Electrically conductive adhesive hydrogels formed from a composition which generally includes a monomer, an initiator, an organic solvent, and a cross-linking agent are suitable for use as skin contact adhesives and, particularly, suitable for use as an electrical interface for disposable medical devices. The present hydrogels provide for reduced skin irritation and/or malodor properties, hydrate a subject's skin, readily wet around a subject's skin surface hair, and protect against burning of a subject upon or due to electrical stimulation through the hydrogel.

Description of the Invention

SUMMARY

The present invention provides for an electrically conductive hydrogel formed from a composition including a monomer, at least one initiator, a cross-linking agent, and an organic solvent. The pH of the hydrogel may be maintained in the range of 3 to 8.5 in the absence of a dual buffer system. An acidic salt or the acid form of a monomer may be used to maintain the pH of the hydrogel in the range of 3 to 8.5. The hydrogel may be formed from a composition that does not include a solubilizer for the at least one initiator. Desirably, the organic solvent is dimethyl sulfoxide and is between about 0.5% and about 5% by weight of the composition. Additionally, the composition may include a buffer.

The monomer of the composition is desirably N,N-Dimethylaminoethyl acrylate dimethyl sulfate quaternary, dimethyl amino ethyl methacrylate, acrylamido methyl propane sulfonic acid or their salts. The monomer desirably is about 10% to about 80% by weight of the composition and is more desirably about 40% to about 75% by weight of the composition.

The cross-linking agent is about 0.01% to about 2% by weight of the composition and the initiator comprises about 0.01% to about 2% by weight of the composition. Desirably, the initiator is a chemical initiator, a photo initiator, or both. When the initiator is a chemical initiator, it may be thermally activated and may be disulfide based, peroxide based, or persulfate based or may be a sodium metabisulfite. Additionally, the initiator may be a hydrophobic initiator.

Additionally, the composition may desirably include skin health agent, which reduces irritation to the skin, particularly irritation caused by the use of dimethyl sulfoxide as an organic solvent. These skin health agents include aloe vera, glycerin, vitamin E, vitamin B, provitamin B, vitamin E acetate, or chitosan.

Another aspect of the invention addresses an electrode which includes an electrically conductive adhesive hydrogel formed from a composition. The composition includes a monomer, at least one initiator, a cross-linking agent, and an organic solvent. The pH of the hydrogel may be maintained in the range of 3 to 8.5 in the absence of a dual buffer system. Desirably, the composition may further include a skin health agent which may include an electrically conductive hypoallergenic layer which is in communication with the electrically conductive hydrogel.

Yet another aspect of the invention addresses a composition for an electrically conductive hydrogel. The hydrogel includes at least one monomer, at least one initiator, a cross-linking agent, and an organic solvent. The pH of the hydrogel may be maintained in the range of 3 to 8.5 in the absence of a dual buffer system.

DETAILED DESCRIPTION

The invention disclosed herein is directed to electrically conductive hydrogels. The hydrogels include a monomer, initiator, cross-linking agent, and an organic solvent. The hydrogels are electrically conductive adhesive hydrogels which are good electrical conductors suitable for use in disposable medical devices, for example. These hydrogels are desirably non-irritating to the skin, are sufficiently wet to adhere to skin, and are readily removable from skin when desired. The organic solvent of the hydrogel acts as a solvent for the initiator and provides a significant cost savings over the use of a solubilizer for the initiator.

It will be appreciated that while reference is generally made throughout this disclosure to a hydrogel, in addition to referring to the end product, the term hydrogel, also may refer to the polymerizing formulation or hydrogel precursor which is converted to a hydrogel upon exposure to certain conditions (e.g., ultraviolet or UV curing, heat, etc.) as discussed elsewhere herein.

In the interests of brevity and conciseness, any ranges of values set forth in this specification contemplate all values within the range and are to be construed as support for claims reciting any sub-ranges having endpoints which are whole number values within the specified range in question. By way of a hypothetical illustrative example, a disclosure in this specification of a range of from 1 to 5 shall be considered to support claims to any of the following ranges: 1-5; 14; 1-3; 1-2; 2-5; 2-4; 2-3; 3-5; 34; and 4-5.

Compared to conventional conductive hydrogel formulations, the hydrogels of the present invention exhibit enhanced polymerization as evidenced by clear or substantially clear gel solutions, the absence of precipitates or presence of only limited precipitates, generally high electrical conductivity values, and are characterized by the absence of solubilizers for the initiator. Thus, the amount of undesirable residual functional monomer and/or other monomeric residues in the hydrogel which are unpolymerized is reduced. The present hydrogels exhibit these enhanced polymerization and electrically conductive properties without the need for expensive solubilizers for the initiator.

An additional advantage of the hydrogels of the present invention is that they may utilize an electrolyte or combination of electrolytes as conductivity enhancers.

Clear gel solutions of the present inventions are demonstrated when there is no residue or precipitates visible in the formulation with the naked or unaided eye. Substantially clear gel solutions are demonstrated by either an amount of residue or precipitate in the solution that does not cause the solution to demonstrate unsatisfactory conductivity values. Generally speaking, satisfactory electrical conductivity values are values ranging from about 30 mS/cm to about 50 mS/cm.

With regard to the functional monomer, it is contemplated that the hydrogels may be formed from any suitable monomer. In at least one aspect of the present invention, the hydrogel may be formed by free radical polymerization in the presence of water. Initiation of the formation of the hydrogel may be begun by ultra-violet curing with an initiator and a multifunctional cross-linking agent. While only one initiator is necessary, the hydrogel precursors may contain one or more second initiators. The initiators can be photo-initiators or chemical initiators such as those activated by heat or by reduction/oxidation (redox) reactions.

While any suitable monomer is contemplated by the present invention, exemplary functional monomers include: N-vinyl pyrrolidone (NVP), hydroxyethyl methacrylate (HEMA), methacrylic acid (MA) or its salt, styrene sulfonic acid (SSA) or its salt, potassium sulfopropyl acrylate (KPSA), dimethyl acrylamide (DMA), dimethyl amino ethyl methacrylate (DMAEMA) or its quaternary salt derivative, acrylamido methyl propane sulfonic acid (AMPS) or its salt, and the combination of any of the above. Additionally, the acid and salt of an exemplary functional monomer may be included in the hydrogel. Desirably, the hydrogels of the present invention are made from various classes of monomers including acrylates, vinyls, amides, esters, etc, of which can be electrically neutral, cationic or anionic. Combination of functional monomers also is possible to achieve desired physical, chemical mechanical and electrical properties. Compared to prior hydrogels, the hydrogels of the present invention hydrate the skin's surface more effectively and lower the skin's electrical resistance resulting in lower generation of heat and lower incidence of burning upon electrical stimulation. In addition, the present hydrogels more effectively wet around skin hair and, consequently, more sufficiently contact a subject's skin resulting in increased efficacy in procedures such as defibrillation as well as reduced heating and burning of skin surfaces and, generally require no preparation of the skin surface prior to use. Further, the present hydrogels are self-preserving and are resistant to degradation because of the compatibility of the monomer with the other ingredients present in the hydrogel.

Generally speaking, the monomer is desirably between about 10 to about 80% by weight of the composition, more desirably between about 40 to about 75% by weight of the composition, and even more desirably between about 50 to about 75% by weight of the composition.

Examples of specific desirable cationic acrylates are: acryloyloxyethyltrimethyl ammonium chloride which is readily available from CPS Chemical Co. (New Jersey) or Allied Colloid (U.K.); acryloyloxyethyltrimethyl ammonium methyl sulfate which is also available from CPS Chemical Co. or Allied Colloid; and, acrylamidopropyltrimethyl ammonium chloride, which is available from Stockhausen (Germany). The desired process for making hydrogels with these exemplary acrylates is described in detail below.

A cationic acrylate hydrogel suitable for the present invention will generally be somewhat clear in color, viscous, and tacky to the touch. The hydrogel tends to be sufficiently adhesive to a subject's skin, yet sufficiently cohesive to be easily removable from the subject's skin and separable from itself. As noted above, the hydrogels suitable for the present invention can be formed by in-situ free radical polymerization of a water soluble monomer in the presence of water, desirably by ultra-violet curing with at least one initiator, multi-functional cross-linking agent(s), and a solvent. For example, an appropriate acrylate monomer, water, electrolyte (e.g. sodium sulfate), initiator or catalyst (e.g., 1-hydroxycyclohexylphenol ketone, etc.), multi-functional cross-linker (e.g., methylene-bis-acrylamide, etc.), and solvent (e.g., dimethyl sulfoxide.) are combined, placed in a mold, and exposed to an appropriate amount of ultra-violet radiation.

Examples of co-monomers which may be used with the present invention include co-monomers soluble in water and, even more desirably, include anionic co-monomers. The amount of co-monomer to be used may be in the range of about 5 to about 50% by weight, desirably about 10 to about 30% by weight, based on the amount of reactants used. Examples of suitable co-monomers include: unsaturated organic carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, and citraconic acid and salts thereof, unsaturated organic sulfonic acids such as styrene sulfonic acid, methallyl sulfonic acid, 2-sulfoethyl acrylate, 2-sulfoethyl methacrylate, 3-sulfopropyl acrylate, 3-sulfopropyl methacrylate, acrylamido-methylpropane sulfonic acid and salts thereof, N,N-dimethylacrylamide, vinyl acetate, other radically polymerizable ionic monomers containing a carbon-carbon double bond, and non-N-vinyl lactam co-monomers useful with N-vinyl lactam monomeric units such as N-vinyl-2-pyrrolidone, N-vinyl-2-valerolactam, N-vinyl-2-caprolactam, and mixtures thereof. Among the ionic monomers enumerated above, particularly desirable selections are 3-sulfopropylacrylate or methacrylate, and salts thereof. Examples of cations involved in the formation of such salts include sodium, potassium, lithium, and ammonium ions. Ionic monomers may be used singly or in a mixture of two or more monomers.

Any suitable organic solvent may be used. The desirability of a specific organic solvent and/or the amount thereof may vary or depend in part on the other components and quantities thereof selected to make up the hydrogel precursor. The use of any organic solvent capable of dissolving the initiator up to an amount equal to the initiator's solubility limit is desired. Suitable organic solvents include, but are not limited to, dimethyl sulfoxide and glycerine.

The organic solvent is adapted to dissolve the initiator (hydrophobic or hydrophilic) and is water soluble. The organic solvent is adapted to dissolve hydrophobic additives such as lipids, anti-oxidants, drugs, and fragrances. Additionally, the organic solvent is adapted to dissolve skin health agents such as aloe Vera, glycerin, vitamin E, vitamin B, provitamin B, vitamin E acetate, or chitosan.

It is contemplated that a organic solvent may be present in a positive amount up to about 20% by weight of the hydrogel precursor and, more desirably, between about 0.5% to about 5% by weight of the hydrogel precursor.

Present hydrogels may include an optional buffer system to help control the pH, prevent discoloration, and/or prevent breakdown due to an extended presence of water (i.e., hydrolysis). The use of a buffer system with the present hydrogel is desired to provide the hydrogel with a commercially suitable shelf-life (i.e., a shelf-life of over one year) without discoloration. Suitable buffers include, but are not limited to, conventional buffers such as sodium hydroxide, sodium potassium tartarate, and/or sodium phosphate monobasic, all of which are commercially readily available from Aldrich Chemical Co., Inc., Milwaukee, Wis.

In addition, the use of buffers also helps to prevent electro-chemical burning of a subject by helping to prevent pH changes and/or shifts as a current is driven through a pair of hydrogel electrodes. Typically, in prior systems, as current is driven through a pair of hydrogel electrodes, one electrode becomes more acidic (i.e., its pH decreases) while the other electrode becomes more basic (i.e., its pH increases). This pH shifting problem is particularly prevalent if current is driven through such electrodes for a long period of time (e.g., over 1 hour), such as during a procedure wherein a patient's heart is being paced. The desired use of a buffer system as is suggested in the present invention helps safeguard against such pH changes as current is driven therethrough and thereby enables use of the electrodes made from the present hydrogel for longer periods (e.g., over 24 hours) without electro-chemical burning.

Therefore, it is desired that buffer (or a suitable alternative as described below) be included to stabilize the resulting polymer, to avoid hydrolysis of the hydrogel, and to avoid pH shifts due to the passage of direct current through the hydrogel. Buffers help both to reduce or prevent corrosion of metal conductors and also are conductivity enhancers themselves. Some buffers prevent undesirable yellowing of the hydrogel. The present hydrogel may include sufficient buffer to maintain the pH of the hydrogel in a range of about 3 to about 8.5, and more desirably about 5.5 to about 7, but the pH may be adjusted as desired. In most aspects of the present invention, a buffer may be present in the hydrogel precursor in an amount up to about 10% by weight, and more desirably from about 0 to about 5% by weight of the hydrogel precursor.

As an alternative to the use of conventional buffers, an amount of the acidic form of the monomer used may be used in the hydrogel precursor to adjust the pH of the hydrogel. Desirably, an amount of the acidic form of the monomer will be combined with the salt of the monomer so that an additional conventional buffer may not be needed. In this regard, pH is conventionally adjusted in hydrogels by utilizing a dual buffer system including a non-monomeric acidic salt such as an aluminum potassium sulfate and an additional buffer having a pH greater than 7 such as sodium hydroxide. For example, conventionally, aluminum potassium sulfate, or another non-monomeric acidic salt, is added to the hydrogel precursor in an amount to stabilize the resulting polymer, however, the amount utilized may result in an unacceptable drop in pH. Because of this drop in pH, sodium hydroxide, or another buffer having a pH greater than 7, is added to the hydrogel precursor to bring the pH up to a satisfactory level.

This dual buffer system creates many potential problems such as buffer incompatibility with the monomer and formation of a substantial amount of precipitates in the hydrogel which may lead to a potential decrease in conductivity.

Additionally, an acidic salt may be used by itself, and not as part of a dual buffer system, to maintain the pH in the desired range.

However, utilizing the salt of the monomer in conjunction with the acid (as a pH adjuster) eliminates potential problems such as buffer incompatibility with the monomer while still increasing shelf life and stability of the monomer solution.

The present invention also contemplates the inclusion of other additives, such as conductivity enhancers, pharmaceuticals, humectants, plasticizers, skin health agents, and the like. These other additives may be included either before or after a curing step. The appropriateness of such additives is generally dependent upon the intended end use of the particular hydrogel.

Any suitable additive or combination of additives such as those suggested above is contemplated. The specific additive and/or the amount thereof which is included may vary or depend in part on the other components and quantities thereof selected to make up the hydrogel. Exemplary skin health agents and/or skin care ingredients include but are not limited to vitamins (e.g., B, D, E, E acetate, etc.), antioxidants, chitosan, aloe Vera, hyaluronic acid (HA), heparin, chondroitin sulfate, dextran sulfate, and collagen IV. Still other exemplary additives may include but are not limited to anti-inflammation agents, anti-oxidants, aesthetic agents (e.g., color dyes to alter appearance of the hydrogels), or fragrances.

Additionally, the skin health agent (i.e. chitosan glycolate, silk hydrolyzate, or polyvinylpyrrolidone) may be an electrically conductive layer which is in communication with the electrically conductive hydrogel. In this regard, the skin health agent may optionally not be present in the hydrogel but may act as a separate hypoallergenic layer in communication with the hydrogel in order to reduce skin irritation of the patient. Desirably, this separate hypoallergenic layer will not decrease the conductivity of the hydrogel.

Additionally, the use of suitable conductivity enhancer is contemplated. The specific enhancer and/or the amount thereof which is included in the hydrogel may vary or depend in part on the other components, and quantities thereof selected to make up the hydrogel. Exemplary conductivity enhancers include but are not limited to salts such as potassium chloride, sodium chloride, potassium sulfate, sodium sulfate and the like. These salts are desired inasmuch as human bodies use them for conduction. Additional examples of salts which may be appropriate are lithium chloride, lithium perchlorate, ammonium chloride, calcium chloride, and/or magnesium chloride. Other chloride salts, iodide salts, bromide salts, and/or halide salts also may be suitable.

Other salts, such as salts of weak organic acids or polymeric electrolytes may be desirable. These salts are compatible with human bodies and with the chemistry of the hydrogels of the present invention and may be used as conductivity enhancers where desired chloride salts might interfere (i.e., corrode) with aluminum and/or stainless steel metal components used to interface the hydrogel with medical equipment. Examples of salts which may be suitable include sodium citrate or magnesium acetate.

Although use of a conductivity enhancer is optional, the amount of conductivity enhancer in a hydrogel of the present invention is desirably in the range of none to an amount which will enhance the conductivity of the hydrogel. For example, if a conductivity enhancer is utilized, the conductivity enhancer may desirably be present in an amount between greater than about 0 (e.g., 0.01%) to about 15% by weight of the hydrogel precursor and, even more desirably, between greater than about 0 (e.g., 0.01%) to less than about 5% by weight of the hydrogel precursor.

The addition of conductivity enhancers may be desired even though the hydrogel of the present invention is a polyelectrolyte ionically disassociated in water and, therefore, conductive. In use, a lower specified quantity of polyelectrolyte (and thus a hydrogel having a correspondingly lower viscosity) may be desired in situations such as when the hydrogel must wet around chest hair. In such cases, the addition of a conductivity enhancer may be useful.

However, while the addition of a conductivity enhancer to a hydrogel or hydrogel precursor has generally been thought to provide for better electrical conductivity when compared to hydrogels without the added conductivity enhancer, it has been discovered that at least some aspects of the present invention which do not include an added conductivity enhancer demonstrate better "in use" conductivity as compared to those hydrogels which included a conductivity enhancer. For example, in certain instances, salts, despite being inherently electrically conductive because of their ionicity, may negatively yield undesirable effects such as the "salting out" effect which may result in phase separation and/or contribute to the reduced conductivity of certain formulations. This is especially true the longer the shelf life a hydrogel may be subjected to.

As indicated herein, an optional buffer and/or one or more of the optional polyelectrolyte additives (e.g., HA, chondroitin sulfate, phospholipids, etc.) may exhibit conductivity enhancing properties; however, the buffer and/or polyelectrolyte additives are not contemplated to be included in the determination of the amount of a conductivity enhancer in the hydrogel as the buffer and/or polyelectrolyte additives may not form a continuous path within the gel and between the gel and the skin.

As is mentioned above, initiators are used in the polymerization of the hydrogel precursors described herein. Examples of initiators which may be used include IRGACURE.RTM. 184 (1-hydroxycyclohexyl phenyl ketone), IRGACURE.RTM.. 2959 (4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-methylpropyl)ketone)), and DAROCURE.RTM. 1173.alpha.-hydroxy-.alpha.,.alpha.-dimethylacetophenone), all commercially available from Ciba Specialty Chemicals. These ultraviolet UV initiators are desired because they are non-yellowing. Other initiators which may maintain the desired water-white and water-clear appearance of the present hydrogels also are desired. Additional examples of suitable initiators (which may be photo initiators or thermal initiators) may include benzoyl peroxide, azo-bis-isobutyro-nitrile, di-t-butyl peroxide, bromyl peroxide, cumyl peroxide, lauroyl peroxide, isopropyl percarbonate, methylethyl ketone peroxide, cyclohexane peroxide, tutylhydroperoxide, di-t-amyl peroxide, dicumyl peroxide, t-butyl perbenzoate, benzoin alkyl ethers (such as benzoin, benzoin isopropyl ether, and benzoin isobutyl ether), benzophenones (such as benzophenone and methyl-o-benzoyl benzoate), actophenones (such as acetophenone, trichloroacetophenone, 2,2-diethoxyacetophenone, p-t-butyltrichloro-acetophenone, 2,2-dimethoxy-2-phenyl-acetophenone, and p-dimethylaminoacetophenone), thioxanthones (such as xanthone, thioxanthone, 2-chlorothioxanthone, and 2-isopropylthioxanthone), benzyl 2-ethyl anthraquinone, methylbenzoyl formate, 2-hydroxy-2-methyl-1-phenylpropane-1-one, 2-hydroxy-4'-isopropyl-2-methyl propiophenone, .alpha.-hydroxy ketone, tetramethyl thiuram monosulfide, allyl diazonium salt, and combinations of camphorquinone and ethyl 4-(N,N-dimethylamino)benzoate. Other suitable initiators may be found in, for example, Berner, et al., "Photo Initiators--An Overview", J. Radiation Curing (April 1979), pp. 2 9.

Although only one initiator is necessary, the hydrogel may contain one or more second initiators. The one or more second initiators can be photo or chemical initiators.

Where there is only one initiator, the amount of initiator is desirably within the range of about 0.01 to about 5% by weight of the hydrogel precursor, more desirably, within the range of about 0.05 to about 2% by weight of the hydrogel precursor and, even more desirably, within the range of about 0.1 to about 0.5% by weight of the hydrogel precursor. Where one or more second initiators are present, the amount of one or more second initiators is desirably within the range of about 0.01 to about 5% by weight of the hydrogel precursor, and more desirably within the range of about 0.05 to about 2% by weight of the hydrogel precursor and, even more desirably, within the range of about 0.1 to about 0.5% by weight of the hydrogel precursor. However, where multiple initiators are present, it is generally desirable that the combined amount of the initiators be about 5% or less by weight of the hydrogel precursor, and more desirably within the range of about 0.02 to about 5% by weight of the hydrogel precursor.

UV curing parameters to achieve desired polymer properties are well known to those skilled in the art. A photo initiator for the present purposes tends to operate by absorbing select wavelengths of UV to produce radical initiating species to induce monomer polymerization. The wavelengths and curing area set the style of UV bulb used in the curing process. Inhibition of polymerization due to dissolved oxygen, monomer inhibitors, or other radical scavenging moieties may be overcome by changing the power, by pulsing, and/or by using initiator accelerators.

It will be appreciated that each photo initiator is responsive to a specific or narrow wavelength range of UV light. At least one aspect of the present invention takes advantage of this property and incorporates two or more photo initiators in a hydrogel precursor. The addition of more than one initiator in a hydrogel precursor allows for a broader range of the energy or range of wavelengths emitted by a UV source to be utilized. The utilization of multiple initiators can further reduce solubility limit concerns and related compatibility concerns, as more efficient polymerization may be able to be achieved with two initiators present in a hydrogel precursor than with either of the initiators used alone at the same overall initiator concentration.

The synergistic effect of initiators has not been previously identified or exhibited in previous hydrogels which incorporated one photo initiator, if any initiator at all. It is further believed that the inclusion of initiators having different rates of initiation and/or the inclusion of initiators which begin initiation of polymerization of the monomer at different times relative to each other (such as that which may be experienced by multiple initiators (e.g., a thermally activated chemical initiator (TACI) and a photo initiator)) contributes to a higher yielding polymerization. That is, for example, where two photo initiators are included, one may have a lower UV wavelength trigger and may be more energetic (providing for a faster rate of initiation and reaction) than the other initiator which is triggered by a higher UV wavelength or range. The faster initiator may also die or be consumed faster than the other. It is contemplated that it may be advantageous to have polymerization occur at different rates and/or at a mixed rate which may not be obtainable with one initiator or with an initiator which is suitable for a particular hydrogel precursor. An example of initiators which are not triggered or activated simultaneously, may be found in the present invention where a photo initiator and a TACI are in a hydrogel precursor, and the photo initiator is triggered by a UV source and reacts with the monomers in the precursor so as to generate heat to trigger the TACI.

While numerous combinations and variations of initiators are possible, it is believed that the combination of multiple initiators provides more favorable kinetics which affords a higher probability of more extensive polymerization of the monomer and/or other monomeric residues.

It is a further discovery of the present invention that a TACI may be included to take advantage of the benefits of multiple initiator polymerization. As some heat is necessary to trigger a TACI, it is contemplated that a TACI will generally be included only where heat will be present in or produced in the hydrogel precursor in a sufficient amount to trigger the TACI. As radical polymerization reactions induced by photo initiators are known to be exothermic and thus to generate heat in response to UV exposure, at least one aspect of the present invention is directed to the inclusion of a TACI in a hydrogel precursor where a photo initiator is also present so as to allow the TACI to take advantage of the heat generated by the radical polymerization reaction induced by a photo initiator. It is also contemplated that a TACI can be included where multiple photo initiators are present. The presence of multiple photo initiators provides for the potential benefits of multiple initiators discussed above yet also provides for the triggering of a TACI where the heat generated by one photo initiator may be insufficient to trigger or fully trigger the TACI (depending on the photo initiators and the TACI involved), whereby the TACI can further promote or complete the polymerization of the functional monomer and other monomeric residues in a hydrogel precursor. Multiple TACIs are also contemplated.

It is believed that literature reports and/or clinical experience lack any report or descriptions of utilizing the combination of one or more photo initiators and a TACI in order to obtain the more complete polymerization of a hydrogel precursor, thereby leading to a more stable, less malodorous, and/or less skin irritating hydrogel.

As is also noted above, cross-linking agents are desirably used to cross-link the present hydrogels. Examples of multi-functional cross-linking agents which may be used include, for example, methylene-bis-acrylamide and diethylene glycol diacrylate which are both commercially available from Polysciences, Inc., Warrington, Pa. Additional examples of cross-linking agents which may be satisfactory for use in the present invention include: poly(ethylene glycol) diacrylate, triethylene glycol-bis-methacrylate, ethylene glycol-bis-methacrylate, ethylene glycol-dimethacrylate, bisacrylamide, triethyleneglycol-bis-acrylate, 3,3'-ethylidene-bis(N-vinyl-2-pyrrolidone), trimethylolpropate trimethacrylate, glycerol trimethacrylate, polyethylene glycol dimethacrylate, and other multifunctional polyacrylate and polymethacrylate crosslinkers.

The amount of cross-linking agent is desirably within the range of about 0.01 to about 2% by weight of the hydrogel precursor and, more desirably, within the range of about 0.05 to about 0.5% by weight of the hydrogel precursor.
 

Claim 1 of 32 Claims

1. A substantially precipitate free electrically conductive hydrogel formed from a composition comprising: a monomer; at least one initiator; a cross-linking agent; and an organic solvent, wherein the composition does not comprise a dual buffer system, the pH of the electrically conductive hydrogel is maintained in the range of 3 to 8.5 in the absence of the dual buffer system and wherein the composition does not comprise a solubilizer for the at least one initiator.
 

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