Nanofiber electrode with a changing three-dimensional shape

Abstract

A nanofiber electrode can be provided. The nanofiber electrode may include a first nanofiber layer and a second nanofiber layer. The nanofiber electrode may further include one or more conductive power supply paths sandwiched between the first nanofiber layer and the second nanofiber layer. At least one of the first nanofiber layer or the second nanofiber layer may be configured to absorb and expand a liquid when exposed to the liquid, thereby changing the three-dimensional shape of the nanofiber electrode.

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims priority to U.S. Provisional Patent Application No. 63 / 351,738, filed Jun. 13, 2022, which is incorporated herein by reference in its entirety. This disclosure relates to nanofiber electrodes that can change their own three - dimensional shape to conform, for example, to the contour of biological tissue.

Background Art

[0002] Electrodes are used medically to measure the electrical parameters of tissue and / or to apply electrical stimulation to tissue. However, there are many challenges in using electrodes for medical purposes. Tissues come in different shapes and sizes and generally do not have a smooth contour. Furthermore, tissues do not provide the electrode with a latch structure or any other type of coupling function. Additionally, electrodes generally must be biocompatible so as not to have an adverse effect on the tissues and homeostasis of the human body. The electrodes should also have sufficient insulation and toughness to withstand the effects of the liquid surrounding the tissue.

Summary of the Invention

[0003] In some embodiments, a nanofiber electrode can be provided. The nanofiber electrode may include a first nanofiber layer and a second nanofiber layer. The nanofiber electrode may further include one or more conductive feed paths located between the first nanofiber layer and the second nanofiber layer. At least one of the first nanofiber layer or the second nanofiber layer may be configured to absorb and expand a liquid when exposed to the liquid, thereby changing the three - dimensional shape of the nanofiber electrode. In some embodiments, a method of fabricating a nanofiber electrode can be provided. The method may include forming one or more conductive feed paths on a first nanofiber layer using a patterned film, wherein at least a portion of the one or more conductive feed paths is positioned between the first nanofiber layer and a second nanofiber layer, the patterned film defining the shape of the one or more conductive feed paths, and at least a portion of the one or more conductive feed paths being covered by the second nanofiber layer. At least one of the first nanofiber layer or the second nanofiber layer may be configured to absorb and expand a liquid when exposed to the liquid, thereby changing the three-dimensional shape of the nanofiber electrode. In some embodiments, a method of using a nanofiber electrode can be provided. The method may include placing the nanofiber electrode into tissue, the nanofiber electrode having a first nanofiber layer, a second nanofiber layer, and one or more conductive feed paths positioned between the first nanofiber layer and the second nanofiber layer. The method may also include exposing the nanofiber electrode to a biological fluid in the vicinity of the tissue and causing at least one of the first nanofiber layer or the second nanofiber layer to absorb and expand the biological fluid, thereby changing the three-dimensional shape of the nanofiber electrode, the changed three-dimensional shape conforming to the contour of the tissue. BRIEF DESCRIPTION OF THE DRAWINGS

[0004]

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DETAILED DESCRIPTION OF THE INVENTION

[0005] The figures are intended to illustrate exemplary embodiments, but it is understood that the present disclosure is not limited to the arrangements and means shown in the drawings. In the figures, the same reference numerals identify at least generally similar elements. The embodiments disclosed herein generally relate to nanofiber electrodes that can change their own three-dimensional shape to conform to the contour of biological tissue. For example, a substantially planar nanofiber electrode may be disposed on biological tissue having a substantially round contour, such as a blood vessel, and the nanofiber electrode may change its substantially planar shape to a substantially annular three-dimensional shape. This three-dimensional shape change not only conforms to the contour of the biological tissue, but also provides a coupling function between the biological tissue and the nanofiber electrode.

[0006] The three-dimensional shape change can be facilitated by the nanofiber layer of the nanofiber electrode. One or more nanofiber layers can expand by absorbing a biological fluid, such as blood, around the biological tissue. This expansion can cause the nanofiber electrode to bend, wrap, or undergo any other three-dimensional shape change. Such expansion can be such that the electrical and chemical properties of the nanofiber layer do not change, the expansion does not affect the electrical measurements and electrical stimulation performed by the nanofiber electrode, and the expansion also does not affect the insulation provided by the nanofiber layer to the conductive feed path. The expansion of one or more nanofiber layers, and thus the change in the three-dimensional shape of the nanofiber electrode, can be further facilitated by a polymer layer. A patterned polymer layer may be attached to one or more of the nanofiber layers, and the polymer layer can also absorb the biological fluid to further enhance the three-dimensional shape change. Similar to the nanofiber layer, it is possible that the electrical and chemical properties of the patterned polymer do not change due to the absorption of the biological fluid. Thus, the nanofiber electrode is robust to the biological environment when placed.

[0007] The nanofiber layer may be made of a biomass material that is biocompatible and biodegradable. In some examples, a biomass material such as chitin may help heal the tissue surrounding the nanofiber electrode. Additionally, carbon nanotubes or silver nanowires used to construct the power supply path may be capable of having no biological adverse effects. Further, the patterned polymer may also be capable of having no biological adverse effects. Accordingly, the embodiments disclosed herein may achieve a significant improvement over conventional electrodes. FIG. 1 shows an exemplary biological environment 100 according to an exemplary embodiment of this disclosure. In some embodiments, the exemplary biological environment 100 may represent a human body environment and / or any other type of biological medium (e.g., an animal body, a tissue culture, etc.). The biological environment 100 may include a nanofiber electrode 102 disposed in tissue 104. As shown in the figure, the nanofiber electrode 102 may conform to the shape / contour of the tissue 104. In some embodiments, the tissue 104 may represent human tissue or animal tissue (e.g., nerve fibers, muscle fibers, etc.).

[0008] The nanofiber electrode 102 may include a plurality of electrical contacts 106a-106i and corresponding plurality of power supply paths 108a-108i. The plurality of electrical contacts 106a-106i may be configured to measure the electrical parameters of the tissue 104. The plurality of power supply paths 108a-108i may be configured to transmit the measured electrical parameters to a connected electronic device (not shown). In some embodiments, the plurality of power supply paths 108a-108i may be configured to transmit an electrical stimulus to the corresponding plurality of electrical contacts 106a-106i, which can then apply the electrical stimulus to the tissue 104.

[0009] The electrical contacts 106a-106i may be exposed to contact the tissue 104, but the power supply paths 108a-108i may be insulated from the environment by a layer of nanofibers. For example, the power supply paths 108a-108i may be located between two layers of insulating nanofibers. In some embodiments, the nanofiber layer of the nanofiber electrode 102 may be configured to change its own shape when exposed to a liquid medium (e.g., a biological liquid medium such as blood). This change in shape may enable the nanofiber electrode 102 to conform to the contour of the tissue 104. For example, as shown in the figure, the tissue 104 has a cylindrical shape and a round cross-section. In such an example, the nanofiber electrode 102 can be wrapped around the tissue 104. One or more nanofiber layers of the nanofiber electrode 102 can absorb liquid without deteriorating and without changing their electrical and chemical properties. Thus, when physically changing its shape so that the nanofiber electrode 102 conforms to the contour of the tissue 104, the power supply paths 108a - 108i remain insulated and the functionality of electrical measurement and electrical stimulation is not affected.

[0010] In some embodiments, in addition to the nanofiber layer, the nanofiber electrode 102 may include a polymer layer (described in detail with reference to FIGS. 3A - 3B below). The polymer layer can also absorb liquid and further change the shape of the nanofiber electrode 102. Thus, the combination of the nanofiber layer and the polymer layer can achieve the desired level of flexibility in the nanofiber electrode 102, which can change to the desired shape during placement and conform to the contour of the biological tissue. In addition to conforming to the contour of the tissue 104, the nanofiber electrode 102 itself can form a connection function to the tissue. Since the nanofiber electrode 102 can be wrapped around the tissue 104, this wrapping can function as a mechanical, non-invasive anchor between the tissue 104 and the nanofiber electrode 102. Thus, additional fixing members may not be required when the nanofiber electrode 102 is placed on the tissue 104.

[0011] FIG. 2A shows an exemplary method 200 for fabricating a nanofiber electrode according to an exemplary embodiment of this disclosure. FIG. 2B shows the progress of fabrication through the discussed steps of method 200 according to an exemplary embodiment of this disclosure. This method may begin at step 202. At step 202, a nanofiber substrate 224 and a polyimide film 222 (merely an example, and other types of materials may also be used) are prepared. In some embodiments, the nanofiber substrate 224 may represent a nanofiber paper substrate. In some embodiments, the polyimide film 222 may include a formed pattern. In some embodiments, the pattern may be formed by laser cutting a desired pattern into a blank polyimide film. The pattern formed on the polyimide film 222 may define the structure of the power supply path in the fabricated nanofiber electrode. That is, the pattern may form openings for the conductive material 226 (as described below) to spread over the nanofiber substrate and take on the shape and size defined by the pattern.

[0012] At step 204, a power supply path may be formed. In some embodiments, sub-steps 205, 206, 208 may be used to form the power supply path. At sub-step 205, the conductive material 226 may be deposited on a combination of the polyimide film 222 and the nanofiber substrate 224. As shown above, the polyimide film 222 includes a formed pattern. When deposited, the conductive material 226 may form a power supply path in the openings of the patterned polyimide film 222. In some embodiments, in order to obtain such functionality, the conductive material 226 may have a desired viscosity so that it can spread over the nanofiber substrate 224 within the laser-cut structure of the patterned polyimide film 222. In some embodiments, the conductive material 226 may include a nanowire suspension. In some embodiments, the conductive material 226 may include a carbon nanotube suspension.

[0013] In sub-step 206, the conductive material 226 may be spread on the nanofiber substrate 224 in the laser-cut pattern of the patterned polyimide film 222. In some embodiments, the spreading may include a filtering process, where a nanowire suspension or a carbon nanotube suspension, for example a solution containing a solute (nanowire, carbon nanotube), acts as a solvent and the nanofiber substrate 224 may act as a membrane for the solute to spread on the membrane. In some embodiments, the conductive material 226 may be mechanically spread, for example by using a spreading arm.

[0014] In sub-step 208, the patterned polyimide film 222 may be peeled off from the nanofiber substrate 224. In some embodiments, once the conductive material 226 and the nanofiber substrate 224 are dry, the patterned polyimide film 222 is peeled off. That is, the patterned polyimide film 222 that provided a structure for the conductive material 226 to spread may no longer be needed after the conductive material 226 has spread to the desired shape and size and dried.

[0015] In step 210, a mask 228 may be applied to the ends of the conductive material 226. When depositing non-conductive nanofibers (such as a passivation layer), the mask 228 may form a barrier layer on the corresponding ends of the conductive material 226. In some embodiments, the mask 228 may be formed from polydimethylsiloxane (PDMS). In step 212, nanofibers 227 may be deposited on the conductive material 226. The nanofibers 227 may form a passivation (e.g., for non-conductive protection) layer on the conductive material 226. In some embodiments, the nanofibers 227 may have physical and / or chemical properties similar to those of the nanofiber substrate 224. In some embodiments, the nanofibers 227 and the nanofiber substrate 224 may have different physical and / or chemical properties. In step 214, the nanofibers 227 may be spread over the conductive material 226. In some embodiments, the nanofibers 227 may be present in a suspension, and the spreading may be by filtration. During filtration, the nanofibers 227 may act as a solute, and the conductive material 226 may act as a membrane for the solute to spread. However, the masked portion of the conductive material 226 may not need to be reached by the spread of the nanofibers 227. In some embodiments, the nanofibers 227 may be mechanically spread, for example, by using a spreading arm. After spreading the nanofibers 227, the conductive material 226 other than the masked portion is located between the nanofiber substrate 224, which is one of the two layers of nanofibers, and the layer formed by the nanofibers 227. Each of the nanofiber substrate 224 and the nanofibers 227 may change its shape when exposed to a liquid medium.

[0016] In step 216, the mask 228 (for example, a PDMS mask) may be removed to expose the electrical contact 230. In step 218, the nanofiber substrate 224 and the nanofibers 227 can be cut into a desired shape to obtain a nanofiber electrode 232 having two power supply paths 234a and 234b formed by the conductive material 226. A part of the conductive material 226 is exposed to form the electrical contact 230 of the nanofiber electrode 232. Here, the nanofiber electrode 232 may be in a state ready to be placed on human tissue.

[0017] In some embodiments, the length of each of the power supply paths 234a and 234b of the nanofiber electrode 232 filaments may be approximately 1 mm, the distance between the power supply paths 234a and 234b may be approximately 300 μm, and the width of the power supply paths 234a and 234b at the thin end may be approximately 200 μm. The thickness of each of the upper nanofiber layer and the lower nanofiber layer (for example, formed by the nanofiber substrate 224) may be approximately 5 μm, while the thickness of each of the power supply paths 234a and 234b may be approximately 2.46 ± 0.135 μm. FIG. 3A shows an exemplary method 300 of generating a nanofiber substrate, such as nanofiber substrate 224, to be used in a nanofiber electrode, according to an example embodiment of this disclosure. FIG. 3B shows the progression of the generation of the nanofiber substrate through the discussed steps of method 300, according to an example embodiment of this disclosure. Method 300 may begin at step 302. At step 302, acrylamide monomer 308 may be set on nanofiber mat 310. Nanofiber mat 310 may be made of a biomass material such as chitin, chitosan. The assembly of acrylamide monomer 308 and nanofiber mat 310 may be performed on an inert, non-reactive substrate 312.

[0018] At step 304, acrylamide monomer 308 may be polymerized. In some embodiments, the polymerization may be performed using ultraviolet light. The polymerization may form a bilayer of polyacrylamide 314 and nanofiber mat 310. At step 306, ablation may be used to generate a pattern in the bilayer structure of polyacrylamide 314 and nanofiber mat 310. In some embodiments, the ablation may include laser ablation. It should be understood that laser ablation does not change the insulating properties of the bilayer structure of polyacrylamide 314 and nanofiber mat 310. That is, even if the pattern includes gaps, the bilayer can still accept and hold a conductive material and insulate the conductive material when the bilayer is exposed to a liquid medium.

[0019] FIG. 4 shows the shape change characteristics of the nanofiber layer generated using the method 300 shown in FIGS. 3A - 3B according to an exemplary embodiment of this disclosure. As shown in the figure, patterning can enable polyacrylamide 314 to expand in a liquid medium without compromising the structural integrity of the overall structure. For example, the planar polyacrylamide 314 and the nanofiber mat 310 form a planar structure 420, which can bend to form a cylindrical structure 422 (having a round cross - section) when exposed to a liquid medium. When dried, the bilayer can return to the original planar structure 420. The change in shape between the planar structure 420 and the annular structure 422 can be possible without chemical changes in the polyacrylamide 314 and the nanofiber mat 310. Thus, if the premise is that it is in a bent shape when inserted into a liquid medium and returns to an unbent shape when not in the liquid medium, the bilayer structure can be a self - folding device. This self - folding property can enable the nanofiber electrode to conform to the contour of biological tissue. The bent structure can further function as a mechanical anchor between the nanofiber electrode and the biological tissue. For example, one or more nanofiber layers of the nanofiber electrode 102 shown in FIG. 1 may be formed using this bilayer structure.

[0020] FIG. 5A shows an exemplary method 500 for generating a nanofiber substrate (e.g., nanofiber substrate 224) from a biomass material according to an exemplary embodiment of this disclosure. FIG. 5B is a diagram showing the progress of the generation of the nanofiber substrate in a factory setting using the discussed steps of method 500 according to an exemplary embodiment of this disclosure. As shown in the figure, the final constructed nanofiber substrate may be in the form of paper. Method 500 may begin at step 502, where biomass raw material 512 extracted from a biological material 510 such as cellulose, chitin, chitosan, and / or silk fibroin may be supplied to an extraction chamber and pressurized by one or more pressure intensifiers. In particular, there may be two pressure intensifiers 514a and 514b that can produce two pressurized slurry streams of the biomass material 512 (e.g., containing a biomass slurry and water). In some embodiments, one or more of the two pressure intensifiers 514a and 514b can pressurize the slurry stream to a relatively high pressure of 245 MPa (megapascals).

[0021] At step 504, the two pressurized slurry streams may be collided. For example, a collision type accelerator 518 may be used to collide the pressurized slurry streams at an oblique angle, and pressurization and collision may generate nanofibers derived from the biomass material 512. In some embodiments, the steps of pressurization and collision may be collectively referred to as water injection. At step 506, the nanofibers may be discharged through a cooler 520. The cooler 520 can reduce the high temperature generated during the steps of pressurization and collision. At step 508, the cooled nanofibers may be filtered through various membranes 522. After filtration, a nanofiber paper substrate 524 can be obtained. The nanofiber paper substrate 524 may be used to fabricate nanofiber electrodes. For example, the nanofiber paper substrate 524 may be used as the nanofiber substrate 224 of method 200 and as the nanofiber mat 310 of method 300. The nanofiber paper substrate 524 can form an insulating portion of the nanofiber electrode.

[0022] The method 500 can be used to generate nanofiber substrates of all kinds of biomass materials. Some non-limiting examples may include cellulose-based nanofiber substrates, chitosan-based nanofiber substrates, chitin-based nanofiber substrates, and silk fibroin-based nanofiber substrates. In some embodiments, each of the nanofiber substrates may have a thickness of approximately 5 μm. In some embodiments, the light transmittance of the nanofiber substrates may be as follows. The chitin-based nanofiber substrate may be more transparent than the chitosan-based nanofiber substrate; the chitosan-based nanofiber substrate may be more transparent than the chitin-based nanofiber substrate; the chitin-based nanofiber substrate may be more transparent than the silk fibroin-based nanofiber substrate.

[0023] FIG. 6 shows an exemplary biomass material for constructing a nanofiber substrate for a nanofiber electrode according to an exemplary embodiment of this disclosure. The biomass material may be used by the method 500 to generate a nanofiber paper substrate 524. As shown in the figure, the crab shell 602 may be used as the biomass material. The crab shell 602 may have a hierarchical structure tissue 604 formed by a complex 606 of chitin nanofibers and proteins. Inside the complex 606 of chitin nanofibers and proteins, a plurality of strands 608 may exist. The strand 608 may have a plurality of nanofibers 610. Therefore, the nanofibers 610 can be extracted from the crab shell 602 by one or more processes 612 such as deproteinization, deashing, degreasing, decolorization, and / or any other type of process. An exemplary process for extracting the nanofibers 610 may be water injection that applies high-pressure water to the biomass. FIG. 7 shows an exemplary transition between wet and dry carbon nanotube electrodes according to an exemplary embodiment of this disclosure. For example, a dry electrode 702 and a wet electrode 704 are shown. As can be seen from the figure, the shape of the dry electrode 702 changed when placed in a liquid medium (e.g., inside the human body).

[0024] FIG. 8 shows another exemplary transition between wet and dry silver nanowire electrodes according to an exemplary embodiment of this disclosure. For example, a dry electrode 802 and a wet electrode 804 are shown. As can be seen from the figure, the shape of the dry electrode 802 changed when placed in a liquid medium (e.g., inside the human body). FIG. 9 shows an exemplary method 900 of using a nanofiber electrode according to an exemplary embodiment of this disclosure. The method 900 may be used to apply electrical stimulation to tissue and / or perform electrical measurements of tissue. In step 902, a nanofiber electrode may be placed on the tissue. In some embodiments, the tissue may have a substantially round contour. For example, blood vessels and nerves can generally be cylindrical with a substantially round cross-section. As discussed throughout this disclosure, the nanofiber electrode may have a first nanofiber layer, a second nanofiber layer, and one or more conductive feed paths located between the first nanofiber layer and the second nanofiber layer.

[0025] In step 904, the nanofiber electrode may be exposed to a biological fluid (e.g., blood) near the tissue, which can cause the nanofiber electrode to change its three-dimensional shape. The shape change can be caused by at least one of the first nanofiber layer or the second nanofiber layer absorbing the biological fluid and then expanding. Further examples of embodiments of the methods and devices described in this invention are proposed in accordance with the structures and techniques described herein. Other non-limiting examples may be configured to be performed separately, or incorporated into any interchange or combination with one or more of any of the other examples shown above or throughout this disclosure. Those skilled in the art will recognize that the present disclosure can be implemented in other specific forms without departing from the spirit or essential characteristics of the present disclosure. Therefore, the embodiments disclosed in the present invention are considered to be illustrative in every respect and not restrictive. The scope of the disclosure is indicated by the appended claims rather than the foregoing description, and it is intended that all modifications and equivalents within the meaning and scope be embraced by the disclosure.

[0026] The steps of the methods discussed herein are merely shown as examples and should not be considered limiting. Methods having alternative, additional, or fewer steps should be considered within the scope of this disclosure. Further, the steps are merely numbered for identification purposes, and the numbering is not intended to imply limitation to the individual steps shown or to a series of steps. It should be noted that the terms "including" and "comprising" should be construed to mean "including but not limited to." Where not expressly stated in the claims, the term "a" should be construed as "at least one," and terms such as "the," "said," etc. should be construed as "at least one," "the at least one," etc. Further, it is the applicant's intention that only claims containing the phraseology "means for" or "steps for" be construed under 35 U.S.C. 112(f). Claims that do not expressly include the phraseology "means for" or "steps for" should not be construed under 35 U.S.C. 112(f).

Claims

1. A first nanofiber layer, A second nanofiber layer, One or more conductive power supply paths located between the first nanofiber layer and the second nanofiber layer A nanofiber electrode comprising: At least one of the first nanofiber layer or the second nanofiber layer is configured to absorb and expand a liquid when exposed to the liquid, thereby changing the three-dimensional shape of the nanofiber electrode. A nanofiber electrode.

2. The nanofiber electrode according to claim 1, wherein at least one of the first nanofiber layer or the second nanofiber layer is formed of a biomass material.

3. The nanofiber electrode according to claim 2, wherein the biomass material comprises at least one of chitin, chitosan, or silk fibroin.

4. The nanofiber electrode according to claim 1, wherein one or more conductive power supply paths are formed of carbon nanotubes.

5. The nanofiber electrode according to claim 1, wherein one or more conductive power supply paths are formed of silver nanowires.

6. The nanofiber electrode according to claim 1, wherein at least one of the first nanofiber layer and the second nanofiber layer comprises a polymer layer having a pattern configured to promote a change in the three-dimensional shape of the nanofiber electrode.

7. The nanofiber electrode according to claim 6, wherein the polymer layer is formed of polyacrylamide.

8. The nanofiber electrode according to claim 1, wherein the nanofiber electrode is configured to be substantially planar when dry and at least a portion of the nanofiber electrode is configured to be substantially annular when exposed to a liquid.

9. Openings of one or more electrical contacts in one or more conductive power supply paths The nanofiber electrode according to claim 1, further comprising:

10. A method of fabricating a nanofiber electrode, comprising: Forming one or more conductive power supply paths in a first nanofiber layer using a patterned film, the patterned film defining the shape of the one or more conductive power supply paths. covering at least a part of the one or more conductive power supply paths with a second nanofiber layer such that at least a part of the one or more conductive power supply paths is located between a first nanofiber layer and the second nanofiber layer; A method, wherein at least one of the first nanofiber layer or the second nanofiber layer is configured to absorb and expand a liquid when exposed to the liquid, thereby changing a three-dimensional shape of the nanofiber electrode.

11. The method according to claim 10, wherein at least one of the first nanofiber layer and the second nanofiber layer is formed of a biomass material.

12. The method according to claim 11, wherein the biomass material comprises at least one of chitin, chitosan, or silk fibroin.

13. The method according to claim 10, wherein the one or more conductive power supply paths are formed of carbon nanotubes.

14. The method according to claim 10, wherein the one or more conductive power supply paths are formed of silver nanowires.

15. The method according to claim 10, wherein at least one of the first nanofiber layer and the second nanofiber layer comprises a polymer layer having a pattern configured to facilitate a change in the three-dimensional shape of the nanofiber electrode.

16. The method according to claim 15, wherein the polymer layer is formed of polyacrylamide.

17. forming one or more electrical contact openings in the one or more conductive power supply paths The method according to claim 10, further comprising.

18. A method of using a nanofiber electrode, comprising: placing the nanofiber electrode on a tissue, the nanofiber electrode having a first nanofiber layer, a second nanofiber layer, and one or more conductive power supply paths located between the first nanofiber layer and the second nanofiber layer; exposing the nanofiber electrode to a biological fluid in the vicinity of the tissue, causing at least one of the first nanofiber layer or the second nanofiber layer to absorb and expand the biological fluid, thereby changing a three-dimensional shape of the nanofiber electrode, the changed three-dimensional shape conforming to the contour of the tissue; The method includes.

19. The method according to claim 18, wherein the contour of the tissue is substantially circular and the changed three-dimensional shape is substantially circular.

20. The step of applying an electrical stimulation to tissue or performing an electrical measurement of tissue using one or more conductive feed paths The method according to claim 18, further comprising

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