Patent Publication Number: US-2006004273-A1

Title: Biological signal sensor on a body surface

Description:
The present application claims priority benefit under 35 U.S.C. § 119(e) from U.S. Provisional Application No. 60/______, filed May 24, 2004, by S. Suave Lobodzinski, titled “A Method and a System for Sensing Biological Signals on the Body Surface,” which is hereby incorporated herein in its entirety by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention relates generally to biomedical sensors, and more particularly, to systems and methods for electrically conductive fibers for biomedical sensors.  
      2. Description of the Related Art  
      The practice of medicine utilizes a variety of sensors to measure and record biological signals on the body surface. These include: electrocardiogram, psycho-galvanic reflex of the skin, lactic acid, oxygen concentration, bio-impedance etc. In the electrocardiography applications, the present day ECG recording techniques utilize either non-polarizing Ag/AgCl or polarizing metal electrodes. The electrodes often have either a snap or a wire connector. In some special applications such as catheterization laboratory or magnetic resonance imaging, carbon electrodes and carbon wires are used instead.  
      Typically, electrodes are one-use products, while lead wires and patient cables are not. Longer-term applications require extensive taping of the electrodes and the connected patient cable to the body, thus making it impractical for longer-term use. Heart monitoring utilizing the ECG electrodes-lead wire-patient cable combinations is used extensively at the coronary and intensive care units in the hospital and in emergency response settings. Typically, the leadwires and patient cables are not sterilized and have been shown to be a source of cross infections in the hospital setting.  
      Other problems are also commonly encountered in long-term ECG monitoring. Long-term contact of gel sealed under the urethane foam electrode cap causes patient skin irritation and/or skin infection. Half-cell potential variations at the skin-electrode interface due to mechanical deformations of the skin surface under the electrodes cause excessive artifacts in the monitored results. Patient movement that pull on the lead electrode wires cause motion artifacts in the monitored results. Excessive patient perspiration under the electrode cap (gel leakage, baseline wonder etc.) also cause artifacts in the monitored results. There can be EM (electromagnetic) interference signals induced in lead wires.  
      In addition, current techniques do not provide patient convenience, such as resistance to water (showers or bath) and mechanical exposure (wearing normal clothing and conducting normal daily activities).  
     SUMMARY OF THE INVENTION  
      Embodiments of the present invention address the needs of the long-term, in-hospital and emergency response monitoring markets by providing an inexpensive, one-time use integrated electrode-leadwire-patient cable system that can be either used as a separate device or integrated into a garment for long term ECG monitoring applications.  
      In an embodiment, a biomedical sensor comprises an electrically conductive fiber, and an ionically conductive medium containing an electrolyte in contact with the electrically conductive fiber. The electrically conductive fiber comprises a multiplicity of flexible, electrically conductive filament cores and two different coatings deposited on the porous outer surface layers of the filaments, where one coating is a thin film having a thickness of about 5 micron of silver ink and where the other coating is a thin film having a thickness about 3 micron silver-silver chloride ink.  
      The silver ink coating contacts the electrically conductive filament core, and the silver-silver chloride ink coating contacts the ionically conductive media containing electrolyte. The electrolyte of the ionically conductive medium diffuses into the porous filament core of the electrically conductive fiber.  
      In an embodiment, the silver ink coating comprises nano silver powder with particles having a diameter of about 20 nm to about 30 nm, and a hydrophobic or hydrophilic polymeric binder. In another embodiment, the silver ink coating further comprises optional resins, and an optional cross linking agent.  
      In an embodiment, the silver-silver chloride ink coating comprises a powder containing approximately 20 nm to approximately 50 nm chlorided silver particles, and a hydrophobic or hydrophilic polymeric binder. In another embodiment, the silver-silver chloride ink further comprises an optional cross linking agent.  
      At least a part of one end of the electrically conductive fiber forms a lead wire that is not coated with silver ink, silver-silver chloride ink, and the ionically conductive medium.  
      At least a part of the lengths of the electrically conductive fibers form a lead wire that is covered by a non-electrically conductive layer of yarn and optionally an isolating medium coating in contact with electrically conductive fiber.  
      At least a part of the other end of the electrically conductive fiber core forms a lead wire termination that is not coated with silver ink, silver-silver chloride ink coatings, and the ionically conductive medium.  
      In an embodiment, the silver ink coating comprises nano silver powder, silver halide, (hfa)Ag(COD), (hexafluoroacetylacetonato) silver(l) (1,5-cyclo-octadiene), and (hfa)Cu(BTMS), where BTMS is Bis (trimethylsilyl)-acetylene, or combinations thereof.  
      The hydrophobic polymeric binder has minimal or little water absorbency.  
      In an embodiment, the flexible, electrically conductive filament core has a thickness from about 0.05 mm to about 0.1 mm. The silver ink coating has a thickness from about 1 micron to about 5 micron. The silver-silver chloride coating has a thickness from about 1 micron to about 5 microns.  
      In an embodiment, the fiber core filament comprises polyaniline, copper sulfide, silver surface treated polyamide, acrylonitrile, or the like.  
      In an embodiment, the biomedical sensor further comprises a low porous carbon-containing coating. The low porous carbon-containing coating comprises carbon powder, where the carbon powder comprises graphite powder, carbon black powder, combinations of graphite powder and carbon black powder, or the like.  
      In another embodiment, the biomedical sensor further comprises a high porous carbon-containing coating. The high porous carbon-containing coating comprises carbon powder, where the carbon powder comprises graphite powder, carbon black powder, combinations of graphite powder and carbon black powder, or the like.  
      In an embodiment, the content of silver-ink in the silver-ink coating ranges from about 60 weight percent to about 90 weight percent, and the content of the hydrophobic or hydrophilic polymeric binder in the silver-ink coating ranges from about 10 weight percent to about 40 weight percent.  
      In an embodiment, the content of silver-chloride ink in the silver-chloride coating is less than about 50 weight percent, and the content of the hydrophobic polymeric binder in the silver-chloride ink coating ranges from about 40 weight percent to about 50 weight percent.  
      In an embodiment, the average adsorbing surface area of the electrically conductive fiber is greater than about 600 m 2 /g. In an embodiment, the average diameter of the conductive fiber core ranges from about 0.05 mm to about 0.1 mm.  
      For purposes of summarizing the invention, certain aspects, advantages, and novel features of the invention have been described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment of the invention. Thus, the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      A general architecture that implements the various features of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention.  
       FIG. 1  is a schematic of an embodiment of a biomedical sensor.  
       FIG. 2  is a schematic of another embodiment of a biomedical sensor.  
       FIG. 3  is a cross-sectional view of an embodiment of biomedical sensor.  
       FIG. 4  is a cross-sectional view of another embodiment of a biomedical sensor.  
       FIG. 5  illustrates an embodiment of the sensor for very long term wear. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       FIG. 1  schematically illustrates an embodiment of a biological signal sensor or biomedical sensor  100 . The biomedical sensor  100  comprises a strand of an electrically conductive fiber  1 , an ECG amplifier or electrocardiograph  4 , and a sensor connector  5  electrically connecting the fiber  1  to the electrocardiograph  4 . The biomedical sensor  100  acquires biological signals through contact with a subject and conducts the biological signals to the electrocardiograph  4 .  
      The strand of the electrically conductive fiber  1  forms a sensor tip  2  and a non-sensing end  14 . The fiber  1  can be a metal-coated synthetic fiber such as, for example, acrylic, nylon, and the like.  
      In an embodiment, the sensor connector  5  comprises a nylon frame that encapsulates the non-sensing end of the fiber  14 , and protruding domes that squeeze the fiber  14  to a contact thus forming an electrical connection between the fiber and the contact. In an embodiment, the connector comprises a plurality of contacts and the fiber  1  comprises a plurality of fibers.  
       FIG. 2  schematically illustrates another embodiment of a biomedical sensor  200 . The biomedical sensor  200  comprises a plurality of sensing fibers  1 , each fiber  1  having the sensor tip  2  and the non-sensing end  14 , a signal processor/radio transmitter  17 , and a network relay device  23 . The signal processor/radio transmitter  17  comprises a sensor connector receptacle  18 , which electrically connects to the sensor connector  5 . The biological sensor  200  acquires biological signals from a subject and conducts the biological signals to the signal processor/radio transmitter  17 .  
      The signal processor/radio transmitter  17  is in communication with the sensing fibers  1  via the connector receptacle  18  and converts the biomedical signals acquired by the sensing fibers  1  into a radio packet for subsequent processing in the wireless network relay device  23 . The signal processor/transmitter  17  attaches to the body surface via an adhesive backing layer  21  having an adhesive  19 . In an embodiment, the adhesive  19  is a skin neutral kind that does not cause skin irritation or dermatitis. In another embodiment, the adhesive  19  is any medical grade adhesive.  
      The signal processor/radio transmitter  17  transmits the biological signals to the network relay device  23 . In an embodiment, the network relay device  23  is a wearable small computer, such as, but not limited to, a personal digital assistant, an iPaq, and the like, that is equipped with a minimum of two network interfaces. A first network interface communicates with the wearable signal processor/transmitter  17  and the second network interface communicates with local or wide area wireless networks, such as, but not limited to, CDMA, Wi-Fi, Bluetooth, and the like. The network relay device  23  further comprises a microprocessor, network communication software, a user interface, a display, and network interface hardware.  
      In an embodiment, the network relay device  23  processes the received biological signals and transmits the processed biological signals via the local or wide area wireless networks. In another embodiment, the network relay device  23  transmits the received biological signals via the local or wide area wireless networks for further processing.  
       FIG. 3  is a cross-sectional view of an embodiment of the sensor tip  2 . The sensor tip comprises the electrically conductive fiber  1 , a coating  3 , and a sensor-backing layer  9 . The coating  3  is adjacent to the fiber  1 . In an embodiment, the coating contacts the fiber  1 . In a further embodiment, the coating  3  is close to the fiber  1 . In an embodiment, the coating  3  is silver-silver chloride ink.  
      The sensor-backing layer  9  adheres the sensor tip  2  to the subject&#39;s skin and promotes the electrical conduction of the biological signals to the sensor  100 ,  200 . The sensor-backing layer comprises outer flanges  10 , a sensor reservoir  6 , and a cavity  7 .  
      In an embodiment, the sensor-backing layer  9  is made of very thin highly breathable, stretchable, polymeric film. The outer flanges  10  of the film are coated with a non-sensitizing, non-irritating medical grade adhesive  11 . In an embodiment, the adhesive  11  is specifically designed for sensitive skin and engineered for longer wear.  
      The sensor reservoir  6  is made of a spongy material that contains skin permeability enhancers, such as, but not limited to, amino fruit acids, glycolic acid, p-aminobenzoic acid derivatives, salicylic derivatives, triazine derivatives, benzimidazole compounds, bis-benzoazolyl derivatives, methylene bis-(hydroxyphenylbenzotriazole) compounds, 3-imidazol-4-ylacrylic acid, benzene 1,4-di(3-methylidene-10-camphosulfonic) acid, urocanic acid, and the like.  
      The cavity  7  in the sensor-backing layer  9  can be filled with a conductive paste or gel  12  to promote the acquisition of the biological signals.  
       FIG. 4  illustrates a cross-section of another embodiment of the sensor tip  2 . The adhesive sensor-backing layer  9  is not shown for clarity. The sensor tip  2  comprises a fiber core  40 , which comprises a plurality of electrically conductive filaments  42 . Examples of filament material are polyaniline, copper sulfide, silver surface treated polyamide, acrylonitrile, and the like.  
      In an embodiment, each filament  42  has a porous outer surface coating. The porous coating comprises carbon powder, which comprises at least one of graphite powder and carbon black powder.  
      In an embodiment, the fiber core  40  has a thickness of approximately 0.05 mm to approximately 0.1 mm, and an average adsorbing surface area of the electrically conductive fiber  1  is greater than approximately 600 m 2 /g.  
      The sensor tip  2  further comprises a coating  44  adjacent to the fiber core  1 . In an embodiment the coating  44  contacts the fiber core  40 . In another embodiment, the coating  44  is close to the fiber core  1 . In yet another embodiment, the coating  44  is deposited on the porous outer surfaces of the plurality of filaments  42 .  
      The sensor tip  2  further comprises an ionically conductive medium  46 , which comprises an electrolyte. The medium  46  is in electrical communication with the electrically conductive fiber core  40 .  
      In an embodiment, the coating  44  comprises a film comprising silver, where the film has a thickness of about 1 to about 7 microns. In another embodiment, the coating  44  comprises the silver film, where the film has a thickness of about 5 microns. In an embodiment, the coating  44  is silver ink.  
      In an embodiment, the silver film coating  44  comprises silver powder comprising a plurality of particles having a diameter of between about 20 nm and about 30 nm, and a hydrophobic or hydrophilic polymeric binder in contact with the plurality of particles.  
      The silver film coating  44  further comprises a resin in or on the silver film coating  44 , and a cross-linking agent that cross-links molecules in the coating  44 . In an embodiment, the silver content in the silver coating  44  ranges from approximately 60 weight percent to about 90 weight percent, and the binder content in the silver coating  44  ranges from approximately 10 weight percent to approximately 40 weight percent.  
      In an embodiment, the silver coating  44  comprises at least one of silver powder, silver halide, (hfa)Ag(COD), (hexafluoroacetylacetonato) silver(I) (1,5-cyclo-octadiene), and (hfa)Cu(BTMS).  
      In an embodiment, the coating  44  is a first coating  48 . The sensor tip  2  further comprises a second coating  50 . In an embodiment, the second coating  50  comprises a film comprising silver-silver chloride, where the film has a thickness of about 1 to about 5 microns. In another embodiment, the coating  50  comprises the silver-silver chloride film, where the film has a thickness of about 3 microns. In another embodiment, the second coating  50  is silver-silver chloride ink.  
      In an embodiment, the silver-silver chloride coating  50  comprises chlorided silver powder comprising a plurality of particles having a diameter of approximately 20 nm to approximately 50 nm, and a hydrophobic or hydrophilic polymeric binder in contact with the plurality of particles. In an embodiment, the silver content of the silver-silver chloride in the silver-silver chloride coating  50  is less than approximately 50 weight percent, and the binder content in the silver-silver chloride coating  50  ranges from approximately 40 weight percent to approximately 50 weight percent.  
      In an embodiment, the silver coating  48  contacts the fiber core  40 , and the silver-silver chloride coating  50  contacts the ionically conductive medium  46 . The electrolyte contained in the medium  46  diffuses into the fiber core  40  of the electrically conductive fiber  1 .  
      Referring to  FIGS. 1, 2 , and  4 , in an embodiment, at least a part of one end of the electrically conductive fiber  1  forms a lead wire and the lead wire does not contact the coating  44 ,  48 ,  50 . In another embodiment, at least a part of one end of the electrically conductive fiber core  40  forms a lead wire termination, and the lead wire termination does not contact any of the silver coating  44 ,  48 , the silver-silver chloride coating  50 , and the ionically conductive medium  46 .  
      In a further embodiment, at least a part of the electrically conductive fiber core  40  forms a lead wire, and the lead wire is at least partially covered by an electrically nonconductive layer of yarn.  
     ECG Sensor Solution as Applied to a Wearable Sensor Shirt  
      The biomedical sensor is very well suited for signal applications with a specialty garment. The biomedical sensor can also be used in conjunction with a garment that is stitched with the electrically conductive fibers  1  and is in communication with the signal processor/transmitter  17  as shown in  FIG. 2 , thus forming an integrated sensor-leadwire-patient cable system.  
      In an embodiment, the biomedical sensor is an ECG sensor. The ECG sensor elements (“electrodes”) are placed on the body surface in preferred ECG locations.  
      The electric coupling between the garment and the ECG sensor is accomplished through a fastening direct mechanical contact of an electrically conductive hook element mounted on an inner surface of the garment with a loop element of the ECG sensor. The garment&#39;s hook element is in electrical communication with an electrically conductive fiber and in electrical communication with a connector.  
      The ECG sensor mounts on the skin surface. The ECG sensor comprises a conductive gel and a thin layer of silver-silver chloride ink deposited on the backing layer of the ECG sensor. An electrically conductive element connects the silver-silver-chloride surface to the loop element of the ECG sensor. The loop element together with garment&#39;s hook element form an electric conduit for conduction of bio currents. The critical skin-electrode interface does not move, thus providing an artifact free ECG signal.  
     ECG Sensor Solution as Applied to a Wireless Body Sensor  
      In an embodiment, biomedical sensors are bonded to the skin directly using pressure-sensitive adhesives. In an embodiment, the biomedical sensors are ECG sensors. In this configuration, the fiber interconnectors link the “electrode” points to a signal processor/transmitter patch. The signal processor/transmitter patch bonds to the skin using a pressure sensitive adhesive layer.  
     ECG Sensor Solution as Applied to a Wireless Body Sensor for Very Long Term Wear (Life Long Monitoring)  
      In an embodiment, illustrated in  FIG. 5 , the biomedical sensor  500  comprises a layer of dermis tattooed with sensor ink. In an embodiment, the biomedical sensor  500  is an ECG sensor and the sensor ink is ECG ink.  
      The transcutaneously placed ECG sensor ink acts as a sub-dermal “electrode” accumulating ionic charges and converting them into electrons. The stratum corneum (dead layer of the skin) acts as an insulator. A metallized ECG sensor film is applied dry on the body surface. Together, the sub-dermal “electrode” and the ECG Sensor on the skin form a capacitor (insulated dry electrode). The changes of the ECG current in the torso generate an AC signal, which can be measured by a high input impedance differential amplifier. The advantages of this capacitor system as used in conjunction with synthetic interconnections include a very long monitoring period, which not possible with other methods.  
      While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.