BACKGROUND OF THE INVENTION

The present invention relates to electrode systems, devices and methods and, particularly, to electrode systems, devices and methods for use in contact with tissue (for example, skin) for electrophysical measurement.

Skin surface electrodes are important components in many medical diagnostic systems including, for example, electrocardiography (ECG), electromyography (EMG), and electroencephalography (EEG). In these systems, the electrode plays a critical role as a transducer converting physiological variables, such as those of the heart, muscles and brain, respectively, in ECG, EMG and EEG, to electrical potentials (sometime referred to as biopotentials). The measured potentials are then amplified and processed by an instrument, such as an electronic measuring circuit and a computer. The workings of skin surface electrodes are dependant on a multitude of mechanisms, such as electrode material, the electrolyte applied to the electrode, body location, and skin properties. The electrode must convert a physiological ionic current into an electronic current receivable and readable by the associated instrumentation. The electrode commonly used in clinical applications is the silver/silver chloride or Ag/AgCl electrode, which is a non-polarizable electrode that is electrochemically stable and generates relatively little noise. When using standard skin surface electrodes such as the silver/silver chloride electrode, two common preparations are typically required to lower the impedance of the electrode and of the skin contacted by the electrode: 1) an electrolyte gel containing Cl−ions is applied to maintain good ionic contact with the skin; and 2) the outmost skin layer, stratum corneum, is abraded, because it is the primary barrier to current flow due to its high ionic resistance.

Affixing surface electrodes manually is time-consuming with a high labor cost, thereby increasing medical care expenses. As the number of electrodes increases, which is desirable in, for example, certain EEG data analysis such as Laplacian mapping and source localization, manual placement of individual electrodes can become impractical, regardless of the cost. Automated placement can be desirable in such procedures. There has thus been interest in developing an automated EEG electrode placement system for use in connection with high-resolution EEG applications.

However, EEG electrodes currently used in the clinical setting exhibit a number of problems related to both manual and automatic placement. For example, such EEG electrodes have a flat contact profile with the scalp and must be delivered to the scalp without trapping hairs. In the manual placement case, various ways to handle the hair, such as combing and parting, are performed by hand. In automatic placement, however, such operations are difficult to perform. Application of electrolyte gel to a large number of electrodes through an automatic system in a reproducible manner is also difficult. In addition, the currently used gel has poor consistency and tends to spread, which could cause interference with neighboring electrodes, especially when high electrode density is required. Further, currently used gels often dry completely in approximately 1 to 2 hours, which presents a problem when long term monitoring (for example, in certain EEG procedures) is desired. Further, the depth of epidermal preparation must be carefully controlled. Otherwise, pain and infection (resulting from over preparation) or high impedance (resulting under preparation) may result. The depth of epidermal preparation is difficult to control automatically. Attempts to reduce or eliminate such problems associated with standard surface electrodes have met with limited success.

It is thus desirable to develop surface electrode systems, devices and methods that reduce or eliminate one or more of the above-identified problems as well as other problems associated with surface electrode systems currently in use.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides an electrode system comprising a flowable and cohesive surface contact element comprising a hydrophilic polymer swollen with an electrolyte fluid, the contact element having a Q′ ratio of at least 5 as defined by the equation

Q′=WWWG
wherein WGis the dry weight of the hydrophilic polymer and WWis weight of water in the sample after absorption of the electrolyte fluid comprising water and an electrolyte salt. The surface contact element can consist essentially of the hydrophilic polymer swollen by the electrolyte fluid.

The contact element can, for example, include individual particles of crosslinked hydrophilic polymer swollen with electrolyte fluid. The contact element is cohesive in that individual parts tend to cohere or stick together. However, the contact elements are highly hydrated and are not tacky such that they stick or adhere to a surface.

The contact element can have a Q′ ratio of at least 6. at least 7, at least 10, or even at least 11. In a number of embodiment, the contact element has a Q′ ratio of at least 1.5 even after drying in air at 37° C. for 6 hours. The contact element can a Q′ ratio of at least 2.0 after drying in air at 37° C. for 6 hours, or even at least 4.0 after drying in air at 37° C. for 6 hours.

The crosslinked hydrophilic polymer can, for example, include polyacrylate or a derivative of polyacrylate. The polyacrylate can, for example, be sodium polyacrylate, potassium polyacrylate or lithium polyacrylate.

The electrolyte fluid can include a penetration enhancer. The penetration enhancer can, for example, include urea.

The electrode system can further include a conductive electrode element in electrical connection with the contact element. The conductive element can, for example, be nonpolarizable. In several embodiments, the conductive element includes a silver/silver chloride probe. In several other embodiments, the conductive element includes a conductive polymer. The conductive element can, for example, include a conductive substrate coated on at least a portion thereof with a conductive polymer.

The electrode system can further include a holder (for example, a “cup” electrode) formed of a conductive material in which the contact element is at least partially positioned.

In another aspect, the present invention provides a method of applying an electrode system to a surface, including: applying a flowable and cohesive contact element including a hydrophilic polymer swollen with an electrolyte fluid to the surface, the contact element having a Q′ ratio of at least 5 as defined by the equation

Q′=WWWG
wherein WGis the dry weight of the individual particles hydrophilic polymer and WWis weight of water in the sample after absorption of the electrolyte fluid comprising water and an electrolyte salt. The contact element can consist essentially of a hydrophilic polymer swollen with an electrolyte fluid

As described above, the contact element can include individual particles of crosslinked hydrophilic polymer swollen by electrolyte fluid.

The Q′ ratio can be least 6, at least 7, at least 10 or even at least 11. In a number of embodiment, the contact element has a Q′ ratio of at least 1.5 after drying in air at 37° C. for 6 hours, at least 2.0 after drying in air at 37° C. for 6 hours or even at least 4.0 after drying in air at 37° C. for 6 hours.

As also described above the crosslinked hydrophilic polymer can be or can include polyacrylate or a derivative of polyacrylate. The polyacrylate can, for example, be sodium polyacrylate, potassium polyacrylate or lithium polyacrylate.

The electrolyte fluid can, for example, further include a penetration enhancer. The penetration enhancer can, for example, include urea.

The method can further include placing a conductive electrode element in electrical connection with the contact element. The conductive element can be nonpolarizable. The conductive element can include a silver/silver chloride probe. In several embodiments, the conductive element includes a conductive polymer. The conductive element can, for example, include a conductive substrate coated on at least a portion thereof with a conductive polymer.

The method can, for example, include flowing the contact element into a holder formed of a conductive material so that the contact element is at least partially positioned within the holder.

In another aspect, the present invention provides an electrode system including a contact element including a cross-linked hydrophilic polymer matrix. The contact element has a Q′ ratio of at least 5 as defined by the equation

Q′=WWWG

wherein WGis the dry weight of the crosslinked hydrophilic polymer and WWis the weight of water in the sample after absorption of an electrolyte fluid comprising water and an electrolyte salt. The contact element can also have a Q′ ratio of at least 6, at least 7, at least 10 or even at least 11. In several embodiments, the contact element has a Q′ ratio of at least 1.5 after drying in air at 37° C. for 6 hours. The contact element can also have a Q′ ratio of at least 2.0, or even at least 4, after drying in air at 37° C. for 6 hours.

In several embodiments, the crosslinked hydrophilic polymer matrix includes (or even consists essentially of) polyacrylate or a derivative of polyacrylate. The polyacrylate can, for example, be sodium polyacrylate, potassium polyacrylate, lithium polyacrylate or combinations thereof.

The electrode system can further include a conductive electrode element in electrical connection with the contact element. The conductive element can be nonpolarizable. The conductive element can, for example, include a silver/silver chloride probe. The conductive element can include a conductive polymer. For example, a conductive probe or substrate can be coated with a conductive polymer. The conductive substrate can, for example, include a metal or conductive carbon.

In several embodiments, the electrolyte solution further includes a penetration enhancer. The penetration enhancer can, for example, include urea.

The contact element can form direct contact (ionic contact) with a surface (for example, a skin surface). Alternatively, the electrode system can further include a flowable and cohesive lower or intermediate contact element (which can also be malleable or formable—that is, capable of being formed into a desire conformation). The intermediate contact element can have a Q′ ratio (as defined above) of at least 5. The intermediate contact element can, for example, include individual particles of crosslinked hydrophilic polymer swollen with electrolyte fluid comprising water and an electrolyte salt. The intermediate contact element can have a Q′ ratio of at least 6, at least 7, at least 10 or even at least 11. The crosslinked hydrophilic polymer of the particles can include polyacrylate or a derivative of polyacrylate. The polyacrylate can, for example, be sodium polyacrylate, potassium polyacrylate, lithium polyacrylate or combinations thereof. The electrolyte fluid absorbed within the particles can include a penetration enhancer. The penetration enhancer can, for example, include urea.

In another aspect, the present invention provides a method of measuring an electrical signal from living tissue including the act of placing a contact element in ionic contact with the tissue. The contact element has a Q′ ratio of at least 5 as defined by the equation

Q′=WWWG

As described above, WGis the dry weight of the crosslinked hydrophilic polymer, and WWis the weight of water in the sample after absorption of an electrolyte fluid comprising water and an electrolyte salt. The contact element can have a Q′ ratio of at least 6, at least 7, at least 10 or even at least 11. The contact element can have a Q′ ratio of at least 1.5 after drying in air at 37° C. for 6 hours. The contact element can also have a Q′ ratio of at least 2.0, or even at least 4.0, after drying in air at 37° C. for 6 hours.

The crosslinked hydrophilic polymer matrix can include polyacrylate or a derivative of polyacrylate. The polyacrylate can, for example, be sodium polyacrylate, potassium polyacrylate, lithium polyacrylate or combinations thereof.

The electrode can further include a conductive electrode element in electrical connection with the contact element. The conductive electrode element can be nonpolarizable. The conductive electrode element can, for example, include or be a silver/silver chloride probe. The conductive element can also include a conductive polymer. The conductive polymer can, for example, be coated upon at least a portion of a conductive substrate (for example, a metal or a conductive carbon).

The electrolyte solution can further include a penetration enhancer. The penetration enhancer can include, for example, urea.

In several embodiments, the living tissue is skin and the contact element is placed in connection with the skin without first abrading the skin.

The method can further include placing a lower or intermediate contact element in contact with the tissue between the tissue and the contact element. The intermediate contact element is flowable and cohesive and has a Q′ ratio of at least 5. The intermediate contact element can include individual particles of crosslinked hydrophilic polymer swollen with an electrolyte fluid including water and an electrolyte salt. The intermediate contact element can have a Q′ ratio of at least 6, of at least 7, of at least 10 or even of at least 11.

The crosslinked hydrophilic polymer of the individual particles can include polyacrylate or a derivative of polyacrylate. The polyacrylate can, for example, be sodium polyacrylate, potassium polyacrylate, lithium polyacrylate or a combination thereof.

The living tissue can, for example, be hair covered skin and the intermediate contact element can be placed in connection with the hair and skin without first abrading the skin and/or without removing the hair.

The electrolyte fluid absorbed within the individual particles can also include a penetration enhancer. The penetration enhancer can, for example, include urea.

In another aspect, the present invention provides an electrode including an electrode element including a conductive polymer. The electrode element can further include a conductive substrate, wherein the conductive polymer is coated on at least a portion of the conductive substrate. The substrate can, for example, include a conductive carbon or a metal. The conductive polymer can, for example, include at least one of polypyrrole, a derivative of polypyrrole, polythiophene, a derivative of polythiopene, polyaniline or a derivative of polyaniline. In several embodiments, the conductive polymer includes poly(3,4-ethylenedioxythiophene) or PEDOT.

Embodiments in which the electrode, including the electrode element, is nonmetallic can, for example, be beneficial in certain uses such as in connection with or in the vicinity of magnetic resonance imaging equipment.

In a further aspect, the present invention provides a method of placing an electrode into ionic contact with tissue including placing a flowable and cohesive contact element including individual particles of crosslinked hydrophilic polymer swollen with electrolyte fluid including water and an electrolyte salt in ionic contact with the skin. As described above, the contact element having a Q′ ratio of at least 5 as defined by the equation

Q′=WWWG

WGis a dry weight of the particles of crosslinked hydrophilic polymer, and WWis weight of water in the contact element after absorption of an electrolyte fluid comprising water and an electrolyte salt into the particles. The contact element can have a Q′ ratio of at least 6, at least 7, at least 10 or even at least 11.

The crosslinked hydrophilic polymer of the individual particles can include polyacrylate or a derivative of polyacrylate. The polyacrylate can, for example, be sodium polyacrylate, potassium polyacrylate, lithium polyacrylate or a combination thereof.

The living tissue can, for example, be hair covered skin and the lower contact element can be placed in connection with the hair and skin without first abrading the skin and/or without removing the hair.

The electrolyte fluid absorbed within the individual particles can include a penetration enhancer. The penetration enhancer can, for example, include urea.

In another aspect, the present invention provides a contact element for use in connection with a surface electrode system comprising a flowable contact element consisting essentially of polyacrylate or a derivative of polyacrylate. The contact element is adapted to absorb an aqueous electrolyte fluid including water and an electrolyte salt so that the contact element has a Q′ ratio of at least 5 as defined by the equation

Q′=WWWG

wherein WGis the dry weight of the crosslinked hydrophilic polymer and WWis the weight of water in the sample after absorption of the electrolyte fluid.

In another aspect, the present invention provides a surface electrode including an elongated tissue contact member including a crosslinked hydrogel matrix, an electrolyte associated with the hydrogel matrix, and a conductive element in connection with the elongated contact member. The surface electrode can further include at least one conductive polymer incorporated within the hydrogel matrix. The electrolyte can, for example, be an ionic electrolyte comprising an electrolyte salt.

The hydrogel can be synthesized from at least one hydrophilic monomer. The at least one hydrophilic monomer can, for example, be hydroxyethyl methacrylate, acrylic acid acrylamide, N-vinyl-2-pyrrolidone, maleic anhydride, vinyl alcohol or an alkylene oxide. The hydrogel can include at least one of alginate, agar, gelatin and collagen, fibrin, glucosaminaoglycan, chitin or chitosan.

The conductive polymer can, for example, be polymerized within the hydrogel. The conductive polymer can also be polymerized outside the hydrogel and incorporated therein.

The conductive polymer can be polypyrrole, polythiophene, polyaniline or a derivative of such conductive polymers.

The elongated contact member can, for example, have a specific operating impedance on skin of less than 50 kΩ*cm2, less than k20 Ω*cm2or even less than k10 Ω*cm2.

A radius of the elongated contact member can decrease over at least a portion of the length thereof. The elongated contact member can, for example, have a generally conical or frustoconical shape.

The elongated contact member can include polyacrylate. The elongated contact member can, for example, include poly(hydroxyethyl methacrylate) having polyacrylate incorporated therein.

In a further aspect, the present invention provides a contact element for use in connection with a surface electrode system including a hydrophilic polymer matrix including at least one conductive polymer incorporated within the hydrophilic polymer matrix.

In still a further aspect, the present invention provides a sensor system for measuring electrical activity within at least a portion of a patient's body including at least one electrode or at least one contact element as described above.

The present invention, along with the attributes and attendant advantages thereof, will best be appreciated and understood in view of the following detailed description taken in conjunction with the accompanying drawings.

