Patent Application
20100076537
1. Field of the Invention
The present disclosure relates to electrode configurations for electrochemically activated systems. In particular, the disclosure relates to electrodes in such electrochemically activated systems, having coverings or coatings, to systems of such electrodes and to methods for operating such systems.
2. Description of the Related Art
During surgical procedures, where sensors and/or electrically actuated tools are used, high performance and well defined behavior are critical. Short circuits between electrodes and/or instruments, undesired reactions at electrode surfaces and the like are events which could lead to malfunction of the tool and severe damage to or even death of the patient.
Examples of such systems are surgical tools based on (electrical or) electrochemical principles such as disclosed in PCT Published International application no. WO 00/78222.
An example of such a tool is provided in
Yet another example of such a tool is shown in
When using electrodes, which are to some extent movable relative to each other, there may be a risk of the electrodes coming into electrical contact with each other, thereby causing a short circuit. This is a problem known to those skilled in the art (see for instance Published US Patent Application No. US2005/0165439).
Medical devices of the above described type are often operated in small spaces or via a lumen extending into the body. Therefore, miniaturization of the tools is one important aspect of the development of this type of surgical tools. Both the small spaces where the tools operate, and the small size of the tool per se, can lead to constrictions on the functionality. The inventors have discovered that one such constriction is the amount of electrolyte, and therewith ions, that is available for the EAP (electro-active polymer) based tool when operating in such small spaces. Lack of ions may lead to reduced functionality, for example in terms of speed of actuation and actuation range. Also, operating in small areas/devices increases the aforementioned risk of short circuiting.
There is thus a need for even safer and more reliable electrochemically activated surgical tools.
For general details on electrochemistry reference is made to textbooks such as “Electrochemical Methods. Fundamentals and Applications”, A. J. Bard and L. R. Faulkner, ISBN 0-471-04372-9. An overview on electroactive polymers can be found in “Electroactive Polymers (EAP) Actuators as Artificial Muscles—Reality, Potential, and Challenges” 2nd ed. Y. Bar-Cohen (ed.) ISBN 0-8194-5297-1. More specific details on conducting polymer based (micro-) actuators can be found in Q. Pei and O. Inganäs, “Conjugated polymers and the bending cantilever method: electrical muscles and smart devices”, Advanced materials, 1992, 4(4), p. 277-278. and Jager et al., “Microfabricating Conjugated Polymer Actuators”, Science 2000 290: 1540-1545).
One class of EAPs (electro-active polymers) are conducting polymers. These are polymers with a backbone of alternating single and double bonds. These materials are semiconductors and their conductivity can be altered from insulating to conducting with conductivities approaching those of metals. Polypyrrole (PPy) is one such conducting polymer and will be taken here as an example.
PPy can be electrochemically synthesized from a solution of pyrrole monomers and a salt as is know to those skilled in the art. After synthesis PPy is in its oxidized, or also called doped, state. The polymer is doped with an anion A−.
PPy can be electrochemically oxidized and reduced by applying the appropriate potential to the material. This oxidation and reduction is accompanied with the transport of ions and solvents into and out of the conducting polymer. This redox reaction changes the properties of polypyrrole, such as the conductivity, color, modulus of elasticity and volume.
Two different schemes of redox are possible:
If PPy is doped with a large, immobile anion A− scheme 1 occurs, which schematically can be written as:
When PPy is reduced to its neutral state, cations M+ including their hydration shell and solvent are inserted into the material and the material swells. When PPy is oxidized again the opposite reaction occurs, M+ cations (including hydration shell and solvent) leave the material and its volume decreases.
If on the other hand PPy is doped with small, mobile anions a−, scheme 2 occurs:
In this case the opposite behavior of scheme 1 occurs. In the reduced state, the anions leave the material and it shrinks. The oxidized state is now the expanded state and the reduced state the contracted. Non limiting example of ions A− is dodecylbenzene sulfonate (DBS-), of a− perchlorate (ClO4-), and of M+sodium (Na+) or lithium (Li+).
The ions (and solvent) that are transferred into and out of the conducting polymer are exchanged from an ion source/sink, i.e. the electrolyte 13. For reliable operation it is important that there is a good availability of ions in the electrolyte so that the functionality of the device is not limited by the ion concentration in the surrounding electrolyte.
The present invention provides even safer and more reliable electrochemically activated surgical tools. In one embodiment, the present invention reduces the risk of short circuiting of electrochemically activated surgical tools, without compromising their function. In another embodiment, the present invention overcomes the problems associated with use of electrochemically activated tools in small spaces or low concentration electrolytes.
These advantages are wholly or partially met by devices, systems, and methods as described herein and as defined by the appended claims.
According to a first aspect, there is provided an electrode system for use in a liquid electrolyte, comprising a first substrate member, a second substrate member, a working electrode, arranged on one of the first and second substrate members, and a counter electrode, arranged on one of the first and second substrate members. The first and second substrate members are movable relative each other. In the alternative, or as a complement, the working electrode is movable relative to the counter electrode. At least one of the electrodes is at least partially provided with a covering, the covering being ion permeable and electrically insulating.
For purposes of this invention, “ion permeable” means sufficiently permeable for the electrode to perform its function. “Electrically insulating” means sufficiently insulating to prevent a short circuit if the electrode is contacted by another, e.g. metallic electrode or conducting polymer electrode.
The covering may be provided on an active part of the electrode. The covering may be in the form of a material layer, a coating, a wrapping, or a housing. Covering one of the electrodes, preferably the counter or auxiliary electrode with an ion conducting layer or ion exchange layer separates the ion conduction from the electrical conduction, thus preventing short circuits. By such an arrangement, a mechanical contact between the electrodes is prevented from leading to electrical contact between the electrode, whereby short circuiting of the electrodes is prevented or counteracted.
The covering may comprise a material, which is ion conducting, but electrically insulating. Alternatively, or as a complement, the covering may be provided as a coating on the electrode. Alternatively, or as a complement, the covering may be provided as a pre-formed part, which is attached to the electrode. Alternatively, or as a complement, the covering may be formed directly on the electrode. Alternatively, or as a complement, the covering may comprise pores or channels for transporting ions (and solvent). Hence, the material may be impermeable, but having pores or through channels sufficient to allow transport of ions and electrolyte. Alternatively, or as a complement, the covering may comprise a web of fibers or wires. Such a web may be a woven or a non-woven web, a mesh, etc.
The covering may be removably arranged on the electrode. There may be a gap between said electrode and the covering. The working electrode may be arranged on the first substrate member. The counter electrode may be arranged on the second substrate member. The working electrode and counter electrode may be arranged on said first substrate member, and said second substrate member may be electrically conducting. The first and second substrate members may form separate units.
The covering may be arranged on the working electrode. In the alternative, or as a complement, the covering may be arranged on the counter electrode. The electrode system may further comprise a reference electrode. Alternatively, or as a complement, the reference electrode, if any, may be provided with the covering.
According to a third aspect, there is provided a method for preventing short circuiting of a working electrode, arranged on one of a first and a second part, a counter electrode, arranged on one of said first and second parts, and optionally a reference electrode, arranged on one of said first and second parts, operating with an electrolyte, wherein the first and second parts are movable relative each other, and/or wherein the working electrode, the counter electrode or the reference electrode, if any, are movable relative to each other, the method comprising at least partially providing at least one of said working electrode, said counter electrode and said reference electrode with a covering that is ion permeable and electrically insulating.
According to a fourth aspect, there is provided a counter electrode for use with a working electrode comprising conducting polymer, in the presence of an electrolyte. The counter electrode comprises a conducting polymer.
Use of such a counter electrode may counteract depletion of ions in the electrolyte, and thereby counteract effects such as the need for over potentials for the redox process and long diffusion paths for the ions, leading to long response times and even decreased final expansion.
Coating the counter electrode with a conducting polymer may avoid undesired reactions, such as gas formation, at the electrode surface. Also, conducting polymer coatings can have favorable effects on performance, e.g. act as an ion source or lower the necessary potential span. It has been noticed by the inventors that metal ions e.g. Au ions are dissolved from the counter electrode and transferred to and deposited on top of the working electrode to form a thin metal layer. This deteriorated the functionality of the working electrode. Yet another advantage of covering the counter electrode with a conducting polymer is that this metal ion transfer and dissolution is prevented.
The conducting polymer of the counter electrode may be same as that of the working electrode. Alternatively, or as a complement, the conducting polymer of the counter electrode may be operable with a different scheme than that of the working electrode. Alternatively, or as a complement, the conducting polymer of the counter electrode may be of a different conducting polymer than that of the working electrode.
The conducting polymer may be provided as a coating on the counter electrode, covering all or part thereof. The counter electrode may be at least partially provided with an ion permeable and electrically insulating covering, such as the ones described with reference to the first three aspects above. The covering may at least partially cover the conducting polymer.
According to a fifth aspect, there is provided system comprising a working electrode, a counter electrode and an electrolyte, wherein the working electrode comprises a conducting polymer. The counter electrode also comprises a conducting polymer.
The conducting polymer of the counter electrode may be same as that of the working electrode. Alternatively, or as a complement, the conducting polymer of the counter electrode is operable with a different scheme than that of the working electrode. Alternatively, or as a complement, the conducting polymer of the counter electrode may be of a different conducting polymer than that of the working electrode.
The conducting polymer may be provided as a coating on the counter electrode, covering all or part thereof. The counter electrode may be at least partially provided with an ion permeable and electrically insulating covering, such as the ones described with reference to the first three aspects above. The covering may at least partially cover the conducting polymer.
A volume or ion concentration of the electrolyte may be so small that ion depletion in a vicinity of the working electrode of said electrolyte significantly reduces system functionality.
The volume of electrolyte may be less than the volume of conducting polymer on the counter electrode, multiplied by a ratio of the ion concentration of the conducting polymer to the ion concentration of the electrolyte, multiplied by a factor A, wherein the factor A is 20, preferably 10, 5, 2 or 1.
The electrolyte may be confined in a three dimensional space, at least one dimension of which being small enough to effectively limit an amount of ions available to for interaction with the working electrode, such that ion depletion of said electrolyte in a vicinity of the working electrode significantly reduces system functionality.
By “reduced system functionality” is meant, for example, a decrease in expansion rate or total expansion, or a current decrease, as compared to a system having a sufficient volume of electrolyte and/or amount of ions available in the electrolyte in the vicinity of the working electrode.
Also, in this context, the “vicinity” means the area or space surrounding the working electrode, and from which ions may be drawn in an amount and rate sufficient to provide an acceptable system functionality—the “acceptable” standard being dependent on the specific application.
The at least one dimension may be less than 10 times a thickness of the conducting polymer at the working electrode, or less than 5 times, or less than 2 times or even less than the thickness of the conducting polymer on the working electrode.
In the above described systems, the working electrode, the counter electrode and the reference electrode, if any, may be so closely spaced apart that they risk contacting each other during normal operation of the system.
The working electrode, the counter electrode, and the reference electrode, if any, may be provided on respective substrate members, which may be separate members.
The working electrode may, upon actuation, be expandable towards the counter electrode. The working electrode may form part of a bender, or bending element, which, upon actuation, bends towards the counter electrode.
In the above described systems, the substrate members may be substantially stationary relative to each other. Alternately, in the above described systems, the substrate members may be movable relative to each other. Further, in the above described systems, the substrate members may interact in a telescoping sliding or inter-sliding manner. In the above described systems, the working electrode, the counter electrode, and reference electrode, if any, may be provided in or on a tubular member. In the above described systems, the tubular member is adapted for insertion into a body lumen.
According to a sixth aspect, there is provided a method for preventing ion depletion in an electrochemical cell comprising a working electrode, a counter electrode and an electrolyte, wherein the working electrode comprises a conducting polymer. The method comprises providing a counter electrode comprising a conducting polymer.
Embodiments will now be described with reference to the appended drawings.
a-4b are side cross sectional views that schematically illustrate the first aspect according to the principles of the present invention.
a-5c are side cross sectional view that schematically illustrate different embodiments of the covering of the first aspect of the present invention.
a-7d are side cross sectional views that schematically illustrate further embodiments of the first aspect of the invention.
a-8b are side cross sectional views that schematically illustrate embodiments of the second aspect of the present invention.
a-9b are side cross sectional views that schematically illustrate further embodiments of the second aspect.
a and 10b are graphs that illustrate a volume expansion and current response related to the second aspect.
A novel class of surgical tools based on (electrical or) electrochemical actuation principles is disclosed in Published PCT Patent Application No. WO 00/78222 A1. One such tool is a micro-anastomosis connector. This is a tubular implant that is used for the reconnection of two ends of a blood vessel (micro-anastomosis). In order to activate such tools at least two electrodes are needed: a working electrode (WE) (14 in
Referring to
Referring to
In
Hence, a standard counter electrode, such as a gold wire or a gold coated piece of silicon, may be coated, for instance using dip coating, spraying, or spin coating with an ion conducting layer. The layer may be cured in an oven at an elevated temperature according to the recipe of the material. Such coating processes are per se known to the skilled person.
In
The covering may be pre-formed and applied to the electrode, or it may be formed directly onto the electrode 40.
In
Such ion conducting coverings do not hinder the electrochemical reactions.
In a similar manner, the working electrode, the reference electrode, or the complete device comprising the working electrode or counter electrode, and/or any reference electrode, may be provided with the covering.
The inventors have recognized that it is not only in cases when the electrically activated medical device and the counter electrode are individually handled tools, separated from one and other, that the ion-conducting, electrically insulating covering of the counter electrode may be advantageous.
As mentioned,
Alternatively, the counter electrode may be placed directly on the medical device, as illustrated in
a schematically illustrates an other example of a device, which may be a valve device, where the counter electrode 51 may be covered to improve functionality. In this device, the volume expansion of the EAP working electrode 55, 55′ may lead to mechanical contact between the working electrode 55 and the counter electrode 51. The covering 52 prevents such electrical contact.
In
In
In
The parts 53 and 54 in
As the PPy expands, it may come into mechanical and thus electrical contact with the counter electrode, leading to short circuit. If the counter electrode is coated with ion exchange layer, mechanical contact does not result in electrical contact and therewith no short circuiting occurs.
Not only the counter electrode may be covered with an electrically insulating and ion conducting coating. Likewise, the conducting polymer comprising working electrode (medical device, surgical tool) may be covered, or both the working and the counter electrode may be covered. If a reference electrode is present, this may also be covered.
In certain systems, such as can be found in catheter based applications of the polypyrrole microactuators, the total volume of the electrochemical cell may be relatively small. Activating the conducting polymer on the working electrode (actuator) may thus deplete a major part of the ions in the electrolyte available in the small electrochemical cell, especially close to the working electrode. This has several negative effects: the conductivity of the electrolyte decreases, leading to a large so called ohmic or iR drop that results in high over potentials needed for the redox process; and long diffusion paths for the ions leading to long response times and even decreased final expansion. The same negative effects occur in systems in which the ion concentration is low. In both cases, one way of supplying excess ions is by supplying a flow of electrolyte, for example by flushing the system. However, in many cases that may not be possible or desirable.
The small electrolyte volume or low electrolyte concentration situation/case can be described/defined as
V
electrolyte
<A*VCP*CCP/Celectrolyte
where Velectrolyte is the volume of the electrolyte, Celectrolyte is the ion concentration of the electrolyte, VCP is the volume of the conducting polymer material, and CCP is the equivalent concentration of the ions in the conducting polymer material. A is a proportionality factor and may, for example equal 20, or 10, or 5, or 2, or 1.
The electrolyte may also be confined in a three-dimensional space, having at least one relatively small dimension.
Such small spaces may be found for example in the case where the conducting polymer operates in a tube, such as a catheter, guidewire or endoscope, of limited cross section, or in a two-dimensional space between a pair of closely spaced members, such as substantially parallel planar or curved members.
For example, at least one dimension of the space, e.g. thickness, diameter, gap distance etc., may be less than 10 times the thickness of the conducting polymer, or less than times, or less than 2 times or even less than the thickness of the conducting polymer.
In order to solve the above described problems, the counter electrode may be covered, for example by being coated, with a conducting polymer. The electrochemical system may thus have two conducting polymer electrodes, and the system can be run in a switching way: The two polymer layers are switched/activated in opposite direction. As the working electrode is oxidized, the counter electrode is reduced and vice versa. This is sometimes referred to as the rocking chair configuration.
Covering the counter electrode with a conducting polymer has several advantages. Most importantly this coating will counteract the above mentioned problem. The counter electrode will function as a second ion source/sink in addition to the electrolyte, thus reducing the ion depletion of the electrolyte near the working electrode and reducing the diffusion layer build up (ohmic or iR drop). Also, it can reduce the amount of electrolyte needed for the device, as there now exist an additional ion source/sink beyond the electrolyte. Another advantage is that the effective surface area of the counter electrode is increased, hence reducing the risk of gas formation. Also, it reduces the risk of dissolution of metal ions of the counter electrode that in turn are deposited on the working electrode. In addition, the counter electrode may be given a well defined redox reaction. Another advantage is that the conducting polymer covered counter electrode may result in lower activation potentials.
a illustrates an embodiment, wherein a counter electrode 51 is covered with an EAP layer 57, preferably a conducting polymer layer.
b illustrates yet another embodiment, where the counter electrode 51 is covered with both an EAP layer 57, preferably a conducting polymer layer, and an ion conducting covering 52, as described with reference to any of
a illustrates a device having a small electrolyte volume. The device 60 has a small cavity or lumen 63 that contains the electrolyte (not shown). The working electrode 61, comprising an electroactive polymer such as PPy, and the conducting polymer covered counter electrode 62 are positioned inside the device in proximity to each other. Such devices may be microchannels in microfluidics or BioMEMS applications, small tubular structures, such a catheters or cannulae, etc.
b illustrates a device 64 comprising the working electrode 61 and covered counter electrode 62. The device itself is inserted into or positioned inside a small cavity or lumen 63 of a separate device, object 65 or body. The device or object 65 may be a blood vessel or other body lumen, a (concentric) tube, such as a catheter, cannula, or a channel. The objects 64 and 65 may constitute (parts of) a single device. As an example, the single device may be a medical device, where reference numeral 64 designates a guide wire and reference numeral 65 designates a catheter. Alternatively, taking
a and 10b show the current and expansion response, respectively, of step activation of PPy in a small volume using different counter electrodes. At t=0 the PPy is reduced by applying −1 V. As can be seen, the response using a Au counter electrode (dashed line) is much slower (lower current and slower expansion) than using a counter electrode that has been covered with a layer of polypyrrole (solid line).
The electrolyte may be blood, blood plasma, salt solutions, contrast solutions, etc. The electrolyte may be a physiological fluid available in the area or space where the device is operated, such as blood, blood plasma, urine etc. Alternatively, the electrolyte may be an ionic solution that is externally applied to the device.
The devices described herein may be medical devices, such as catheters (such as guide catheters, balloon catheters), endoscopes, guidewires, leads (such as for cardiac rhythm management, internal defibrillators, infusion), electrodes, cannulas, embolic protection devices, introducers, sheaths, etc. The device may be a device that is temporarily inserted into the body lumen during a longer or shorter time period, or a device that is (permanently) implanted into the body.
The electroactive polymer may be a conducting polymer comprising pyrrole, aniline, thiophene, para-phenylene, vinylene, and phenylene polymers and copolymers thereof, including substituted forms of the different monomers.
Although other modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0600734-8 | Mar 2006 | SE | national |
This PCT application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/787,162, filed Mar. 30, 2006, which is incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP07/02536 | 3/20/2007 | WO | 00 | 5/29/2009 |
| Number | Date | Country | |
|---|---|---|---|
| 60787162 | Mar 2006 | US |
