Concentric annulus microneedle electrode and preparation method thereof

Abstract

The invention provides a concentric annulus microneedle electrode and a preparation method thereof, and the electrode comprises: a base layer having a concentric annulus structure; the microneedles are positioned above the base layer and are arranged on each stage of circular ring of the concentric circular ring structure; the microneedle side conducting layer is located above the microneedles, and the microneedle side conducting layer is used for converting the bioelectric current into electronic current; the non-microneedle-side conductive layer is located below the base layer and connected with the microneedle-side conductive layer on the side face of the base layer, and the non-microneedle-side conductive layer is used for forming conductive connection and connected with an external wire; the modification layer is located above the microneedle side conducting layer, and the modification layer is used for making contact with the skin and reducing the skin-electrode contact impedance of the conducting layer. The electrode provided by the invention is used for collecting electroencephalogram signals and Laplacian electroencephalogram signals, has the characteristics of low skin-electrode contact impedance, high signal-to-noise ratio of collected signals and high signal space precision, does not need to use conductive paste, and can realize long-term high-quality signal collection.

Description

Technical Field

[0001] The present invention relates to the technical field of brain-computer interface, and in particular to a concentric circular microneedle electrode and a preparation method thereof. Background Art

[0002] As a wearable brain-computer interface technology, electroencephalogram (EEG) plays an important role in the diagnosis and treatment of brain-related diseases and mental illnesses. At present, the wet electrode acquisition scheme using silver / silver chloride electrodes and conductive paste is considered to be the "gold standard" for EEG acquisition electrodes. However, wet electrodes are troublesome to wear and need to be cleaned after use. At the same time, due to the rapid drying of the conductive paste, it cannot achieve the goal of long-term portable acquisition. In addition, the spatial accuracy of EEG signals is low due to the volume conduction effect during the transmission process; the EEG signals at the measurement site are often the superposition of many sources. This causes the interference of non-correlated sources on the measurement site and the high correlation of the measurement signals of adjacent electrodes.

[0003] Woon-Hong Yeo et al. wrote an article titled “VR-enabled portable brain-computer interfaces via wireless soft bioelectronics” in Biosensors and Bioelectronics 2022 Vol. 210. The article introduces a microneedle electrode that can pierce the stratum corneum of the skin without damaging the dermis, thereby reducing the electrode-skin contact impedance, improving the signal-to-noise ratio, and achieving long-term high-quality EEG signal acquisition; however, the microneedle electrode still has the problem of low spatial accuracy. W. Bseio et al. wrote an article titled “Tri-polar concentric ring electrode development for laplacian electroencephalography” in IEEE Trans Biomed Eng 2006 Vol. 53 Issue 5 Pages 926-33. They proposed that concentric ring electrodes be used to estimate the Laplace potential of the central circle site; using Laplace EEG signals can reduce interference from distant sources, improve the selectivity of electrodes for close-range sources, and reduce the correlation of signals measured by adjacent electrodes. However, the search found that the existing concentric ring electrodes are mostly made of metal materials, which have high electrode-skin contact impedance and low signal-to-noise ratio, which will affect the quality of signal acquisition. In the concentric ring electrodes, the calculation of Laplace EEG requires the use of the signal of each ring, and the influence of metal dry electrodes is more obvious.

[0004] The Chinese invention patent with application publication number CN115363591A discloses an electrode array structure for multi-type neural signal collection and its preparation method. The conductive layer includes Laplace electrodes and single-point electrodes. The Laplace electrodes are electrodes with concentric ring structures. The Laplace electrodes and single-point electrodes are used together to realize the collection of different types of neuronal signals in vivo. This patent is an implantable probe electrode and cannot be applied to wearable scalp brain electrodes. The problems existing in the above-mentioned concentric ring electrodes still exist. Summary of the invention

[0005] In view of the defects in the prior art, the object of the present invention is to provide a concentric ring microneedle electrode and a preparation method thereof.

[0006] The present invention is achieved through the following technical solutions:

[0007] According to one aspect of the present invention, there is provided a concentric ring microneedle electrode, comprising:

[0008] a base layer having a concentric ring structure;

[0009] Microneedles are located above the base layer, and the microneedles are arranged on each level of the concentric ring structure;

[0010] A microneedle-side conductive layer, located above the microneedle, and used to convert biological current into electronic current;

[0011] A non-microneedle side conductive layer, located below the base layer and connected to the microneedle side conductive layer at the side of the base layer, the non-microneedle side conductive layer is used to form a conductive connection and connect to an external wire;

[0012] The modification layer is located above the conductive layer on the microneedle side, and the modification layer is used to contact the skin to reduce the conductive layer skin-electrode contact impedance.

[0013] Furthermore, the number of the concentric ring structures is determined according to the requirement of acquiring the signal.

[0014] Furthermore, the number, density and arrangement of the microneedles are determined according to the requirements for obtaining signals.

[0015] Furthermore, the surface of the microneedle is provided with a structure that is conducive to penetration and forming stable contact.

[0016] Furthermore, the height of the microneedle is 100-800 μm.

[0017] Furthermore, the material of the conductive layer on the microneedle side is gold or silver chloride, and the thickness of the conductive layer on the microneedle side is 50-1000 nm.

[0018] Furthermore, the material of the non-microneedle side conductive layer is gold or silver chloride, and the thickness of the non-microneedle side conductive layer is 50-1000 nm.

[0019] Furthermore, the material of the modification layer is iridium oxide or platinum black, and the thickness of the modification layer is 50-1000 nm.

[0020] Furthermore, the base layer is made of a flexible material that can penetrate the skin, and the thickness of the base layer is 5-500 μm.

[0021] According to another aspect of the present invention, a method for preparing the above-mentioned concentric ring microneedle electrode is provided, the method comprising:

[0022] According to the shape of the microneedles on the concentric ring structure, a microneedle male mold is made;

[0023] Make the master mold by reverse molding;

[0024] pouring the base material into the master mold, curing it, and demoulding it to obtain a base layer with microneedles;

[0025] Cutting the substrate with microneedles to form a concentric ring structure;

[0026] Conductive layers are prepared on both sides of the base layer to form a microneedle-side conductive layer and a non-microneedle-side conductive layer;

[0027] A modification layer is formed on the conductive layer on the microneedle side to obtain a concentric ring microneedle electrode.

[0028] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0029] 1. The electrode provided by the present invention is a wearable brain electrode, which is used for collecting EEG signals and Laplace EEG signals. By introducing a microneedle structure on the concentric ring structure and providing a modification layer in contact with the skin above the conductive layer on the microneedle side, the skin-electrode contact impedance of the concentric ring electrode is reduced, the signal-to-noise ratio is improved, and high-quality signals are collected;

[0030] 2. The present invention realizes the estimation of Laplace potential through the design of the concentric ring structure of the wearable electrode, so that the electrode can shield the long-distance interference source and reduce the correlation of adjacent electrode signals, thereby improving the spatial accuracy;

[0031] 3. The concentric ring microneedle electrode prepared by the present invention has high flexibility and a high degree of fit with the scalp. There is no need to use conductive paste when collecting EEG signals, which saves tedious cleaning steps. It is easy to use and can be used for a long time. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0033] Figure 1 Schematic diagram of the structure of concentric circular microneedle electrodes in one embodiment of the present invention;

[0034] Figure 2 Schematic diagram of the process of preparing a concentric circular microneedle electrode in one embodiment of the present invention;

[0035] In the figure, the corresponding reference numerals are: 1-modification layer, 2-microneedle side conductive layer, 3-base layer, 4-non-microneedle side conductive layer. DETAILED DESCRIPTION

[0036] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0037] In the description of the present invention, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0038] The embodiment of the present invention provides a concentric ring microneedle electrode for recording EEG signals and Laplace EEG signals, which is a wearable EEG electrode. Figure 1 The electrode comprises a base layer 3, microneedles, a microneedle-side conductive layer 2, a non-microneedle-side conductive layer 4 and a modified layer 1, wherein: the base layer 3 has a concentric ring structure; the microneedles are located above the base layer 3, and the microneedles are arranged on each level of the concentric ring structure, and each level of the ring serves as the substrate of the electrode, and the microneedles are used to solve the problems of high skin-electrode contact impedance and low signal-to-noise ratio; the microneedle-side conductive layer 2 is located above the microneedles, and the microneedle-side conductive layer 2 is used to convert biological current into electronic current; the non-microneedle-side conductive layer 4 is located below the base layer 3 and connected to the microneedle-side conductive layer 2 on the side of the base layer 3, and the non-microneedle-side conductive layer 4 is used to form a conductive connection and connect to an external wire; the modified layer 1 is located above the microneedle-side conductive layer 2, and the modified layer 1 is used to contact the skin, further reducing the conductive layer skin-electrode contact impedance, thereby further improving the contact characteristics of the conductive material with the skin.

[0039] In the embodiment of the present invention, the structure of the base layer 3 can be a two-stage concentric ring, a three-stage concentric ring, etc. Figure 1 It is a three-stage concentric ring structure. The more the rings, the better the shielding effect for distant sources and the lower the correlation between adjacent electrodes. As the number of concentric ring structures increases, the selectivity for close-range sources increases, but the complexity of signal acquisition also increases. The number of concentric ring structures is determined according to the needs of signal acquisition.

[0040] In the embodiment of the present invention, the microneedles are arranged at a high density on each level of the ring. As the number and density of microneedles increase, the contact impedance decreases accordingly. For different signal acquisition requirements, the arrangement of microneedles is also different. For example, a denser arrangement is required in a specific brain area to achieve more comprehensive signal collection. Therefore, more dense microneedles can be arranged in the required brain area, and microneedles can be arranged more sparsely in other brain areas. The number, density and arrangement of microneedles are determined according to the needs of signal acquisition.

[0041] In some embodiments, the microneedle surface is provided with a structure that is conducive to penetration and forming a stable contact. For example, the microneedle surface has a gear structure, which can increase the friction with the skin after penetration and form a stable contact.

[0042] In some embodiments, the height of the microneedle is 100-800 μm. The higher the height of the microneedle, the lower the contact impedance. Therefore, within an acceptable contact impedance range, a microneedle with a lower height can be selected to reduce micro-trauma to the skin.

[0043] In some embodiments, the material of the microneedle side conductive layer 2 is a conductive material such as gold or silver chloride. If the microneedle side conductive layer 2 is too thin or too thick, it may affect the resistance of the electrode itself, thereby affecting conduction. Preferably, the thickness of the microneedle side conductive layer 2 is 50-1000nm.

[0044] In some embodiments, the material of the non-microneedle side conductive layer 4 is any conductive material such as gold or silver chloride. If the non-microneedle side conductive layer 4 is too thin or too thick, it may affect the resistance of the electrode itself, thereby affecting conduction. Preferably, the thickness of the non-microneedle side conductive layer 4 is 50-1000nm.

[0045] In some embodiments, the material of the modification layer 1 is a biocompatible electrode modification material such as iridium oxide or platinum black, which can increase the specific surface area and reduce the electrode-skin contact impedance. If the modification layer 1 is too thin or too thick, it may affect the resistance of the electrode itself and thus affect the conduction. Preferably, the thickness of the modification layer 1 is 50-1000nm.

[0046] In some embodiments, the base layer 3 is made of a flexible material that can penetrate the skin, and for example, the base layer 3 is any flexible material that has sufficient mechanical strength to penetrate the stratum corneum of the skin, such as polyimide and polyurethane. The thickness of the base layer 3 is 5-500 μm.

[0047] In the above embodiment of the present invention, the electrode has the characteristics of low skin-electrode contact impedance, high signal-to-noise ratio and high signal spatial accuracy. The above electrode has high flexibility and high fit with the scalp. There is no need to use conductive paste when collecting EEG signals, and long-term high-quality signal collection can be achieved.

[0048] Another embodiment of the present invention provides a method for preparing the above-mentioned concentric ring microneedle electrode, referring to Figure 2 , the method comprising:

[0049] S1, such as Figure 2 As shown in (a), a microneedle male mold is made according to the shape of the microneedles on the concentric ring structure. Specifically, it can be achieved by steel needle combination or 3D printing technology;

[0050] S2, such as Figure 2 (b) is shown, and a female mold is made by inverting the mold; specifically, the above-mentioned microneedle male mold can be replicated by polydimethylsiloxane or purple clay material to prepare a female mold;

[0051] S3, such as Figure 2 As shown in (c), the base material is poured into the master mold, solidified, and demolded to obtain a base layer with microneedles; specifically, this can be achieved by pouring a polyimide precursor, imidizing it, and then demolding it;

[0052] S4, such as Figure 2 As shown in (d), the base layer with microneedles is cut to form a concentric ring structure; specifically, this can be achieved by laser cutting;

[0053] S5, such as Figure 2 As shown in (e), a conductive layer is prepared on both sides of the base layer to form a microneedle side conductive layer and a non-microneedle side conductive layer; specifically, this can be achieved by double-sided sputtering of gold;

[0054] S6, such as Figure 2 As shown in (f), a modification layer is formed on the conductive layer on the microneedle side. Specifically, it can be achieved by sputtering iridium oxide or electroplating platinum black to obtain a concentric ring microneedle electrode.

[0055] The performance test of the prepared concentric ring microneedle electrode is as follows:

[0056] (1) Impedance test: The contact impedance density (normalized expression of contact impedance, calculated by multiplying contact impedance by contact area) of the concentric ring microneedle electrode in this embodiment is 1.64 kΩ·cm2 (10Hz), significantly lower than that of AgCl electrode (20.46kΩ·cm 2 (10Hz) and is superior to the standard wet electrode (4.43kΩ·cm 2 (10Hz));

[0057] (2) Signal cross-correlation test: Compared with traditional microneedle electrodes, the cross-correlation of adjacent electrode signals collected by the concentric ring microneedle electrodes in this embodiment is significantly reduced, from 0.8-0.9 to 0.1-0.2. Cross-correlation refers to the degree of correlation between two signals, with a value of 0-1, and the lower the value, the weaker the cross-correlation. Traditional microneedle electrodes have low spatial accuracy, overlapping signals collected by adjacent electrodes, and high cross-correlation; while in this embodiment, the electrodes collect high-quality Laplace EEG signals through a concentric ring microneedle structure, which reduces the cross-correlation of adjacent electrode signals and improves spatial accuracy.

[0058] The electrode provided in the above embodiment of the present invention is a wearable brain electrode for collecting EEG signals and Laplace EEG signals. By introducing a microneedle structure on the concentric ring structure and setting a modification layer in contact with the skin above the conductive layer on the microneedle side, the skin-electrode contact impedance of the concentric ring electrode is reduced, and the signal-to-noise ratio is improved. Through the design of the concentric ring structure, the estimation of the Laplace potential is realized, so that the electrode can shield the long-distance interference source, reduce the correlation of adjacent electrode signals, and improve the spatial accuracy; the concentric ring microneedle electrode prepared in the above embodiment of the present invention has high flexibility and high fit with the scalp. When collecting EEG signals, there is no need to use conductive paste, which saves cumbersome cleaning steps, is easy to use and can be used for a long time.

[0059] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various modifications or variations within the scope of the claims, which does not affect the essence of the present invention. The above preferred features can be used in any combination without conflicting with each other.

Claims

1. A concentric ring microneedle electrode, characterized in that: include: a base layer having a concentric ring structure; Microneedles are located above the base layer, and the microneedles are arranged on each level of the concentric ring structure; A microneedle-side conductive layer, located above the microneedle, and used to convert biological current into electronic current; A non-microneedle side conductive layer, located below the base layer and connected to the microneedle side conductive layer at the side of the base layer, the non-microneedle side conductive layer is used to form a conductive connection and connect to an external wire; The modification layer is located above the conductive layer on the microneedle side, and the modification layer is used to contact the skin to reduce the conductive layer skin-electrode contact impedance.

2. The concentric ring microneedle electrode according to claim 1, characterized in that: The number of the concentric ring structures is determined according to the requirement of acquiring the signal.

3. The concentric ring microneedle electrode according to claim 1, characterized in that: The number, density and arrangement of the microneedles are determined according to the requirements for obtaining signals.

4. The concentric ring microneedle electrode according to claim 1, characterized in that: The surface of the microneedle is provided with a structure that is conducive to penetration and forming stable contact.

5. The concentric ring microneedle electrode according to claim 1, characterized in that: The height of the microneedle is 100-800 μm.

6. The concentric ring microneedle electrode according to claim 1, characterized in that: The material of the conductive layer on the microneedle side is gold or silver chloride, and the thickness of the conductive layer on the microneedle side is 50-1000nm.

7. The concentric ring microneedle electrode according to claim 1, characterized in that: The material of the non-microneedle side conductive layer is gold or silver chloride, and the thickness of the non-microneedle side conductive layer is 50-1000 nm.

8. The concentric ring microneedle electrode according to claim 1, characterized in that: The material of the modification layer is iridium oxide or platinum black, and the thickness of the modification layer is 50-1000nm.

9. The concentric ring microneedle electrode according to claim 1, characterized in that: The base layer is made of a flexible material that can penetrate the skin, and the thickness of the base layer is 5-500 μm.

10. A method for preparing the concentric ring microneedle electrode according to any one of claims 1 to 9, characterized in that: include: According to the shape of the microneedles on the concentric ring structure, a microneedle male mold is made; Make the master mold by reverse molding; pouring the base material into the master mold, curing it, and demoulding it to obtain a base layer with microneedles; Cutting the substrate with microneedles to form a concentric ring structure; Conductive layers are prepared on both sides of the base layer to form a microneedle-side conductive layer and a non-microneedle-side conductive layer; A modification layer is formed on the conductive layer on the microneedle side to obtain a concentric ring microneedle electrode.

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