Advancements in Electrode Materials for Brain‑Computer Interface

Technology

Shuyue Xue

Bioengineering, School of International Education, Beijing University of Chemical and Technology, Beijing, China

Keywords: Brain‑Computer Interface (BCI), Electrode Materials, Biocompatibility.

Abstract: BCI technology become highly focus with the delevopment of neuroscience. It uses biology signal in brain to

cure diseases. Despite of the input scale, the electrode material has been divided into non-invasive electrodes,

semi-invasive electrodes and invasive electrodes. Non-invasive electrodes is safe but weak in spatio-temporal

resolution; Semi-invasive electrodes are implant by injection using special rheoligical preperties; Invasive

electrodes can ensure the strength and the quality of EEG signals but the surgery is risky. People still find it

hard to deal with the biocompability problems. This paper talking about three kinds of electrodes, their

features, the materials they’re using and the reason. Due to these information BCI materials is widely use in

the field of medical and aerospace. They start the discussion on optimizing material formulations and

manufacturing processes, improving material multifunctionality, solving material degradation and infection

problems, and developing materials integrated with energy harvesting and storage functions. This paper aims

to give a general and specific view of the materials BCI electrodes are using, and inspire people to dig out

other complex and useful materials in the future.

1 INTRODUCTION

Nowadays, with the development of high-standard

technology, people pay attention not only to building

up intelligent machines but to using technology to

feedback on the human body. As the action center of

the human body, the study of the brain has become

famous.

BCI (Brain computer input) is a field major in

using electrical devices to detect brain signals, which

aims to treat pathological symptoms by interfering

with brain behavior using bio-electrical signals, how

to create a safe and sufficient material to avoid harm

to the brain and the decreases of the number of active

electrodes checkpoints caused by BCI implant and

develop signal strength at the same time have become

a focus. Multiple implant material choices are

available, including non-intrusive dry electrodes, wet

electrodes, and semi-dry electrodes. The dry

electrode is more efficient than the wet electrode and

has more flexible changes in materials. However, it

results in a relatively high skin contact impedance.

Wet electrode has good signal quality and is not

sensitive to motion artifacts. However, the

preparation before use is cumbersome, there are

health risks and it is prone to short circuits. Semi-dry

electrodes combine the advantages of wet and dry

electrodes. However, there are problems such as

complex molding and large volume. Each electrode

has its advantages, but none of them have a relatively

comprehensive performance.

Scientists have studied finding new materials and

have some experimental products. Truly effective and

scalable electrodes have yet to be developed. The

biocompatibility may become an evaluation standard

when discussing the electrode, and new electrode

ingredients are needed to raise the biocompatibility

scales. This article aims to discuss the advantages and

disadvantages of different types of electrodes, and

further summarize the current application status,

problems, and optimization directions of these

electrodes, to put forward feasible optimization

suggestions for the future development of BCI

electrodes.

2 DIFFERENT TYPES OF

ELECTRICAL MATERIALS

BCI electrodes work inside the brain, and others work

for physical things. That’s why it’s necessary to put a

Xue, S.

Advancements in Electrode Materials for Brain-Computer Interface Technology.

DOI: 10.5220/0014399100004933

Paper published under CC license (CC BY-NC-ND 4.0)

In Proceedings of the 1st International Conference on Biomedical Engineering and Food Science (BEFS 2025), pages 53-57

ISBN: 978-989-758-789-4

strong cut-off between them. Normal electrodes

develop to face increasing facility needs. To

strengthen the transmission efficiency, high elastic

modulus, and high density are needed, and they will

ignore the low bio-compatibility in some cases, for

they only need to make sure people won’t be harmed

by touching them by hand. But BCI electrodes are

different. As a natural part of human beings, the brain

is born wildly and surely will resist things outside.

What’s even worse is that the electrode is made of

conductive material which is a build-up of ingredients

with a large difference compared with the brain.

That’s why the BCI electrode with low elastic

modulus, high porosity wet softness, and good bio-

compatibility is needed (He, et al.,2020). This paper

will focus on this in further detail by dividing the

types of electrodes by the scale of input.

In conclusion, as the degree of implantation

increases, the collected signals become more precise.

As the degree of implantation decreases,

biocompatibility is becoming better and safer, and the

rejection reaction is weaker. The degrees of

implantation ranging from low to high are classified

as non-intrusive electrodes, semi-invasive electrodes,

and invasive electrodes.

2.1 Non-Intrusive Electrodes

They have low risk and high safety, with good

biocompatibility, wearability, and low energy

consumption. And they are developing towards being

more flexible, compact, lightweight and comfortable.

However, they are weak in spatio-temporal

resolution, wake-up response sensitivity, stability and

anti-interference ability. Due to the distance of signal

selecting, they have poor and unstable signal quality.

Non-implantable electrodes are mainly used for

signal acquisition on the skin surface. The flexibility,

conductivity, and biocompatibility of the materials

are crucial. Polymer materials such as polyimide and

polyurethane have low stiffness and can conform well

to the skin, increasing the contact area with the skin,

reducing contact resistance, and minimizing motion

artifacts. Carbon-based materials, such as carbon

nanotubes and graphene, not only have excellent

electrical conductivity, which can efficiently conduct

bioelectrical signals, but also possess good flexibility

and chemical stability, contributing to the

improvement of electrode performance.

Nanomaterials like nanocellulose, with their

abundant sources, low cost, high biocompatibility,

and unique micro-structures, also play an important

role in non-implantable electrode materials. They can

endow the electrodes with good mechanical

properties and biocompatibility, enabling non-

implantable electrodes to meet the comfort

requirements for long-term wearing while ensuring

the quality of signal acquisition (He et al., 2020)

2.2 Dry Electrode

Dry electrode includes mems electrodes, non-contact

electrodes and ordinary contact electrodes. Dry

electrodes using dry electrode microneedles pierce

the stratum corneum. The signal quality is high but

there is discomfort and infection risk. Non-contact

electrodes collect signals from a distance. They are

lightweight but easily affected by motion artifacts.

Ordinary contact dry electrodes directly contact the

scalp. They have diverse structures and adapt to the

contact between hair and scalp through special

designs (Yuan et al., 2021).

2.3 Wet Electrodes

Conductive paste is needed to reduce impedance. It

has good signal quality and is insensitive to motion

artifacts. However, the preparation before use is

cumbersome, may cause skin discomfort, there is a

risk of short circuit, and the gel will affect stability

(Kim et al., 2017).

2.4 Semi-Dry Electrode

Combining the characteristics of wet and dry

electrodes, it contains electrolytes and releases them

during use. This avoids the problems of high

impedance of dry electrodes and cumbersome

preparation of wet electrodes. However, it has

shortcomings such as complex molding and large

volume. It is a current research hotspot and has

development potential (Bates, 2017).

2.5 Semi-Invasive Electrodes

Semi-invasive electrodes using injection to implant

electrodes to reduce patient pain and avoid acute

immune response during implantation. Compared

with traditional invasive surgery, this minimally

invasive operation can accurately position the

electrode in a specific brain region with minimal

damage to surrounding tissues. They can improve the

strength and quality of electroencephalogram (EEG)

signals. However, some accidents still may happen.

Like the material does not move smoothly in the

BEFS 2025 - International Conference on Biomedical Engineering and Food Science

needle tube and is prone to folding or tangling; Or

Local bursting may occur during injection.

The materials for semi-implantable electrodes

need to balance injectability and biocompatibility (Li,

et al., 2018). Hydrogel-based materials are widely

used due to their unique rheological properties. Under

external stimuli, hydrogels can undergo a state

transition, changing from a sol state that is easy to

inject to a stable gel state, enabling precise injection

into specific brain regions. Their three-dimensional

porous network structures are not only conducive to

the exchange of nutrients to maintain cell viability but

also provide abundant sites for cell adhesion. They

mimic the extracellular matrix environment, which

can induce the growth of neurons and their synapses

towards the electrode sites and achieve close binding,

effectively reducing the rejection reaction and

ensuring the long-term stable operation of the

electrodes in the brain environment.

2.6 Invasive Electrodes

Invasive electrodes can ensure the strength and

quality of EEG signals with high spatial resolution,

high signal-to-noise ratio and wide frequency range.

They are able to be used for a long time and are less

affected by motion artifacts and external noise. They

are the most risky experiment (Shen, et al., 2021).

Surgical procedures are expensive and cumbersome

and safety remains a major issue. They meet

difficulties in electrode size design, which may

compress nerves or lead to high impedance. They

may also cause immune response problems.

Implantable electrodes need to be directly

implanted into the brain, so the materials are required

to have excellent biocompatibility, mechanical

properties, and stability. Natural biomaterials, for

example, have elastic and shear moduli similar to

those of brain tissue, which can effectively reduce

mechanical damage to the brain, as if they are tailor-

made for the brain. Their porous structures are

beneficial for cell adhesion and growth. It's like

providing a suitable habitat for neurons, promoting

the integration of the electrodes with nerve tissues

and reducing the risk of immune reactions.

Meanwhile, some smart materials such as shape-

memory polymers possess unique shape-memory

effects and variable modulus properties. During the

implantation process, they can change their shapes

under external stimuli for easy implantation. After

implantation, they can return to their preset shapes

and closely adhere to the brain tissue, providing a

guarantee for long-term and stable signal acquisition

and stimulation.

3 APPLICATIONS

BCI, as the name goes, is a technology that works on

the brain and aim to cure brain diseases. So it mainly

focuses on medical area. It builds up a new

connection between brain and the machine through

detecting brain signals. In this way, it helps people

with physical disability. Like the paralyzed young

man who wore an exoskeleton using BCI technology

to detect active signals in brain and kick the football

without an external order successfully in 2014 (Chih,

et al., 2010).

Non-invasive electrode is used for preliminary

EEG signal monitoring, such as the initial diagnosis

of epilepsy. Its high safety, without the need for brain

implantation, reduces the risk of infection and other

hazards, making it suitable for frequent use in daily

medical scenarios and highly acceptable to patients.

Semi-invasive electrode is used for in-depth

research on brain nerve activities, such as exploring

the signal transmission mechanism between neurons.

Semi-invasive electrodes can accurately locate

specific brain regions to obtain high-quality nerve

signals. At the same time, it avoids the significant

damage and immune responses that invasive

electrodes may cause, providing a more reliable

research tool for researchers.

It also plays a role in the treatment of some nervous

system diseases, such as deep-brain stimulation

treatment for Parkinson's disease. It can accurately

place the electrodes in the target brain region, provide

more precise stimulation, and reduce the impact on

surrounding normal tissues, improving the treatment

effect and reducing side effects.

Invasive electrode is suitable for the treatment of

severe nervous system diseases, such as the

restoration of motor function in paralyzed patients

(Spüler, 2017). Invasive electrodes can directly

obtain deep-brain nerve signals, with high signal

quality and stability. They provide more precise

movement control signals for paralyzed patients,

helping them regain some motor abilities.

In some high-end brain-computer interface (BCI)

experiments and applications, such as developing

prosthetics capable of complex motion control.

Invasive electrodes can provide richer and more

accurate nerve signals, enabling prosthetics to more

precisely simulate natural human movements and

improving patients' quality of life.

Advancements in Electrode Materials for Brain-Computer Interface Technology

Moreover, the skills of detecting brain technology

not only work on medical field. It can also work in the

place that is not suit to use normal connecting

method, like in the aerospace industry. BCI can both

work on helping astronauts to finish complex task and

monitoring their mental health (Gianluca et al., 2019)

4 DISCUSSION

In the realm of BCIs, the selection of materials holds

utmost importance in dictating the performance of

electrodes. Currently, although a variety of electrode

materials exist, each with its own set of advantages

and drawbacks, continuous research efforts are

driving the evolution of BCI material precursors

towards enhancing biocompatibility, optimizing

signal acquisition and transmission capabilities, and

augmenting material multifunctionality.

Biomimetic materials, such as hydrogels, have

shown great potential in the BCI field. Their three-

dimensional porous network structures and

hydrateGd environments similar to the extracellular

matrix contribute to promoting neuron growth and

reducing rejection responses. In the future,

researchers will focus on refining the formulation and

fabrication processes of biomimetic materials. By

modifying natural biomaterials, they aim to replicate

the extracellular matrix's physical structure more

accurately and endow the materials with more precise

biological activity-regulating functions. For example,

the introduction of specific bioactive molecules like

nerve growth factors and cell adhesion peptides into

hydrogels can guide the oriented growth and

differentiation of neurons, strengthening the

integration between electrodes and nerve tissues and

further enhancing biocompatibility.

Intelligent biomaterials, like shape-memory

polymers, can change their shapes and moduli in

response to external stimuli, meeting the diverse

needs of BCI electrodes during implantation and

operation. Future developments in this area will likely

lead to materials with faster response times and more

diverse response mechanisms. Scientists may create

materials that respond simultaneously to multiple

stimuli, such as temperature, electric fields, and

magnetic fields. This multi-responsiveness will

enable precise control of electrode performance. For

instance, during implantation, an external magnetic

field can soften the material for easy insertion into

specific brain regions, and a subsequent temperature

change can restore it to its original rigid state,

ensuring close contact with brain tissues and stable

signal acquisition.

Carbon-based materials, including carbon

nanotubes and graphene, have excellent electrical

conductivity, flexibility, and chemical stability, and

are already used in BCI electrodes (Li et al., 2023). In

the future, these materials will see innovations in

preparation techniques and structural designs.

Advanced nanomanufacturing technologies will be

employed to create carbon-based materials with

tailored morphologies and structures. For example,

graphene materials with hierarchical porous

structures can increase the specific surface area,

improving signal acquisition efficiency, while also

enhancing flexibility and breathability to minimize

adverse effects on the skin or brain tissues.

Researchers will also explore new ways to combine

carbon-based materials with other substances, such as

polymers and biomaterials, to enhance their overall

performance synergistically.

With the progress of quantum technology,

quantum materials are emerging as potential new

precursors for BCI electrodes. Quantum materials

possess unique quantum properties, such as the

quantum tunneling effect and the quantum Hall

effect, which hold great promise for significantly

improving electrode signal transmission speed and

sensitivity. Quantum dot materials, capable of single-

photon-level signal detection, can be used in BCIs to

precisely capture subtle electrical signal changes in

the brain. Although the application of quantum

materials in the BCI field is currently in its early

stages, continued research is expected to bring

revolutionary advancements to BCI technology.

Material degradation and infection are common

issues during the use of BCI electrodes. Future BCI

materials are expected to integrate self-healing and

antibacterial functions. By incorporating self-healing

groups, like polymers with disulfide bonds, and

antibacterial components, such as metal

nanoparticles, these materials can repair themselves

when damaged. The disulfide bonds can reform under

certain conditions, restoring the material's integrity,

and the metal nanoparticles can inhibit bacterial

growth, reducing the risk of infection. This dual-

function design will extend the electrode lifespan and

enhance the reliability of BCI systems (Lin, et al.,

2023).

To ensure the long-term stable operation of BCI

devices and reduce their dependence on external

power sources, integrated materials for energy

harvesting and storage will be a research focus.

Scientists may develop BCI electrode materials based

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on thermoelectric materials and supercapacitors.

These materials can convert the body's heat energy

into electrical energy and store it. For example,

thermoelectric coatings on the material surface can

utilize the temperature difference between the body

and the environment to generate electricity, which is

then stored in built-in supercapacitors. This energy-

self-sufficient design will improve the portability and

practicality of BCI devices, making them more

suitable for various applications.

5 CONCLUSION

In conclusion, the field of BCI electrodes is at a

crucial juncture of development. Currently available

non-intrusive, semi-invasive, and invasive electrodes

all have their own sets of advantages and

disadvantages, and no single type can fully meet all

requirements. Non-intrusive electrodes offer safety

and comfort but suffer from poor signal quality; semi-

invasive electrodes balance signal quality and safety

to some extent but face challenges like material

injection issues; invasive electrodes provide high-

quality signals but carry significant risks. Continuous

research is promoting BCI material precursors in the

direction of enhancing biocompatibility, optimizing

signal acquisition and transmission capabilities, and

increasing material versatility.

Looking ahead, future research should focus on

several key aspects. Biomimetic materials, such as

hydrogels, can be further optimized to better mimic

the extracellular matrix and precisely regulate

biological activity, thus enhancing biocompatibility.

Intelligent biomaterials like shape-memory polymers

hold promise for achieving more precise control of

electrode performance through multi-responsive

capabilities. Carbon-based materials are expected to

see breakthroughs in preparation techniques and

structural designs to improve signal acquisition

efficiency and reduce adverse effects. Quantum

materials, despite being in the early stage of

application, may revolutionize BCI technology with

their unique quantum properties. Additionally,

developing materials with integrated self-healing and

antibacterial functions, as well as those for energy

harvesting and storage, will be essential for

enhancing the reliability and portability of BCI

systems. By addressing these aspects, people can

expect to overcome the current limitations of BCI

electrodes and bring about more efficient, safe, and

user-friendly BCI technologies, which will not only

benefit patients with neurological disorders but also

find wider applications in various fields such as

aerospace and entertainment.

REFERENCES

Bates, M. From brain to body: New technologies improve

paralyzed patients’ quality of life. IEEE Pulse.

Chang, C.-W., Ko, L., Lin, F., Su, T., & Jung, T.

Drowsiness monitoring with EEG-based MEMS

biosensing technologies. Geropsych: The Journal of

Gerontopsychology and Geriatric Psychiatry.

Di Flumeri, G., Aricò, P., Borghini, G., Sciaraffa, N., & Di

Florio, A. The dry revolution: Evaluation of three

different EEG dry electrode types in terms of signal

spectral features, mental states classification and

usability. Sensors (Basel, Switzerland), 19(6), 1513.

He, G., Dong, X., & Qi, M. From the perspective of material

science: A review of flexible electrodes for brain-

computer interface. Materials Research Express, 7(10),

102001.

Kim, D.-H., & Kim, H. W. Materials for flexible and

implantable bioelectronics. Materials Today, 20(3),

126–141.

Li, J., Cheng, Y., Gu, M., Yang, Z., Zhan, L., & Du, Z.

Sensing and stimulation applications of carbon

nanomaterials in implantable brain-computer interface.

International Journal of Molecular Sciences, 24(6),

5182.

Li, Y. H., Li, W. G., Ding, B., Wu, D. W., Liu, Z. X., He,

I., Zhou, W., & Xu, Z. National report on space

medicine progress. Chinese Journal of Space Science.

Sheng, X. J., Qin, Z., Xu, H. P., Shu, X. K., & Guo, Y. Soft

ionic-hydrogel electrodes for electroencephalography

signal recording. Science China: Technological

Sciences (English Edition), 2.

Spüler, M. A high-speed brain-computer interface (BCI)

using dry EEG electrodes. PLoS ONE, 12(2),

e0172400.

Yuan, H., Li, Y., Yang, J., Li, H., Yang, Q., Guo, C., Zhu,

S. M., & Shu, X. State of the art of non-invasive

electrode materials for brain-computer interface.

Micromachines (Basel), 12(12), 1521.

Advancements in Electrode Materials for Brain-Computer Interface Technology