CA2115441A1

CA2115441A1 - Two-phase composites of ionically-conductive pressure-sensitive adhesive; biomedical electrodes

Info

Publication number: CA2115441A1
Application number: CA002115441A
Authority: CA
Inventors: Timothy M. Dietz; Robert A. Asmus; Rosa Uy
Original assignee: Individual
Current assignee: 3M Co
Priority date: 1991-11-15
Filing date: 1992-10-30
Publication date: 1993-05-27
Also published as: EP0616505B1; US5338490A; DK0616505T3; DE69213758T2; JP3457308B2; JPH07500994A; EP0616505A1; DE69213758D1; AU3057992A; WO1993009713A1; AU662582B2

Abstract

A two-phase composite of ionically-conductive pressure-sensitive adhesive (14, 36), biomedical electrodes (10, 30) using the composite and methods of preparing the composite and the electrode are disclosed. The continuous phase is a hydrophilic, solid state pressure-sensitive adhesive composition ionically-conductive regardless of an amount of water present in the composition. The discontinuous phase are domains of a hydrophilic pressure-sensitive adhesive which enhances adhesion of the composite to mammalian skin while maintaining acceptable alternating current impedance of the composite.

Description

W ~ 93/09713 PCT/US92/09329 ~llS4~1 B70medlcal electrode provlded wlth two-phase composltes conductlYe9 pressure-senslt~ve adhes~ve.

Fi~ld of the In ention This inv~ntion r~late~ to composit~s of a csntinuous pha~e of an ionically-conductive, hydrophilic, solid state, pre~ure-~en~itive adhesive having domains of hydrophobic, pressur~-~snsitive a~he0ive disper~ed therein~ Thi~ invention also relat~s to biomedical alectrodeR ueing 3uch compo~ite~ a~ a ionically-conductive medium, and methods of preparing ~uch compo~i~es and electrods~.

Backaround of the Invention Modern medicine u~e~ many ~sdical procedure~ where electrical ~ignals or currents are r~ceived from or delivered to a patient's body. The ~nterface between medical eguipment used in ths~e procsdures and the ~kin of the patient is u~ually ~ome sort of biomGdical electrode. Such an electrode typically includes a conductor which mu~t ba connected electrically to the eguipment, and a conductive medium adhered to or otherwise contacting 3kin of a pati2nt.
Among the therap4utic procedures uBing biomedical electrode~
are transcutanQou~ electronic nerve stimulation (TENS) device~ us6d for pain managemant; neuromu~cular stimulation (N~S) uoed for treating condition~ ~uch ao 3coliosis; defibrillation ele~trode3 to dispenoe electrical energy to a che~t cavity of a mammalian patient to d~brillate heart baat~ of the patient; and disper~ive electrod~ to rsceivs electrical en0rgy dlspensed into an inci~ion made during electro~urgery.
Among diagnostic procedures u~ing biomedical electrodes are monitor0 o electrical output from body functions, such as elsctrocardlogram ~CG) for monitoring heart acti~ity and for diagnos$ng heart abnormalitie~.

W O 93/09713 PCT/Us92/09329 211~4l For each diagnostic, therap4utic, or electrosurgical procedure, at least one biomedical electrode having an ionically conductive medium containing an electrolyte i8 adhered to or otherwi~e contacting mammalian skin at a location o~ interest and also electrically connected to electrical diagnostic, ~herapeutic, or electrosurgical equipment. A critical component of the biomedical electrode iB the conductive medium serving ae the interface between mam~alian skin and diagno~tic, therapeutic, or electro3urgical equipment.
BiomÆdical electrode~ are used among other purpose~ to monltor and diagno~e a patient' B cardiovascular activity.
Diagnostic electrode~ are u~ed to monitor the patient immediately and ~re only applied to the patient for about fi~e to tan min~tes.
Mon~toring electrode~ are ueed on patients in i~tenRive care for up to three d~y~ continuou~ly. Holter electrode~ are used to monitor a patient during ~trenuou~ and daily activities.
All of these biomedical electrode~ are used to record cardiovascular activity although each electrode requirae ~pecific feature~ to be eucces~ful. The diagnostic electrode doee not have to remain adhered to a patient for exten3ive period~ but doe~ have to adhere to hairy, oily, dry and wet ~kin effectvely for the five to ten minutes of use. The monitoring electrodc ha~ to adhere for a ~-longer period of t~me although the patient i3 often immobile during the monitoring period. The Holter electrode i~ susceptible to 2S disruption from adhesion due to physical motion, per~piration, water, etc., and therefore requires the be~t adhesion and at the eame tLme comfort and electrical performance.
The ionically conductive medium which serves ae an interface between the ~kin of a mammalian patient and the electrical in~trumentation rangee ~rom conductive gele and creame to conductive pre~ffure sens~tive adhesivee. However, while conductive media can bs pres~ure ~ensit~ve ~dhaeives, for monitoring or Holter biomedical electrode use, euch conductive adhesives are not adeguate alone to mainta$n~adhe~ion to _ l~an ~kin. Hypoallergenic, hydrophobic preesure een~itiv~ adhe~ives are employed around the conductive ~edium to provide the reguired mammalian akin adhe~ion. U.S. Pat.
No. 5,012,810 ~Strand et al.) and U.S. Pat. Nos. 4,527,0Q7;
4,539,996; 4,554,924~ and 4,848,353 tnll Engel) diwlo~e biomedical electrode~ wh~ch have a hydrophobic pree~ure ~en~itive adhe~ive eùrrounding the conductive medium.
-W ~ 93~09713 2 1 1 5 4 4 1 PCT/US92/og329 Conductive media are typically hydrophilic and needwater or an aqu~ous ionic ~ystem to provide required ionic conductivity betw~en m~mmalian skin and electrical diagnostic, therapeutic, or electrosurgical in~trumentation. ~ydrophilic pressure ~en~itive adhe~ives generally have less skin adhesion than hydrophobic adhesives. SomRtimes, ~uch hydrophilic pressure-~ensitive adh~sives can not func~ion as adhe~ives to ma~malian skin for the period of tim~ nec~esary to completa a m~dical procedure.
To impro~e the tack of conductive hydrogals, tackifiers have b~en add~d. U.S. Pat. No. 4,593,053 (Jevne et al.) disclo~e~
the ~ddit$on of poly-2-acrylamido-2-methyl propane sulfonio acid, its e~lt~, polyacrylic acid, polystyrene sulfonic acid or salts thareof, karaya, xanthan, guar, or locust bean gwms in ~n amount of 2 to 20 we$ght psrcent to incr-~se tackiness of gel containing polyvinylpyrrolidone and polyvinyl alcohol.
Also, adhesive additi~es h~ve been u~ed in the formation of the ~olid phase of a matrix ueeful a~ a medical band~ge. U.S.
Pat. No. 4,307,717 (Hy~e~ et al.) discloses the ~ddition of vinyl acetate dioctyl -;-maleate copolymer to intensify the tackiness of the bandage.
Rather than employ a single phase hydrogel for the conductive medium, U.S. ~at. No. 4,588,762 (Mruk et al.) diecloses a heterogsneous, pressure-~ensitive, electrically conductive adhe~ive for dispo~able biomedical electrodes con~isting of a vi~coQlastic polymeric adhesive phase and an electrically conductive aqueous phase containlng a water receptive polymer, humectant, `and an electrolyte. Both phase~ are intimately interdispersed and the ~dhe~ive iB applied as a relatively thin film on a supporting ~0 substrate. The final film constitutes a heterogeneou~ sy~tem in which the aqueou~ zones or ialand0 defined by the water receptive poly~er 0xtend through the thickness of the film and are digtributed throughout ths expan~e of a continuou~ matrix con0i~ting of the adhecive~ol y r. ~owever, to be electr~cally conductive, such 35 ~ones or islands must contact both mammalian ~kin and electricallyconductiv~ mater~als in the biomed~cal electrode. If ~uch zones or islands do not transverse the thickne~s of the film, they are electrical dsad ends.
PCT International Publication WO 91/09633 (A~mus) disclo~e~ a two-pha~e composite of a continuou~ pha~e of a pressure W O 93/09713 P~T/USg2/09329 2~1~4~1 sensitive adh~ive matrix having di~per~ed tharein ~wollen, di~cret gel particl~. If such particles were ionically conductive, such particles could not transmit ~lectrical ~ignal~ betw2en mammalian ~kin and ~l~ctrical inatrumentation unle~ such particles ~ransversed the thicknes~ of the continuous phase.

Summarv of the Invention The present invention solve~ the problem in the art of improving mammalian ~kin adhesion for ionically-conductive, hydrophil~c, ~olid stat~, pres~ur~ nsitive adhe~ive~ useful in biom~dical olectrodes without affectin~ ad~ers~ly the ionic-conductivity of the pr~ssure-~en~iti~e adhesive.
~ Adhesives of the present in~ention do not rely on the electrical conductivity of aqu~ous zon~s or gel particles in a continuou~ pr~ure-~en~itive adhesive pha~e to traDRvorse the thickne~e of the phaee. Nor do adhesiv~s of the prea2nt invention require a hydrophobic pr~asure senaitive adheaive to impart adh~ivenaas.
The pr~0ent invention provides a ionically-conductive, pres~ure-sensLt~vo ~dhesiva which cAn function on mammalian skin over a longer period of contact without 10B~ of pr~ssure-~eneitive ~ropertie3 than hydrophilic pre~sure-sen~itive adhesives previously Xnown.
The preaent invention comprise~ a two-phase compoaite of ionically-conductive, pressure-sensitive 2dhesiv2. The ionically-conductive, pressure-~ensitive adhesive compri~es a cont~nuou~ pha~e of hydrophilic, ~olid ~tate pressure-sen itive adhesive conposition ionically-conductive regardles0 of an a unt of water preQent in the compo~ition, and a discontinous phase of domains of hydrophobic, prec~ure-~2n~itive adhe~ive composition present in the continuous phaae in an amount to enhancs pre~sure-~ensitive adhe~ive propertie~
for cont~cting mnmmalian ~k$n while maintaining acceptab}~
alternatin~ current imF~dancs.
The present invention achieves the purpose~ of a hydrophilic, Lonically-conductive medium for a biomedical electrode with the advantag~s of improved mammalian skin adhesion but without lofl~ of slectrical propsrtieEI.
~hs pro~ent invent$on providea an advantage that a two-phase composite can be applled or coated on conductor member3 of .

W O 93/09713 2 i 1~ PCT/USg2/09329 biomedical ele~trodes in a thickne~ about four times thinner than thicknens of a conventional hydrophilic pre~ure ~ensiti~e adhe~ive in a biomedical electrode. This results in a }ower profile biomedical electrode suitable for more flaxible and ver~atile uses.
The present invention alao provides the advantage of Rmplnying the b~nefits of both pha~e~ of the two-phaee composite of the present invention: ionic conductivity and moi~ture ab~orption provided by the continuou~ phase and hypoallergenic, enhanced adhesion provid~d by the di~contin~ou~ phas2.
Th~ present in~e~tion also provides the advantage of ad~usting the _ lian ekin adheeion of the two-pha~e compo~ite by controlling tbe ~mount of hydrophobic pres~ure 3en~itivs adhesive .:
particle~ disper~ed in th~ continuous, hydrophilic, solid state, pre~3ur~-~ensiti~e adhe~ive. .~.
1~ The preee~t invention al~o compriae~ a bio~edical ~lectrode comprl~ing a conductive medium of a two-pha~e composite of the pre~ent $nvention and means for electrical communication interactin~ b4twesn the conducti~e m~dium and electrical d~agno~tic, th~rapeutic, or electro~urgical equipment.
Th~ pre~ent invention al~o compri~es a method of preparing a two-phn~e compoaite of the present invention, compri~ing the ~teps of:
(a) mixing ~olvat$ng polymer, ionic salt, and an amount of essentially non-volatile pla~ticizer ~ufficient to form a coheaive, hydrophilic solid ~tate pres~ure-sen~itive adhesive, into a ~olvent which i~ esaentially volatile above ambient tempsrature~
to form a first su~p~n~ion or solution;
~b) mixing a latex or solution of hydrophobic pre~sure-~ens$tive adhe~ive into the first suspension or ~olution in a weight ratio of from about 196:1 to about 6:1 of fir8t ~uBpsn~ion or ~olution:l~tex or ~olution to form a combined mixture; (c) ca~ting the combined mixture onto a sub~trate; and (d) removing the solvent to form a two-pha~ compo~$te. ~hen the ~ubstrate on wh~ch the comb~ned_m~xture Lc cast has an electrically conduct~ve surface, a biomedical electrode 1~ formed.
~mbodiment~ of the invention are de~cribed in relatisn to the Drawing.

W ~ ~3/~9713 PCT/US92/09329 21~441 srief D~scriPtion of the Drawinq FIG. 1 i~ a top plan view of a biomedical electrode containing a two-pha~e composi~2 of the pra~ent in~ention as the conductive medium.

PIG. 2 is a sectional view of the biomedical electrode of FIG. 1.

FIG. 3 i~ a top plan view of a dispersive el~ctrode containing a two-pha~e compo~ite of the pre~ent invention as the conductive ~-msdium.

FIG. 4 iB a ~ectional view of the biomedical electrode o~ FIG. 3.
Embodim~nts of the Invention Continuous ~ha~e_of Ioniçallv-Conductive. H~drophilic~ Solid State. ~-Pre~sure-Sensitive Adhe~ive 2~
Th~ continuous phase iB a solid ~tate conductive prQ~sure-sensitivs adheeive composition which is ionically-conductise regardles~ of the a~ount of water prssent during manufacture, storage or u~e, Solid state conductive pre~sure-~sn~itive adheaive compssitions are not ~uscaptible to a 10~B Ofconductivity due to dehydration of water or other volatile components after manufacture and prior to completion of u~e. Nor i~
the conductivity of such adhesives i~paired by the ab~orption of wat~r into such adh~ive~ in humid atmosphsric condition~.
Solid ~tate pres~ure-sensit~ve adhe~ive~ can be made with min~mal amounts of water pre~ent during manufactur~. Such adh~s~ves can be otored in humid or arid condition~ without protection f rom atmospheric moisture. Such adhesive~ can be u~ed without~regard to the amount of at~oepheric moisture or body fluid~
or exudate lik~ly to b4 encountered during diagnostic, therapsutic, or elsctro~urgical procedures. In short, the~e pre~sure-3en~itive adhe~ive~ solYe the problem of requiring water to achiev2 ionical conductivity in conductiv¢ media in b~om~dical electrodaa which contact mammal~an ~kin. Solld state conductive pr~sure-sen~itive adhesive compo3~tions function independently of the prasence or WO 93/Og713 2 1 1 ~i ~ 4 1 P~/US92/09329 ab~ence of water. Water ie accommodated in such adhssives, but not required for uee.
A ~olid ~tate conductiv~ pressure-~en~itive adhe3ive compo~ition, ionically-conductive regardless of an amount of water 5 preeent in the compo~ition, comprisas a polymer electroly~e complex and an es~entially non-volatile pl~st~cizer in an amount ~ufficient to form a coheffi~e, pliable, pre~sure-sansitive adhe~i~e.
A polymQr elactrolyte complex compri~ a solid ~olution ~: :
of ionic salt diu~ol~ed in a ~olvating poly~er. A conductive solid ~olution iB achie~d through d~ociation of ionic ~alt~ by a solvating polymer, forming a cat$on-polymar co~pl~x and ite counterion. The catlon-polymEr complex occur~ with direct intersctLon o~ non-carbon atom~ in the polymer chain.
A ~olvating polymer csn be either a homopolymer whqre ~ch ~onomeric u~ h~ at lea~t one ionizing non-carbon atam or a copolym~r whera at l~a~t one monomeric unit has at least one ionizing non-carbon atom contained in a psndant group to the monomeric unit. Nonlimiting exampl~s of a non-c~rbon atom in a monomeric unit include oxygen, nitrogan, sulphur, and pho~phorus.
Solvnting polymer i~ pre~ent in a ~olLd ~tate conductive preseure-sen~iti~e adhasi~e in an amount from about 5 to 50 weight percent, and preferably from about 20 to about 45 weight percent, of the adhe~iYe Of pos~ible ~olvating polymer~, cross}inked poly(N-vinyl lact2m)t cro0slinksd polyacrylamide or it8 ionic forms; cros~linked polyacrylic acid or lts aalts; cro~slinked poly~2-acryl~mide-2-methylpropanesulfonic ac~d), itB salts, crosslinked copolymers of the acid, crosslinked copolymers of salt~ of the acld, or mixture3 thereof~ or combinations of these solvating polymers are preferred.
Of the~e preferred solvating polymers, a crosalinked polyt~-vinyl lactam~ is e~p3cially preferred.
Cro~slink~d poly(N-vinyl lactam) can be cro~linked from either a noncro~slinked homopolymer or a noncrosslinked copolymer containiy~g~N-vinyl lactam monomsr$c units. Such crosslinked poly(N-vinyl lactam) is swell~ble in a plasticizer biocompatible with mammalian ~kin.
Preferably, noncros~linksd homopolymer or noncroaalinked copolymer is ~oluble in pla~ticizer biocompatible with mammalian ~kin in the ~b~ence of radiation crosslinking. Preferably, N-vinyl , W O 93/09713 P ~ /US92/Og329 211S4~1 lactam monomeric unit~ comprise a majority of total m~nomeric unit of the polymer.
Nonlimiting examples of N-vinyl lactam monomer~ are N-vinyl-2-pyrrolidone; N-vinyl-2-~alerolactam; N-vinyl-2-caprolactam;
and mixture~ of any of the foregoing. Preferably, the N-vinyl lac~am i~ N-vinyl-2-pyrrolidone. Preferably, the poly(N-vinyl lactam) i~ a ho~opolymer of N-vinyl-2-pyrrolidone.
Nonlimiting axample~ of non-N-vinyl lactam comonomers u~eful with N-~inyl lactam mono~eric unit~ include N,N-dimethylacrylamide, acrylic acid, mathacrylic acid, hydroxyethylMethacrylate, acrylamide, 2-acrylamido-2-methyl-1-propane ~ulfonic acid or ite ~alt, and vinyl acetate.
~he N-v~nyl lact2m ~vnomeric unit~ compri~e no less than ~ about 5~ weight percent of th~ monomeric units pre~ent in ~he poly~N-vinyl lactam) in ~olid ~tate form. ~ore preferably, the N
vinyl lactam mon~meric un$t~ comprise 70 to 100 percent by weight of the poly(N-vinyl lactam) and mo3t pre~erably 90 to 100 percent by weight of the poly~N-vinyl l~ctam)~
Nonoro~alinked polytN-vinyl lactam) homopolymer and poly(N-vinyl pyrrolidone)/poly vinyl acetate cQpolymers are com~ercially available. Nonlimiting ex~mple~ of commercially available poly(N-vinyl pyrrolidone) u~eful for the present invention include Aldrich Chemical Co. of Wilwau~ee, WI, BASF of Parsippany, NJ, and ISP (GAF) of Wayne, NJ.
Poly(N-vinyl lactam) can have a Fikentscher X-value of at least X-15 and preferably at least R-60, and mo~t preferably at leaat K-90. Fikentscher R-values are de~cribed in Molyneaux, Wa~er-Soluble Polymer~: Properties and Behavior, Vol. 1, CRC Press, 1983, pp. 151-152.
After expo~ure to ionizing radiation, poly(N-vinyl lactam) can have a Swelling Capacity, S, millilitere of liquid ~orbed per gram of polymer, of at leaet about 15 in water, preferably about 20-35 ~n water, and moet prefsrably about 25 in water. ~ ~
Swelling Capacity correlates to a meaeurement of polymer ewelling as a ~unction of chemical croeslinking unite in poly(N-vinyl lactam), according to the equation:

S ~ C(~1/3 _ ~ 1/3 W 0 93/09713 2 1 1 ~ 4 ~ 1 PCT/us~2/0~329 where S i~ a m~asur~mont of water ~orbed per gram of polymer, C is a con~tant characteri~tic of the polymer, i.e., milliliter~ of water sorbed per gram of polymer, ~ i~ the average number of backbone carbon atom~ ~n the polymer ~egment~ between S cro~slinked ~un~tions, and ~0 i~ the a~erage number of backbone carbon atoms in the polymer e~gmsnts betw~en crosslinked junction~
wh~n S i~ zero. Swelling capacity and this equation are discussed in ~rred~ ol~cular Interpretations of Sorption in Polym~r~ Part In~ dvances in Pol~mer_Seience Vol. 99, Springer-Verlag, Berlin H~idelberg Ger~any (pp. 21-36, l991).
PolytN-vinyl lactam) u~ful in the pre~ent invention can be in any form ~uaceptible to being cros~link¢d, but preferably i8 in a solid ~tat~ form. Nonlimiting examples of ~olid Qtate form~
~nclude parti~leA, pellet8, sheets, ntrand~, ~iber~,; membran~a, fLlms, and other three dim~nsional functional form~. Prefarably, poly(N-vinyl lactam) i~ in the form of particle~ of a ~ize from about 0.1 micromcters to about 250 micrometera and preferably from about 10 micromster~ to about 75 miCrometQra.
Poly(N-vinyl lactam) can be crosslinked u~ing bulk polym~rization in the pre~ence of a chemical cro~linking agent, ~olution polymerization in the presence of a chemical cros01inking ngent, thermal polymerization in the pre~ence of a chemical cro~linking ag2nt, or photo-initiated polymerization in the prqeence of a chemical cros~linking agent. Preferred cros~linked polymerization method~ include free-radical polymerization method~
employ~ng ch~mical cro~slin~ng agent~ ~uch as that disclosed in U.S. Patent No. 4,848,353 ~Engel) or EPO Publication 0 322 098 ~Duan).
Poly(N-~inyl lactam) can al80 ~e crosslinked u~ing ionizing r~diation ~uch as that discloeed in Int~rnational A~plication Serial Number 07/792,442 (Docket No. 45911PCTlA), Cros~linkQd polyacrylamide or its ionLc formst cro~01inked polyacrylic acid or it~ aalt0; crosslinked poly(2-acrylnmide~2-methylpropane~ulfonic acid), it0 3alt~, cros31inked copolymer~ of the acid, cros~linked copolymer~ of salt~ o~ the acid, or m~xtures thereof; or combination0 of these crosQlinked ~olvating polymer~ can be prepared by using fres-radical polymerization method0 known to tho~e skilled in the art.
To render a ~ol~ating polymer pre~ure-~ensitive 49 adhe~ive, the pla0tlcizer can be an es~entially non-volatile liquid 2 1 ~ ~ 4 1 1 PCI`/US9~/~932~
or combination of liquids which can swell the ~olvatinq polymer an~
which i~ biocompatible with mammalian skin.
E~sentia}ly non-volatile means that a plasticizer a~
used in the pre~nt invention will render a polymer elsctrolyte complex of solvating polymer and ionic salt sufficiently cohesive and pliable ~uch that leas than ten percent (10~) of a given volume of plas~icizer evaporates after exposure to a temperature of procesning ths compo~ition or to a temperature of storage conditions .
Non-limiting axamples of assentially non-volatile plasticizers include polyhydric alcohols (e.g., ethylene glycol, propylæne glycol, uorbitol, polyethyl~ne glycol (200-600 M.W.3, and glycerin) and other pla~ticiz~r~ which are non volatile in ambient conditione and do not cau~Q mammalian skin irritation or toxic r~action.
~ s~entially non-volatile plasticizer can be added in an ~mount uu~fici~nt to form a cohesive and pliable preesure-sensitive adhes~ve. Th~ amount of plastici2er to be added depend~ on the type of ~olvating polym~r empl~yed and the extent of crosslinking in the polymer. To achieve a presQure-~en~itive adhesive, the e~entially non-vo}atile plaat~cizer can be added to aolvat~ng polymer ranging from about 50 to about 95 wsight percent of the solid ~tate co~ductive pres~ure-een~itive adhe~iqe composition. When the solvating polymer i~ crosslin~ed poly~N-vinyl lactam), the amount of pla~ticizer can rang~ from about 50 to 75 weight percent of the co~po~ition. The amount of plasticizer can range from 65 to about 95 weight percent when the colYating polymer i8 CroB~linked polyacrylic acid, cro~linked polyacrylamide; or poly~2-acryl~mido-2-methyl ~ulfonic acid), it~ aalts, copolymer~ of the acid, copolymere of the salt, or mixtures thereof. Within the~e range~, one can adju~t the amount o~ pla~ticizer employed to control adhesi~e properties of the polymer electrolyte complex.
of e~sent~ally non-volatile plasticizers, glycerin and polyethyl~ne glycol nre preferred, with polyethylene glycol mo~t preferred. Glycerin and polyethylene glycol can be uc2d in mixture3. ~lycerin can compri~e up to 100 weiqht percent of the es~entlally non-Yolatile p}a~ticizer. Preferably, polyethylene glycol can compri~e up to 100 weight psrcent of the e~entially non-volatlle pla~tic~zer. Polyethylene glycol of either 300 W 0 93/097l3 2 1 1 ~ 4 ~ ~ PCT/Us92/0~329 mol~cular w~ight or 400 molecular weight i~ preferred, with 300 molecular weight more preferred.
Unexpect~dly, solid ~tate conductive pre~sure-sen~itive adhe~ive compo~itions do not r~quire the use of water, or the retention of water or any other volatile liquid capable of vaporization at ~mbient condition~, as a plasticizer for polymer electrolyte complex to provide ionic conductivity. By relying on e~sentially non-volatile plasticizer~ to form cohesive, pli~ble solid sta~e conduct~ve pre~sure-~ensitive adhesives, biomedical eloctrode~ employing ~uch 801~ d state conductive pressure-sQn~itive adhesives are le~8 apt to have ionic conductivity altersd by dehydration of a component o the so~position.
While solid state conduct~e pres~ure-~ensitive adhe~ive compoeitions do not require water to be present, ~uch compo~ition~
~ can accommodate the pre~Qnca of water in ~uch co~po~ition without -losing ionic conductiv$ty or adhe~ive p~rformance. Thu~, solid state conductiv~ pressur~-~ensitive adhe~iYe compositions function rogardle~ of the amount of water pre~ent during manufa~ture, ~torage, or use.
Solvating polymers contain one or more $onic ~alt~ in a~ount~ suffic~ent to interact with non-carbon atoms of ths sol~ating polymer in order to form polymer electrolyte compl~xes which can bs plasticLzed to form solid state conductive pres~ure-~ensitive adhesive composition~. In effect, solid ~tate conductive pre~ure-sensitive adhesive composition i~ a matrix of (a) a conducti~e solid solution of one or more ionic salts di0sociating in a ~olvating polymer and (b) an essentially non-volatile plasticizer preoent, if any, in an amount sufficient to render ths matrix cohe0ive znd pliable, and preferably pres~ure-~en~itivQ adheoive.
Thu~ unexpectedly, the interaction of ionic ~alts with the solvating polymer providea ionic conductivity for the compo~ition.
Ionic or polar oolvent~ such as water previously Qmployed in polyelectrolyte compo~ition~ are not neceo~ary to provide ionic conductiyylty ~n a conductive medium of a blom~dical electrode Non-l~miting exampleo of ionic salts useful for lnteraction w~th the ~olvating polymer include llthium chloride, l$th~um perchlorate, oodium citrate, and preferably pota~sium chlorlde.
To provide ~cceptable ionic conductivlty, ~o~ic salto cnn be preoent in amounts from about 0.5 w~$ght percant to about 5 W O 93~9713 PCT/US92/0~329 211~441 weight percent of the ~o}id state conductive pressure-sensitive adhesive composition. Preferably, ionic aalts are present in amounts from about 2 to about 3 weight percent of the ~olid ~tate conductive pressure-sensitive ~dhe~ive composition.
Discontinuou~ Pha~e of ~omains of Hvdrophobic Pres~ure Sen~itive Adhe~ive In medical applications, hydrophobic pre~sure-sensitive adhe~ive mu~t be tacky at rcom te~perature as well a~ at skin temperature of patients. Al~o, the adhesive mu~t be dermatogically acc~ptable, i.e., after continuous contact with skin~ there i~
little ~dh~iv~ res$due upon rQmoval and ~here i~ no significant ~r~action with Dkin during adhesion.
The adhssive strength of th~ discontinuou~ hydrophobic px~ssure-eens~tiv~ adhe~ive pha~e of the composit~ dep~nd~ on the type of pr~sure-~ensitive adhe~i~e cho~enO The adhesives must provide ~ufficient adh~iv~ ~trength to adhere the two-phase cOmpO8i t~ to th~ ~Xin o~ th~ patient for longer p~riods of time than provided by ionic~lly-conductiv~, hydrophilic, solid ~tat~, preseure-~ensitivo adha~iv~s ~lone.
The hydrophobic pressur~-nensitive adhe~ive~ can be polymeric adhesiv~ comp~sitions prepared from a combination of monomQr~, homopolymer~, copolymers and tacki~iers, or blend~ thereof to produce polymeric adhc~ive composition~ containing polyacrylateq, polyolefin~, ~ilicone adhesives, natural or synthetically derived rubber base adhesives, or polyvinyl ether~.
The prs~ure-~en~itive adhe~ives useful in the composite are hydrophobic in order to resist interaction with the hydrophilic, solld state, pressure-sen~itiv2 adhesive continuous pha~e or with moi~ture or other body exudate gathering at the skin or ekin opening during use. The composite retains it~ strong adhesivene~ even in the presence of water and humectant. Exces~ moi~ture iB t~ken away from the ak~n surface by the continuous pha~e of ionically-conductive, hydrophllic, ~olid state, prQssure-sen~itive adhe~ivQ.
Preferred adhosives are ~crylic pres~ure-~en~itive adhesive copolymer~ co~pri~ing "A~ and ~B~ monomers a~ follow~: Monomer A i~
a hydrophobic monomeric acrylic or methacrylic acid ~ter of alkyl alcohol, the alkyl alcohol containing 4 to 10 carbon atoms, preferably 6 to 10 carbon ato~s, more preferably 6 to 8 carbon atsm~, and m9~t pr~ferablj 8 carbon atoms. ExEmples of suitable A

.,, ~ , W ~ 93/~97l3 2 1 1 ~ I PCT/US92/~9329 monomers are n-butyl, n-pentyl, n-hexyl, i~oheptyl, n-nonyl, n-decyl, i~ohexyl, 2-ethyloctyl, isooctyl and 2-ethylhexyl acry}ate~. The mo~t pr~ferr~d monomer i8 isooctyl acrylate.
~onomer B i8 a reinforcing monomer comprising acrylic acid; methacrylic acid; alkyl acrylates and methacrylat~s zontainin~
1 to 3 carbon atom~ in the alkyl group; acrylamide; methacrylamide;
lower alkyl-substituted acrylamides (i.e., the alkyl group containing 1 to 4 oarbon atoms) ~uch as tertiary-butyl acrylamide;
diac~tone acrylamide; N-vinyl-2-pyrrolidone; vinyl sthers such as vinyl tertiary-butyl ~ther; Qubstituted ethylenes such a~
derivatives of maleic anhydridc, dimethyl itaconate and monoethylformat~5 or vinyl perfluoro-n-butyrate~ The prsferred B
monG~e~s are acrylic acid, acrylamid~ ~nd N-vinyl-2-pyrrolidone.
The mo~t preferrQd B monomer iB ~-~inyl-2-pyrrolidone.
The A monomer in ~uch copolymer i~ present in the pr~ssure-~ensitiv~ adhesi~e copolymer in an amount by weight of about 85 to 98 percent by weiqht, and preferably about 90 to 98 p~rc~nt by weight of th~ weight of all monomers in the copolymer~
The B monomer in ~uch a copolymer i3 present in the pre~0ure-~nsitive adhe~ive copolymar in an amount by weight of about 2 to about 15 p~rc~nt by weight, and pr~ferably about 2 to 10 percent by wa$ght of the weight of all monomers in the copolymer.
In addition to A and B monomers, polyetyrene can be added to form a desirabla copolymer of isooctyl acrylate/acrylic acid/po}y~tyrene in a weight fraction ratio of 96:2:2 and having an inher~nt viscosity of 1.35 dl/g.
Most preferably, the pre~sure-een~itive adhesive of the present invention ie an i~ooctyl acrylate/N-vinyl pyrrolidone cop~lymer in a wei~ht fraction ratio of 91:9 and ha~ing an inherent ::
vL~co~ity of about 1.6 dl/g.
The adhs~ive copolymer~ of the above type are known and their method o~ preparation is well known to thoae ekilled in the art, having bsen deacrLb2d for exampls, in U.S. Patent RE 24,906 of Ulrich._ Sinc~ ths pre~sure-sen~itive adh~iv4s d~ecribad above are inherently rubbery and tacky and are 9uLtably heat and light ~table, there ie no need to add tackifLer~, crosslLnkers, or stabilizer~.
Howsver, ~uch may ~e added if deeirsd.
$he availability and prepar~tion of other pre~sure-~ensitive adhe0ive~ u0efu~ Ln the pre~Bnt invention are described in the litsrature. In ths Handboo~ of Prae~ure-Sensitivs Adhe~i~e -W O 93/~9713 PCT/US~2/09329 211~441 Technslooy 2nd Ed., Sataa, Editor, (Von No~trand Reinhold, New Yor~
1989), a number of type~ of u~eful pres~ure-sensitive adhe~ive~ are discu~sed: natural rubber adhesives; A-B-A block copolymer~ uch as polystyrene-polybutadiene-polystyrene (S-B-S), polystyrena-polyi~oprene-poly~tyrene (S-I-S), polystyrene-polyt~thylane/butylene)-polystyrene (S-~B-S), and polystyrene-poly~ethyl~ne/propylene)-polystyren2 (S-EP-S) polymer~);
butyl rubbere and polyi~obutylene; vinyl ether polym~r~; ~ilicone~;
polyi~oprene; butadiene acrylonitrile rubber; polychloroprene;
lQ atactic polypropylsn~; and addLtional descriptions o acrylic adhe~ive~ and acrylic dispsr~ion~.
Desirably among the~e available pre~ur~-~ensitiYe adhesives, ~ilicone pre~ure-~en~itive adhe~ives ~uch as tho~e dL3clo~ed in U.S. Patent 4,039,707) and polystyrene-poly~oprene-poly~tyrene A-B-A blook copoly~er~ (such as tho e di~clo~d in U.S. Patent 3,935,338) ar8 u~eful.
~nexpectedly, hydrophobic pre~sure ~enaitive adhe~ives can be dispQr~ed into the continuou~ pha~e of ~olid s~ate pre~sure-sensiti~e adhesive from either water-based latexe~ or from ~olvent-based ~olutions. Shus, th~ method of praparation of co~po~i~e~ of the pre~ent invantion doe~ not limit the selection of hydrGphobic Rras~ure s~neitive adheaives ueeful in the præsent in~ention.

Method of PreDarin Two-Pha~a Com~osite Ths ~reparation of two-phaee composita~ of the pr~sent invæntion followe proces~e~ æmployed for the formation o~
hydrophilic, solid state, pres~ure-sensitive adhe~ive~ with the addition of hydrophobic pres~ure-~ensitive adhe~ive to form a di~continuous phase di~per0ed therein. Thus, any of the method~ of preparation of a ~vlid state conductive pres~ure-0ensitive adheRive compoaition can be employed if th~ addition of hydrophobic pres~ure-~en~itive adhesive i8 not di~ruptive to th~ form~tion of the continuous phase. Preforably, the two-phase compoaite i~ made by m~xing 3n ~qu~ous mixtur~ of the hydrophilic, 001id ~tat~, pro~cure-sansitive adhe~va with a hydrophobic pre~ure-~ensitive adhe~ive ~u~pended in an agueou0 latex or dissolved in volatila solvent, followed by casting of the comp4site on a substrate, and drying of water ~nd other volatile sslvent to yield a two-phaae compo~ite.
~ixture ratio~ by weight of continuou~ phaae of hydrophilic pslymQr compo8ition: discontinuou~ phass o~ hydrophobic , .

W 0 93/Og713 211~ 4 41 PCT/US92/Og329 pr~ure-0en~itive adhe~ive, which include ~olvent weights, can range of about 196:1 to about 6:1. Preferably, the mix~ure ratio by weight rangeff from about 95:1 to 16:1.
~ixing may be accompli~hed by uBing a "Laboratory Disper3ator, Series 2000, Model 84~ mixer, commercially available from Prem~er ~ill Corporation-of Reading, Pennsylvania. Nixing processes occur at ambi~nt temperatures and pres~ures. The mixing should continue until the two pha~es are intimately int~rdisper~ed, r~gardles~ of method of alternative preparation~ described ~bove.
Then the mixing i~ stoppad to allow for the removal of any bubble~
created dur~ng the mixing procees.
Th~ compos~te ~ixtur~ iB spread or coated onto a relea~e - liner-and volatil~ aolvent ~ removed. Volatile ~olvent iB removed, i generally by application of heat or o~her drying mechanLRm.
Volatile solvent CoQprises about 75 weight perc2nt of the hydrophilic polymer composition-mixture and about 50 weight percent of the latex mixture containing hydrophobic pr~ssure-seneitive ~dhesive particles. AB drying occurs, the domain~ of hydrophobic pres~ure-senEitive adhesive remain dispersed around a continuous phase of hydrophilic, solid state pressure-se~eitive adhQsive composition. The tsmperatures of ~vaporating th~ vol~tile ~-~ol~nt~e) without adversely affecting the remaining hydrophobic pressure-eensitive adhe~ive particles or hydrophilic, solid state, pre~sure-s~n itive adhesive continous phase depands upon the type of volatile solv~nt~l employed. Generally, however, the mi~ture i9 drLed at temperatures between about 50C and about 75C.
AB a result, mixture ratio~ by weight of about 196:1 to 6:1 prior to drying result in a dried compoeite ratio by weight of continuous phasesdi~continuous phase of about 98:1 to 3:1, respectively, when the hydrophobic pressure-sen~itive adhesivs ~olids are 50 w~ight percent of the latex or Holution. If the hydrophobic pre6sure-0enoitive adhesive solid0 are 25 weight percent of the latex or solution, the dried composite ratio by weight can range f~Qny~bout 196sl to about 6:1. Preferably, the dried co~posite ratio by weight ranqe8 from about 60:1 to 8:1; and most preferably from about 9:1 to about 21:1.
Filme of two-phase composite~ of the pre~ent inYention hav~ng thlckne~eo of from about 0.05 mm to ~bout I mm, desirably fram about 0.07 mm to about 0.38 mm, and preferabiy fro~ about 0.18 mm to about 0.25 mm. Thereafter, depending on the desired W O 93/097~3 PCT/US92/09329 4 ~ 1 application, the layer of composite may be applied to a backing material by laminating.
For example, a preferr~d method of preparing a two-phase compo~ite from an essentially non-volatile solid state conductive pres~ure-~ensit.ve adhe~ive c~mpo~ition can employ a minimum number of ecologically compatible manufacturing steps. The solvating polymer, ionic ~alt, and ee6entially non-volatile plasticizer, if any a~ needed, are mixed into a ~olvent which i~ essentially volatile at or above ambient temp~rature3, ~uch as water, ethanol, mathanol, or i~opropanol. To this mixture i~ addsd a ~olution of hydrophobic prs~sure-sen~iti~ ~dh~i~e. A qua~tity of th~
resultin~ mixture of sol~ating polymer, ionic ~a~, and any ee~ntially non-volatil~ pla~t~cizer pre~ent ~n th~ volatile ~ol~ent i~ then cast onto a ~urfaca of a ~ubstrate, which can b~ an inert sub~trate such aB a liner for ~tor~ge befors further proce~ing or a surface of a sean~ for el~ctrical cGmmunication having an electrically conduc~Lve ~urfac~. Then the volatile 301vent i8 e~sentially evaporated by the application of heat, microwave energy, infrared energy, convective air flow or the li~e, in ordsr to form the non-vol~tile solid state conductive pr~ur2-~ensitive adhe~ive continous phaaa with do~ains of hydrophobic pr~Hure-~ensitive adhe~ive di~per~ed therein. Typically, a drying ov~n heated to about 65~C can be employed. A product liner can optionally be laminated over the field of the two-pha~ composite to protect that field from eontamination. An extremely thin coating of the two-pha~e composite can be applied to a ~ub~trate 0urface. Coating thickne~es can range from about 0.125 mm to about 1.25 mm and prsferably from about 0.75 mm to about 1 mm, to yield after ~aporation of solve~t a eoating thiekne~s ranging from about 0.05 mm to about 0~38 mm and preferably from about 0.18 mm to about 0.25 mm. With thi~ extreMely thin coating on a flexible, electrically eonduet~ve ~ubstra~e, a low profile and conformable biomedical eleetrode ean be made.
~ ~ ~wo-phase eompo~ites of the pro~ent invention ean have frsm about 30 gram~/2.54 em to about 290 gram~/2.54 em adhesion to ~kin aeeording to the t~st m~thod identified below. Praferably, ~kin adheaion ean range from about 50 gram~/2.54 em to about 150 grams/~m. Mo~t prefsrably, ~in adhe~ion ean range from about 60 grams/2.54 cm to abou~ 120 gra~/2.54 em.

W ~ 93/09713 2 1 1 ~ ~ ~ 1 PCT/US92/093~9 Two-phase composite~ of the preRent invention are tran~lucent or tran~parent to x-rays, making biomedical el~ctr~des made from such compo~ites suitable for medical procedures where x-ray diagno~tic procedure~ are al~o em~loyed.

Pre~aration of ~vdro~hobic Pr~s~ure-sensitive AdheAive The preparation of hydrophobic pre~ure-~ensitive adho~ive ueeful for forming domain~ of enhanced adhesiveness depends on the type o ~dhesive, the type of polymer~zation (e~g., addition or condcn~ation), and the poly~erization technique (e.g., bulk, ~olution, ~u~psn~ion or ~ulsion polymeriz~tion).
Tho preesure-s~nsitivQ ~dhacive polymerizat~on techniqus cho~en i~ ~elect~d from con~entional polymerization technigue~) known for a particular pr~ur~ n~itiv~ adh~sive. Sources of polymerization prep~ration te~hniques include Or~anic Polvmer Chemistrv, R.J. Saundex~, Chapman and Hall (Halsted Publishing, New York, 1973), A~lied PolYmer Science, R. W. Tess and G. W. ~oehlein, Am~r~can Ch~mical Sociaty (American Chemical Society, Wa~hington, D~C., 1981), ~nd prin~i~eleB of Pol~merization. George Odien, ~iley-Int2recience ~John Wil~y and Ssns, New York, 1981), and the ~andbook of Pre~e~re-3enoitive Adheoive Technoloov. ?nd Ed.. supra.
For example, acrylic preosure-~en6itive adhe~ives may be prepared according to U.S. Patent RE 24,906. When prepared by solution polymerization, the monomcro are soluble in solvent~, commonly ethyl acetate, cyclohexane, toluene, and n-heptane. The polymer i8 aloo u~ually ~oluble in the solvent allowing a pure polymer to be coated onto a eurface and then dried. When prepared by amul~ion polymerization, the latex of water-in~oluble polymers in ~ater maintains a pha0e ~eparation until removal of the water.
Pressure-~enaitive adheoives may be prepared by ~olution polymerisation fro~ A-B-A block copolymers, natural rubber, styrene-butadiene, polyieoprene, butyl rubber, polyisobutylene, polychloroprene, and blsnd~ ther~of. Pellat3 of the commercially ~vail~b~ polymer are mixed into a solvent and heated in the presence of tackifiers and often plasticizer~, in order to dsvelop a non-rigid polymer havin~ the requi~ite tack. Chapter~ 11, 1 , 14, and 19 of the Handbook o Preaeure-oensitive Adhenive Technoloqy 2nd d., referenced above, discuooes the choiceo of materlal~ and ~ethods of preparatLon. A frequently used tackif~er iB polyterpene resin.

W O g3/~g713 PCT/vs92/09329 The rubber bseed adh~ive~ may alno be prepared in a latex. For example, s~yrene and butadiene may be di~R2r~ed in water with an emul~ifier (such as qodium alkyl ben2ene sulfonate) and an initiator (3uch a~ pota~sium p~r~ulfate). Polymerization occur~
typically anaerobically with mixing for about 16-24 houre at 60C.
Chapter 12 of the Handbook of Pres~ure-sen~itive Adhesive Technolo~v 2nd ~d., ~upr~, de~rib~s ~uch latex preparation proce~aes.
Sili~:os~e pr~s~urc-sen~tive ~dha~ive~ are u~ually com~ercially ~u~pl~ed in a hydrocarbon ~olvcnt. Upon s~aporation, the ~iliconee ~xhibit pre~sure-~nsitiv2 adhssive propertie3. A8 de~crib~d in Chapt~r 18 of the Handbook of Pre~ure-sensitive Adh~sive Technolooy~nd ~d., 8upra, a cataly~t (such as an organic paroxide, an ~mino ~ilane~ or a metal ~alt of an orga~ic ac~d) i~
a~ded to reinforce tha silicon~ networ~, increasiny cohe8i~enes~.
Th~ poly~rizat~o~ of ~inyl cther ho~opolymers may bs carried out ~y batch proce0~ing, or continuoua procensing in bulk or in ~olution. Whichever proce~sing i~ used, cationic initi~tor~ such as BF3 or AlC13 are pre~ent. Copolymers of vinyl ethers and acrylate~ ~re polymerizæd by free radical em~laion polymerization in water witb po~ass~um paroxodi~ulfats. Chapter 17 of the Handbook of ~-Pre0sure-3en~itiYe Adhe3ive TechnoloqY 2nd ~d., ~upra, de~cr$bes the polymerization.
If volatile ~olvent~ are necessary or desir~ble ~or the preparation of the pres~ure-~ensitive adhesive, ~uch ~olvent~ can be aliphatic or aromatic hydrocarbon~, such as heptane, toluene, xylene, and the like and blends containing other miscible ~olvent~
~uch a0 ethyl acetate.

Uaefulne~ of the_Invention ~iomedical Electrode~
BiGmsdical electrodes employinq two-pha~e composites of the pre~ent invention are useful for diagnostic, therapeutic, electro~urgical, or other medical purpo~es. In it~ mo~t ba~ic form, a bio~edic~l electrode comprises a conducti~e medium contacting mammalian ~kin and a means for electrical communication interacting between the conductive medium and electrical diagno~tic, therapeut~c, or electro~urgical equipment.
Among the diagno~tic and therapeutic procedures u~ing biom2dical electrode~ are transcutaneous electronic nerve stimulation ~T~NS) devicea u~ed for pain management, nauromuscular W 0 93/0~713 2 i 1 ~ ~ 4 1 PCT/US92/09329 stimulation ~NMS) used for treating conditions such a~ scoliosis, and monitor~ of elei~trical output from body function~, such as ~lectrocardiogram (~XG) u~ed for monitoring heart activity and dia~nosins heart i~bnQrmalities.
FIGS. 1 and 2 show either a di~po~ble diagnostic electrocardiogram (~R&) or a transcutaneou~ electrical nerve stimulation (TENS) electrode 10 on a reloase liner 12. Electrode 10 includeii3 a field 14 of a biocompatible i~nd adh~sive csnductLve medium for cont~cting mammalian skin of a patient upon removal of protective rel~ai~ liner 12.
Electrode 10 includes mean~ for electrical communication 16 compri~ing a conductor member havinq a conductive interface portion 18 contacting field 14 of conductive medium and a tab ~ portion 20 not cont~cting field 14 of conductive medium ~or iI~chanical and ~lectrical contact with eleotrical instrumentation (not ~hown). Mean~ 16 for electrical communication includes a conductive layer 26 coated on at least the side 22 contactin~ field 14 of conductive mQdium.
It is fore~een that a typical ~XG conductor member 16 will comprise a strip of material having a thickne~ ~f ~bout 0.05-0.2 millimetera, such a~ polyester $ilm and hav~ a coating 26 on side 22 of 0il~er/silver chloride of about 2.5-12 mLcrometers, and preferably a~out 5 micrometers thic~: thereon. Presently preferred ~-$8 a polye~tar film commercially availabl~ ae ~ellinexn 505-300, 329, 339 film from ICI Americaa of Hopewsll, VA coated with a ~ilver/sllYer chloride ink commercially available a3 "R-300" ink from Ercon, Inc. of Waltham, MA. A T~NS conductor member 16 can be made of a non-wo~en web, such as a web of polye~ter/cellulose fibsrs commercially a~ailable a~ "Manniweb" web from Lydall, Inc. of Troy, NY and have a carbon ink layer 26 commercially avaLlable as ~SS24363~ ink from Acheson Colloids Company of Port ~uron, MI on ~ide 22 thereof. To enhance mechanical contact bstween an electrode clip (not shown) and conductor member 16, an adhesively-backed polyethyl~ne tape can be applied to tab portion 20 on the 0ids opposite ~ide 22 having ths conduet~Ye coating 26. A surglcal tape commercially available from 3M Company as Blenderm" tape can be ~mployed for thi~ purpose.
Another type of therapeutic procedure, which can employ a blomedical electrode having a two-pha~e compo8ite of the present invent$on, i~ the di0pensing of electrlcal energy to the chest -cavity of a mammalian patient to defibrillate abnormal heart beats of the patient. Delivery of a high voltags (e.g., 2000 volts), high current (a.g., 40 amp8 ) electrical charge through one biomedical electrode and receipt of that electrical charge through another biomedical slectrode completes tha ~lectrical circuLt. An example of an electrode useful for defibrillation i~ di~clossd n U.S.
Patent 3,998,215 (Anderson et al.).
Another type of therapeutic procedure in~olving application of electrical current to skin of a patient iB
iontophor~sis, which deliver~ an iontophoretically active pharmacsutical to or t~rough mammalian ~kin with aid of an el~ctrical curr~nt.
~ l~ctrosur~ery can u8e a biomedical el~ctrode u~ing a two-pha~e compo~it~ of the presant invention. In thi~ instancs, the biomedical ~lectrode ~9rv~ to receive in a disp~r~ed f~shion alectrical ~ignal~ introduced to the patient at ~n incision ~ite uaing an el~ctro-surgical cutting electrode. An slectro-~urgical ~ystem u~ually comprise~ a g~nerator providing high-frequency alternating current on demand under monitored conditions, the cutting ~lectrode hav$ng an extrQmely high-currRnt d~nsity ~nd a fl~t di~perslYe biom~dical electrode having a Yery larg~ surf~ce area to provlde a low-current density. The di0persive biomedical electrode i5 placed in Lntimate and co~tinuous contact with a portion of the mammalian ~kin which iB not subject to the ~urgical procedure. The alternating current circuit ie comp}eted through the body of the patient between the disper~ive biomedical electrod2 and the cutting electrode. Disconnection of the di~per~i~e electrode e~ther from contacting tbe patient or from the generator could ~ub~ect the patient to electrical burne where the alternating current circuit l~aves th~ body of the patie~t.
A disper~ive electrode i3 Been in FIGS. 3 and 4.
Dispersive electrode 30 compriss~ an insulating backing 31 coat~d on one surface wlth a biocompatible pre~ure-sen~itive adh~ive 32.
Ths ~a~king 31 can be a closed cell polyethylene foa~. An eie~trode plate 33 adheres to a pDrtion of the biocompatible preo~ur~-sen~ltive adhes~ve 32. The Qlectrods plste 33 can be an aluminum foll on a conformsble polymeric backing 34, e.~., poly~ter, having alum3num depos~t~d on one surface. The electrode plate 33 has an integrally s~sociated connector tsb 35 ~uited to el~ctrically connsct th~ dispers~ve electrode 30 to a leadwire which in use iq W O 93/09713 2 1 1 S ~ ~ 1 PCT/US92/0932~

connQcted to an slectrosurgery generator. A field of ioni~ally conductive adhesive 36 of the pre~ent invention coats the entire ionically conductiYe ~urface of electrode plate 33 except the connector tab 35. An insulating ~trip 37 do~ble coated with pres~ura-een~itive adhe~ive covers that portion of the surfac~ of the ~onnecting tab 35 which underlL~s the backing 31 and biocompatible pr~aure-sensit$va adhe~ive 32. The bac~Lng 31 and biocompatible pres~ure-sen~itive adhe~ive 32 have an apron 38 extending beyond the periphery of tha alectrode plate 33 and 10 slectrically-conductive adh~sive 36. ~pron 38 and inE~ulating strip 37 ~srvs to inoulate the electrode plate 33 from direct coIltact with -a patient'~ ~k~n, thereby avoiding thermal burne and from contact - with other conductorf~ (e.g., blood or water~ which may result in an electric:al ~hort circuit. Suppo~ting connecting t~b 35 ~ ~ a re~nforc~n5~ lay~r 39 of nonwoven polyeBter contacting adhesive 32 and hav~ng a ~ingle coated adhe~ive layer contacting tab 35. An optional release lin2r 40 can be uaed to protect adhesive~ 32 and 36 prior to use.
Prsf erably, to achieve excellent adhe~ion and 1GW
impedance el~ctrical contact w~ th a patient 18 skin ( avoi ding hot ~pots or lo~ of contract due to ~otion), ~urface area of pla~e 33 and adhe~ive 36 of the pr~ent invention are about 130 cm2.
Preferably, tho adhef~iv~ 36 of the pre~ent invention i~ coated about 0.5 n~n thit:k.
Other ex~mple~ of biomedical electrode3 which can u~e two-pha~s composite~ according to the pre~ent invention as conduot~ve adhe~ive field~ include electrode~ disclo~ed in u.s. Pat.
No. 4,527,0B77 4,539,996; 4,554,924; 4,848,353 (all Engel~;
4,846,185 ~carlm); 4,771,713 (Robarts); 4,715,382 ~Strand~, 5,012,810 ~Strand et al.); and 5,133,356 ~Bryan et al.). When uaed for di~gno~tic ERG procedures, electrods~ ~hown in FIGS. 1 and 2 are pr~forred. When used for monitoring electrocardtcgram ~CG) procedure~, electrode~ disclosed in U.S. Patent No. 5,012,810 are prefor~d~ ~hen u~ed for defibrillation procedure3 or electro~urglcal procedure~, electrodes shown in F~GS. 3 and 4 or diaclo~ed in V.S. Patent No~. 4,539,996 and 4,848,353 are preferred.
1n ~o~e instance~, the mean~ for electrical communication c~n be an electr~cally conductive t~b extending from ~he poriphery of th~ biomQdical electrode8 ~uch a~ that sQen in U.S.
P~t. NO. 4,848,353 or can be a conductor member extending through a W O 93J097l3 PCT/US92/09329 211~
nlit or seam in a in~ulating backing member, such as that ~een in U.S. Patent No. 5,012,810. Otherwiee, the means for electrical communication can be an eyelet or other snap-type connector ~uch a6 that dieclosed in U.S. Pat. No. 4,846,185. Alternatively, an electrically conductive tab ~uch as that seen in U.S. Pat. No.
5,012,810 can have an eyelet or other snap-type connector secured thereto. Further, the mean~ for electrical c~mmunic~tion can be a lead wire ~uch as that seen in U.S. Patent No. 4,771,783.
Regardless of the type of me~n~ for electrical communication employed, two-pha~e composites of the present invention can reside a~ a field of conductive adhe~ive on a biom4dical electrode for diagnostic, th~rapeutic, or electrosurgical purpo~es.
~ethod~ of making two-phase prQs~ur2-~e~itive adhesive c~mpo~ltes of tha pr~e~t in~ention as conduc~ive media for biomed~cal electrode~ ~nclude a batch proce~s or in a continuou~
line proce~s. If prepared by a continuous proce~, the laminate of a linar, ~ield of two-phase composite of the pre~ent ~nvsntion, and ~ubstrate can b~ wound on a roll for bulk packaging and further proce~aing or can be cut using dies known to those ~killed in he art into individual unit~, ~uch as biomedical electrodss or biom~dical elsctrode subassemblies, for furthsr procas~ing. U.S.
Pat. No. 4,795,516 ~Strand) and U.S. Pat. No. 4,798,642 (Craighead et al.) disclo~e proce~ses and equipment useful for a continuous manuf~cture of biomed~cal electrodes involving the di~pensing of strips of material from rolls and overlaying ~uch strip~ in a regi~tered continuous manner in order to prepare a strip of electrodes.
Fox example, one method of continuous strip aa~embly can be the coatlng of a two-pha~e com2osite of the present invention on an electrically conductive surface about 8.9 cm wide, with the coating applied to about the center 5.1 cm aection of ~uch width.
After ~vaporation of ~olvent from the mixture, th~ ~oated electrically co~ductive 0urface can b9 bisected along the ~trip and also cu~_orthogonally at about 2.54 cm interval~, yielding a number of ~lectrode~ 10 ceen in Fig. 1 having dimen8ion~ of about 2.54 cm x 4.4 cm wlth a conductive intsrface portion 18 of 2.54 cm x 2.54 cm and a tab portlon 20 of 2.54 cm x 1.9 cm.
A~ another example, one method of aa~embly for a dl~percive elec*rode can be the coating of a mixture of two-pha~e compo3ite of the pr~ent invention on a wcb having an elactrically . , ~

W O 93~97l3 2 11 .~ 4 ~11 PCT/US92/09329 conductive ~urface about 24 cm wide, with the coating applied to an 18.4 cm section on one ~ide of the web. After evaporation of sQlvent, the web i~ then orthogonally cut and laminated to a conformable backing, yielding an electrode ~een in Figure 3 having an overall dimension of 10 cm x 23 cm.

A further de~cription of the invention may be found in the following axamplao using the following experimental procedure~.

Skin Adhe~ion Test Biomadical electrodes were cut to have dimen~ions of about 2.54 cm x 4.4 cm with a conductive int~rface portion of 2.54 cm x 2.54 cm and a tab portion of 2.54 cm x 1.9 ~m. The electxode~
w~r~ applied on the back~ of hu3an sub~ects p~rpendicular to the backbon~ and rolled with a 2 ~g roller tD in~ur~ uniform application. The electrodas were removed promptly a~ter application :~
from the back u3ing a ~echanical pulling device termed an adhe~ion :~
te~ter. Thi~ device con~ists of a motor driven ~crew drive which pull~ a 11.4 kg t~st line to which i8 att~chsd a metal clip which i~ -2.54 cm wide. The metal clip i~ attached to ~ach ~leGtrGde at itB
2.54 cm w~dth during pulling te~ting. El~ctrode~ w~re pulled in a plane parall~l (180) to the back and parallel to the lcng ax~ 8 of the elRctrode at a rate of 13-14 cm/min. The adhe~ion i8 reported in ~rams/2.54 cm and ba~ed on an average of values from initiation of peel to antire removal of the electrode.
~5 Skin and Back-to-Back Alter atin~ Current Im~e~ance_Test~
Skin impedance wa~ mea~ured u~ing a 4800A Vector Impsdance Meter manufactured by Hewlett Pa~kard of Palo Alto CA on hu~an arm~. Bio~sdical electrodes were placed on the paneli~t0' arms and measured for alternating current impadance in ~OhmB at a frequency of 10 Hz. Alternating current impedance wa0 measured uaing an Xtratek ET-65A ECG ~lectrode Te~ter from Xtratek Company of Lenexa, ~an~ae. Me~urement0 were conducted in the conventional ~anner _n ~lectrod~ pair~ connected ~back-to-back~
(~dhe~i~s-to-adhesivs) u~ing a 1GW ls~el signal suitable for msasurements on ~CG electrode~. The impedance at 10 Hz wa0 recorded. The A~sociation for ths Advancement of Medical Instrumentation (AANI) has adopted accsptablQ alternating current impedance at a frequsncy of 10 ~z to bs le~s than 2000 Ohm~ for W O 93/09713 PCT/US92/0~32 "back-to-back" electrode Lmpedance. Leas than about 500 kOhm~ ha~
been found acceptable for human skin impedance.

ExamDleE~

Example 1--Chemical Cro~linking of PVP
A two-pha~e composite W28 prepared in the following m&nner. Cro~sl~nked polyvinylpyrrolidone (PVP) WaB prepared according to the ~rocedure of ~xample 23 of U.S. Pat. No. 4,931,282 ~A~mu~ et al.) u~ing 0.16 weight percent ethylid~ne-b~sov~nylpyrrolidone. The PVP wa~ swollen in water and precip$tat~d by acetone addition to ramove rRsidual monsmer~, dried, and then ground into particles of less than 150 m$crometer~ in diumeter. About 9 gram~ o~ PVP particl~ werq then ~wollen in a glyc~rin ~21 grams), w~ter (50 grams)~ KCl (D.8 gr~ms) ~olution for 24 hours. To thi~ pre~sure-3en~iti~e ndhQsive wa~ added 20 gram~ of an AqU~U~ baae latex of hydrophobic pre~sure-~ensitive adhesive (com~rcially ~va~lsble as ~obond 60 ~crylate latex (50 wt.% aolid~) from Rohm and Haa~) by slow addition with st~rring and an additional 40 gram0 of water. Tha mixture wa~ then ~tlrred mechanically to ensure completo inter~ixing of the latex into the hydrophilic~ ~olid otate, pre~surs-~ensitive adhesive mixtura.
The mixture wa~ coated at approximately 0.5 mm on~o a backing of polye~ter having a ~urface coated with ~ 1700 silver ink from ~rcon, Inc. of Waltham, MA thereon. The mixture on the backing wa~ dried in the oven ~t 93~C for 2 hour~. The final dried conductive medium of two-phase compo~ite wa~ approximately 0.1 mm thi~k~ A relea~e liner wa~ placed on the conductive medium to protoct the ~dhe~ivene~ of the conductive med~um.
Skin impedance properties were te~ted after application to human ~kin of thrae individuals. The average ~kin ~mpedance on three human sub~ect~ using a total of 11 samples was 165kOhm~. For all three individual~, the adhe~ive properties were qualitatively accept~l~ wi~h good aggre~aive adhesion, no rs~idue upon removal, and no skin irritation.

2xample~ 2-20 and Co~parison ~xample~ 21 and 22-- Irradiation Cro~slinking PVP, ~ormation of Solid State Conductive Pres~ure-~en~l~ive Adhesive Compo~ition, Yormation of Two-Pha~e Compo~te, and Preparation and Testing of Biomedical Electrode~
-W O 93/0~713 2 1 1 S 4 ~ 1 PCT/US92/09329 ApproxLmately 100 grams of noncro~slinked poly(N-vinyl pyrrolidone) com~arcially available from BASF of Parsi~pany, NJ as ~olid particle~ having a size from about 10 micrometer~ to ~bout 75 micrometer~ were placed in a res~alable plaQtic bag, purged with nitrogen for 15 minutss, and irradiated with qamma radiation of 155 kGy~ u3ing a cobalt-60 high energy ~ource to produce crosslinked solid poly(N-vinyl pyrrolidon2).
A mixtura was pr~par~d in which 33 grams of ~ro~slinked poly(N-vinyl-2-pyrrolidone) homopolymer wa~ added to a ~olution con~isting of 65 grnms of polyethyl~n~ glycol (400 ~.W. from 8ASF of Par~ippany, NJ), 2 grams pota~01um ~hlor~de and 300 grams of water.
The m~xture wa~ ~tirred until ~quilibrated. To thi~ ~ixture wae bl~nd~d vari~u~ hydrophobic pr~ssure-sensitiv~ adhQ~ive for~ulation~
in a rang~ of m~xture ratio~ by w~ight to prepare a variety of two-pha~e CompoB~te ex~pl~s 0~ thQ pre~ent invcntion identifiad in Table 1 for ~xamplas 2 to 20 and Compari~on Example 21. Comparison Example 22 wa~ prspared without blending of any hydrophobic pre~oure n~t~Y~ adhesive formulation into tha ~olid ~tate conductive pr~ure-~nsitiva adhasi~e compo~ition prior to preparing ta~t biom~d~cal elactrodc~.
To prepare th~ electrodes, two-pha~e cs~posite pre~ure-sen~iti~e adhssive for each Example 2-20 and Compari~on ~xample 21 and solid stats pre~sure-~ensiti~e adh~ive for Comparison Example 22 w~e 0trip-coated horizontally on the cenker of a 8.89 cm x 17.78 cm polye~ter bAcking coated wLth ~ilver. The ailver had a conductance of 0.5 ~hOB and was 7.62 micrometera thick. ~ach mixture wae coatsd on an ~rea of 5.08 cm x 17.78 cm at approximately 76.2 ~icrometers thick. Each mixture was dried in an oven at 66C
for 15-20 minutea. BiomRdical electrode3 were made by cutting the dr~sd sheet into 2.54 cm x 4.2 cm ~trip consi~ting of a 2.54 x 2.54 cm conductiv~ adhesive cont~cting area and a connecting tab of 2.54 x 1.6 cm lead wire conn~ction area. DC Offset wa~ ~aasured using an Xtratek ET-65A BCG electrode tester from Xtrntek of Lenexa, Kansas to determ$n~ ~f DC off~et was w~thin the AA~I ~tandard of 1e8B than 100 m~olts throughout the te~t duration.

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Table 1 shows that ~kin adh~sion can be greatly improved by the mixing of an appropriate amount of a given hydrophobic pre~aure-~ensitive adhesive into a ~olid ~tate conductive pre3sure-sensitive adhe~ive composition. Depending on the amount of ~kin adhesion de~ired, the mixture ratio by weiqht of hydrophilic, solid state, pres~ure-sensitive adhe~ive mixture to hydrophobic, pre~aure-sensitive adhesive can vary from a weight ratio by weigh~ of from ~bout 196:1 to about 6:1 to yield a composite ratio by weight ranging ~rom 196:1 to about 3:1. Only in the inatance of Compari~on ~xample 21 did a two-pha~e composite formulation yield an unacceptable AC impedance according to AAMI standards. In the case of preferred examp}es 2-6, each m~xture ratio by weight produced upon drying a two-phase co~posita having a composite ratio by weight of ~lue $dent$cal to the mixture rat$o, becau~e both the ~olid state pressure-sens$t$ve adhes$ve and the IOA/NVP copolymer were di~p~rsed in liquid~ at 25 weight percent aolids. Comparing ~xample8 4 and 22, it iB seen that as l$ttle a~ 0.02 weight percent of hydrophob$c pre~sure-~ensitive adhes$ve in the dried two-phase composite nearly doubles sk~n adhesion without adver~ely affecting e$ther AC impedance or ~kin impedance. S$milar favorable compnr$~ons can be made between the result~ of ~xamplea 9, 10, 11, 15, 19, and 20 with Comparison Fxample 22.
The pre~ent invention is not limited to the`above embodiment~.
For an appreciation of the scope of the pre~ent invention, the cla$ms follow.

Claims

What is claimed is:

1. A two-phase composite of ionically-conductive, pressure-sensitive adhesive, comprising:
a continuous phase of hydrophilic, solid state pressure-sensitive adhesive composition ionically-conductive regardless of an amount of water present in the composition, and a discontinous phase of domains of hydrophobic, pressure-sensitive adhesive composition present in the continuous phase in an amount to enhance pressure-sensitive adhesive properties for contacting mammalian skin while maintaining acceptable alternating current impedance.

2. A biomedical electrode (10), comprising:
(a) a conductive medium (14) comprising a two-phase composite of Claim 1; and (b) means for electrical communication (16) interacting between said conductive medium and electrical diagnostic, therapeutic, or electrosurgical equipment.

3. The two-phase composite according to Claim 1 and used in electrode of Claim 2, wherein the hydrophilic, solid state pressure-sensitive adhesive comprises:
(a) a polymer electrolyte complex, and (b) an essentially non-volatile plasticizer present in an amount sufficient to form a cohesive, pliable, pressure-sensitive adhesive;
said polymer electrolyte complex comprising a solvating polymer and an ionic salt;
said solvating polymer comprising a homopolymer where each monomeric unit has at least one ionizing non-carbon atom or a copolymer where at least one monomeric unit has at least one ionizing non-carbon atom contained in a pendant group to the monomeric unit; wherein the hydrophobic pressure-sensitive adhesive is a polymeric adhesive composition prepared from a combination of monomers, homopolymers, copolymers and tackifiers, or blends thereof to produce polymeric adhesive compositions containing polyacrylates, polyolefins, silicone adhesives, natural or synthetically derived rubber base adhesives, or polyvinyl ethers;
and wherein the continuous phase and the discontinous phase have a composite ratio by weight of from about 196:1 to about 3:1 continuous phase:discontinuous phase.

4. The two-phase composite according to Claim 3, wherein said solvating polymer comprises crosslinked polyacrylamide and its ionic forms; crosslinked polyacrylic acid and its salts;
crosslinked poly(2-acrylamide-2-methylpropane sulfonic acid), its salts, crosslinked copolymers of the acid, crosslinked copolymers of salts of the acid, or mixtures thereof; or combinations thereof; and wherein the plasticizer is present in an amount of from about 65 to about 95 weight percent of the solid state pressure-sensitive adhesive composition to form a cohesive, pliable and pressure-sensitive adhesive composition.

5. The two-phase composite according to Claim 3, wherein said solvating polymer is crosslinked poly(N-vinyl lactam) present in an amount of from about 5 to about 50 weight percent of the solid state pressure-sensitive adhesive composition;
wherein said plasticizer is a polyhydric alcohol comprising glycerin, polyethylene glycol (200-600 M.W.), or mixtures thereof and is present in an amount of from about 50 to about 75 weight percent of the composition;
and wherein said ionic salt comprises lithium chloride, lithium perchlorate, sodium citrate, potassium chloride, or mixtures thereof present in an amount of from about 0.5 to about 5 weight percent of the solid state pressure-sensitive adhesive composition.

6. The two-phase composite according to Claim 1 and used in the electrode of Claim 2, further comprising an iontophoretically active pharmaceutical associated with the composite.

7. The biomedical electrode according to Claim 2, wherein said electrical communication means comprises a conductor member (16) having a conductive interface portion (18) contacting said conductive medium and a tab portion (20) not contacting said conductive medium.

8. A method of preparing a two-phase composite of Claim 1 and as used in the electrode of Claim 2, comprising the steps of:
(a) mixing solvating polymer, ionic salt, and an amount of essentially non-volatile plasticizer sufficient to form a cohesive, hydrophilic solid state pressure-sensitive adhesive, into a solvent which is essentially volatile above ambient temperatures to form a first suspension or solution;
(b) mixing a latex or solution of hydrophobic pressure-sensitive adhesive into the first suspension or solution in a mixture ratio by weight of from about 196:1 to about 6:1 of first suspension or solution:latex or solution to form a combined mixture;
(c) casting the combined mixture onto a substrate; and (d) removing the solvent to form a two-phase composite of Claim 1 and used in the electrode of Claim 2.

9. The method according to Claim 8, wherein said substrate has an electrically conductive surface and wherein the biomedical electrode of Claim 2 is formed from said two-phase composite on said surface.