Sensor

• US 3,912,614 A
• Filed: 12/10/1973
• Issued: 10/14/1975
• Est. Priority Date: 01/10/1972
• Status: Expired due to Term

• Current Assignee: C.R. Bard, Inc. (Becton, Dickinson & Co)
• Original Assignee: Capistiano Hideo Watanabe, Stanford B. Spracklen
• Inventors: Spracklen, Stanford B., CAPISTIANO HIDEO WATANABE
• Application Number:
  US05/423,164
• Time in Patent Office: 673 Days
• US Class Current: 600/345
• CPC Class Codes: A61B 5/14542 for measuring blood gases A61B5/14551 takes precedence
• CPC Class Codes: A61B 5/1473 invasive, e.g. introduced into the body by a catheter A61B5/1482 takes precedence
• CPC Class Codes: G01N 27/40 Semi-permeable membranes or partitions

Abstract

A sensor for in vivo amperometric measurement of selected components, dissolved oxygen for example, of blood, cells and biological fluids generally and for general analytical use is disclosed. The sensor includes an electrode assembly which has a noble metal electrode covered with a thick hemispherical membrane consisting essentially of a sparingly cross-linked hydrophilic polymer hydrogel which reversibly dries and imbibes greater than 20% aqueous fluid while maintaining structural integrity. Hydrophilic polyhydroxyl ethyl methacrylate is the preferred polymer.

Claims

1. IN AN ELECTRODE ASSEMBLY WHICH INCLUDES AN ELECTRODE, SUPPORTING STRUCTURE FOR THE ELECTRODE AND A SELECTIVELY PERMEABLE MEMBRANE COVERING THE ELECTRODE TO PREVENT DIRECT CONTACT OF FLUID TO BE TESTED WITH THE ELECTRODE AND PERMIT SELECTED CONSTITUENTS OF THE FLUID TO MIGRATE THROUGH THE MEMBRANE FOR ELECTROCHEMICAL REACTION OF THE ELECTRODE, THE IMPROVEMENT WHEREIN THE MEMBRANE CONSISTS ESSENTIALLY OF HYDROPHILIC POLYHYDROXYL ETHYL METHACRYLATE.

2. In an electrode assembly which includes an electrode, supporting structure for the electrode and a selectively permeable membrane covering the electrode to prevent direct contact of fluid to be tested with the electrode and permit selected constituents of the fluid to migrate through the membrane for electrochemical reaction at the electrode, the improvement wherein the membrane consists essentially of a hydrogel of a cross-linked hydrophilic polymer and of 20 to 97 percent of an aqueous liquid, said polymer being a copolymer of a major amount of a polymerizable monoester of an olefinic acid selected from the group consisting of acrylic and methacrylic acid, said monoester having a single olefinic double bond, with a minor amount of a polymerizable diester of one of said acids, said diester having at least two olefinic double bonds, said monoesters and diesters being water soluble, said monoester having a hydrophilic functional group.

3. The improved electrode assembly defined in claim 2 wherein at least one of said monoester and of said diester is an ester of a polyhydric alcohol selected from the group consisting of ehtylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol and polyvinyl alcohol.

4. An electrode assembly in vivo electrochemical measurements which comprises an electrode, supporting structure for the electrode and a thick hydrogel membrane covering the electrode to prevent direct contact of the fluid to be tested with the electrode and to permit selected constituents of the fluid to be tested to migrate through the membrane for electrochemical reaction at the electrode, the hydrogel consisting essentially of a cross-linked hydrophilic polymer, said polymer being capable of reversibly being dried and of imbibing from 20 to 97 percent of an aqueous liquid without loss of structural integrity and consisting essentially of a hydrogel of a cross-linked hydrophilic polymer and of 20 to 97 percent of an aqueous liquid, said polymer being a copolymer of a major amount of a polymerizable monoester of an olefinic acid selected from the group consisting of acrylic and methacrylic acid, said monoester having a single olefinic double bond, with a minor amount of a polymerizable diester of one of said acids, said diester having at least two olefinic double bonds, said monoesters and diesters being water soluble, said monoester having a hydrophilic functional group.

5. The improved electrode assembly defined in clAim 4 wherein the hydrophilic polymer is polyhydroxyl ethyl methacrylate.

6. The improved electrode assembly defined in claim 5 wherein the membrane has a hemispherical configuration where the migration takes place.

7. The improved electrode assembly defined in claim 5 wherein the electrode has a flat surface covered by the membrane and the outer surface of the membrane is hemispherical in shape.

8. The improved electrode assembly defined in claim 4 wherein at least one of said monoester and of said diester is an ester of a polyhydric alcohol selected from the group consisting of ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol and polyvinyl alcohol.

9. The improved electrode assembly defined in claim 8 wherein the membrane has a hemispherical configuration where the migration takes place.

10. The improved electrode assembly defined in claim 8 wherein the electrode has a flat surface covered by the membrane and the outer surface of the membrane is generally hemispherical in shape.

11. The improved electrode assembly defined in claim 8 wherein the membrane thickness is from about one to about eight times the diameter of the exposed electrode.

12. The improved electrode assembly defined in claim 11 wherein the membrane thickness is from about one to about five times the diameter of the exposed electrode, the exposed electrode is flat and has a diameter of from about 0.001 to about 0.020 inch, and wherein the membrane is in configuration where the migration takes place.

13. The improved electrode assembly defined in claim 4 wherein the membrane has a hemispherical configuration where the migration takes place.

14. The improved electrode assembly defined in claim 4 wherein the electrode has a flat surface covered by the membrane and the outer surface of the membrane is hemispherical in shape.

15. In an electrode assembly which includes an electrode, supporting structure for the electrode which leaves only the tip of the electrode exposed and a selectively permeable membrane covering the electrode to prevent direct contact of fluid to be tested with the electrode and permit selective constituents of the fluid to migrate through the membrane for electrochemical reaction at the electrode, the improvement wherein the membrane consists of essentially of a hydrogel material, having a thickness of from about one to eight times the diameter of the exposed electrode, the exposed electrode being flat and having a diameter of from about 0.001 to about 0.020 inch, the membrane being hemispherical in shape, being thicker in the center than at the edges.

16. The electrode defined in claim 15 wherein the thickness of the hydrogel membrane is from about one to about five times the diameter of the exposed electrode.