PT104882A - A DRY AND ACTIVE ELECTRODE FOR BIO-SIGNS USING AS AN INTERFACE MATERIAL AN ORGANIC-INORGANIC HYBRID - Google Patents

Abstract

The invention herein is a bioelectrode that is characterized by the use of an organic-inorganic hybrids obtained by the sun-gel method used as the skin-electric interface. Furthermore, the incorporation of a signal preamplifier and signal processing circuit in a flexible PCB leaves this electromagnetic device less susceptible to variations in the impedance in the electro-skin interface, thus reducing objects introduced by motion and noise. The ORGANIC-INORGANIC HYBRID INTERFACE MATERIAL HAS NEVER BEEN USED PREVIOUSLY FOR THIS TYPE OF APPLICATION AND THROUGH THE INCORPORATION OF ALL PARTS DESCRIBED HEREIN, RESULTS, THEREFORE, IN THE INVENTION OF A NEW DRY, ACTIVE AND FLEXIBLE ELECTRODE. In summary, this invention consists of a novel dry and flexible electrolyte which, in combination with the above-described electronics, uses an organic-inorganic hypo as an electrode-skin interface material.

Description

A DRY AND ACTIVE ELECTRODE FOR BIO-SIGNS USING AS AN INTERFACE MATERIAL AN ORGANIC-INORGANIC HYBRID "

Field of the Invention The invention herein is a bio-electrode which is characterized by the use of an organic-inorganic hybrid obtained by the sol-gel method as the electrode-skin interface. In addition, incorporating a preamplifier and signal processing circuit into a flexible PCB leaves this electrode less sensitive to impedance variations at the electrode-skin interface thereby reducing artifacts introduced by noise.

BACKGROUND OF THE INVENTION The most popular electrode used today for the measurement of bio-electric signals is the silver / silver chloride electrode. Although some good results have been obtained, this type of material presents several problems, such as the deterioration of electrical properties and allergic reactions. Although this electrode has its advantages, it entails considerable disadvantages. Some of the advantages and disadvantages of this electrode are shown below.

Advantages The low cost of the electrodes allows their non-reuse 1

A simple design ensures reliability when properly secured to the patient.

A good signal quality when the signal is used for a short period of time.

Disadvantages The electrode has an impedance at the relatively large electrode-skin interface, thus becoming very sensitive to electromagnetic interference and movement.

A difference in impedance of the electrode-skin interface caused by electrolyte dehydration introduces noise within the system. This means that in prolonged measurements the electrolyte needs to be reapplied regularly.

To lower the impedance at the electrode-skin interface, the skin needs to be prepared which is time-consuming and has drawbacks, especially in prolonged measurements.

There are some toxicological concerns about the use of electrolytic gel. Although rare, some cases of dermatitis have been reported.

As stated in the foregoing summary, the three major disadvantages of the wet electrode are: 0 noise introduced into the system due to impedance differences at the electrode-skin interface as well as noise introduced due to electromagnetic interference. 2 0 consumption of time and discomfort associated with the process of skin preparation

On prolonged measurements the electrolyte needs to be reapplied regularly. The former is especially important when measuring bioelectrical signals of very low amplitudes. In the literature, dry and active electrodes have been pointed out as a solution to these problems. Active electrodes are distinguished from conventional electrodes because they have a device for converting impedance at the signal detection site. As noted above, the impedance difference in the skin is one of the major sources of noise. Due to the large input impedance of the operational amplifier, the measurement system becomes less sensitive to impedance changes at the electrode-skin interface.

The active electrodes can generally be classified into two groups: wet and active electrodes and dry and active electrodes. Wet and active electrodes are usually the electrodes that use silver / silver chloride as interface material. These electrodes are similar to conventional electrodes, except that they incorporate electronics at the signal detection site.

The dry and active electrodes may be comprised of various types of materials, such as an inert metal such as platinum, a metal having an outer ceramic layer, or a polymer. Some authors also refer to conductive particle charged adhesives, such as graphite or silver, although it has been found that these materials degrade the adhesive properties. Another author also refers to the use of carbon nanotubes that penetrate the outer layer of the skin. Despite the good results that can be achieved, penetration into the skin brings some toxicological concerns. One of the main reasons for research on active electrodes is the choice of interface material. This part of the electrode is in direct contact with the skin and therefore is one of the first points of introduction of noise in the measuring system. The chosen material must be a good conductor, it must also be flexible and have a long signal stability. Flexibility is important as it allows the electrode to adapt to the contours of the human body.

Documents that have been found related to the design of dry and active electrodes for bio-signal monitoring are listed below. However none of these patents use the interface material used in the present patent that we propose. Title: Biosignal electrode Registration number: US 5337748 4

Assessed properties Design properties for our product Substrate material Flexible substrate Electronics None present Interface material 'Ag / AgCl ccm adhesive properties fc *. * Impact on our concept and design Although the electrode described here does not use electronics the flexibility of this electrode is very interesting. Also the interface material and its adhesive properties is something that could adapt to our advantages.

Title: Skm Impedance matched Biopotential electrode Registration number: US 2005177038 Rated properties Important design properties for our product Substrate Non-Flexible Insulation Encapsulation Electronics Preamplifier for Impedance Transformation Interface Material Molded Rubber Sheet, Carbon Suspension Iv / " The electrode shown is encapsulated in a non-conductive body with a conductive layer on a single side. The interface material may be a molded rubber sheet containing a carbon suspension. In addition, the patent has also been tested with different types of elastomers, neopren and rubbers containing silica. The patent also relates to substrates having low volume conductivity. This can be an important line in relation to our patent. 5 Title: Biopotential sensor electrode Registration number: US 6434421 Rated properties Important design properties for our product Substrate A non-flexible closed body Electronics An impedance transformation circuit and wireless system for wireless signal transmission. Interface material A hybrid solution of dry materials and insulators: ¾ .- ···· --- ·;; !; 'ν': υ'νΧν $ ·; · Ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν Impact in our concept and design This sensor is a combination of capture and stimulation devices. The device shown here uses wireless transmission to transfer its signal to the data acquisition system. The interface material is a mixture of conductive and dielectric material. This configuration forms a capacitor, such as a sensor element. Conductive metal may be gold, platinum, etc. This design does not have the flexibility that our product presents. In addition this hybrid electrode is called hybrid because of the combination of conductive and dielectric materials, which makes it dry, as well as an isolated electrode. Title: A dry electrode system for detection of biopotentials Registration number: US 4669479 Rated properties Important design properties for our product Substrate Hard substrate Electronics Preamplifier for impedance transformation. Battery for operation. Interface material Polyurethane foam loaded with carbon 6

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Impact on our concept and design The device shown here uses an elastic interface material, which consists of carbon-laden polyurethane foam. The device operates through batteries, which are located on the connector side, greatly increasing the size of the invention. Title: Electrode for measurement of weak bioelectrical signals Record number: US6622035 Rated properties Important design properties for our product Substrate Hard substrate Electronics Pre-amplifier circuit for impedance transformation. Battery for operation. Interface material Micro needles made of metal or conductive plastic μ In our concept and design - 'X. 'V' .v; ·, R > .vj, .v ·% \ L '\ ov.N > . i, v s. . '; Λ N V I N s vt' v " \ - x *; v SN 'Ν Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ Λ. This product uses micro needles to penetrate the top of the skin layer. This brings some toxicological concerns. The shape of the substrate and the integration of the electronics in the back of the substrate are similar to the design adopted in the present patent. 7

Title: A dry-type active electrode for monitoring of biopotencies Registration number: PT 102999 Rated properties Irrportant design properties for our product Substrate Rigid transformer Electronics Circuit amplifier for transforming an impedance and a signal processing circuit Interface material Disc titanium-coated stainless steel Impact on our concept & design > The f ··: · - " The product shown here uses a stainless steel disc coated with a layer of titanium dioxide. The preamplifier is also similar to our product. Despite the good results obtained with this system the product does not have the flexible properties that ours has. 8 Title: Non-polarizable dry biomedical electrode Registration number: US 5003978 Rated properties Important design properties for our product Substrate Hard, non-polarizable Electronics Not present, see US 4669479 Interface material Rubber or conductive foam 1 4- r *, The product presented here may use various types of interface materials, such as conductive foams. What's more, this electrode also has flexible properties.

While many patents have the same aim, which is to capture low amplitude bioelectrical signals such as EEG, EMG or EKG, the inventions differ in the use of the material associated with the electrode-skin interface. Many patents adopt a similar method for decreasing the impedance of the skin-electrode interface by using electronics with specific operating amplifiers and combining with a good interface material, the signal-to-noise ratio (SNR) being considerably improved. We have also found several patents that have some similarities with respect to the flexibility, form and use of electronics. However, we can unequivocally conclude that no patents were found that use the organic-inorganic hybrid material called di-ureasil solely as an interface material, or in combination with electronics as a dry and active electrode, which gives a high degree of innovation to our proposal. 9

Summary of the Invention The method presented in this patent application describes a dry and active electrode in combination with the use of a novel interface material with novel features, this being one of the required points. The invention presented herein is an electrode which can be aggregated to the skin in order to capture electrophysiological signals caused by the activity of the heart, brain or muscles. The electrode is flexible and therefore can adapt to the contours of the human body. The electrode is especially suitable for the detection of signals from an electrocardiogram (ECG), although it can be readily adjusted for any other bioelectrical signals, such as EEG signals or EMG signals. Depending on the electrophysiological signal, and therefore, for each application mentioned above, the shape, size and electrical properties of the proposed electrode can be changed. As an example, it may be noted that in EEG a large amount of electrodes is present on a small surface and therefore a smaller electrode could be preferable. Furthermore, since an EEG is much smaller in amplitude the conductivity of the interface material can be improved, consequently changing the electrical properties, so as to adapt it to the characteristics of the signal to be measured. As for EMG studies, muscle movement may interfere with the electrode-skin interface. With the present method we can increase the electrode and add some adhesive properties to maintain a high level of signal quality. Further, the electrode manufactured according to the method proposed herein can be used in intelligent textiles or even integrated into fabrics. The proposed electrode consists of the following elements: a sensor consisting of a PCB made of flexible substrate with the interface material deposited on its surface. At the top of the small flexible PCB is the electronic circuit and metal knob or the easy-to-connect conductive fabric for a device for measuring and integrating into fabrics and other smart textiles, such as " vital jacket ", a developed product by the University of Aveiro. The sensor is made from a flexible substrate and coated with an organic-inorganic hybrid material prepared by the sol-gel method, which interfaces with the outer skin layer. The sensor captures the signal by injecting it into the electronic circuit. The electrical contact between the organic-inorganic hybrid and the PCB made of flexible substrate is effected, but not limited, by conductive textiles, conductive fabric fibers or copper wires. The interface material - an organic-inorganic hybrid prepared by the sol-gel method - has never been used previously as a biosensor and therefore constitutes one of the innovative features of this product. The organic-inorganic hybrid used as interface material performs similarly to wet electrodes. In addition, it can also be added to fabrics and thus enable the use of intelligent textile sensors. The sensor incorporates an impedance matching circuit and signal processing. As with all active electrodes, the circuit has high input impedance and low output impedance, but also incorporates a high-pass filter for signal conditioning. The circuit can be powered by a small 3.6V lithium battery, or an isolated power supply to prevent the risk of electric shock. The voltage can be as low as 3.3V, 3.0V or up to 2.7V until the circuit stops working.

FIG. 1: Top view of the electrode 1 - PCB made of flexible substrate 2 - Operational amplifier (op-amp) 3 - Mounting knob 4 - Connector cable 5 - Voltage inverter FIG 2: Electrode lower view 1 - PCB made of flexible substrate 6 - Dry organic and inorganic active electrode

attached to the PCB FIG 3: Mechanical drawing of the electrode according to FIG 2, 3 7 - Electrode view 8 - Electrode side view 9 - Material deposition 10 - Top mounted button 12 FIG 4: Block diagram and diagram electric element of the dry and organic-inorganic active electrode 4a) Block diagram 11- Organic-inorganic hybrid material 12- High-pass filter 13- High impedance pre-amplifier 14- Voltage inverter 15- Output for biosynthesis acquisition 4b) Circuit Preamplifier 4c) Voltage Inverter 4d) Signal and Power Connector FIG 5: Experimental Setup 16 - Dry and Active Electrode RA (Ríght Arm - right arm) 17 - Dry and Active Electrode LA (Left Arm) 18 - Silver humidifier / silver chloride RA (right arm) 19 - Silver wet / silver chloride LA (left arm) 20 - Silver chloride reference humid electrode 21 - Biosynthesis acquisition system 22 - Computad or FIG 6: ECG segments for 6 a) Dry and active electrode 6 b) Ag / AgCl electrodes 13 6 c) and 6 d) Estimated power spectral density (PSD) calculated for 5 complete hours of acquisition.

Sampling frequency is 150Hz.

DETAILED DESCRIPTION

Figures 1, 2 and 3 show the mechanical properties of the electrode. According to Figure 1 the electrode is constructed from a flexible substrate (1) which gives it all the mechanical strength. The electronic components (2, 4) are mounted on the top of the substrate. We opted for a flexible substrate, allowing the electrode the ability to adapt to the contours of the human body. Figure 1 also shows the knob (3) such that the electrode can be attached to the fabric. A small connector (5) connects the electrode to its power supply and signal acquisition. In figure 2 we can see the organic-inorganic hybrid (6) added to the button on the flexible substrate (1). Initially the material is poured into a mold, which is mounted on the electrode of a typical thickness of 2 to 5mm, which can be modified according to the intended final application. After drying between 24 and 72 hours, the mold is removed and a solid and flexible material is obtained. Figure 3 shows the typical mechanical dimensions of a specimen of our electrode. The electrode is about 10 to 50 mm in diameter and about 2 to 5 mm in height. The material is about 10 to 60 mm in diameter and about 2 to 5 mm in height. The button is about 10 to 20 mm in diameter and about 14 in 5 to 10 mm in height. All of these dimensions can be changed for different purposes in the future.

Figure 4 shows the electrical diagrams and diagrams of the electrode. In figure 4A we can see the schematic diagram, which describes the dry and active electrode globally. In figure 4B we can see the preamplifier, which consists of an operational amplifier, a resistor and a capacitor. The resistor and capacitor form a high-pass filter with a cutoff frequency of 0.03Hz thus eliminating DC fluctuations. The tested configuration for ECG signals used a 5G-ohm resistor and a 10nF capacitor, but can be easily modified according to the required requirements. The operational amplifier was chosen for its low power consumption and small size. The power supply used can decrease from 5 to 2.7V and the current consumption is 25μΑ to 5V. Moreover this operational amplifier has a very large input impedance, typically > 10 Ω. To make the device as universal as possible we used a 4C voltage inverter to generate a negative voltage source for the operational amplifier. The dual feed configuration gives the op amp more precision and greater dynamic range. We chose a voltage inverter for our invention. The inverter is a small package and is perfectly suited for applications that run on battery power. Due to the low power consumption the efficiency of the voltage inverter is > 90%. The 50 ohm resistor and the 100nF capacitor form a low-pass filter with a cutoff frequency of 31 kHz to filter the inverter switching frequency. 15

To test our new dry and active electrodes and compare them with Ag / AgCl electrodes we use a wireless biopotential acquisition system (21), Figure 5. The data acquisition system can accept and feed the new dry and active electrodes (16, 17) using the conventional Ag / AgCl electrode (18, 19, 20) for comparison. For each channel an analog low pass filter was applied with the cutoff frequency of 100Hz to eliminate high frequency noise. Also a 0.03Hz high pass filter was applied to eliminate DC fluctuations. Both channels were tested at 150Hz and the analog-to-digital converter (ADC) used had an 8-bit resolution. As can be seen in Figure 5, both types of electrodes were simultaneously applied to the volunteer's body. Prior to placing the Ag / AgCl electrodes in contact with the skin, an electrolytic gel was applied. Our dry and active electrodes were used without resorting to any electrolytic gel or to a specific preparation of the skin. Both signals were acquired for 5 hours under laboratory conditions. The results obtained for both types of electrodes are shown in Figures 6a and 6b. Figure 6a shows a 10 second segment of data acquisition for the dry and active electrodes and Figure 6b shows the acquisition of data for the Ag / AgCl electrodes. By comparing the data we can see that both types of electrodes suffer minimal interference from the power lines, which are visible in figures 6c and 6d in the peak at the frequency of 50Hz. Although it is a small difference, we can conclude that the dry and active electrodes have similar characteristics related to the interferences of the feed line when compared to the Ag / AgCl electrodes. Moreover, by looking at the 0 to 10 Hz frequency region in Figures 6c and 6d we can conclude that the dry and active electrode has less amplitude than the Ag / AgCl electrode. This may be related to the position of the electrode in the body, which may exhibit differences in signal amplitude and shape. There is also some movement artifact present in figure 6b, but with less intensity compared to figure 6a. The results presented here prove the clear concept of operation for practical applications. The synthesis for obtaining the interface material is described below. The raw material used in this synthesis can be altered according to the intended application. The material used as interface material is an organic-inorganic hybrid prepared by the sol-gel process. This process involves the transition from a liquid material (&quot; sol &quot;) to the solid state (&quot; gel &quot;). The suns are a dispersion of particles in liquid, termed colloids. These colloids are solid particles having a diameter of 1 -100 nm, dispersed in a solvent. A gel is a rigid network interconnected with pores of sub-micrometric dimensions and polymer chains whose average length exceeds one micrometer. A simple example involving the sol-gel process is gelatin. Initially gelatine is a powder, to which is added a solvent, which in this case is water. The mixture is then heated to moderate temperature (<100 ° C) and the solvent evaporates from the pores (through hydrolysis and polycondensation reactions), then gelatin forms. While the proposed materials are prepared by the sol-gel process, the final product is a flexible solid material that can be produced in any shape and size. The organic-inorganic hybrids described in this patent are called &quot; di-ureiasils &quot;.

Di-ureiasils consist of variable length polyethylene oxide (POE) chains, grafted at both ends, to siloxane domains through urea bridges. This means that the material has an organic component, which in our case consists of a carbon-based chain and an inorganic part, which consists of an organosilic network. These two components are connected through covalent bonds. The most obvious advantage of organic-inorganic hybrids is that they can favorably combine the properties of organic compounds with those of inorganic systems in a single material. Furthermore, the material used in this case as interface material was doped with iron, but could also have been doped with an alkali metal (e.g. Li, K) or any other transition metal, for example Fe, Au or Ag.

A typical procedure for the synthesis of the di-ureiasyl matrix (in this case dU (2000), which has a high molecular weight polymer chain) doped with Fe 2+ is used in two steps: In the first step, 1.5 g , 75 mmol) of precursor diamine ED-2001 was dissolved in 5 mL of tetrahydrofuran (THF) in an ultrasonic bath. Then 0.39 ml (1.5 mmol) of 3-isocyanatopropyltriethoxysilane (ICPTES) was added under stirring at the ICPTES: ED-2001 molar ratio of 18 2.0. The mixtures were further stirred for 24 hours at room temperature under nitrogen (N2) atmosphere. In the second step, 0.5956 g (1.52 mmol) of ((NH4) 2Fe (SO4) 2) was dissolved in 1.0 mL 2.0 mol / L HCl at the molar ratio of n = [O] / [Fe2 +] = 20. In this case, [O] represents the number of OCH2CH2 units in the ED-2001 polymer chain per Fe2 + cation. When the ((NH4) 2Fe (SO4) 2) was fully dissolved a clear green solution was obtained which was then added dropwise with stirring to the solution performed in the first step. After a short time, this sun shifted to a viscous solution, which was poured into a mold. Gelling occurs between 2 to 5 minutes and the resulting organic-inorganic hybrid can be used as an electrode-skin interface material in the new dry and active electrode proposed in this patent.

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Claims (8)

A flexible organic and inorganic active electrode for detecting bioelectrical signals, characterized by the following elements: an active electrode, including a flexible organic-inorganic hybrid material (6) added but not limited to a flexible electronic substrate (1) and electrically connected to a pre-amplifier (2, 5), which is located on the PCB made of flexible substrate. A flexible organic and inorganic active electrode according to claim 1 characterized in that the dry and active electrode uses an organic-inorganic hybrid material (6) connected to the electronics by a flexible PCB attached to the organic-inorganic hybrid material, offering a flexible and flexible working dry electrode favoring better contact with the skin. A flexible organic and inorganic active electrode according to claims 1 and 2 characterized in that the pre-amplifier circuit (4b) in combination with a high-pass filter, comprising a resistor and a capacitor (4b), and has an applied positive and negative voltage (4c). A flexible organic and inorganic active electrode according to claim 3, characterized by a metal button (3) or a conductive fabric, which allows a simple connection to a metering and integration device in clothing and other intelligent textiles for long-term monitoring of bio-electrical signals. A flexible organic and inorganic active electrode according to claim 3 characterized in that an electrode with PCB made of flexible substrate fully fixed in the organic-inorganic hybrid material then creates an electrode which is completely surrounded by the organic-inorganic hybrid material . A flexible organic and inorganic active electrode according to claims 1, 2, 3, 4 and 5 characterized in that the electrical contact between the organic-inorganic hybrid and the PCB made of flexible substrate but not limited to the conductive tissue or copper wire. A flexible organic and inorganic active electrode according to claims 1, 2, 3, 4, 5 and 6 characterized in that the flexible organic-inorganic hybrid material which can be doped with transition metals, such as Fe, Au or Ag. A flexible organic and inorganic active electrode according to claims 1, 2, 3, 4, 5 or 6 characterized in that the flexible organic-inorganic hybrid material is doped with alkali metals such as K or Li. March 3, 2010 2