A bionic three-dimensional soft and elastic cortical microelectrode and its preparation method

Abstract

The present invention discloses a bionic three-dimensional soft and elastic cortical microelectrode and a preparation method thereof. A claw-shaped structure is provided around the electrode contact. After being bent, it can fully wrap and adhere to the soft and elastic silicone convex platform, thereby ensuring that the flexible polymer film microelectrode has both high mechanical strength and conformal contact ability. During the preparation, first, a two-dimensional flexible microelectrode is fabricated on a silicon wafer deposited with a metal sacrificial layer based on MEMS technology, and then immersed in a hydrochloric acid solution to corrode the metal sacrificial layer, so that the microelectrode is released from the silicon wafer. Then, the microelectrode is pushed into a mold with cylindrical pits by a capillary glass tube. Next, liquid soft silicone is injected into each pit one by one to completely fill all the pits. Finally, after the liquid soft silicone is completely solidified, the microelectrode is lifted and separated from the mold. The present invention effectively solves the balance problem between the substrate thickness and the conformal attachment ability of the current flexible polymer film microelectrode, and provides an important reference for the development of new minimally invasive implantable brain-computer interface electrodes.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomedical electronics, and particularly relates to a bionic three-dimensional soft and elastic cortical microelectrode and a preparation method thereof. Background Art

[0002] The integration of microelectromechanical systems (MEMS) technology and flexible electronics technology provides an important basis for the development of high-precision and high-flexibility brain science research tools. Implantable flexible cortical microelectrodes are based on the above technologies. One of the development directions is how to improve the conformal attachment performance between the electrodes and the cerebral cortical sulci and gyri to ensure that stable electroencephalogram signals can be collected at all electrode sites. However, in order to improve the conformal attachment ability, the prior art often chooses to reduce the thickness of the flexible polymer film substrate or use intrinsically softer materials such as silicone and hydrogel, which poses new challenges to ensuring the mechanical strength and reliability of the substrate.

[0003] Methods such as using ultra-thin polymers, super-elastic low-modulus substrate materials, reticular or finger-shaped substrate designs, and introducing three-dimensional micro-protrusion structures at electrode points have certain problems to varying degrees: thinning of the substrate or reticular hollow structure design will cause a decrease in the mechanical strength of the electrode, and it is easy to be damaged by external forces during operation or implantation; super-elastic low-modulus materials such as silicone have poor MEMS processing compatibility and it is difficult to guarantee the microfabrication accuracy; the micro-protrusions at electrode points mostly adopt the method of raising the polymer under the metal layer, lacking elastic contact deformation ability. Therefore, developing cortical microelectrodes with a soft elastic micro-boss structure is of great significance for ensuring conformal attachment to brain tissue.

[0004] After searching the prior art, Guo Z et al. wrote an article "A polyimide-based 3D ultrathin bioelectrode with elastic sites for neural recording" in Journal of Microelectromechanical Systems, 2018, 27(6): 1035-1040, proposing a three-dimensional ultrathin flexible electrode with a warped electrode point structure similar to a cantilever beam, which can achieve common contact with the cerebral cortical surface and improve the relative flexibility between adjacent electrode points. However, this structure will undergo stress relaxation over time and it is difficult to maintain a stable warping and rebounding ability in the long term.

[0005] Yan Z et al. wrote the article "Three-dimensional mesostructures as high-temperature growth templates, electronic cellular scaffolds, and self-propelled microrobots" in Proceedings of the National Academy of Sciences, 2017, 114(45): E9455-E9464. By pre-stretching a silicone rubber elastic substrate, a flexible polyimide electrode with titanium / silicon dioxide (Ti / SiO2) locally deposited on the back and 8 electrode points exposed on the surface was attached and the original length of the elastic substrate was restored. The region deposited with Ti / SiO2 and the silicone rubber elastic substrate were firmly bonded through a condensation reaction to form strong chemical bonds. The electrode underwent out-of-plane deformation due to buckling to form a three-dimensional scaffold for cell regeneration. However, on the one hand, the ends of the three-dimensional scaffold were prone to debonding from the elastic substrate, resulting in the inability of the electrode points to effectively maintain the three-dimensional buckling structure. On the other hand, the mechanical strength of the three-dimensional buckling structure of the electrode was insufficient. After undergoing large-pressure deformation, it was difficult to restore its original appearance, and even cracks or breakages would appear at the positions of the supporting legs of the three-dimensional scaffold.

[0006] In Chinese Patent CN110367978B, a three-dimensional buckling structure flexible neural electrode and its preparation process were disclosed. A three-dimensional buckling structure was formed through mechanical guidance. Through the pre-stretching deformation provided by the elastic substrate, the two-dimensional planar structure electrode was formed into a three-dimensional buckling structure flexible neural electrode under extrusion, so that the metal electrode points bulged upward to ensure that the metal electrode points were in contact with the cerebral cortex under the extrusion deformation of the gravity of the elastic substrate. On this basis, the present invention will further improve the electrode contacts to improve the mechanical strength during contact. Summary of the Invention

[0007] To overcome the deficiencies of the prior art, the present invention provides a bionic three-dimensional soft and elastic cortical microelectrode and a preparation method thereof. A claw-shaped structure is provided around the electrode contact. After being bent, it can fully wrap and bond to the soft and elastic silicone convex platform, thereby ensuring that the flexible polymer film microelectrode has both high mechanical strength and conformal contact ability. During preparation, first, a two-dimensional flexible microelectrode is fabricated on a silicon wafer deposited with a metal sacrificial layer based on MEMS technology, and then it is immersed in a hydrochloric acid solution to corrode the metal sacrificial layer, so that the microelectrode is released from the silicon wafer. Then, the microelectrode is pushed into a mold with cylindrical pits using a capillary glass tube. Next, liquid soft silicone is injected into each pit one by one to completely fill all the pits. Finally, when the liquid soft silicone is completely solidified, the microelectrode is lifted and separated from the mold. The present invention effectively solves the balance problem between the substrate thickness and the conformal attachment ability of the current flexible polymer film microelectrode, and provides an important reference for the development of new minimally invasive implantable brain-computer interface electrodes.

[0008] The technical solution adopted by the present invention to solve its technical problems includes the following steps:

[0009] A bionic three-dimensional soft and elastic cortical microelectrode includes an electrode module, an electrode flexible substrate, electrode metal wires, and electrode pads; the electrode module includes an electrode arm structure, an electrode contact, an electrode claw-shaped structure, and a soft and elastic silicone convex platform;

[0010] The electrode pads are arranged on the surface of the electrode flexible substrate; the electrode metal wires are arranged inside the electrode flexible substrate; a plurality of electrode modules are connected to the same number of electrode pads in one-to-one correspondence through the electrode metal wires;

[0011] The electrode claw-shaped structure includes a plurality of electrode claws; the electrode contact is arranged at the central position of the electrode claw-shaped structure, and the upper end face of the electrode contact is exposed; the central part of the electrode claw-shaped structure adheres to the top end face of the soft and elastic silicone convex platform; a plurality of electrode claws are evenly distributed around the electrode contact, and the electrode claws are bent along the edge of the top end face of the soft and elastic silicone convex platform and then adhere to the periphery of the side face of the soft and elastic silicone convex platform; a plurality of holes are opened on the electrode flexible substrate, and the lower end face of each soft and elastic silicone convex platform is parallel to the electrode flexible substrate and extends into a hole of the electrode flexible substrate;

[0012] The electrode arm structure is strip-shaped, arranged between any two electrode claws and adheres to the side face of the soft and elastic silicone convex platform; the lower end of the electrode arm structure is electrically connected to one end of the electrode metal wire, and the upper end of the electrode arm structure is electrically connected to the electrode contact.

[0013] Preferably, root slits are provided on both sides of the bending part of the electrode claw, and the width of the root slits is 8 - 12 micrometers, and the length is 30 - 50 micrometers.

[0014] Preferably, the material of the electrode flexible substrate is a polymer thin film material of one of polyimide PI, parylene, polyethylene terephthalate PET, and SU-8 negative photoresist, and the total thickness of the electrode flexible substrate is 10 to 50 microns.

[0015] Preferably, the metal layer of the electrode contact is made of gold, platinum, or iridium, and is deposited on the electrode flexible substrate by a sputtering or thermal evaporation process. The diameter of the electrode contact is 100 microns, and the thickness of the metal layer is 50 to 300 nanometers.

[0016] Preferably, the soft silicone rubber boss is made of polydimethylsiloxane PDMS or other medical-grade silicone rubber soft materials.

[0017] Preferably, the arm length of the electrode arm structure is 380 microns and the width is 170 microns; the claw length of the electrode claw is 160 microns and the width is 120 microns.

[0018] A method for preparing a bionic three-dimensional soft elastic cortex microelectrode includes the following steps:

[0019] Step 1: Based on MEMS technology, on a silicon wafer deposited with a metal sacrificial layer, a two-dimensional flexible microelectrode based on a polymer thin film material is fabricated; the silicon wafer with the two-dimensional flexible microelectrode is immersed in a hydrochloric acid solution, the metal sacrificial layer is corroded, the two-dimensional flexible microelectrode is released and floats on the liquid surface, and then it is washed with deionized water and dried on a hot plate.

[0020] The two-dimensional flexible microelectrode includes an electrode flexible substrate, an electrode arm structure, an electrode contact, an electrode claw-shaped structure, an electrode metal wire, and an electrode pad; the electrode pad is arranged on the surface of the electrode flexible substrate; the electrode metal wire is arranged inside the electrode flexible substrate; a plurality of electrode arm structures are connected to the same number of electrode pads one by one through the electrode metal wires.

[0021] The electrode claw-shaped structure includes a plurality of electrode claws; the electrode contact is arranged at the center position of the electrode claw-shaped structure, and the upper end surface of the electrode contact is exposed; a plurality of electrode claws are evenly distributed around the electrode contact; a plurality of holes are formed in the electrode flexible substrate, and each electrode claw-shaped structure is located in a hole of the electrode flexible substrate.

[0022] The electrode arm structure is strip-shaped and is arranged between any two electrode claws; one end of the electrode arm structure is connected to one end of the electrode metal wire, and the other end of the electrode arm structure is connected to the electrode contact.

[0023] Step 2: Use multiple glass molds with cylindrical pits. Use a capillary glass tube to push the electrode arm structure, electrode contact, and electrode claw-shaped structure of each two-dimensional flexible microelectrode into the cylindrical pits of the glass mold. The direction of the electrode contact is downward and closely adheres to the bottom of the pit, so that the electrode arm structure and the electrode claw-shaped structure closely adhere to the side wall of the pit. Subsequently, perform annealing stress relief treatment in a high-temperature oven;

[0024] Step 3: Remove the capillary glass tube, and inject liquid PDMS soft silicone into each pit of the glass mold one by one, so that it completely fills the mold pit, and heat and cure it to form a soft and elastic silicone convex platform;

[0025] Step 4: Wait for the liquid PDMS soft silicone to completely solidify, lift the two-dimensional flexible microelectrode, and separate it from the glass mold to obtain a bionic three-dimensional soft elastic cortex microelectrode with a soft elastic silicone convex platform.

[0026] Preferably, the soft elastic silicone convex platform in Step 3 is a monolithic soft elastic silicone substrate with a convex platform, specifically:

[0027] After the electrode arm structure, electrode contact, and electrode claw-shaped structure of the microelectrode are closely attached to the mold with pits, use a spin coater to directly spin-coat a liquid soft silicone of a set thickness uniformly on the back of the two-dimensional flexible microelectrode. After the silicone cures, a monolithic silicone layer that fills the mold pit is formed. Finally, lift the two-dimensional flexible microelectrode and separate it from the mold to obtain a bionic three-dimensional soft elastic cortex microelectrode with a monolithic soft elastic silicone substrate with a convex platform.

[0028] Preferably, the silicon wafer is a 4-inch silicon wafer, and the hydrochloric acid solution is a 3% hydrochloric acid solution.

[0029] Preferably, in Step 1, when drying on a hot plate, heat at 40 °C for 10 minutes.

[0030] The beneficial effects of the present invention are as follows:

[0031] 1. The electrode of the present invention has a claw-shaped structure with unique bionic characteristics, and after bending, it can fully wrap the soft silicone and form a soft elastic micro-convex platform;

[0032] 2. Under the action of its own gravity, the three-dimensional soft elastic cortex microelectrode of the present invention can form an elastic deformation contact relationship with the surface of the cerebral cortex sulcus, ensuring that stable electroencephalogram signals can be collected at all electrode sites;

[0033] 3. The present invention can take into account the mechanical strength and conformal adhesion ability of the microelectrode. Description of the Drawings

[0034] Figure 1 It is a schematic diagram of the overall three-dimensional structure of the bionic three-dimensional soft elastic cortex microelectrode of the present invention.

[0035] Figure 2 Schematic diagram of the two-dimensional flexible microelectrode of the present invention.

[0036] Figure 3 Comparison diagram of the local three-dimensional structure of the electrode points of the bionic three-dimensional soft elastic cortex microelectrode of the present invention and the plant "Aspidistra elatior".

[0037] Figure 4 Process flow chart for the preparation of the bionic three-dimensional soft elastic cortex microelectrode of the present invention.

[0038] Figure 5 Schematic diagram of the process of attaching the bionic three-dimensional soft elastic cortex microelectrode of the present invention to the surface of the cerebral cortex, where (a) is the undeformed state of the microelectrode before contact, and (b) is the deformed state of the microelectrode after contact.

[0039] Figure 6 Schematic diagram of the two-dimensional and three-dimensional structures of the bionic three-dimensional soft elastic cortex microelectrode of the present invention.

[0040] Figure 7 Three-dimensional structure diagram of the bionic three-dimensional soft elastic cortex microelectrode of the present invention with an integral soft elastic silicone substrate with convex platforms.

[0041] Reference numerals: Column 1 of "Aspidistra elatior", Petal 2 of "Aspidistra elatior", Electrode flexible substrate 3, Electrode arm structure 4, Electrode contact 5, Electrode claw-shaped structure 6, Soft elastic silicone convex platform 7, Bionic three-dimensional soft elastic cortex microelectrode 8, Electrode metal wire 9, Electrode pad 10, Cerebral cortex 11, Narrow slit at the root of the electrode claw 12, Integral soft elastic silicone substrate with convex platforms 13. Detailed implementation manners

[0042] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0043] A bionic three-dimensional soft elastic cortex microelectrode and its preparation method of the present invention. The bionic inspiration of the microelectrode contact is derived from the plant "Aspidistra elatior" of the Liliaceae family, which has important practical value and innovative significance for obtaining stable cortical electroencephalogram signals at accurate coordinates in the target brain area, and can effectively solve the problems that the relative position of the electrode points is not easy to control and it is difficult to form a reliable contact with the brain tissue.

[0044] A bionic three-dimensional soft elastic cortex microelectrode includes an electrode module, an electrode flexible substrate 3, an electrode metal wire 9, and an electrode pad 10; the electrode module includes an electrode arm structure 4, an electrode contact 5, an electrode claw-shaped structure 6, and a soft elastic silicone convex platform 7;

[0045] The electrode pad 10 is arranged on the surface of the electrode flexible substrate 3; the electrode metal wire 9 is arranged inside the electrode flexible substrate 3; a plurality of electrode modules are connected to the same number of electrode pads 10 in one-to-one correspondence through the electrode metal wire 9;

[0046] The electrode claw-shaped structure 6 includes a plurality of electrode claws; the electrode contact 5 is arranged at the central position of the electrode claw-shaped structure 6, and the upper end face of the electrode contact 5 is exposed; the central part of the electrode claw-shaped structure 6 is attached to the top end face of the soft elastic silica gel boss 7; the plurality of electrode claws are evenly distributed around the electrode contact 5, and the electrode claws are bent along the edge of the top end face of the soft elastic silica gel boss 7 and then attached to the periphery of the side face of the soft elastic silica gel boss 7; a plurality of holes are formed in the electrode flexible substrate 3, and the lower end face of each soft elastic silica gel boss 7 is parallel to the electrode flexible substrate 3 and extends into one of the holes of the electrode flexible substrate 3;

[0047] The electrode arm structure 4 is strip-shaped, arranged between any two electrode claws and attached to the side face of the soft elastic silica gel boss 7; the lower end of the electrode arm structure 4 is electrically connected to one end of the electrode metal wire 9, and the upper end of the electrode arm structure 4 is electrically connected to the electrode contact 5.

[0048] Preferably, root slits are arranged on both sides of the bending position of the electrode claw, the width of the root slits is 8-12 microns, and the length is 30-50 microns.

[0049] Preferably, the material of the electrode flexible substrate 3 is a polymer thin film material of one of polyimide PI, parylene, polyethylene terephthalate PET, and SU-8 negative photoresist, and the total thickness of the electrode flexible substrate 3 is 10-50 microns.

[0050] Preferably, the metal layer of the electrode contact 5 is made of gold, platinum or iridium, and is deposited on the electrode flexible substrate 3 by a sputtering or thermal evaporation process. The diameter of the electrode contact 5 is 100 microns, and the thickness of the metal layer is 50-300 nanometers.

[0051] Preferably, the soft elastic silica gel boss 7 is made of polydimethylsiloxane PDMS or other medical-grade silicone rubber soft materials.

[0052] Preferably, the electrode arm structure 4 has an arm length of 380 microns and a width of 170 microns; the electrode claw has a claw length of 160 microns and a width of 120 microns.

[0053] A preparation method of a bionic three-dimensional soft elastic cortex microelectrode includes the following steps:

[0054] Step 1: Based on MEMS technology, on a silicon wafer deposited with a metal sacrificial layer, a two-dimensional flexible microelectrode based on a polymer thin film material is fabricated; the silicon wafer with the two-dimensional flexible microelectrode is immersed in a hydrochloric acid solution, the metal sacrificial layer is corroded, the two-dimensional flexible microelectrode is released and floats on the liquid surface, and then it is washed with deionized water and dried on a hot plate;

[0055] The two-dimensional flexible microelectrode includes an electrode flexible substrate 3, electrode arm structures 4, electrode contacts 5, electrode claw structures 6, electrode metal wires 9, and electrode pads 10; the electrode pads 10 are disposed on the surface of the electrode flexible substrate 3; the electrode metal wires 9 are disposed inside the electrode flexible substrate 3; a plurality of electrode arm structures 4 are connected to the same number of electrode pads 10 in one-to-one correspondence through the electrode metal wires 9;

[0056] The electrode claw structure 6 includes a plurality of electrode claws; the electrode contact 5 is disposed at the central position of the electrode claw structure 6, and the upper end face of the electrode contact 5 is exposed; a plurality of electrode claws are evenly distributed around the electrode contact 5; a plurality of holes are formed in the electrode flexible substrate 3, and each electrode claw structure 6 is located in a hole of the electrode flexible substrate 3;

[0057] The electrode arm structure 4 is strip-shaped and is disposed between any two electrode claws; one end of the electrode arm structure 4 is connected to one end of the electrode metal wire 9, and the other end of the electrode arm structure 4 is connected to the electrode contact 5;

[0058] Step 2: Use a plurality of glass molds with cylindrical pits, and use a capillary glass tube to push the electrode arm structures 4, electrode contacts 5, and electrode claw structures 6 of each two-dimensional flexible microelectrode into the cylindrical pits of the glass molds. The electrode contact 5 faces downward and is closely attached to the bottom of the pit, so that the electrode arm structures 4 and electrode claw structures 6 are closely attached to the side walls of the pit, and then annealing stress relief treatment is completed in a high-temperature oven;

[0059] Step 3: Take out the capillary glass tube, and inject liquid PDMS soft silicone into each pit of the glass mold one by one, so that it completely fills the mold pit, and heat and cure it to form a soft and elastic silicone boss 7;

[0060] Step 4: Wait for the liquid PDMS soft silicone to completely solidify, lift the two-dimensional flexible microelectrode, and separate it from the glass mold to obtain a bionic three-dimensional soft and elastic cortex microelectrode 8 with a soft and elastic silicone boss 7.

[0061] Preferably, the soft and elastic silicone boss in Step 3 is a monolithic soft and elastic silicone substrate with a boss, specifically:

[0062] After the electrode arm structures 4, electrode contacts 5, and electrode claw structures 6 of the microelectrode are closely attached to the mold with pits, use a spin coater to directly spin-coat a liquid soft silicone with a set thickness evenly on the back of the two-dimensional flexible microelectrode. After the silicone is cured, a monolithic silicone layer filling the mold pit is formed. Finally, lift the two-dimensional flexible microelectrode and separate it from the mold to obtain a bionic three-dimensional soft and elastic cortex microelectrode 8 with a monolithic soft and elastic silicone substrate with a boss 13.

[0063] Preferably, the silicon wafer is a 4-inch silicon wafer, and the hydrochloric acid solution is a 3% hydrochloric acid solution.

[0064] Preferably, in step 1, when drying on a hot plate, it is heated at 40 °C for 10 minutes. Specific embodiments:

[0066] The present invention provides a bionic three-dimensional soft and elastic cortical microelectrode and its preparation method, which can effectively ensure that the microelectrode protrudes a certain height, and always maintains a low-stress and stable contact between the electrode and the dura mater after implantation, while ensuring that the electrode has a certain mechanical strength and can withstand a certain pressure.

[0067] The bionic three-dimensional soft and elastic cortical microelectrode can form a three-dimensional soft and elastic silicone convex platform on the back of the electrode contact through a reverse molding method.

[0068] The bionic three-dimensional soft and elastic cortical microelectrode forms a claw-shaped structure around the electrode contact through a flexible substrate, and can be fully wrapped and adhered to the surface of the soft and elastic silicone convex platform after being bent.

[0069] The overall size and the number of electrode contacts of the bionic three-dimensional soft and elastic cortical microelectrode can be determined according to the cerebral cortex area to be covered. Among them, the diameter of the electrode contact is 20 - 200 microns, which can be used to capture electrocorticography (ECoG) signals of the cerebral cortex; there is a claw-shaped structure on the microelectrode, and the claw length is 50 - 500 microns.

[0070] The electrode flexible substrate of the bionic three-dimensional soft and elastic cortical microelectrode can select polymer thin film materials such as polyimide (PI), parylene, polyethylene terephthalate (PET), SU-8 negative photoresist, etc., and the total thickness of the flexible substrate is 10 - 50 microns.

[0071] The electrode metal layer of the bionic three-dimensional soft and elastic cortical microelectrode can select materials such as gold, platinum, iridium, etc., and is deposited on the electrode flexible substrate through process schemes such as sputtering or thermal evaporation. The thickness of the electrode metal layer is 50 - 300 nanometers.

[0072] The soft and elastic silicone convex platform uses soft materials such as polydimethylsiloxane (PDMS) or other medical-grade silicone rubbers. The height of the soft and elastic silicone convex platform can be structurally designed according to actual needs and realized through a customized concave mold.

[0073] In a specific embodiment, referring to Figure 1 and Figure 3 shown, it is a comparison diagram of the local three-dimensional structure of the electrode point of the bionic three-dimensional soft and elastic cortical microelectrode and the plant "Aspidistra elatior" and a schematic diagram of the overall three-dimensional structure of the microelectrode. Among them, the structures of the column 1 of the plant "Aspidistra elatior" and the petals 2 of the plant "Aspidistra elatior" are very similar to the structure of the electrode of the present invention;

[0074] As Figure 4As shown, the preparation process flow of the bionic three-dimensional soft and elastic cortical microelectrode is mainly divided into the following four steps:

[0075] The first step: Based on MEMS technology, on a 4-inch silicon wafer deposited with a metal sacrificial layer, a two-dimensional flexible microelectrode based on a polyimide (PI) flexible polymer thin film material is fabricated. The silicon wafer with the two-dimensional flexible microelectrode is immersed in a 3% hydrochloric acid solution, and the metal sacrificial layer is corroded. The two-dimensional flexible microelectrode is released and floats on the liquid surface, and then it is washed with deionized water and heated on a hot plate at 40 °C for 10 minutes. Here, the total length of the microelectrode is 16.5 mm, the thickness is 10 μm, the electrode arm structure has 4 arms with a length of 380 μm and a width of 170 μm, the electrode contact has a diameter of 100 μm, and the electrode claw-shaped structure has 6 claws with a length of 160 μm and a width of 120 μm; as Figure 2 shown;

[0076] The second step: A glass mold with cylindrical pits is precisely processed by laser. The electrode arm structure 4, electrode contact 5, and electrode claw-shaped structure 6 of the two-dimensional flexible microelectrode are pushed into the pits of the mold with a capillary glass tube. The electrode contact 5 faces downward and closely adheres to the bottom of the pit, and the electrode claw-shaped structure 6 is bent to closely adhere to the side wall of the pit. Subsequently, annealing stress relief treatment is completed in a high-temperature oven;

[0077] The third step: The capillary glass tube is taken out, and liquid PDMS soft silicone is injected into each pit of the glass mold one by one to completely fill the pits of the mold, and then it is heated and cured;

[0078] The fourth step: After the liquid PDMS soft silicone is completely solidified, the microelectrode is gently lifted to separate it from the glass mold, and a bionic three-dimensional soft and elastic cortical microelectrode 8 with a soft and elastic silicone boss 7 is obtained.

[0079] As Figure 5 shown, this embodiment provides a schematic diagram of the attachment process of the bionic three-dimensional soft and elastic cortical microelectrode on the surface of the cerebral cortex, where the cerebral cortex is 11. As Figure 5 shown in (a), before contact, the soft and elastic silicone under the microelectrode is basically not deformed, and the depth is 380 μm; as Figure 5 shown in (b), after contact, the soft and elastic silicone under the microelectrode deforms, and the depth can reach 200 - 300 μm. The microelectrode utilizes the deformation ability of the silicone to form a three-dimensional boss structure under the electrode contact, so that under its own gravity, an elastic deformation contact relationship is formed with the surface of the cerebral cortex sulcus and gyrus in contact, ensuring that all electrode contacts can collect stable electroencephalogram signals.

[0080] In another specific embodiment, the electrode claw-shaped structure is improved, as Figure 6As shown, it is a schematic diagram of the two-dimensional and three-dimensional structures of a bionic three-dimensional soft and elastic cortical microelectrode, where there is a slit 12 at the root of the electrode claw. The specific preparation process is the same as that of Example 1, except that the structure of the electrode claw shape 6 is improved. On the basis of the original claw shape structure, electrode claw root slits 12 are added on both sides of the bending part of each claw piece to reduce the stress concentration caused by bending, so that when it adheres to the bottom and side walls of the mold, it can adhere to the mold more easily and tightly. Here, the diameter of the electrode contact 5 is 100 microns, the width of the electrode claw shape structure 6 is 120 microns, the length is 160 microns, the width of the electrode claw root slit 12 is 10 microns, and the length is 40 microns.

[0081] In another specific embodiment, the structure of the soft and elastic silicone boss is replaced, such as Figure 7 As shown, it is a schematic diagram of the three-dimensional structure of a bionic three-dimensional soft and elastic cortical microelectrode with a monolithic soft and elastic silicone substrate containing a boss, where there is a monolithic soft and elastic silicone substrate 13 containing a boss. In the bionic three-dimensional soft and elastic cortical microelectrode 8, the soft and elastic silicone boss 7 is replaced with a monolithic soft and elastic silicone substrate 13 containing a boss. In the specific preparation process, after the electrode arm structure 4, the electrode contact 5 and the electrode claw shape structure 6 of the microelectrode are closely attached to the mold with pits, a certain thickness of liquid soft silicone is directly spin-coated evenly on the back of the microelectrode as a whole by a spin coater. After the silicone is cured, a monolithic silicone layer filling the pits of the mold is formed. Finally, the microelectrode is gently lifted and separated from the mold to obtain a bionic three-dimensional soft and elastic cortical microelectrode with a monolithic soft and elastic silicone substrate 13 containing a boss. This substrate has a greater weight and can form a more closely elastic deformation contact relationship with the surface of the cerebral cortex it contacts under its own gravity. At the same time, it avoids the delicate and time-consuming process of injecting silicone into the pits of the mold one by one, and can effectively improve the preparation efficiency of the bionic three-dimensional soft and elastic cortical microelectrode.

Claims

1. A bionic three-dimensional soft and elastic cortical microelectrode, characterized in that, It includes an electrode module, an electrode flexible substrate, electrode metal wires, and electrode pads; the electrode module includes an electrode arm structure, an electrode contact, an electrode claw structure, and a soft elastic silicone convex platform; The electrode pads are arranged on the surface of the electrode flexible substrate; the electrode metal wires are arranged inside the electrode flexible substrate; multiple electrode modules are connected to the same number of electrode pads in one-to-one correspondence through the electrode metal wires; The electrode claw structure includes multiple electrode claws; the electrode contact is arranged at the central position of the electrode claw structure, and the upper end face of the electrode contact is exposed; the central part of the electrode claw structure is attached to the top end face of the soft elastic silicone convex platform; multiple electrode claws are evenly distributed around the electrode contact, and the electrode claws are bent along the edge of the top end face of the soft elastic silicone convex platform and then attached to the surrounding side faces of the soft elastic silicone convex platform; root slits are arranged on both sides of the bending part of the electrode claws, the width of the root slits is 8 - 12 microns, and the length is 30 - 50 microns; multiple holes are opened on the electrode flexible substrate, and the lower end face of each soft elastic silicone convex platform is parallel to the electrode flexible substrate and extends into one hole of the electrode flexible substrate; The electrode arm structure is strip-shaped, arranged between any two electrode claws and attached to the side face of the soft elastic silicone convex platform; the lower end of the electrode arm structure is electrically connected to one end of the electrode metal wire, and the upper end of the electrode arm structure is electrically connected to the electrode contact.

2. The bionic three-dimensional soft and elastic cortical microelectrode according to claim 1, wherein The material of the electrode flexible substrate is a polymer thin film material of one of polyimide PI, parylene, polyethylene terephthalate PET, and SU-8 negative photoresist, and the total thickness of the electrode flexible substrate is 10 - 50 microns.

3. The bionic three-dimensional soft and elastic cortical microelectrode according to claim 1, wherein The metal layer of the electrode contact is made of gold, platinum, or iridium material, and is deposited on the electrode flexible substrate through a sputtering or thermal evaporation process scheme. The diameter of the electrode contact is 100 microns, and the thickness of the metal layer is 50 - 300 nanometers.

4. A bionic three-dimensional soft and elastic cortical microelectrode according to claim 1, wherein The soft elastic silicone convex platform uses polydimethylsiloxane PDMS or other medical-grade silicone rubber soft materials.

5. The bionic three-dimensional soft and elastic cortical microelectrode according to claim 1, wherein The electrode arm structure has an arm length of 380 microns and a width of 170 microns; the electrode claw has a claw length of 160 microns and a width of 120 microns.

6. A preparation method of the bionic three-dimensional soft and elastic cortical microelectrode as described in claim 1, characterized in that, It includes the following steps: Step 1: Based on MEMS technology, on a silicon wafer deposited with a metal sacrificial layer, a two-dimensional flexible microelectrode based on a polymer thin film material is fabricated; the silicon wafer with the two-dimensional flexible microelectrode is immersed in a hydrochloric acid solution, the metal sacrificial layer is corroded, the two-dimensional flexible microelectrode is released and floats on the liquid surface, and then it is washed with deionized water and dried on a hot plate; The two-dimensional flexible microelectrode includes an electrode flexible substrate, an electrode arm structure, an electrode contact, an electrode claw structure, electrode metal wires, and electrode pads; the electrode pads are arranged on the surface of the electrode flexible substrate; the electrode metal wires are arranged inside the electrode flexible substrate; multiple electrode arm structures are connected to the same number of electrode pads in one-to-one correspondence through the electrode metal wires; The electrode claw structure includes multiple electrode claws; the electrode contact is arranged at the central position of the electrode claw structure, and the upper end face of the electrode contact is exposed; multiple electrode claws are evenly distributed around the electrode contact; multiple holes are opened on the electrode flexible substrate, and each electrode claw structure is located in one hole of the electrode flexible substrate; The electrode arm structure is strip-shaped and is arranged between any two electrode claws; One end of the electrode arm structure is connected to one end of the electrode metal wire, and the other end of the electrode arm structure is connected to the electrode contact; Step 2: Use multiple glass molds with cylindrical pits. Use a capillary glass tube to push the electrode arm structure, the electrode contact, and the electrode claw-shaped structure of each two-dimensional flexible microelectrode into the cylindrical pits of the glass molds. The direction of the electrode contact is downward and closely adheres to the bottom of the pit, so that the electrode arm structure and the electrode claw-shaped structure closely adhere to the side wall of the pit. Subsequently, perform annealing stress relief treatment in a high-temperature oven; Step 3: Take out the capillary glass tube, inject liquid PDMS soft silicone into each pit of the glass mold one by one, so that it completely fills the mold pit, and heat and cure it to form a soft and elastic silicone convex platform; Step 4: Wait for the liquid PDMS soft silicone to completely solidify, lift the two-dimensional flexible microelectrode, and separate it from the glass mold to obtain a bionic three-dimensional soft elastic cortex microelectrode with a soft and elastic silicone convex platform.

7. The preparation method of the bionic three-dimensional soft and elastic cortical microelectrode according to claim 6, wherein The soft and elastic silicone convex platform in Step 3 is a monolithic soft and elastic silicone substrate with a convex platform, specifically: After the electrode arm structure, the electrode contact, and the electrode claw-shaped structure of the microelectrode are closely attached to the mold with pits, use a spin coater to directly spin coat a liquid soft silicone with a set thickness evenly on the back of the two-dimensional flexible microelectrode as a whole. After the silicone is cured, a monolithic silicone layer filling the mold pit is formed. Finally, lift the two-dimensional flexible microelectrode and separate it from the mold to obtain a bionic three-dimensional soft elastic cortex microelectrode with a monolithic soft and elastic silicone substrate with a convex platform.

8. The preparation method of the bionic three-dimensional soft and elastic cortical microelectrode according to claim 6, characterized in that, The silicon wafer is a 4-inch silicon wafer, and the hydrochloric acid solution is a 3% hydrochloric acid solution.

9. The preparation method of the bionic three-dimensional soft and elastic cortical microelectrode according to claim 6, characterized in that, In Step 1, when drying on a hot plate, heat at 40 °C for 10 minutes.

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