Electrodes, medical devices, systems, and methods of manufacture

Abstract

The present invention provides an electrode having a substrate and an electrically conductive polymer film layer on an exposed surface, the film layer having a capacitance per area of at least 0.5 F / cm2 and / or a thickness of between 50 [mu] m and 1000 [mu] m. There is also provided a medical device having a plurality of electrodes wherein at least one of the electrodes comprises a polymeric film layer having a capacitance per area of at least 0.5 F / cm2, as well as a system comprising the medical device, a method of treating a spinal cord lesion and a method of making the electrodes.

Description

Technical Field

[0001] The present invention relates to electrodes, medical devices, systems and methods of treatment and manufacture. The present invention particularly, but not exclusively, relates to implantable devices, for example for the treatment of spinal cord injuries. Background Art

[0002] Spinal cord injury (SCI) is a serious condition that affects more than 1.5 million people worldwide, including 250,000 to 500,000 new cases each year. SCI occurs when bundles of neurons in the spinal cord are damaged, resulting in permanent loss of sensation, movement, and organ control below the site of the lesion.

[0003] SCI also imposes a socioeconomic burden on individuals, their families, and the healthcare systems that support them.

[0004] There are currently no treatments for the primary injury. Therefore, treatment is usually limited to treating the secondary injury, such as by performing decompressive surgery followed by rehabilitation to promote tissue growth to restore some of the lost function.

[0005] Electrical stimulation of neural tissue using implantable electrodes has shown promise for SCI treatment. It is well known that electric fields applied to neurons with damaged nerve tracts promote and guide the regeneration of new axons. When DC electric fields are applied to the spinal cord for several weeks after injury (called OFS - oscillatory field stimulation), recovery of neurological deficits has been observed in animal models and human SCI patients.

[0006] However, translation of OFS technology into clinical applications has stagnated over the past decade. This is largely due to the lack of an appropriate implantable platform to deliver the electric field to spinal cord tissue. Previous OFS testing has relied on the use of redesigned pacemaker leads, which are bulky, require additional surgery to remove the lead and battery after treatment delivery, and can cause secondary damage to sensitive neural tissue. At least one reason for this is the low capacitance of implantable electrodes, so several electrodes are required to provide the necessary electric field at the implant site. Summary of the invention

[0007] The present invention aims to solve one or more of the above problems.

[0008] Aspects of the present invention are directed to providing devices and electrodes therefor that can deliver OFS without using invasive surgery or using minimally invasive surgery.

[0009] Aspects of the present invention are directed to methods of treating spinal cord injury using electrical stimulation achieved by a novel device.

[0010] In the most general case, aspects of the invention provide electrodes and devices incorporating electrodes having high capacitance, particularly for delivering sustainable electric field therapy at low and ultra-low frequencies. Further aspects relate to methods of making such electrodes and therapeutic methods using electric fields.

[0011] A first aspect of the present invention provides a medical device having a plurality of electrodes, wherein at least one of the electrodes comprises a polymer film layer having a thermal conductivity of at least 0.1 F / cm 2 Capacitance per unit area.

[0012] Preferably, the film has a F / cm 2 Capacitance per unit area, preferably 1F / cm 2 , more preferably at least 5F / cm 2 In some embodiments, the membrane layer may have a thermal conductivity up to 10 F / cm 2 Capacitance.

[0013] In the standard cyclic voltammetry range of 1 volt, 0.1F / cm 2 The capacitance corresponds to 100mC / cm 2 A similar relationship occurs for other capacitance values ​​given in this paper, such as 0.5 F / cm2 in the standard cyclic voltammetry range of 1 volt. 2 The capacitance corresponds to 500mC / cm 2 charge storage capacity.

[0014] Preferably, the capacitance of the membrane layer is sufficient to maintain at least 100 μA / cm between the electrodes. 2 The non-Faradaic current density is maintained for a period of at least 100 seconds.

[0015] Preferably, the thickness of the film layer is between 50 μm and 1000 μm. More preferably, the thickness of the film layer is above 100 μm, and more preferably above 250 μm. The thickness of the film layer can increase the capacitance.

[0016] The device of this aspect can generate an electric field for therapeutic purposes. For example, in some embodiments, the electric field can be used in OFS to guide neural tissue regeneration through the lesion site of spinal cord injury. The device is intended to provide a uniform electric field across the lesion site while minimizing the surgical wound area.

[0017] In a preferred embodiment, the membrane layer is formed from PEDOT / PSS, which is a biocompatible conductive polymer.

[0018] The conductive polymer layer may be attached to a conductive surface, which may take a variety of forms, such as: one or more thin wires; thin metal foil (1 μm-50 μm); wire mesh; metal film (<1 μm); or metal particles or flakes embedded in a polymer film. However, in certain embodiments, the polymer layer itself may be sufficiently conductive to obviate the need for a conductive surface.

[0019] Preferably, the device is flexible. In some embodiments, the flexibility of the device allows it to conform to the spinal cord area or other area of ​​the body where the device is to be implanted. Flexibility can also facilitate minimally invasive removal surgery, in which the electrode is removed through a small incision.

[0020] In most embodiments, one side of the electrode will be insulated so that current flows primarily through the exposed conductive polymer layer.

[0021] In particular embodiments, the device may have a bending radius of no more than about 2 mm, preferably no more than 1.5 mm, and more preferably no more than 0.5 mm. The bending radius is measured based on the inner curvature and is the minimum radius at which a component (in this case, the device) can be bent in at least one direction without damaging it. The bending radius defined here refers to elastic deformation as opposed to plastic deformation, such that a device bent to a radius greater than the minimum bending radius under an applied force will at least partially return to its original shape when the applied force is removed. In other words, in these embodiments, the device of this aspect can be bent to an inner curvature of 2 mm, for example by rolling up when the device is configured for insertion into a patient, and then unfolding (e.g., spreading out) to an extended, less curved configuration (e.g., a substantially planar configuration), and still function exactly as it did before bending. Alternatively, the device can be rolled up or bent in an implanted form to conform to the implantation area, or can be bent to match the skin surface for wearable applications.

[0022] The device may further comprise a pulse generator coupled to the electrodes and arranged to control the electric field between the electrodes.The pulse generator may be coupled to the electrodes by wires, or may be coupled wirelessly by any known communication protocol.

[0023] Preferably, the pulse generator is arranged to ensure that the voltage between the electrodes does not exceed 1.2 V. 1.2 V is the "water window" above which voltages can lead to water decomposition and other Faradaic reactions that may produce toxic by-products.

[0024] The pulse generator may be set so that the voltage between the electrodes reverses polarity with a period of at least 300 seconds. The long period allows axonal regeneration to occur in the direction of polarity prior to the reversal to stimulate axonal regeneration from the other side of the lesion. Typically, the OFS oscillation period is in the range of 2 minutes to 30 minutes, more typically 10 minutes to 15 minutes.

[0025] In certain embodiments, the device has an overall thickness of less than 1.5 mm and / or a width of less than 2 cm. Thus, the device is very small and therefore suitable for implantation, for example, through a percutaneous incision.

[0026] In certain embodiments, the device is an implantable device. Preferably, the implantable device of these embodiments is configured for implantation and / or removal through an incision no larger than 1 cm, and thus can be used in minimally invasive surgery, such as percutaneous surgery.

[0027] Preferably, the device is configured to receive power wirelessly from an independent power source. Wireless transmission of power to an implanted device is well known, and the device of this aspect may utilize any known technology suitable for this purpose. Wireless transmission of power allows the power source to be located external to the patient when the device is implanted, so the power source can be larger than in the case of an implantable power source, and can also be easily replaced and / or recharged.

[0028] A further aspect of the present invention provides a system for treating spinal cord injury, the system comprising: a medical device according to the first aspect above, including some, all or none of the optional and preferred features of that aspect, wherein the device is an implantable device; and a pulse generator coupled to electrodes of the device and configured to generate a varying electric field between the electrodes.

[0029] Preferably, the pulse generator is also implantable.

[0030] The pulse generator may be coupled to the electrodes via wires, or may be coupled wirelessly via any known communication protocol. Where the pulse generator is wirelessly coupled, it need not be implantable (but may be implantable in certain embodiments).

[0031] The system may further include a power supply. Preferably, the power supply is wirelessly coupled to the pulse generator. This allows the power supply to be located outside the patient's body in a configuration where the pulse generator is implanted, so the power supply can be larger than in the case of an implantable power supply and can also be easily replaced and / or recharged.

[0032] Preferably, the pulse generator is arranged to ensure that the voltage between the electrodes does not exceed 1.2 V. 1.2 V is the "water window" above which voltages can lead to water decomposition and other Faradaic reactions that may produce toxic by-products.

[0033] The pulse generator may be configured so that the voltage between the electrodes reverses polarity with a period of at least 300 seconds. The long period allows axonal regeneration to occur in the direction of polarity prior to the reversal to stimulate axonal regeneration from the other side of the lesion. Typically, the OFS oscillation period is in the range of 2 minutes to 30 minutes, more typically 10 minutes to 15 minutes.

[0034] A further aspect of the invention provides a method for treating a spinal cord lesion in a patient, the method comprising the steps of: percutaneously implanting a plurality of electrodes at locations proximate to the patient's spinal cord and on opposite sides of the lesion; applying an electric field between the electrodes to stimulate axonal regeneration; and periodically reversing the polarity of the electric field to stimulate axonal regeneration from the other side of the lesion.

[0035] The implanted electrode may be an electrode according to the aspects further described below, or may be part of a device according to the first aspect above, including some, all, or none of the optional and preferred features of any aspect, but not necessarily the optional and preferred features of only one of these aspects.

[0036] Preferably, the implantation step is performed during decompressive surgery, which is a known method for treating secondary effects of spinal cord injury.

[0037] Preferably, the method further comprises the step of percutaneously removing said electrode after said treatment.

[0038] A further aspect of the present invention provides an electrode having a substrate and a conductive polymer film layer on an exposed surface, the film layer having a conductivity of at least 0.1 F / cm 2 Capacitance per unit area.

[0039] Preferably, the film has a F / cm 2 Capacitance per unit area, preferably at least 1F / cm 2 , more preferably at least 5F / cm 2 In some embodiments, the membrane layer may have a thermal conductivity up to 10 F / cm 2 of capacitance.

[0040] A further aspect of the present invention provides an electrode having a substrate and a conductive polymer film layer on an exposed surface, the film layer having a thickness between 50 μm and 1000 μm.

[0041] Preferably, the thickness of the film layer is above 100 μm, more preferably above 250 μm.

[0042] In both aspects, the electrode preferably has a thickness of no more than 1.5 mm and a width of no more than 1.5 cm. This allows the electrode, together with any associated components, to be implanted by a minimally invasive surgical approach, such as percutaneously.

[0043] The electrodes of these aspects may be used as electrodes of the medical device of the first aspect described above.

[0044] A further aspect of the present invention provides a method for manufacturing an electrode, the method comprising the steps of: coating the surface of a conductive substrate with a film layer of the conductive polymer using a solution of the conductive polymer, and soft-baking the substrate and the film layer until the film layer reaches a thickness of at least 50 μm; and hard-baking the resulting structure.

[0045] The electrode formed by the method may be an electrode according to the above aspects, including some, all, or none, but not necessarily, of the optional and preferred features of those aspects.

[0046] The method may further comprise the step of coating the surface of the substrate to be coated with the conductive polymer film layer with an adhesion promoting layer (such as a hydrophilic polymer, such as PVA) before coating the conductive polymer film layer.

[0047] According to a further aspect of the present invention there is provided a method of treating the human or animal body, the method comprising implanting a medical device or electrode according to the above aspects.

[0048] Unless otherwise stated, any features (including optional or preferred features) described with respect to one of the above aspects are also applicable in combination with the apparatus, system and method of any other above aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The present invention is described below by way of example with reference to the accompanying drawings, in which:

[0050] Figure 1 It is a diagram of the operating principle of OFS;

[0051] Figure 2 The use of implanted electrodes to deliver OFS according to an embodiment of the present invention is shown;

[0052] Figure 3 A system according to an embodiment of the present invention is shown;

[0053] Figure 3 shows an apparatus according to an embodiment of the present invention;

[0054] Figure 4 Shows Figure 3 A device configured to conform to a curved surface having dimensions similar to the spinal cord;

[0055] Figure 6 shows simulation results of electrical potentials in spinal cord tissue generated by a device according to an embodiment of the present invention;

[0056] Figure 7 A single electrode according to an embodiment of the present invention is shown;

[0057] Figure 8 is a potentiometric graph showing use of a device according to the invention in an in vitro test for approximately 12 hours;

[0058] Fig. 9 is a schematic diagram showing steps of manufacturing an electrode according to an embodiment of the present invention; and

[0059] Fig.10 is a cyclic voltammogram of an electrode according to an embodiment of the present invention. DETAILED DESCRIPTION

[0060] Embodiments of the present invention are described below in conjunction with the treatment of SCI using OFS. However, it should be understood that this is only one use for electrodes, devices, and systems according to embodiments of the present invention. In other embodiments not described in detail herein, electrodes, devices, and systems according to embodiments of the present invention can be, for example, used in wearable applications (e.g., for wound healing).

[0061] Figure 1 Extract from reference (1) illustrating the working principle of OFS. The continuous electric field enhances the regeneration of damaged axons 2a, 2b above the lesion 1. Growth is stimulated toward the negative pole. Thus, in OFS, the polarity of the applied electric field is periodically switched, in an alternating manner, allowing axons 2b below the lesion 1 to be directed cranially toward the brain to restore sensory perception, and axons 2a above the lesion 1 to be directed caudally toward the periphery to restore motor control.

[0062] The electric field in the OFS is typically maintained for several minutes (2-30 minutes, more often 10-15 minutes) in each direction between periodic polarity switching, requiring electrodes with high capacitance. Originally proposed OFS systems attempted to achieve this by using a set of six relatively large pacemaker electrodes. However, the large surgical wound area of ​​these pacemakers resulted in increased risk to the patient and provided suboptimal electric field distribution across the lesion site.

[0063] Embodiments of the present invention provide methods of delivering OFS, as well as devices and systems that can deliver OFS, which can be implanted via minimally invasive surgery (eg, percutaneously).

[0064] Figure 2 Components of a system 10 for treating SCI according to an embodiment of the present invention are schematically shown. The system 10 comprises two implantable electrodes 20 which, in use, are implanted in a spinal cord region S of a patient P by laminectomy and are arranged approximately equidistantly on either side of a known lesion site 1. Examples of electrodes 20 according to further embodiments of the present invention are described in more detail below.

[0065] Electrode 20 is connected or coupled to an implantable pulse generator ("IPG") 30. Although Figure 2 The connections in are shown as wired connections, but wireless connections by any known means are also possible. Figure 2 The IPG 30 in FIG. 1 is shown as being implanted within the body of the patient P, but it may also be located externally. The IPG 30 may be implanted at a location close to, but not directly within or adjacent to, the spinal cord region S, such as the gluteal region. This means that the IPG 30, while preferably small to allow implantation without major surgery, need not itself be of a size, shape or material suitable for implantation in the spinal cord.

[0066] An example of an IPG 30 is a pulse generator chip from Teliatry, Inc. of Richardson, Texas, which is essentially a cuboid and glass-encapsulated, measuring 11 mm x 7 mm x 1.5 mm. This is small enough to be implanted and removed by minimally invasive surgery.

[0067] Figure 3 A system according to an embodiment of the present invention is shown. The implanted components of the system are as described above with respect to Figure 2 The system also includes a controller 40 having an external PCM lithium-ion rechargeable battery pack and an induction coil 31 implanted under the patient's skin to wirelessly power the implanted components via known wireless power transfer methods. The system may also include a wireless device, such as a mobile handheld terminal 50, which can control the stimulation via an application running on the device and send instructions to the controller 40.

[0068] Advances in microfabrication and materials science have enabled a new generation of neural implant technology (2, 3). Devices according to embodiments of the present invention include ultra-flexible parylene sheets that can conform to the surface of neural organs, combined with conductive polymer electrodes that can deliver higher currents in a small space than their traditional metal counterparts.

[0069] By adapting thin film conductive polymer implant technology to the requirements and properties of the injured spinal cord, the device can be used to more effectively deliver OFS therapy to SCI patients, inducing post-injury regeneration and improving their recovery. In embodiments of the invention, the device and system are implanted at the time of decompression surgery.

[0070] Figure 4 A device 11 according to an embodiment of the invention is shown. The device has a thin flexible parylene substrate 15 with two polymer electrodes 20 formed spaced apart on the substrate. An extension 13 of the substrate may provide a connection to a wireless power source and / or controller (e.g., an IPG 30 as described above), or may provide conductors for a wired connection to a power source and / or controller.

[0071] Figure 5 Shows such as Figure 4 The device 11 shown in FIG. 1 , which has been rolled up around a tube having a diameter of 1 cm, demonstrates how the device 11 can flexibly conform to a curved surface similar in size to the spinal cord, and how the electrodes 20 can be positioned so that they are spaced axially along the spinal cord. In order to conform to the patient's spinal cord in this manner, preferably the device 11, or at least the portion of the device 11 in which the electrodes 20 are mounted, has a curvature radius of 2 mm or less.

[0072] Electrode 20 is coated with a conductive polymer PEDOT:PSS, which provides a 100-fold increase in electrode capacitance for the same surface area compared to metal electrodes (4, 5). PEDOT:PSS coatings have previously been shown to be biocompatible. The capacitance of polymer electrode 20 has been further increased by creating thicker electrodes, as discussed further below.

[0073] The combination of high capacitance PEDOT:PSS electrodes 20 and a thin flexible substrate 15 that can conform to the shape of the spinal cord enables devices according to embodiments of the present invention to maintain a uniform electric field across the injury site, thereby providing optimal conditions for directed axonal regeneration.

[0074] Already developed Figure 2 and Figure 3 The computational model of the system shown, Figure 2 and Figure 3 The system shown uses Figure 4 and Figure 5 Device shown. Figure 6 A model of the electric field distribution in a simulated spinal cord between two electrodes is shown. The simulation shows that two epidurally placed high capacitance polymer electrodes can maintain a uniform electric field throughout the spinal cord. It is known that the magnitude of the electric field in the range of 10mV / mm is sufficient to guide cell growth.

[0075] In the above about Figure 4 and Figure 5 In the depicted embodiment, the device has two electrodes 20 mounted on a single substrate 17. However, in alternative embodiments of the invention, the electrodes 20 are separate and formed individually on their own substrates. Figure 7 An example of such an electrode 20 is shown. Figure 3 and Figure 4 As shown in the device, Figure 7 The device shown may have further components formed on substrate 17 which may provide connections to a wireless power source and / or controller (eg, IPG 30 as described above), or may provide conductors for wired connection to a power source and / or controller.

[0076] Figure 8 The use of a device according to the invention in an in vitro test is shown to demonstrate that a safe and stable electric field can be achieved. The figure shows an OFS-type variation with a period of about 15 minutes. The electrode in the test had a PEDOT:PSS layer with a thickness of about 250 μm. Figure 8 The electrodes were shown to be able to maintain the desired electric field (600 μA) while also keeping the voltage below the "water window" of about 1.2 V. Potentials above the "water window" can lead to water decomposition and other Faradaic reactions that can generate toxic byproducts. Therefore, when the device is implanted in the spinal cord area of ​​a patient, operation of the device within the desired range reduces the risk of damage to surrounding neural tissue.

[0077] Fig. 9 A method of manufacturing an electrode according to an embodiment of the present invention is shown. The fabrication starts with a clean gold substrate 201. The gold substrate is immersed in 50 mL of 1 mM cysteamine solution and then a PVA layer 202 is spin coated on one surface.

[0078] A PTFE wall is formed around the prepared substrate to allow drop casting of PEDOT:PSS to produce a PEDOT:PSS layer 203 on the PVA layer 202. Further amounts of PEDOT:PSS are added every 15 minutes while the electrode is soft baked until the desired thickness is reached. Soft baking is a process in which the electrode is heated to a temperature (and for a period of time) that causes the film to partially but not completely dry. For thick PEDOT:PSS films such as those used in the electrodes described above, such soft baking is typically in the range of 100°C for 10 minutes. Typically, electrodes of embodiments of the present invention have a thickness between 50μm-500μm.

[0079] Once the desired thickness of PEDOT:PSS is reached, the electrode is hard-baked for 1 hour and the composite electrode 20 is then removed from the PTFE well. In contrast to a soft bake, a hard bake is a heating at a temperature (usually but not always higher than the soft bake temperature) sufficient for a time to completely dry the film and complete any heat-driven reactions (such as cross-linking). In the method shown, the hard bake includes heating at 130°C for 1 hour or more.

[0080] Drop casting of PEDOT:PSS allows for much thicker layers to be obtained than using current electrochemical deposition or solution-based spin coating methods. The inventors have found that, contrary to current belief, increasing the thickness of PEDOT:PSS can produce electrodes with a corresponding increase in capacitance (in particular, the increase in capacitance does not saturate as previously expected once the thickness exceeds significantly 1 μm), and without requiring changes to other properties of the PEDOT:PSS layer, such as porosity.

[0081] Fig.10 is a cyclic voltammogram of an electrode according to the present invention, which is prepared according to the above reference Fig. 9 The electrode has a thickness of 200 μm and an area of ​​0.25 mm 2 、The volume is 0.05mm 3 PEDOT:PSS film.

[0082] The voltammogram was scanned at 5 mV / s between 0.0 V and 0.8 V and showed a 521 mC / cm 2 This corresponds to a charge storage capacity of 0.65 F / cm 2 Capacitance.

[0083] The foregoing description is merely exemplary in nature, and those skilled in the art will appreciate that modifications and variations to the disclosed embodiments are possible within the scope of the claims. The invention is defined by the claims.

[0084] References

[0085] (1) Li, Jianming, Weak direct current (DC) electric fields as a therapy for spinal cord injuries: review and advancement of the oscillating fieldstimulator (OFS), Neurosurgical Review, 42, 825-834 (2019). https: / / doi.org / 10.1007 / s10143-018-01068-y.

[0086] (2)Someya,T.;Bao,Z.;Malliaras,G.G.The Rise of Plastic Bioelectronics,Nature 2016,540(7633),379-385。https: / / doi.org / 10.1038 / nature21004。

[0087] (3)Bettinger,C.J.;Ecker,M.;Kozai,T.D.Y.;Malliaras,G.G.;Meng,E.;Voit,W.Recent Advances in Neural Interfaces—Materials Chemistry to ClinicalTranslation,MRS Bulletin 2020,45(8),655–668。https: / / doi.org / 10.1557 / mrs.2020.195。

[0088] (4)Proctor,C.M.;Rivnay,J.;Malliaras,G.G.Understanding VolumetricCapacitance in Conducting Polymers,Journal of Polymer Science Part B:PolymerPhysics 2016,54(15),1433–1436。https: / / doi.org / 10.1002 / polb.24038。

[0089] (5)Rivnay,J.;Leleux,P.;Ferro,M.;Sessolo,M.;Williamson,A.;Koutsouras,D.A.;Khodagholy,D.;Ramuz,M.;Strakosas,X.;Owens,R.M.;Benar,C.;Badier,J.-M.;Bernard,C.;Malliaras,G.G.High-Performance Transistors for Bioelectronicsthrough Tuning of Channel Thickness,Science Advances 2015,1(4),e1400251。https: / / doi.org / 10.1126 / sciadv.1400251。

[0090] All of the above references are incorporated herein by reference in their entirety.

Claims

1. A medical device having a plurality of electrodes, wherein: At least one of the electrodes comprises a polymer film layer having a thermal conductivity of at least 0.5 F / cm 2 Capacitance per unit area.

2. The medical device according to claim 1, wherein: The thickness of the film layer is between 50 μm and 1000 μm.

3. The medical device according to claim 1 or claim 2, wherein: The film layer is formed of PEDOT / PSS.

4. A medical device according to any one of the preceding claims, wherein: The device is flexible.

5. The medical device of any of the preceding claims, further comprising a pulse generator coupled to the electrodes and arranged to control the electric field between the electrodes.

6. A medical device according to any one of the preceding claims, wherein: The device has an overall thickness of less than 1.5 mm and / or a width of less than 2 cm.

7. A medical device according to any one of the preceding claims, wherein: The device is an implantable device and is preferably configured to be implanted and / or removed through an incision no larger than 1 cm.

8. A medical device according to any one of the preceding claims, wherein: The device is configured to receive power wirelessly from an independent power source.

9. A system for treating spinal cord injury, the system comprising: The medical device according to any one of the preceding claims, wherein the device is an implantable device; and A pulse generator is coupled to the electrodes of the device and is configured to generate a varying electric field between the electrodes.

10. The system according to claim 9, wherein: The pulse generator is implantable.

11. The system of claim 9 or claim 10, further comprising a power supply wirelessly coupled to the pulse generator.

12. A system according to any one of claims 9 to 11, wherein: The pulse generator is wirelessly coupled to the electrodes.

13. A system according to any one of claims 9 to 12, wherein: The pulse generator is set to ensure that the voltage between the electrodes does not exceed 1.2V.

14. A system according to any one of claims 9 to 13, wherein: The pulse generator is configured to cause the voltage between the electrodes to reverse polarity with a period of at least 300 seconds.

15. A method for treating a spinal cord lesion in a patient, the method comprising the steps of: implanting a plurality of electrodes percutaneously at locations proximate to the patient's spinal cord and on opposite sides of the lesion; applying an electric field between the electrodes to stimulate axonal regeneration; and The polarity of the electric field is reversed periodically to stimulate axonal regeneration from the other side of the lesion.

16. The method according to claim 15, wherein: The implantation procedure is performed during decompression surgery.

17. A method according to claim 15 or claim 16, further comprising the step of percutaneously removing the electrode after the treatment.

18. An electrode having a substrate and a conductive polymer film layer on an exposed surface, the film layer having a conductivity of at least 0.5 F / cm 2 Capacitance per unit area.

19. An electrode having a substrate and a conductive polymer film layer on an exposed surface, the film layer having a thickness between 50 μm and 1000 μm.

20. An electrode according to claim 18 or claim 19, wherein The electrode has a thickness of no more than 1.5 mm and a width of no more than 1.5 cm.

21. A method for manufacturing an electrode, the method comprising the steps of: Coating a conductive polymer film layer on the surface of a conductive substrate using a conductive polymer solution, and soft-baking the substrate and the film layer until the film layer reaches a thickness of at least 50 μm; and The resulting structure is hard baked.

22. The method according to claim 22, further comprising the steps of: Prior to coating the conductive polymer film layer, the surface of the substrate to be coated with the conductive polymer film layer is coated with an adhesion promoting layer.

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