Implantable flexible microelectrode array and preparation method thereof

Abstract

The present invention provides an implantable flexible microelectrode array, which includes: a flexible polymer substrate, on which a site pit for accommodating an electrode is provided; an electrode provided in the site pit, the electrode including a first metal layer and a second metal layer; a smooth liquid-injected porous surface layer covering the flexible polymer substrate; wherein the smooth liquid-injected porous surface layer includes: a first nanocone structure formed on the surface of the second metal layer, a second nanocone structure formed on the surface of the flexible polymer substrate, and a lubricant injected into the pores of the first nanocone structure and the second nanocone structure. The present invention also provides a method for preparing the flexible microelectrode array as described above. The flexible microelectrode array of the present invention reduces the adsorption capacity of the implanted electrode to glial cells, and improves the stability of the implanted electrode by reducing the adhesion of astrocytes and microglia on the implanted electrode.

Description

Technical Field

[0001] The invention belongs to the technical field of biomedical engineering, and in particular relates to an implantable flexible microelectrode array and a preparation method thereof. Background Art

[0002] Neuroprosthetic devices can restore patient function to impaired and pathologically affected functions such as neurological disorders, sensory loss, amputation, and spinal cord injury. It is also important to restore brain communication and neuroprosthetics through brain-computer interface (BCI) devices, which require the implantation of flexible microelectrode arrays (fMEAs) to receive and transmit neural electrical signals from the brain.

[0003] How to maintain the stability of implanted flexible microelectrode arrays for long-term use is an important issue. The central nervous system (CNS) of the human brain is composed of neurons and glial cells. Neurons occupy half of the central nervous system, and the rest are glial cells. Glial cells support the natural homeostasis of the brain to maintain the biological activity of neurons. When the implanted electrode is implanted into the brain, the blood-brain barrier (BBB) ​​is destroyed, and a series of inflammatory reactions occur after the electrode is implanted into the cortical tissue. Further, the influx of serum proteins (including albumin and fibronectin) activates the inflammatory response of nearby glial cells. Glial cells are composed of astrocytes and microglia. They are active around the implantation site and are easily adsorbed on the implanted electrode. 6-8 weeks after the electrode is implanted, microglia divide and migrate to the location where proinflammatory cytokines are released, and eventually transform into dense glial scars (several hundred microns thick). Neuronal degeneration is caused by acute and chronic inflammatory responses that eventually block blood vessels on neural communication pathways. The central nervous system has a central defense mechanism that activates microglia around the implant interface to restore damage when an inflammatory response occurs. The central nervous system also activates astrocytes within the first few days near the implant site to heal the wound. Due to glial scars, the interface between the implanted electrode and the central nervous tissue is severely damaged, and electrical coupling is lost, resulting in severe degradation of the recording / stimulation function of the implanted electrode and eventual failure.

[0004] How to reduce the adhesion of astrocytes and microglia on implanted electrodes to reduce scar formation around the implanted electrodes and thus improve the stability of the implanted electrodes is a problem that needs to be solved. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides an implantable flexible microelectrode array and a preparation method thereof, so as to reduce the adsorption capacity of the implanted electrode to glial cells and improve the stability of the implanted electrode by reducing the adhesion of astrocytes and microglia on the implanted electrode.

[0006] To achieve the above-mentioned object of the invention, one aspect of the present invention is to provide an implantable flexible microelectrode array, comprising:

[0007] A flexible polymer substrate, wherein the flexible polymer substrate is provided with site pits for accommodating electrodes;

[0008] An electrode is disposed in the site pit, wherein the electrode comprises a first metal layer and a second metal layer;

[0009] A smooth liquid-injected porous surface layer is disposed on the flexible polymer substrate; wherein,

[0010] The smooth liquid-infused porous surface layer includes: a first nanocone structure formed on the surface of the second metal layer, a second nanocone structure formed on the surface of the flexible polymer substrate, and a lubricant injected into pores of the first nanocone structure and the second nanocone structure.

[0011] Specifically, the heights of the first nanocone structure and the second nanocone structure are respectively 100 nm to 300 nm.

[0012] Specifically, the material of the first metal layer is Ti, the material of the second metal layer is Pt, and the lubricant is silicone oil.

[0013] Specifically, the thickness of the first metal layer is 10 nm to 25 nm, and the thickness of the second metal layer is 100 nm to 400 nm.

[0014] Specifically, the thickness of the flexible polymer substrate is 5 μm to 15 μm.

[0015] Specifically, the material of the flexible polymer substrate is PI.

[0016] The present invention also provides a method for preparing the above-mentioned implantable flexible microelectrode array, which comprises:

[0017] The flexible polymer substrate and the electrode formed in the flexible polymer substrate are prepared by combining a photolithography process and a sputtering deposition process;

[0018] The smooth liquid-injected porous surface layer is prepared on the flexible polymer substrate, comprising: preparing a first nanocone structure on the surface of the second metal layer by an electrochemical deposition process, preparing a second nanocone structure on the surface of the flexible polymer substrate by a reactive ion etching process; and injecting the lubricant into the pores of the first nanocone structure and the second nanocone structure.

[0019] Specifically, the step of preparing the flexible polymer substrate and the electrode by combining a photolithography process and a sputtering deposition process comprises:

[0020] A first flexible polymer film layer is prepared on a rigid substrate by a spin coating process;

[0021] Coating a photoresist on the first flexible polymer film layer, and forming a photoresist mask through an exposure and development process;

[0022] Under the shielding of the photoresist mask, sputtering and depositing the first metal layer and the second metal layer in sequence on the first flexible polymer film layer;

[0023] Stripping the photoresist mask to obtain the electrode on the first flexible polymer film layer;

[0024] coating the first flexible polymer film layer to form a second flexible polymer film layer;

[0025] performing dry etching on the second flexible polymer film layer to expose the electrode;

[0026] The first flexible polymer film layer is peeled off from the rigid substrate to prepare a flexible polymer substrate containing the electrode.

[0027] Specifically, the electrochemical deposition process is a three-electrode system electrochemical deposition process, wherein the electrode located on the flexible polymer substrate is a working electrode, the Pt electrode is a counter electrode, and the Ag / AgCl electrode is a reference electrode; the etching gas in the reactive ion etching process is O 2 .

[0028] Specifically, the lubricant is injected so that the lubricant wets and adheres to the surfaces of the first nanocone structure and the second nanocone structure to form a stable liquid surface, and after the injection is completed, the flexible polymer substrate is tilted and placed for a certain period of time to remove excess lubricant.

[0029] The implantable flexible microelectrode array provided in an embodiment of the present invention forms a smooth liquid-infused porous surface (SLIPS) on the surface of the microelectrode array, which reduces the adsorption capacity of the implanted electrode to glial cells. After the microelectrode array is implanted in the body, the adhesion of astrocytes and microglia on the implanted electrode can be reduced, thereby reducing the formation of glial scars around the implanted electrode and improving the stability of the implanted electrode.

[0030] In addition, the method for preparing the flexible microelectrode array provided by the embodiment of the present invention has a simple process, is easy to implement, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1is a schematic structural diagram of a flexible microelectrode array provided by an embodiment of the present invention;

[0032] Figure 2 is a schematic diagram of the cross-sectional structure of a flexible microelectrode array provided by an embodiment of the present invention;

[0033] Figure 3 is an exemplary illustration of a process flow for preparing a flexible polymer substrate containing the electrode in an embodiment of the present invention;

[0034] Figure 4 is an exemplary illustration of a process flow for preparing a smooth liquid-injected porous surface layer on a flexible polymer substrate in an embodiment of the present invention;

[0035] Figure 5 is a SEM image of the Pt nanocone structure prepared in Example 1 of the present invention;

[0036] Figure 6 and Figure 7 is an electrical test curve diagram of the electrode sample prepared in Example 1 of the present invention;

[0037] Figure 8 It is a redox characteristic curve diagram of the electrode sample prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical scheme and advantages of the present invention clearer, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. Examples of these preferred embodiments are illustrated in the accompanying drawings. The embodiments of the present invention shown in the accompanying drawings and described according to the accompanying drawings are merely exemplary, and the present invention is not limited to these embodiments.

[0039] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the solutions according to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0040] The present invention first provides an implantable flexible microelectrode array. Figure 1 and Figure 2 The flexible microelectrode array includes a flexible polymer substrate 1 and a plurality of electrodes 2 arranged on the flexible polymer substrate 1. A pad 3 is arranged at the edge of the flexible polymer substrate 1, and the electrode 2 is connected to the pad 3 through a wire 4.

[0041] Figure 2 FIG. 1 is a cross-sectional schematic diagram of an implantable flexible microelectrode array provided in an embodiment of the present invention (only one electrode 2 is shown as an example in the figure). Figure 2As shown, the flexible polymer substrate 1 is provided with a site pit 11 for accommodating an electrode 2, the electrode 2 is arranged in the site pit 11, the electrode includes a first metal layer 21 and a second metal layer 22, and the flexible polymer substrate 1 is also provided with a smooth liquid-injected porous surface layer 5, and the smooth liquid-injected porous surface layer 5 covers the entire surface of the flexible polymer substrate 1.

[0042] Specifically, the smooth liquid-injected porous surface layer 5 includes: a first nanocone structure 23 formed on the surface of the second metal layer 22, a second nanocone structure 12 formed on the surface of the flexible polymer substrate 1, and a lubricant 6 injected into the pores of the first nanocone structure 23 and the second nanocone structure 12, wherein the lubricant 6 wets and adheres to the surfaces of the first nanocone structure 23 and the second nanocone structure 12 to form a stable liquid surface.

[0043] The implantable flexible microelectrode array as described above forms a smooth liquid-infused porous surface (SLIPS) on the surface of the microelectrode array, which reduces the adsorption capacity of the implanted electrode to glial cells. After the microelectrode array is implanted in the body, it can reduce the adhesion of astrocytes and microglia on the implanted electrode, thereby reducing the formation of glial scars around the implanted electrode and improving the stability of the implanted electrode.

[0044] Furthermore, the first nanocone structure 23 is formed on the surface of the second metal layer 22 by an electrochemical deposition process, and its material is the same as that of the second metal layer 22. Therefore, after the first nanocone structure 23 is formed on the surface of the electrode 2, the surface area of ​​the electrode is increased, which can effectively reduce the impedance of the electrode and improve the electrical signal transmission performance of the flexible microelectrode array.

[0045] In a preferred embodiment, the heights of the first nanocone structure 23 and the second nanocone structure 12 are respectively 100 nm to 300 nm; the thickness of the smooth liquid-injected porous surface layer 5 depends on the height of the nanocone structure. Usually, after the lubricant 6 is injected, the liquid level of the lubricant 6 will be slightly higher than the nanocone structure to form a stable liquid surface.

[0046] In a preferred solution, the material of the first metal layer 21 is Ti, the material of the second metal layer 22 is Pt, and the lubricant 6 is silicone oil.

[0047] In a preferred embodiment, the thickness of the first metal layer 21 is 10 nm to 25 nm, and the thickness of the second metal layer 22 is 100 nm to 400 nm.

[0048] In a preferred solution, the thickness of the flexible polymer substrate 1 is 5 μm to 15 μm, and the shape and size of the electrode 2 are optimized according to actual needs, and the shape can be, for example, circular, square or rectangular.

[0049] In a preferred embodiment, the material of the flexible polymer substrate 1 is polyimide (PI).

[0050] An embodiment of the present invention provides a method for preparing the above-mentioned implantable flexible microelectrode array, the preparation method comprising the following steps:

[0051] Step S10: preparing the flexible polymer substrate and the electrode formed in the flexible polymer substrate by combining a photolithography process and a sputtering deposition process.

[0052] In a preferred embodiment, see Figure 3 , the step S10 comprises:

[0053] S11, such as Figure 3 As shown in (a), a first flexible polymer film layer 1a is prepared by spin coating on a rigid substrate 100. The rigid substrate 100 is, for example, a silicon wafer or glass.

[0054] S12, such as Figure 3 As shown in (b), photoresist is coated on the first flexible polymer film layer 1a, and a photoresist mask 200 is formed by an exposure and development process.

[0055] S13, such as Figure 3 As shown in (b), under the shielding of the photoresist mask 200, the first metal layer 21 and the second metal layer 22 are sequentially sputter-deposited on the first flexible polymer film layer 1a.

[0056] S14, such as Figure 3 As shown in (c), the photoresist mask 200 is peeled off to obtain the electrode 2 on the first flexible polymer film layer 1a.

[0057] S15, such as Figure 3 As shown in (d), a second flexible polymer film layer 1 b is formed by coating on the first flexible polymer film layer 1 a , and the second flexible polymer film layer 1 b covers the entire surface of the first flexible polymer film layer 1 a and covers the electrode 2 .

[0058] S16, such as Figure 3As shown in (e), the second flexible polymer film layer 1b is dry-etched to expose the electrode 2. The first flexible polymer film layer 1a and the second flexible polymer film layer 1b after etching and thinning constitute a flexible polymer substrate 1, and a site pit 11 for accommodating the electrode 2 is provided on the flexible polymer substrate 1, and the electrode 2 is located in the site pit 11.

[0059] S17, such as Figure 3 As shown in (f), the first flexible polymer film layer 1a is peeled off from the rigid substrate 100 to prepare a flexible polymer substrate 1 including the electrode 2.

[0060] Step S20, preparing and forming the smooth liquid-injected porous surface layer on the flexible polymer substrate.

[0061] In a preferred embodiment, see Figure 4 Combined with Figure 3 (Only one electrode structure is shown in the figure as an example), the step S20 includes:

[0062] S21, such as Figure 4 -(a) and Figure 4 As shown in (b), a first nanocone structure 23 is prepared on the surface of the second metal layer 22 by an electrochemical deposition process.

[0063] Preferably, the electrochemical deposition process is a three-electrode system electrochemical deposition process, wherein the electrode 2 located on the flexible polymer substrate 1 is a working electrode, a Pt electrode is a counter electrode, and an Ag / AgCl electrode is a reference electrode.

[0064] S22, such as Figure 4 As shown in (c), a second nanocone structure 12 is prepared on the surface of the flexible polymer substrate 1 by a reactive ion etching (RIE) process. In a preferred embodiment, the etching gas in the reactive ion etching process is O 2

[0065] S23, such as Figure 4 As shown in (d), the lubricant 6 is injected into the pores of the first nanocone structure 23 and the second nanocone structure 12 to prepare the implantable flexible microelectrode array.

[0066] In a specific solution, the lubricant 6 is injected so that the lubricant 6 wets and adheres to the surfaces of the first nanocone structure 23 and the second nanocone structure 12 to form a stable liquid surface, thereby preparing the smooth liquid-injected porous surface layer 5 on the flexible polymer substrate 1. After the injection is completed, the flexible polymer substrate 1 is tilted for a certain period of time to remove excess lubricant.

[0067] Example 1

[0068] In this embodiment, the material of the flexible polymer substrate is selected as polyimide (PI), the first metal layer in the electrode structure is selected as Ti, the second metal layer is selected as Pt, and the lubricant is selected as silicone oil to explain the technical solution of the present invention in more detail.

[0069] See also Figure 3 and Figure 4 In this embodiment, the flexible microelectrode array is prepared according to the following process steps:

[0070] (1) A first PI film with a thickness of 5 μm was prepared on a silicon substrate by a spin coating process, and then a photoresist mask was formed on the first PI film. The exposure window of the mask pattern (corresponding to the pattern of the electrode to be deposited) was circular with a diameter of 200 μm.

[0071] (2) Under the shielding of the photoresist mask, a 20 nm thick Ti metal layer and a 100 nm thick Pt metal layer are sputtered and deposited in sequence on the first PI film, and then the photoresist mask is peeled off to obtain an electrode pattern including the Ti metal layer and the Pt metal layer on the first PI film.

[0072] (3) Spin coating and curing the first PI film to form a 5 μm thick second PI film, wherein the second PI film covers the entire surface of the first PI film and covers the electrode pattern.

[0073] (4) Dry etching the second PI film to expose the electrode pattern. The first PI film and the second PI film after etching and thinning form a flexible polymer substrate, and the second PI film surrounds the electrode pattern to form a site pit for accommodating the electrode, and the electrode pattern is located in the site pit.

[0074] (5) Peeling off the first layer of PI film from the silicon substrate to prepare a PI substrate including the electrode pattern.

[0075] (6) A Pt nanocone structure is prepared on the surface of the Pt metal layer through an electrochemical deposition process of a three-electrode system.

[0076] Specifically, the PI substrate containing the electrode pattern obtained in step (5) is used as the working electrode, the Pt electrode is used as the counter electrode, and the Ag / AgCl electrode is used as the reference electrode, wherein the electrolyte contains the following components: 10 mM (NH 4 ) 2 PtCl 6 、7.5mMPtCl 4 , 25 mM NaH2 PO 4 and 0.425M Na 2 HPO 4 .

[0077] Before the electrochemical deposition process: clean the surface of the microelectrode pattern in acetone solution and 2 SO 4 The solution was subjected to 20 cyclic voltammetric scans at a scanning voltage of -0.2 V to +1.2 V (relative to the potential of the Ag / AgCl reference electrode) and a scanning rate of 100 mV / s. The electrolyte was degassed by nitrogen bubbling.

[0078] The specific conditions and parameters of the electrochemical deposition process are: electroplating at a constant potential of -0.6 V for 900 s using chronoamperometry.

[0079] Based on the above process, a Pt nanocone structure is prepared and formed on the surface of the Pt metal layer of the electrode pattern. Figure 5 is a SEM image of the Pt nanocone structure prepared in this example. Figure 5 It can be known that the Pt nanocone structure enables the electrode pattern to be formed into a rough surface and increases the surface area.

[0080] (7) A PI nanocone structure is formed on the surface of the PI substrate by a reactive ion etching process. In this embodiment, the etching gas in the reactive ion etching process is O 2 , the gas flow rate is 20sccm, the pressure is 14pa, the power is 150w, and the etching time is 10min.

[0081] (8) On the PI substrate, silicone oil is injected into the pores of the Pt nanocone structure and the PI nanocone structure, so that the silicone oil wets and adheres to the surface of the Pt nanocone structure and the PI nanocone structure to form a stable liquid surface, that is, a smooth liquid-infused porous surface (SLIPS) is formed. The sample is then tilted at an angle of 60° for 8 hours to remove excess silicone oil, and finally an implantable flexible microelectrode array is prepared.

[0082] The implantable flexible microelectrode array prepared in the above embodiment forms a smooth liquid-injected porous surface on the surface of the microelectrode array, which reduces the adsorption capacity of the implanted electrode to glial cells. After the microelectrode array is implanted in the body, it can reduce the adhesion of astrocytes and microglia on the implanted electrode, thereby reducing the formation of glial scars around the implanted electrode, thereby improving the stability of the implanted electrode.

[0083] On the other hand, the Pt nanocone structure in this embodiment makes the electrode pattern form a rough surface and increases the surface area, which can effectively reduce the impedance of the electrode and improve the electrical signal transmission performance of the flexible microelectrode array. This embodiment performs impedance testing on some samples in the above preparation process, and the test samples include: the sample with a flat electrode surface obtained in step (5) (sample 1), the sample with a nanocone structure obtained in step (6) (sample 2), and the final flexible microelectrode array sample obtained in step (8) (the electrode surface is a nanocone structure and covered with a smooth injection porous surface, sample 3).

[0084] Figure 6 and Figure 7 is a graph related to the electrical test of samples 1-3 of this embodiment, wherein: Figure 6 The curves representing the impedance of electrode samples 1-3 as a function of frequency are shown. Figure 7 The curves representing the phase angle of electrode samples 1-3 as a function of frequency are shown.

[0085] from Figure 6 From the impedance curve with frequency, we can see that when the signal frequency is high, the impedance of sample 1 is the largest, the impedance of sample 2 is the smallest, and the impedance of sample 3 is slightly increased compared to sample 2 but also greatly reduced compared to sample 1. The data of the impedance test results when the frequency of the test signal is 1KHz are shown in Table 1 below.

[0086] Table 1

[0087] Test samples Impedance value (kΩ) Impedance reduction ratio relative to sample 1 (%) Sample 1 20.38 / Sample 2 3.21 84.24 Sample 3 4.68 77.03

[0088] It can be seen from Table 1 that the impedance value of sample 1, whose electrode surface is flat, is very large, which is not conducive to the recording and stimulation of nerve cell signals by the implantable microelectrode array. The electrode surface of sample 2 is a nanocone structure, which increases the surface area, so the impedance value is greatly reduced, and the impedance reduction ratio reaches 84.24%. Sample 3, that is, the electrode structure finally obtained by the present invention, has a slightly increased impedance compared to sample 2 due to the addition of a smooth liquid-injected porous surface, but the impedance value is reduced by 77.03% compared to sample 1, which is still excellent for recording and stimulating nerve cell signals.

[0089] In this example, cyclic voltammetry (CV) was used to study the redox characteristics of the above samples 1-3, and the following results were obtained: Figure 8 The characteristic curve is shown. Figure 8 It can be seen that the electrode structure provided by the present invention has good redox properties.

[0090] The above is only a specific implementation of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A method for preparing an implantable flexible microelectrode array, characterized in that: include: A first flexible polymer film layer is prepared on a rigid substrate by a spin coating process; Coating a photoresist on the first flexible polymer film layer, and forming a photoresist mask through an exposure and development process; Under the cover of the photoresist mask, sputtering and depositing a first metal layer and a second metal layer in sequence on the first flexible polymer film layer; Stripping the photoresist mask to obtain the electrode on the first flexible polymer film layer; coating the first flexible polymer film layer to form a second flexible polymer film layer; performing dry etching on the second flexible polymer film layer to expose the electrode; Peeling the first flexible polymer film layer off the rigid substrate to obtain a flexible polymer substrate containing the electrode; Prepare a first nanocone structure on the surface of the second metal layer by an electrochemical deposition process, and prepare a second nanocone structure on the surface of the flexible polymer substrate by a reactive ion etching process; injecting a lubricant into the pores of the first nanocone structure and the second nanocone structure to form a smooth liquid-injected porous surface layer; Wherein, the material of the first metal layer is Ti, the material of the second metal layer is Pt, and the lubricant is silicone oil.

2. The method for preparing an implantable flexible microelectrode array according to claim 1, characterized in that: The electrochemical deposition process is a three-electrode system electrochemical deposition process, wherein the electrode located on the flexible polymer substrate is the working electrode, the Pt electrode is the counter electrode, and the Ag / AgCl electrode is the reference electrode; the etching gas in the reactive ion etching process is O2.

3. The method for preparing an implantable flexible microelectrode array according to claim 1, characterized in that: The lubricant is injected so that the lubricant wets and adheres to the surfaces of the first nanocone structure and the second nanocone structure to form a stable liquid surface. After the injection is completed, the flexible polymer substrate is tilted and placed for a certain period of time to remove excess lubricant.

4. The method for preparing an implantable flexible microelectrode array according to claim 1, characterized in that: The heights of the first nanocone structure and the second nanocone structure are respectively 100 nm to 300 nm.

5. The method for preparing an implantable flexible microelectrode array according to claim 1, characterized in that: The thickness of the first metal layer is 10 nm to 25 nm, and the thickness of the second metal layer is 100 nm to 400 nm.

6. The method for preparing an implantable flexible microelectrode array according to any one of claims 1 to 5, characterized in that: The thickness of the flexible polymer substrate is 5 μm-15 μm.

7. The method for preparing an implantable flexible microelectrode array according to claim 6, characterized in that: The material of the flexible polymer substrate is PI.

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