evaporation, which can deposit metal coatings on various flexible polymer film substrates such as PI, PET, FEP, LCP, PEEK, PPS, etc. It can cover a full range of metals including gold, silver, copper, aluminum, tin, nickel, titanium, platinum, etc. The substrate width can reach 350mm, and the ultimate vacuum degree can reach 1 × 10 ⁻⁴ Pa.

8、 From Laboratory to Clinical: Accelerating Industrialization Process

Market data:The global flexible neural electrode market is expected to reach a scale of 480 million US dollars by 2025, a year-on-year increase of 34%; The flexible brain electrode market has become a dual focus of capital and research with a scale of 4.27 billion US dollars and a growth rate of 37.2%.

9、 Conclusion

The essence of implantable cortical microelectrodes is to find an engineering balance between "high-density neural recording" and "long-term biocompatibility". Traditional silicon-based electrodes have traded rigidity for high signal-to-noise ratio and mature MEMS manufacturing processes, but have been losing ground in the face of the softness and dynamics of the brain. Flexible polymer based electrodes take mechanical adaptation as a breakthrough point, using materials such as PI, Parylene, LCP, PEEK to match the softness of brain tissue, and constructing low impedance and high stability conductive interfaces using precision gold/platinum plating processes.

Understanding the material logic of flexibility - why PI instead of silicon, why gold instead of copper, why 5B level adhesion is crucial to the survival of electrodes - is the key to upgrading cortical microelectrodes from "laboratory devices" to "clinical tools". In this paradigm shift from rigidity to flexibility, precision coating technology has always been the core variable determining the upper limit of electrode performance.