Method for exposing a soft 3D conical silicon gel nerve electrode tip

Abstract

The application provides a soft 3D conical silica gel nerve electrode tip exposure method, which comprises the following steps: in the first step, resin male and female molds are made based on a light-curing 3D printer; in the second step, the patterning of a soft silica gel insulation layer at an electrode point is realized through alignment and pressure covering between the resin male and female molds; in the third step, the solidified soft silica gel insulation layer is transferred to a acrylic mold with a conical groove by using a water-soluble adhesive tape; and in the fourth step, a conductive silica gel is scraped to fill the conical groove of the acrylic mold, and an insulating silica gel encapsulation layer is spin-coated. According to the application, the insulation encapsulation layer and the internal conductive structure of the 3D nerve electrode point are both based on soft silica gel materials, the same-matrix silica gel encapsulation of the 3D nerve electrode point and the direct exposure of the electrode tip are realized, and the problems of insufficient bonding force caused by the heterogeneous material interface between the insulation layer and the conductive layer of the current soft 3D nerve electrode and the difficulty in the exposure patterning of the 3D electrode tip can be effectively solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of bio-medical electrical technology, and particularly relates to a method for exposing a soft 3D conical silicon gel nerve electrode tip. BACKGROUND

[0002] Minimally invasive implantable brain-computer interface neural electrodes are crucial for the treatment of neurological diseases. However, traditional flexible 2D planar neural electrodes are difficult to conformally attach to the cerebral cortex, and hard 3D penetrating neural electrodes are easily wrapped by glial cells, which seriously affects neural signal acquisition and stimulation regulation. During signal acquisition, the recorded neural signal amplitude will be greatly attenuated, and the signal-to-noise ratio will be reduced. During stimulation regulation, the stimulation voltage will be multiplied to reach the threshold current, which is easy to cause tissue damage. Soft 3D neural electrodes effectively solve these two key problems, not only realizing the direct contact of the neural electrode with the brain tissue without causing brain tissue damage, but also avoiding the appearance of neural glial cells on the electrode surface, which can achieve effective neural signal acquisition and stimulation regulation.

[0003] However, how to realize the exposure of the soft 3D neural electrode only at the electrode tip area to precisely collect and stimulate the brain tissue and avoid the escape of electrical signals to the tissue fluid around the 3D electrode tip is a key problem to be solved. Traditional minimally invasive implantable neural electrodes are mostly based on micro-electro-mechanical system (MEMS) technology, involving key steps such as photolithography, etching, and transfer printing, which requires the material to be stable enough, not easy to deform, and have a relatively high etching rate. However, the Young's modulus of soft silicone material is low, which has high elasticity, and is easily deformed by centrifugal force during spin coating, mask alignment pressure, and thermal stress during high-temperature treatment, which seriously affects the photolithography precision. Moreover, the low surface energy and surface chemical inertness of the soft silicone material surface can cause poor adhesion of the photoresist, which may fall off due to physical erosion or chemical corrosion during development, causing overdevelopment and further affecting the pattern size and precision. In addition, the etching rate of soft silicone material is very low, which significantly increases the process complexity and cost. Finally, soft silicone material is easily adsorbed and expanded in organic solvents (such as acetone), which deforms or even degrades, affecting the accurate transfer of the pattern. Therefore, traditional MEMS technology is only suitable for 2D planar patterning, and 3D patterning with high aspect ratio is more difficult, and soft silicone material exacerbates this problem. How to precisely and controllably expose the tip of the soft 3D neural electrode has been a serious challenge.

[0004] After searching the prior art, it was found that S. P. DeWeerth et al. of Georgia Institute of Technology, USA, in the paper "A stretchable microneedle electrode array for stimulating and measuring intramuscular electromyographic activity" published in IEEE Transactions on Neural Systems and Rehabilitation Engineering, 2016, 25(9): 1440-1452, developed a stretchable microneedle electrode array consisting of a polydimethylsiloxane (PDMS) substrate, stretchable wires formed by PDMS doped with gold powder, and stainless steel needle electrodes. The base, wires and 3D hemispherical electrode points of the electrode are all soft materials, with good flexibility and stretchability. However, the electrode exposes the tip by piercing through the soft 3D hemispherical electrode point with a rigid stainless steel needle, without directly solving the problem of exposing the tip of the soft 3D electrode point.

[0005] To avoid introducing rigid microneedles into soft 3D electrodes to achieve electrode point tip exposure, Flavia Vitale et al. of the University of Pennsylvania, USA, in the paper "MXene-infused bioelectronic interfaces for multiscale electrophysiology and stimulation" published in Science Translational Medicine, 2021, 13(612): eabf8629, developed a class of soft, high-resolution, large-scale 3D bioelectronic interfaces realized by Ti3C2 MXene (a two-dimensional transition metal carbide nanomaterial) and scalable solution processing. The electrode is based on laser patterning process for rapid prototyping and customizing array geometry, and uses a biopsy punch to cut through the top packaging layer to expose the 3D electrode contact. However, this 3D electrode point exposure process lacks reliable and accurate control of the exposed area, and can only form a cylindrical soft 3D electrode point. Moreover, the insulating coating of the 3D electrode point is different in nature from the conductive material of the electrode, and is prone to delamination failure.

[0006] To prepare a soft 3D cone-shaped electrode, Peng Shi et al. of City University of Hong Kong reported in Science Advances, 2024, 10(47): eadq9207 "Multifunctional hydrogel electronics for closed-loop antiepileptic treatment" that a soft 3D cone-shaped neural electrode based on hydrogel was prepared by filling a hydrogel solution into a PDMS mold with a cone-shaped groove and inducing polymerization by UV irradiation to achieve a soft 3D hydrogel cone-shaped electrode point. However, the soft 3D cone-shaped electrode point is completely exposed without an insulating layer, and cannot achieve precise focusing of neural signal acquisition and stimulation regulation.

[0007] Similarly, CN118163355A discloses a method for preparing a soft 3D hydrogel microneedle electrode array. The method uses a silicon mold with a cone-shaped groove, a silica hard mask, and injection molding of a conductive hydrogel precursor solution to finally form a cone-shaped soft 3D hydrogel electrode point. The preparation process is simple, low cost, and easy to realize large-scale production. However, the soft 3D cone-shaped electrode point is also completely exposed without an insulating layer, and only the tip is exposed.

[0008] From the analysis of the above prior art, it can be seen that the existing soft 3D cone-shaped silicone neural electrode has the problems of easy delamination and cracking of the insulating layer, difficulty in exposing the tip, and inability to accurately control the exposed area. SUMMARY

[0009] The purpose of the present application is to solve the defects and gaps in the prior art, and to provide a soft 3D cone-shaped silicone neural electrode tip exposure method, which can effectively realize the encapsulation of soft silicone 3D neural electrode points with the same matrix silicone and direct exposure of the electrode tip, effectively solving the problems of easy delamination and cracking of the insulating layer, difficulty in exposing the tip of the soft 3D neural electrode, and the difficulty in patterning soft silicone materials with traditional MEMS technology.

[0010] To achieve the above purpose, the technical solution provided by the present application is:

[0011] On the one hand, a soft 3D cone-shaped silicone neural electrode tip exposure method is provided, comprising the following steps:

[0012] Step 1, resin male and female molds are made based on light-cured 3D printer, the multiple protrusions of the male mold and the multiple grooves of the female mold are isosceles trapezoidal cross-section structures, the length of the top side of the trapezoids of the protrusions and the corresponding grooves are equal, the height and the bottom angle of the trapezoids of the male mold are greater than those of the female mold, so as to form a structured gap when aligned and overlaid, and the dimensions of the trapezoids of the male mold and the female mold are determined according to the pattern of the neural electrode to be formed;

[0013] Step 2, spin-coat insulating silicone on the surface of the resin female mold, and then align and overlay the resin male and female molds;

[0014] Step 3, cure the insulating silicone to obtain a 3D electrode point soft silicone insulating layer that has been patterned and formed, and then remove the resin male mold;

[0015] Step 4, use water-soluble adhesive tape to bond the surface of the soft silicone insulating layer on the resin female mold, and transfer it to an acrylic mold with internal tapered grooves, and then dissolve the water-soluble adhesive tape with water, wherein the number and distribution of the tapered grooves in the acrylic mold are consistent with those of the trapezoidal resin female mold, but the height is greater, and the taper angle determines the exposed shape of the 3D electrode point to be formed;

[0016] Step 5, blade-coat conductive silicone to fill the tapered grooves of the acrylic mold, and dry and cure to form a soft silicone conductive area inside the electrode point, thereby obtaining a formed 3D tapered silicone electrode point;

[0017] Step 6, spin-coat an insulating silicone encapsulation layer and dry and cure, and demold to obtain a soft 3D tapered silicone neural electrode point array with exposed tips.

[0018] Further, step 4 can be replaced by the following steps:

[0019] Step 4.1, spin-coat photoresist to fill the internal grooves of the cured soft silicone insulating layer;

[0020] Step 4.2, irradiate ultraviolet light to cure the photoresist;

[0021] Step 4.3, use water-soluble adhesive tape to bond the surface of the cured photoresist, and transfer it together with the soft silicone insulating layer to an acrylic mold with internal tapered grooves;

[0022] Step 4.4, dissolve the water-soluble adhesive tape with water;

[0023] Step 4.5, heat a dimethyl sulfoxide solution to dissolve the photoresist.

[0024] Further, in step 1, the depth of the protrusions and the grooves is 50-1000 μm, and the bottom angle of the trapezoids is 10°-170°.

[0025] Further, the resin punch and the die are made of one or more photocuring resin materials selected from polyurethane acrylate, epoxy acrylate, epoxy resin and composite photocuring resin.

[0026] Further, in steps 2 and 6, the insulating silica gel is made of one or more of polydimethylsiloxane, linear three-embedded copolymer and Ecoflex / Dragonskin series platinum-catalyzed silicone rubber.

[0027] Further, in step 4, the acrylic mold with a conical groove is made by numerical control milling and polished to make the surface smooth.

[0028] Further, in step 5, the conductive silica gel is obtained by uniformly mixing multi-walled carbon nanotube powder in insulating silica gel material, with a doping mass ratio of 5% to 30%, and a tube length of a single carbon nanotube of 2 to 50 microns.

[0029] Further, the photoresist is selected from SU-8 photoresist or AZ photoresist.

[0030] The application also provides a method for exposing the tip of a soft 3D conical silica gel neural electrode, comprising the following steps:

[0031] Step 1: making a conical resin punch and die based on a photocuring 3D printer, the multiple protrusions of the punch and the multiple grooves of the die are all dome-shaped structures, the dome sizes of the protrusions and the corresponding grooves are the same, the height and the base angle of the punch cone are larger than those of the die cone, so as to form a structured gap when aligned and pressed, and the dimensions of the punch trapezoid and the die trapezoid are determined according to the pattern of the neural electrode to be formed;

[0032] Step 2: spraying a release agent on the surface of the resin punch, spin coating insulating silica gel on the surface of the resin die, and then aligning and pressing the resin punch and the die;

[0033] Step 3: curing the insulating silica gel to obtain a 3D electrode point soft silica gel insulating layer that has been patterned and formed, and then removing the resin punch;

[0034] Step 4: scraping conductive silica gel to fill the conical grooves of the resin die, and drying and curing to form a soft silica gel conductive area inside the electrode point, thereby obtaining a formed 3D conical silica gel electrode point;

[0035] Step 5: spin coating an insulating silica gel encapsulating layer and drying and curing, and demolding to obtain a soft 3D conical silica gel neural electrode point array with tip exposure.

[0036] The advantages of the application are:

[0037] 1. In this invention, the insulating encapsulation layer and internal conductive structure of the 3D neural electrode points are both based on soft silicone material, realizing the same matrix silicone encapsulation of the 3D neural electrode points and direct exposure of the electrode tips.

[0038] 2. This invention is based on the preparation of resin silicone molds by photopolymerization 3D printer. The patterning of soft silicone encapsulation layer is achieved by direct alignment and pressing between molds, and the transfer is achieved by water-soluble tape. It can quickly, accurately and controllably prepare tip-exposed soft silicone 3D neural electrodes without delamination and cracking failure.

[0039] 3. The present invention also uses cured photoresist as a transfer support layer, which can avoid the alignment difficulties and low transfer accuracy caused by the easy deformation of the soft ultra-thin silicone structure during the transfer process.

[0040] 4. This invention also designs a one-step molding process for precise tip exposure of soft silicone 3D neural electrodes without transfer printing, which effectively reduces the difficulty of the process and further improves the accuracy of tip exposure of soft silicone 3D neural electrodes. Attached Figure Description

[0041] The above and / or other features and advantages of the present invention will become more readily understood from the following description with reference to the accompanying drawings, which are not drawn to scale and some features are enlarged or reduced to show details of specific parts.

[0042] Figure 1 This is a schematic diagram of the soft 3D cone-shaped silicone neural electrode array structure of the present invention;

[0043] Figure 2 This is a schematic diagram of the deformation of the soft 3D conical silicone neural electrode with exposed tip under pressure according to the present invention;

[0044] Figure 3 This is a flowchart illustrating the tip exposure process of the soft 3D conical silicone neural electrode of the present invention.

[0045] Figure 4 This is a schematic diagram of the photoresist-assisted transfer optimization process of the present invention;

[0046] Figure 5 This is a schematic diagram of the optimized direct molding process without transfer printing according to the present invention.

[0047] In the figure: 1-Exposed tip area; 2-Exposed tip insulation area; 3-Soft substrate; 4-Exposed pad area; 5-Wire; 6-Pressure source; 7-Trapezoidal resin punch; 8-Trapezoidal resin die; 9-Conical acrylic die; 10-Conical resin punch; 11-Conical resin die. Detailed Implementation

[0048] The present invention will now be described in detail with reference to the accompanying drawings and exemplary embodiments thereof. It should be noted that the following detailed description of the present invention is for illustrative purposes only and is not intended to limit the scope of the invention.

[0049] This invention provides a method for exposing the tip of a soft 3D conical silicone neural electrode, which has significant practical value and innovative significance for achieving precise neural signal acquisition and stimulation. It can effectively solve the problems of inconsistency between the insulating layer and electrode material of current soft 3D neural electrodes, difficulty in tip exposure, and lack of reliable and precise control over the exposed area, and provides support for innovative process research of soft 3D neural electrodes.

[0050] The overall structure of the soft 3D cone-shaped silicone neural electrode array prepared according to the present invention is as follows: Figure 1 As shown, the electrode is made entirely of soft silicone material and includes multiple soft electrode points. Each soft electrode point has a 3D conical structure, including a tip exposure area 1 based on conductive silicone and a tip insulation area 2 based on insulating silicone. The neural electrode array also includes a soft substrate 3, a pad exposure area 4, and wires 5, exhibiting flexibility and stretchability. The precise exposure of the soft electrode points' tips, combined with the soft silicone material, enables the soft 3D electrode to withstand pressure deformation without failure, facilitating precise focused neural signal acquisition and stimulation, and making it suitable for long-term implantation.

[0051] A schematic diagram of the structure of the tip-exposed soft 3D conical silicone neural electrode prepared according to the present invention under pressure deformation is shown below. Figure 2 As shown. Unlike traditional rigid 3D microneedle neural electrodes, the 3D neural electrode of this invention is entirely based on silicone material, including a soft electrode tip and a soft base 3. This 3D neural electrode contains no metal material, and the entire electrode array has the same low Young's modulus characteristics as silicone material, allowing it to be stretched, bent, or undergo elastic deformation without failure. It can not only maintain its shape and adhere to the cerebral cortex but also adapt to brain tissue deformation caused by changes in intracranial pressure. Under the action of an external pressure source 6, the soft 3D conical silicone neural electrode of this invention can withstand pressure deformation, and the exposed area 1 and the insulating area 2 of the electrode tip will not delaminate, crack, or fail, thus not affecting normal neural signal acquisition and stimulation. The soft and stable 3D conical silicone neural electrode is of great significance for long-term and effective in vivo implantation of neural signal acquisition and stimulation.

[0052] The following is a detailed description of the method for exposing the tip of a soft 3D conical silicone neural electrode provided by the present invention.

[0053] A method for exposing the tip of a soft 3D cone-shaped silicone neural electrode according to an exemplary embodiment of the present invention includes the following steps:

[0054] Step S1: Based on the photopolymerization 3D printer, a resin punch and a die are made. The multiple protrusions of the punch and the multiple grooves of the die are all isosceles trapezoidal cross-section structures. The top edge lengths of the trapezoids of the protrusions and the corresponding grooves are equal. The height and base angle of the punch trapezoid are larger than those of the die trapezoid, so as to form structured gaps during alignment and pressing. The dimensions of the punch trapezoid and the die trapezoid are determined according to the pattern of the neural electrode points to be formed.

[0055] Step S2: Spin-coat insulating silicone onto the surface of the resin die, and then align and press the resin punch and die together.

[0056] Step S3: Cure the insulating silicone to obtain a patterned 3D electrode point soft silicone insulating layer, and then remove the resin punch.

[0057] Step S4: Use water-soluble tape to adhere the soft silicone insulating layer surface on the resin cavity mold and transfer it to the acrylic mold with conical grooves inside. Then dissolve the water-soluble tape with water. The number and distribution of conical grooves in the acrylic mold are the same as those in the trapezoidal resin cavity mold, but the height is greater. The cone angle determines the exposed shape of the tip of the 3D electrode point to be formed.

[0058] Step S5: Apply conductive silicone to fill the conical groove of the acrylic mold, and dry and cure it to form a soft silicone conductive area inside the electrode point, thereby obtaining a shaped 3D conical silicone electrode point.

[0059] Step S6: Spin-coat an insulating silicone encapsulation layer and dry and cure it, then demold to obtain a soft 3D cone-shaped silicone neural electrode array with exposed tips.

[0060] According to the present invention, the depth of the protrusions and grooves is 50 to 1000 μm, and the angle of the trapezoidal base angle is 10° to 80°.

[0061] The resin punch and die may optionally be made of one or more UV-curable resin materials selected from polyurethane acrylate, epoxy acrylate, epoxy resin and composite UV-curable resin.

[0062] In steps 2 and 6, the insulating silicone may be made from one or more of polydimethylsiloxane (PDMS), linear triblock copolymer (SEBS), and Ecoflex / Dragonskin series platinum-catalyzed silicone rubber.

[0063] In step S4, the cone-shaped groove is generally dome-shaped to form an arc-shaped 3D electrode point exposure area. When the arc surface can better adhere to the cerebral cortex, it will not cause brain tissue damage.

[0064] Reference Figure 3 This embodiment can be implemented through the following steps:

[0065] Step (1): Based on a photopolymer 3D printer, a trapezoidal resin punch 7 and a trapezoidal resin concave mold 8 are fabricated. The punch and concave molds are isosceles trapezoidal structures with different base angles. The height of the isosceles trapezoid of the punch is 200 micrometers, and the height of the isosceles trapezoid of the concave mold is 100 micrometers. The top edge length of both the punch and the isosceles trapezoid of the punch is 100 micrometers, but the base edge length of the isosceles trapezoid of the punch is 150 micrometers, and the base edge length of the isosceles trapezoid of the concave mold is 200 micrometers. The base angle of the isosceles trapezoid of the punch is approximately 60 degrees, and the base angle of the isosceles trapezoid of the concave mold is approximately 55 degrees. Therefore, during the alignment and pressing, the upper surface of the trapezoidal structure will be tightly pressed and aligned, while structured gaps will appear in the side wall area of ​​the trapezoidal structure. The gap size is 1 to 30 micrometers (1 micrometer at the narrowest point and 30 micrometers at the thickest point), which are used to pattern and fill the insulating silicone in step 2 to form the electrode tip insulation area 2.

[0066] Step (2): Spray silicone release agent (silicone oil type release agent or polytetrafluoroethylene (PTFE) type release agent) onto the surface of the trapezoidal resin punch 7. Spray 3 to 5 times to ensure that a layer of release agent is attached to the surface of the trapezoidal resin punch 7.

[0067] Step (3): Spin-coat insulating silicone on the surface of the trapezoidal resin concave mold 8 at a speed of 750 rpm. The resulting silicone thickness is 200 micrometers, ensuring that the insulating silicone completely fills the trapezoidal groove of the concave mold.

[0068] Step (4): Align and press the trapezoidal resin punch 7 and trapezoidal resin die 8 together so that the upper surfaces of the trapezoidal punch and die are tightly pressed together without gaps to prevent uncured liquid insulating silicone from seeping in.

[0069] Step (5): Place the trapezoidal resin punch 7 and trapezoidal resin die 8, which are aligned and pressed together and kept in a tight state, in an oven at 100°C for 60 minutes to allow the insulating silicone to fully cure.

[0070] Step (6): Slowly remove the trapezoidal resin punch 7 to obtain the patterned insulating silicone electrode tip insulation area 3. Its shape and size are determined by the dimensions of the trapezoidal resin punch 7 and trapezoidal resin die 8 in step (1) (including the height of the isosceles trapezoid, the top edge, the bottom edge dimensions and the bottom angle).

[0071] Step (7): Use water-soluble adhesive tape to bond the cured insulating silicone surface from step (5) to demold the patterned insulating silicone electrode tip insulation area 3 from the surface of the trapezoidal resin mold 8 for the next transfer step. The water-soluble tape is 200 micrometers thick and can be completely dissolved in deionized water.

[0072] Step (8): The insulating area 3 at the electrode tip is precisely transferred to the conical acrylic cavity 9 with conical grooves inside. The number, distribution, and bottom angle of the conical grooves are the same as those of the trapezoidal resin cavity 8, but the height is greater, at 150 micrometers. The conical acrylic cavity 9 is made by high-precision CNC milling and polished to make its surface smooth.

[0073] Step (9): Immerse the water-soluble tape in deionized water until it is completely dissolved. It takes 20 minutes for the water-soluble tape to completely dissolve in water.

[0074] Step (10): Apply conductive silicone to fill the conical groove of the conical acrylic mold 9, and place it in an oven to dry and cure at 100℃ for 60 minutes. The conductive silicone is obtained by uniformly mixing multi-walled carbon nanotube powder with a tube length of 30 micrometers into insulating silicone, with a doping mass ratio of 5% to 30%, particularly 15%. The tube length of a single carbon nanotube is 2 to 50 μm. Actual measurements show that conductive silicone with a 15% doping ratio can achieve a sheet resistance as low as 5 Ω / square. A doping ratio greater than 30% will increase the Young's modulus of the conductive silicone, which is detrimental to maintaining the overall softness of the 3D neural electrode. A doping ratio less than 5% will result in the inability to reach the percolation threshold and thus non-conductive.

[0075] Step (11): Spin-coat insulating silicone and dry and cure it. Spin-coat speed is 750 rpm, oven temperature is 100℃, time is 60 minutes, and the thickness of the resulting silicone soft substrate 4 is 200μm.

[0076] Step (12): Demold the encapsulated finished electrode from the surface of the conical acrylic concave mold 9 to obtain a soft 3D conical silicone neural electrode array.

[0077] In this embodiment, during the transfer process in step S4, because the thickness of the insulating region 3 at the tip of the patterned insulating silicone electrode is extremely small (1-30 micrometers), the insulating region 3 at the electrode tip is prone to deformation and surface adhesion during the transfer process, leading to a significant decrease in transfer accuracy or even transfer failure. To solve this problem, this embodiment proposes a photoresist-assisted transfer method, which improves the tip exposure accuracy of the soft silicone 3D neural electrode by increasing the transfer accuracy.

[0078] Specifically, step S4 can be replaced by the following steps:

[0079] Step S4.1: Spin-coat photoresist to fill the internal grooves of the cured soft silicone insulating layer;

[0080] Step S4.2: Irradiate with ultraviolet light to cure the photoresist;

[0081] Step S4.3: Use water-soluble tape to bond the cured photoresist surface and transfer it together with the soft silicone insulating layer to the acrylic mold with conical grooves inside.

[0082] Step S4.4: Dissolve the water-soluble tape in water;

[0083] Step S4.5: Heat the dimethyl sulfoxide solution to dissolve the photoresist.

[0084] Preferably, the photoresist can be SU-8 photoresist or AZ photoresist.

[0085] Reference Figure 4 The photoresist-assisted transfer optimization process proposed in this embodiment can be achieved through the following steps:

[0086] Step (1): After aligning and pressing the trapezoidal resin punch 7 and trapezoidal resin die 8 to pattern the insulating area 2 at the electrode tip and demolding the punch, spin-coat SU-8 photoresist. Initially, spin-coat at a low speed of 500 rpm for 10 seconds, then maintain a low-to-medium speed of 800 rpm for 60 seconds to ensure uniform spread of the SU-8 photoresist. Then, irradiate with ultraviolet light to cure the SU-8 photoresist at an ultraviolet light intensity of 20 mW / cm². 2 The exposure time is 100 seconds. Finally, post-exposure baking is performed at a temperature of 95℃ for 10 minutes to allow the SU-8 photoresist to complete the cross-linking reaction.

[0087] Step (2): Use 200-micron thick water-soluble tape to bond the cured SU-8 photoresist surface to facilitate the next step of transfer printing.

[0088] Step (3): Demold the electrode tip insulation area 3 from the surface of the photocurable resin 3 mold and transfer it to the conical acrylic mold 9.

[0089] It is worth noting that the insulating region 3 at the electrode tip is made of soft silicone with a thickness of 1 to 30 micrometers (1 micrometer at the narrowest point and 30 micrometers at the thickest point), which is prone to deformation or surface adhesion during the transfer process, leading to transfer failure. The cured SU-8 photoresist provides support during the transfer process, which helps to ensure that the insulating region 3 at the electrode tip maintains its original shape and achieves precise transfer.

[0090] Step (4): Soak the water-soluble tape in water. After 20 minutes, the water-soluble tape will be completely dissolved.

[0091] Step (5): Heat the dimethyl sulfoxide (DMSO) solution to 80°C and completely immerse the cured SU-8 photoresist. Maintain the DMSO temperature at 80°C and immerse for 6 hours to completely dissolve the SU-8 photoresist.

[0092] It is worth noting that organic solvents such as acetone are difficult to dissolve fully cross-linked and cured SU-8 photoresist, but readily dissolve the conical acrylic mold 9. However, heated DMSO solution can slowly dissolve SU-8 photoresist 4, but its dissolving ability for the conical acrylic mold 9 is very weak. Therefore, choosing heated DMSO solution as the solvent allows for the complete removal of the SU-8 photoresist support structure with almost no impact on the conical acrylic mold 9, facilitating the final step of conductive silicone molding.

[0093] Step (6): Apply conductive silicone to fill the conical groove of the conical acrylic mold 9, and place it in an oven to dry and cure at 100°C for 60 minutes to obtain the formed 3D conical silicone electrode point. The subsequent encapsulation and release steps are the same as in the above embodiment.

[0094] Therefore, as described above, in this embodiment, the insulating encapsulation layer and internal conductive structure of the 3D neural electrode points are both based on soft silicone material, realizing the same matrix silicone encapsulation of the 3D neural electrode points and direct exposure of the electrode tips. In addition, this embodiment uses a photopolymer 3D printer to prepare resin silicone molds, and the patterning of the soft silicone encapsulation layer is achieved by direct alignment and pressing between molds, and the transfer is achieved by water-soluble tape. This enables the rapid, precise, and controllable preparation of tip-exposed soft silicone 3D neural electrodes without delamination or cracking failure.

[0095] According to the present invention, in order to further improve the accuracy of tip exposure of soft silicone 3D neural electrodes, a high-precision dedicated photopolymerization 3D printer can be used to directly print a conical resin mold with a dome-shaped conical groove, realizing a direct molding optimization process for tip exposure of soft 3D silicone electrode points without transfer printing. This is because only with sufficiently high resolution can a dome-shaped conical structure be printed. In the above embodiments, the low-resolution general-purpose photopolymerization 3D printer can only print flat-top trapezoidal structures. Although high-resolution photopolymerization 3D printers have higher equipment costs, they will greatly reduce process costs and complexity, and improve process accuracy.

[0096] In this regard, a method for exposing the tip of a soft 3D cone-shaped silicone neural electrode according to another exemplary embodiment of the present invention includes the following steps:

[0097] Step S1: Conical resin punches and dies are fabricated using a photopolymer 3D printer. The punch has multiple protrusions and the die has multiple grooves, all of which are dome-shaped conical structures. The dome dimensions of the protrusions and the corresponding grooves are the same. The height and bottom angle of the punch cone are larger than those of the die cone to form structured gaps during alignment and pressing. The dimensions of the punch trapezoid and the die trapezoid are determined according to the pattern of the neural electrode to be formed.

[0098] Step S2: Spray release agent onto the surface of the resin punch, spin-coat insulating silicone onto the surface of the resin die, and then align and press the resin punch and die together.

[0099] Step S3: Cure the insulating silicone to obtain a patterned 3D electrode point soft silicone insulating layer, and then remove the resin punch.

[0100] Step S4: Apply conductive silicone to fill the conical groove of the resin mold and dry it to cure, forming a soft silicone conductive area inside the electrode point, thereby obtaining a shaped 3D conical silicone electrode point.

[0101] Step S5: Spin-coat an insulating silicone encapsulation layer and dry and cure it, then demold to obtain a soft 3D cone-shaped silicone neural electrode array with exposed tips.

[0102] Reference Figure 5 This embodiment can be implemented through the following steps:

[0103] Step (1): Conical resin punch 10 and conical resin concave mold 11 are fabricated using a photopolymer 3D printer. At this stage, the protrusion and groove structure is optimized from the trapezoidal shape in the above embodiment to a domed cone shape, thus avoiding subsequent transfer steps. Therefore, there is no need to worry about deformation of the electrode tip insulation area 3 during the transfer process, or alignment issues during the transfer process. The protrusion height is 200 micrometers, and the concave depth is 150 micrometers. The bottom angle of the domed cone of the protrusion is 70 degrees, and the bottom angle of the domed cone of the concave is 50 degrees. Then, a release agent is sprayed onto the surface of the conical resin punch 10, and insulating silicone is spin-coated onto the surface of the conical resin concave mold 11.

[0104] Step (2): Align and press the conical resin punch 10 and conical resin die 11 together. The dome area will be tightly pressed and aligned, and structured gaps will appear in the side wall area to pattern and fill the insulating silicone. The gap size is 1 to 20 micrometers (1 micrometer at the narrowest point and 20 micrometers at the thickest point). Then, dry in an oven to cure the insulating silicone at 100°C for 60 minutes.

[0105] Step (3): Slowly remove the conical resin punch 10 to obtain the patterned electrode tip insulation area 3.

[0106] Step (4): At this point, the conical resin mold 11 can replace the conical acrylic mold 9 in the above embodiment. Therefore, there is no need for a transfer step. The conductive silicone is directly scraped to fill the conical groove of the conical resin mold 11, and then placed in an oven to dry and cure at 100°C for 60 minutes to obtain the formed 3D conical silicone electrode point.

[0107] Step (5): Spin-coat insulating silicone and dry and cure it. Spin-coat speed is 1000 rpm, oven temperature is 100℃, time is 60 minutes, and the thickness of the resulting soft substrate 4 is 150μm.

[0108] Step (6): Demold the molded finished electrode from the surface of the conical resin mold 11 to obtain a soft 3D conical silicone neural electrode array.

[0109] Therefore, as described above, in this embodiment, the insulating encapsulation layer and internal conductive structure of the 3D neural electrode points are also based on soft silicone material, realizing the same matrix silicone encapsulation of the 3D neural electrode points and direct exposure of the electrode tip. In addition, the one-step molding process of soft silicone 3D neural electrodes without transfer printing effectively reduces the process difficulty and further improves the accuracy of tip exposure of soft silicone 3D neural electrodes.

[0110] Finally, it should be noted that the features mentioned and / or shown in the above description of exemplary embodiments of the present invention can be combined in the same or similar manner with one or more other embodiments, combined with features in other embodiments, or substituted for corresponding features in other embodiments. These combined or substituted technical solutions should also be considered to be included within the scope of protection of the present invention.

Claims

1. A method for exposing a soft 3D conical silicon gel neural electrode tip, characterized in that, Comprising the following steps: Step 1, making resin male and female molds based on light-cured 3D printer, the multiple protrusions of the male mold and the multiple grooves of the female mold are all isosceles trapezoidal cross-section structure, the length of the top side of the trapezoid of the protrusion and the corresponding groove is equal, the height and the bottom angle of the trapezoid of the male mold are larger than those of the female mold, so as to form a structured gap when aligned and overlaid, the size of the trapezoid of the male mold and the female mold is determined according to the pattern of the neural electrode to be formed; Step 2, spin-coating insulating silicone on the surface of the resin female mold, and then aligning and overlaying the resin male and female molds; Step 3, curing the insulating silicone to obtain a 3D electrode point soft silicone insulation layer that has been patterned and formed, and then removing the resin male mold; Step 4, using water-soluble adhesive tape to bond the surface of the soft silicone insulation layer on the resin female mold, and then transferring it to a acrylic mold with internal conical grooves, and then dissolving the water-soluble adhesive tape with water, wherein the number and distribution of the conical grooves in the acrylic mold are consistent with the trapezoidal resin female mold, but the height is larger, and the taper angle determines the exposed shape of the 3D electrode point to be formed; Step 5, scraping conductive silicone to fill the conical grooves of the acrylic mold, and then drying and curing to form a soft silicone conductive area inside the electrode point, thereby obtaining a formed 3D conical silicone electrode point; Step 6, spin-coating an insulating silicone encapsulation layer and drying and curing, and then demolding to obtain a soft 3D conical silicone neural electrode point array with exposed tips.

2. The method of claim 1, wherein the soft 3D tapered silicone neural electrode tip exposure is characterized by, Step 4 is replaced by the following steps: Step 4.1, spin-coating photoresist to fill the internal grooves of the cured soft silicone insulation layer; Step 4.2, irradiating ultraviolet light to cure the photoresist; Step 4.3, using water-soluble adhesive tape to bond the surface of the cured photoresist, and then transferring it together with the soft silicone insulation layer to a acrylic mold with internal conical grooves; Step 4.4, dissolving the water-soluble adhesive tape with water; Step 4.5, heating dimethyl sulfoxide solution to dissolve the photoresist.

3. The method of claim 1 or 2, wherein the method is performed by a soft 3D conical silicon gel neural electrode tip exposure method, characterized in that, In step 1, the depth of the protrusion and the groove is 50-1000 μm, and the bottom angle of the trapezoid is 10°-170°.

4. The method of claim 1 or 2, wherein the soft 3D tapered silicone neural electrode tip exposure is characterized by, The resin male and female molds are made of one or more light-cured resin materials selected from polyurethane acrylate, epoxy acrylate, epoxy resin, and composite light-cured resin.

5. The method of claim 1 or 2, wherein the soft 3D tapered silicone neural electrode tip exposure is characterized by, In steps 2 and 6, the insulating silicone is made of one or more of polydimethylsiloxane, linear three-embedded copolymer, and Ecoflex / Dragonskin series platinum-catalyzed silicone rubber.

6. The method of claim 1 or 2, wherein the soft 3D tapered silicone neural electrode tip exposure is characterized by, In step 4, the acrylic mold with conical grooves is made by numerical control milling and polished to make the surface smooth.

7. The method of claim 1 or 2, wherein the method is performed by a soft 3D conical silicon gel neural electrode tip exposure method, characterized in that, In step 5, the conductive silicone is obtained by uniformly mixing multi-walled carbon nanotube powder in the insulating silicone material, with a doping mass ratio of 5%-30%, and a tube length of individual carbon nanotubes of 2-50 μm.

8. The method of claim 2, wherein the soft 3D tapered silicone gel neural electrode tip exposure is characterized by, The photoresist is selected from SU-8 photoresist or AZ photoresist.

9. A method for exposing a soft 3D conical silicon gel neural electrode tip, characterized in that, Comprising the following steps: Step 1, based on the light curing 3D printer to make the conical resin male mold and female mold, the male mold and the female mold are both dome-shaped conical structures, the dome size of the convex and the corresponding groove is the same, the height and the bottom angle of the male mold are larger than those of the female mold, so as to form a structured gap when aligned and pressed, and the size of the trapezoidal male mold and the female mold is determined according to the pattern of the to-be-formed neural electrode; Step 2, spray a release agent on the surface of the resin male mold, spin coat insulating silicone on the surface of the resin female mold, and then align and press the resin male mold and the female mold; Step 3, make the insulating silicone cured to obtain a 3D electrode point soft silicone insulation layer which has been patterned and formed, and then take off the resin male mold; Step 4, blade coat the conductive silicone to fill the conical groove of the resin female mold, and then dry and cure to form a soft silicone conductive area inside the electrode point, thereby obtaining a formed 3D conical silicone electrode point; Step 5, spin coat an insulating silicone encapsulation layer and dry and cure, and then demold to obtain a soft 3D conical silicone neural electrode point array with exposed tips.

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