Bioadhesive compositions and biomedical electrodes containing them

#This invention relates to bioadhesive compositions, particularly electrically conductive hydrogel compositions having bioadhesive properties. The invention further relates to biomedical skin electrodes incorporating such hydrogel bioadhesive compositions that are electrically conductive.

#Biomedical skin electrodes are widely used in a variety of situations, whenever for example it is required to establish an electrical connection between the surface of the body of the patient and external medical equipment for transmission of electrical signals.

#Modem medicine uses many medical procedures where electrical signals or currents are received from or delivered to a patient's body. The interface between medical equipment used in these procedures and the skin of the patient is usually some sort of biomedical electrode. Such electrodes typically include a conductor which must be connected electrically to the equipment, and a conductive medium adhered to or otherwise contacting skin of the patient, and they are of varying types with a wide variety of design configurations which will generally depend on their intended use and whether for example they are to be used as transmission electrodes or sensing i.e. monitoring electrodes.

#The invention will be further described with reference to the graphs of FIGS. 1 to 5 of the accompanying drawings and the following Examples in connection with bioadhesive compositions suitable for use in medical skin electrodes or in fixation products.

#In 20 parts of polyethylene glycol diacrylate (pEG600) (product of UCB Chemicals marketed under the trade name designation of Ebacryl 11) were dissolved 6 parts of 1-hydroxycyclohexyl phenyl ketone (product of Ciba and marketed under the trade name designation of Irgacure 184). The solution so produced is herein designated solution A (XL/PI). Separately, 50 parts of the potassium salt of 3-sulphopropyl acrylate (SPA) (product of Raschig) were dissolved in 50 parts water to form solution B. A further solution designated solution C consisted of 50 parts water, 50 parts of the sodium salt of 2-acrylamido-2-methylpropane sulphonic acid (NaAMPS) product of the Lubrizol Corporation and marketed as a 50% aqueous solution under the trade name LZ2405). Mixtures of solutions B and C in the ratios of 100:0, 90:10, 60:40, 50:50, 40:60, 10:90 and 0:100 were made to form pre-gel solutions. To 80 parts of each of these pre-gel solutions, 0.15 parts of solution A, 5 parts potassium chloride and 20 parts distilled water were added. The pre-gel solutions were coated onto siliconised release paper at a coat weight of 0.8 kilograms per square meter and exposed to ultraviolet radiation by being passed under a medium pressure mercury arc lamp at a speed of 5 meters per minute to form clear self supporting gels. The residence time under the lamp was 4 seconds. The storage moduli(G′) of 20 mm diameter discs stamped from the gels were recorded on a Rheometric Scientific RS-5 rheometer at 37° C. The G′ values at 1 rad are recorded in Table 1. Silver/Silver chloride electrodes were assembled from the gels by placing 25 mm by 25 mm samples onto silver/silver chloride coated plastic eyelets (product of Micron Medical Products and marketed as plastic eyelets 107). The impedances of the gels were recorded by contacting the gelled electrodes face to face via the gels and connecting to an Xtratek ET-65A ECG electrode tester (product of Xtratek of Lenexa, Kans.). The impedance data are recorded in Table 1. The percentage of freezing water present in the gels, also recorded in Table 1, were obtained by cooling small weighed samples of gel (ca. 2 mg) in sealed aluminium pans to −70° C. and heating at 10° C. per minute in a Perkin Elmer differential scanning calorimeter, DSC2. Using a calibration graph produced from samples of pure water, the area under the observed endotherm peaks was converted to the weight of freezing water in the sample. With the exception of the gels containing 90 and 100 parts SPA, the gels produced had acceptable tack and peel properties on the skin. From the data in Table 1 relatively linear changes in storage modulus and freezing water content are obtained on increasing or decreasing the SPA to NaAMPS ratio. The changes in impedance are small but surprisingly appear to be non linear.

#In the above Example, and in the following Examples wherever parts are mentioned they are meant as parts by weight unless otherwise specified. 1 TABLE 1 NaAMPS 80 72 48 40 32 8 0 SolutionC SPA 0 8 32 40 48 72 80 SolutionB Distilled 20 20 20 20 20 20 20 Water XL/PI 0.15 0.15 0.15 0.15 0.15 0.15 0.15 SolutionA KCl 5 5 5 5 5 5 5 G′(Pa) @ 4,198 3,389 2,471 2,205 1,759 703 492 1 rad/s Impedance 44 43 41 41 39 38 38 (Ohms) % 20 24 30 34 35 41 44 Freezing Water

#In 20 parts of polyethylene glycol diacrylate (pEG600) (product of UCB Chemicals marketed under the trade name designation of Ebacryl 11) 6 parts of 1-hydroxycyclohexyl phenyl ketone (product of Ciba and marketed under the trade name designation of Irgacure 184) were dissolved. (This solution is designated solution A) (XL/PI). Separately 58 parts of the potassium salt of 3-sulphoproylacrylate (SPA) (product of Raschig) were dissolved in 58 parts distilled water to form solution D. A further solution designated solution E consisted of 42 parts water, 58 parts of the sodium salt of 2-acrylamido-2-methylpropane sulphonic acid (NaAMPS) (a product of the Lubrizol Corporation marketed as a 58% aqueous solution under the trade name LZ2405A). Mixtures of solutions D and E in the ratios 100:0, 90:10, 60:40, 50:50, 40:60, 10:90 and 0:100 were made to form pre-gel solutions. To 100 parts of each of these pre-gel solutions, 0.17 parts of solution A and 3 parts potassium chloride were added. The pre-gel solutions were coated onto siliconised release paper at a coat weight of 0.8 kilograms per square meter and passed under a medium pressure mercury arc lamp at a speed of 5 meters per minute to form clear self-supporting gels. Storage moduli, impedances and % freezing water were measured as in Example 1 and are recorded in Table 2. As in the gels described in Example 1 the changes in the elastic or storage modulus G′(Pa) are linear with respect to the increasing or decreasing ratio of NaAMPS to SPA. However, surprisingly both the impedance and % freezing water content exhibit distinct non-linear behaviour. All the gels produced possess acceptable tack and peel strength against skin. The gels with NaAMPS:SPA ratios in the range of 60:40 to 40:60, however, have a better balance of reusability and peel strength. 2 TABLE 2 NaAMPS 100 90 60 50 40 10 0 SolutionE SPA 0 10 40 50 60 90 100 SolutionD XL/PI 0.17 0.17 0.17 0.17 0.17 0.17 0.17 SolutionA KCl 3 3 3 3 3 3 3 G′(Pa) @ 15,142 14,333 11,073 10,672 9,920 6,280 5,199 1 rad/s Impedance 62 61 49 46 43 40 40 (Ohms) % 0 0 0.5 1 1.8 23 25 Freezing Water