A wearable biopotential acquisition system based on graphene electrodes

Abstract

The system proposed in the present invention is a wearable electrocardiogram system comprising an integrated glove component equipped with a mobile exploring electrode arranged at the tip of the index finger. This innovative biopotential acquisition approach harnesses graphene's qualities and allows the user to place said electrode anywhere within the reach of his / her body. While conventional textile-based wearable applications primarily only focus on single-channel ECG measurements (namely, LEAD I, II, III), the innovative paradigm of the present invention makes it possible to capture multi-channel ECG data reliably and accurately.

Description

[0001] A WEARABLE BIOPOTENTIAL ACQUISITION SYSTEM BASED ON GRAPHENE ELECTRODES

[0002] TECHNICAL FIELD

[0003] The present invention relates to acquiring and using biometric data by application and usage of wearable peripherals on a body. In particular, the present invention relates to providing a means to monitor patients which is based on graphene electrodes for multichannel biopotential (e.g., electrocardiogram) measurements.

[0004] PRIOR ART

[0005] Electrocardiogram (ECG) provides a wide array of data on the functionality of a subject's heart by measuring the electrical properties of human and mammal cardiovascular systems from skin surface. Accordingly, ECG is based on the ability to detect the electrical activity using conductive patterns on the skin of a subject, which is then monitored as a voltage versus time graph. In a typical ECG setting, sticky Ag / AgCI (silver / silver chloride) electrodes are placed as biopotential sensors on various parts of the body, and the potential difference is measured across various combinations of these electrodes. In general use, it is common to position one electrode on the left arm and another on the right arm, with an additional reference electrode placed anywhere on the body as a LEAD I configuration (i.e., bipolar electrocardiography); however, it should be noted that the diagnostic utility of this configuration is very limited within medical ECG framework.

[0006] In medical ECG, a thorough examination of a heart's activity from multiple angles is performed by strategically positioning six electrodes on the chest and four on the limbs. For three of the four electrodes on the limbs (right arm, left arm and left foot or leg), it was noted that when one end is in contact with the skin and a high resistance is connected to the other ends, and the high resistance outputs of these three electrodes are collected at the same common node, the common node would have an electrical zero potential (this however is controversial) and this point, referred to as the Wilson Central Terminal (WCT), would be located in the center of the chest region on the frontal plane of the body as a virtual (imaginary) electrode with approximately zero potential. This approach was later improved and led to electronically more accurate configurations, thus creating unipolar leads in addition to the existing bipolar leads. The limb electrodes consist of one electrode on the left arm, one on the right arm, and one on the left leg. There is also a reference electrode on the right leg; however, this electrode is not used to measure the potential difference but only to reduce noise artifacts and establish a common ground. On the other hand, the chest electrodes, namely, V1 to V6, consist of six sensors placed along the fourth and fifth intercostal space. To summarize briefly, a standard ECG sheet typically comprises 12 traces, of these, six are derived from the chest leads (unipolar chest leads) by WCT and three are obtained from the unipolar limb leads whose signal levels are increased (augmented) by modifying the WCT as the Goldberg Central Terminal (i.e., when creating a typical WCT, whichever of the three electrodes located in the limbs is to be connected to a positive electrode, the negative electrode at that point is removed, and the leads, which do not contact the skin, of the remaining two negative electrodes are connected to the same node via a high resistance, thereby obtaining a zero potential at the node to which they are connected, referred to as Goldberg Central Terminal), and the remaining three are obtained from the limbs, and referred to as bipolar limb leads.

[0007] In recent years, wearable technology has evolved from basic activity trackers such as smartwatches and bracelets to high-quality medical products that can be worn for extended periods of time with the highest level of reliability and patient comfort. The diagnostic accuracy and practicality of long-term out-of-hospital ECG have previously demonstrated to be superior compared to instant clinical ECG assessments in several cases, therefore it is crucial to ensure convenient clinical measurements in a home setting, particularly for vulnerable groups such as the elderly and infants, as it can provide significant advantages in the managing of cardiovascular diseases. Conventional sensors used in medical ECG procedures are usually made of Ag / AgCI, referred to as wet electrodes. While they have proven to be quite useful for instant measurements, many studies have reported adverse effects of such type of disposable electrodes when left on the skin for prolonged periods, making them inconvenient for long-term measurements.

[0008] Graphene stands out among many functional materials used in ECG electrode construction due to its thermal and electrical conductivity, durability, and the ability to maintain the properties such as flexibility, softness, and breathability of various textile or polymer-derived flexible materials used as base materials in making wearable electrodes or smart clothing. Graphene-based textiles can be used to obtain other biopotentials as well.

[0009] A state-of-the-art document US 10,824,230 B1 proposes a wearable graphene textile-based electro-ocular monitoring and object interaction system. According to the teaching of this patent, an electrooculogram based human computer interaction / human machine interface (HCI / HMI) system is proposed, comprising wearable graphene textiles, a signal acquisition system for obtaining biopotentials from the human body, and a processor for the processing of said biopotentials acquired through said signal acquisition system for enabling and facilitating human machine interactions in various settings. Another state-of-the-art document US 9,986,925 proposes a method of use and an electrocardiography system (8) comprising an electrocardiography device (10) with two electrodes (14 and 18) and a portable computing device (11). US 2018 / 020,937 discloses a solution adapted to be worn on the finger, wrist, behind the ear and / or on the head, and comprises a first electrode (10) and a second electrode (12). The first electrode (10) is configured to locate on a surface of the device which will contact the skin of the user while the user wears the wearable structure.

[0010] US 1 1 ,013,462 discloses a ring-shaped device (100) for ECG measurement. The ring (100) comprises a first electrode (252) arranged on its inner surface to be in contact with the user's skin and a second electrode (254) arranged on the outside, which can be touched to any desired position on the body. It is disclosed that the user can wear a plurality of rings (100) to obtain multiple ECG measurements at the same time.

[0011] AIMS OF THE INVENTION

[0012] An aim of the invention is to develop devices enabling reliable and accurate measurement of biopotential data outside hospital settings.

[0013] Another aim of the invention is to provide a device with which electrocardiogram data can be obtained within the framework of wearable technology principles in a manner which overcomes the limitations of conventional wet electrodes.

[0014] A further aim of the invention is to provide an innovative armband tailored for capturing clinically meaningful ECG measurements with various ECG leads, in other words, multichannel 12-leads, by exploiting the intrinsic qualities of graphene.

[0015] Yet another aim of the invention is to provide an ECG data acquisition device in the form of an armband including a glove that is seamlessly connected to the biceps region via a textile piece extending so as to cover a part of the elbow and the forearm.

[0016] BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The figures, whose descriptions are given below, aim to exemplify a wearable electrocardiogram acquisition device whose advantages with respect to the state of the art are already summarized above and will be discussed in detail hereinafter.

[0018] The figures should not to be construed as limiting the scope of protection as defined in the claims, and are not to be referenced solely in interpreting the scope of said claims without regarding the technique in the description.

[0019] Figure 1 is a view of a wearable biopotential acquisition device according to an embodiment of the present invention, on an individual. Figure 2 is view of a wearable biopotential acquisition device according to an embodiment of the present invention, on an individual from another angle.

[0020] Figure 3A-B are amplitude vs. time graphs comparing the performances of Ag / AgCI electrodes (A) and graphene textile electrodes (B) according to an embodiment of the present invention.

[0021] Figure 4 shows impedance vs. frequency graphs comparing the skin impedance performances of Ag / AgCI electrodes and graphene textile electrodes according to an embodiment of the present invention.

[0022] Figure 5 is a view showing standard electrode placement positions on a human body according to an embodiment of the present invention.

[0023] Figure 6 shows amplitude vs. time graphs of biopotentials captured with Ag / AgCI and graphene textile electrodes from said standard electrode placement positions according to the present invention.

[0024] Figure 7 is a comparison of biopotentials captured with Ag / AgCI and graphene textile electrodes at said standard electrode placement positions in a WCT-less configuration according to the present invention.

[0025] Figure 8 is a comparison of biopotentials captured with Ag / AgCI and graphene textile electrodes at said standard electrode placement positions with WCT configuration according to the present invention.

[0026] DETAILED DESCRIPTION OF THE INVENTION

[0027] For a better understanding of the present invention, the elements in the figures included in the description of the invention are individually numbered and each numbered element is described below.

[0028] 10) User

[0029] 20) Biopotential acquisition device

[0030] 21) Primary component

[0031] 22) Secondary component / Glove component

[0032] 23) Tertiary component / Connection component

[0033] 31) AgCI electrode curve

[0034] 32) Graphene electrode curve

[0035] 40a-f) V1-V6 electrode leads 41) Graphene electrode graph

[0036] 42) Ag / AgCI electrode graph

[0037] The present invention is essentially a biopotential acquisition device (20) harnessing the intrinsic qualities of graphene. The present invention in which graphene textile electrodes are used, comprises three electrodes, one of which is an exploring electrode sewn at the fingertips of at least one finger, preferably the index finger, on a glove. This electrode is fully mobile, giving the user (10) the freedom to position said electrode anywhere on his / her body within reach. This flexibility enables biopotential data measurements to be taken from multiple angles and from any desired location on the body. Said biopotential data can be selected from the group including electrocardiogram, electrooculogram, electroencephalogram and electromyogram. According to at least one embodiment, the biopotential data of the invention is electrocardiogram.

[0038] The fundamental notion behind the present invention is to realize a medical-level multichannel electrocardiogram and in general, biopotential acquisition using a minimum number of sensing elements with maximum feasibility and comfort on a health monitoring garment adapted to be fashionably used with standard garments and other clothing items for daily use. To that end, the paradigm comprises a total of three electrodes in the biopotential acquisition device (20) in the form of an armband. Two of these three electrodes are located on the upper arm and one on the fingertip of the index finger. In various embodiments of the invention, the electrode, which is preferably arranged at the tip of the index finger, can also be used by being placed on another finger.

[0039] According to an embodiment of the invention, an upper arm component is provided as a primary component (21). Said primary component (21) surrounds the limb at biceps level, comfortably adapting thereto. While the upper arm component has a geometric shape adapted to surround the biceps and triceps region circumferentially, e.g., a geometric trapezoid shape according to an embodiment, the secondary component (22), which is the glove component, is shaped using a variety of rectangular shapes, including the tertiary component (23), which is the middle bridge component which connects the primary component (21) to the secondary component (22). There may also be embodiments where several curvature points are incorporated at the edges of the fingertips to enhance the aesthetic appeal. To visually distinguish the electrodes from the fabric of the garment on which they are to be applied, there can also be an additional fabric in a contrasting color. According to an embodiment, while the particle distance of the finger components in the secondary component (22) is set to 5 mm due to their small size, the particle distance of the upper arm component, which is the primary component (21) of the armband, is set to 10 mm. In the biopotential acquisition device (20) proposed according to an embodiment of the present invention, the electrodes to be used in signal acquisition are prepared using bamboo nylon textile, carefully coated with reduced graphene and seamlessly integrated into cotton fabric during final assembly. Said electrodes are manufactured by way of an electrode coating application referred to as dip-dry-reduce, which comprises sequentially the steps of dipping, drying and reduction. Qualities such as surface texture, tightness and thickness are of great importance in textile coating, and careful control of these parameters is crucial throughout the process. In order to obtain the optimal storage result, a number of textiles including bamboo nylon, polyester and cotton can be used in the present invention. According to a particularly preferred embodiment of the invention, due to its notably low surface roughness, which results in a uniformly applied graphene oxide (GO) coating, nylon is preferred as plain textile to ensure optimum coating uniformity. A large piece of bamboo nylon textile is coated by dipping it in a water-based graphene oxide solution with a concentration of 4 mg / ml following the application referred to as the Hummer's method in the art. After the coated fabric is preferably allowed to dry at 80°C and preferably on a hot plate, it is subjected to reduction by being immersed in a sodium borohydride solution. Following the reduction process, said large textile piece is immersed in deionized (DI) water for cleansing. This step is applied to remove any chemical residue from the fiber surface and to ensure that only reduced graphene oxide (rGO) flakes remain adhered to the textile. Then, the resulting product is carefully placed on a hot plate in a glass container to air-dry for a sufficient length of time to get rid of the remaining excess moisture. Throughout the reduction of graphene oxide (GO), a noticeable transformation occurs in the colors of the textiles and it can be observed that the textiles transition from a brown hue to a dark black hue. This color shift is a direct consequence of the removal of oxygen-containing groups from the material's surface, which brings about a significant enhancement in electrical conductivity. Thus, the alteration in textile color serves as a valuable qualitative indicator of the effectiveness of the reduction process. While thermal reduction can be used as a production method according to an embodiment of the invention, it is important to consider the risk of textile disintegration at elevated temperatures. However, in preferred embodiments of the invention, the approach of coating with a graphene GO (graphene oxide) solution followed by a chemical reduction is preferred due to its greater appeal in terms of production.

[0040] As a result of this process, in said large fabric piece, after obtaining a resistance of in the range of about 0.5 kQ to 1 kQ upon measuring 1 cm square fabric pieces from both sides, small pieces are created in a required number to prepare dry electrodes for integration into the armband. The parts which can be obtained from this piece of fabric must be adapted for human dimensions. According to an embodiment, these parts acting as electrodes are formed in pieces of 1 .5 centimeters by 2 centimeters in size.

[0041] According to an embodiment of the invention, rubber isolation tapes are adhered using an adhesive, preferably a textile adhesive, just beneath the conductive textiles to establish a sturdy support and ensure the necessary pressure when in contact with the skin. In addition, snap fasteners are used to secure the dry electrodes in place. In an of the embodiments of the invention, thin metal wires with a diameter of 250 micrometers can be soldered to establish the connection with these metal snap fasteners The resulting electrodes have a standalone and regular shape and can be replaced if damaged, while also being mountable to the designated locations on the armband form biopotential acquisition device (20).

[0042] The primary component (21), which is the upper arm component of the armband, consists of a dual-layer design. The first layer, in direct contact with the skin, comprises two electrodes: the reference electrode and the first differential electrode (the second differential electrode which enables potential difference measurements, is disposed at the tip of the index finger). The second layer, the outermost one, acts as a protective cover. In this design, the biopotential circuit is arranged between two layers and the upper layer conceals this circuit for aesthetic appeal. This clever construction creates a stylish and seamless look by ensuring that no cables or circuits are visible externally, as well as enabling a comfortable use which does not affect daily life.

[0043] According to an embodiment of the invention, a biopotential circuit is used in the primary component (21). This biopotential circuit is envisaged to comprise the features of information processing, memory, wired-wireless connection, input and output. According to an embodiment, this biopotential circuit can be configured to be an open-source data acquisition unit equipped with no additional mechanical amplification and filtering. Alternatives present in the art for this purpose include applications and solutions such as OpenBCI's Cyton Board, but it is also possible to use a circuit comprising multiple channel inputs, particularly configured for biopotential acquisition. According to particular applications, the raw data obtained through said biopotential circuit can first be stored as .txt files in a local server and then be processed and compiled using custom-written scripts.

[0044] According to an embodiment of the invention, the fingertip electrode is integrated into the glove component (22) of the armband during the assembly thereof. For this integration, the fingertip fabric is cut horizontally and opened to allow insertion of a metal fastener beneath the outer layer. There are embodiments in which an additional thin layer of fabric is sewn beneath this outer layer to ensure that the user (10) would not experience any discomfort from the wiring, and such embodiments can be considered as improvements enhancing comfort and thus usability. Said additional layer is configured to extend at least from the fingertip housing the electrode to the electronic portions disposed in the primary component (21) associated with the upper arm, and this layer constitutes the connection component, which is the tertiary component (23).

[0045] According to an embodiment of the invention, said biopotential circuit is envisaged to perform particular filtering and signal processing actions. According to an example, as an action to improve the signal-to-noise ratio, powerline interference noise can be eliminated at 50 Hz and 100 Hz from the normalized ECG signals. This can be achieved by applying a notch filter with a Q-factor of 35. Subsequently, a bandpass filter can be implemented to effectively filter out noise components which are below 5 Hz or above 50 Hz. A fifth-order moving average filter can be used to improve the overall quality of the signal.

[0046] The performance improvement of graphene textile electrodes over conventional Ag / AgCI electrodes in signal-to-noise ratio is quantitatively demonstrable. Comparison of the signals received with Ag / AgCI and graphene textile electrodes reveals that, while known Ag / AgCI electrodes yield an SNR of 14.76 dB with RMS noise of 75.82 / JV, graphene textile electrodes are superior to conventional electrodes as they exhibit an SNR of 15.91 dB SNR with RMS noise of 67.93 nV. Here, although electrode placement may justify some of the marginal dB differences, such numbers are a numerical indicator of the graphene textile ECG paradigm of the present invention being a strong alternative to Ag / AgCI electrodes, which have been accepted as the gold standard so far.

[0047] The armband developed and proposed according to the present invention is characterized by a device (20) adapted not only for surface-level heart rate measurements in a single-ECG trace, but also, and more importantly, a mobile biopotential measurement system exhibiting 12-lead ECG trace capabilities, which can be worn on a certain region of a body, housing a minimum number of fabric electrodes and electronic circuits, and enabling a userto optionally capture various biopotentials such as ECG, EOG, or EEG from the regions where the electrodes are located, by touching the electrodes on the fingers to his / her own body, or, in another embodiment, to the body of another living being by positioning the electrodes appropriately.

[0048] According to an embodiment, the disclosed invention is a wearable electrocardiogram system comprising an integrated glove component equipped with a mobile exploring electrode arranged at the tip of the index finger. This innovative biopotential acquisition approach allows the user (10) to place the electrode anywhere within the reach of his / her body. While conventional textile-based wearable applications primarily only focus on singlechannel ECG measurements (namely, LEAD I, II, III), the innovative paradigm of the present invention makes it possible to capture multi-channel ECG data reliably and accurately. Figure 6 displays the graphs of measurements taken with graphene-based electrodes (41) and conventional Ag / AgCl-based electrodes (42) at conventional chest electrode positions V1 to V6 (40a-f), and a great qualitative similarity is observed in terms of signal-to-noise ratios and biopotential quality. Referring to Figures 7 and 8, the relationships of Ag / AgCI electrode curves (31) and graphene electrode curves (32) with and without Wilson Common Terminal configuration represent such similarity.

[0049] According to particular embodiments, the invention may envisage a few modifications in the number of electrodes on the glove unit. According to an embodiment, there are two electrodes in the glove unit and said two electrodes allow measurements to be taken between any two points on a body other than the user's (10) own. In this case, said embodiment makes it possible to acquire biopotential data from another body.

[0050] According to other particular embodiments, the invention may be used for interaction between multiple living beings or a living being and a computer. According to a particular embodiment of the invention, the graphene electrode associated with the glove component can be used to acquire biopotential data of another living being, e.g. a subject other than the user (10) who has and wears the primary (21) and secondary (22) components on his / her body. For example, the user 10 may obtain a measurement by pressing the electrode on the glove component onto a related position on the chest of another person from whom the electrocardiogram is sought to be acquired. This may be a human, as well as an animal. For this, electrodes would be touched in favorable configurations to obtain biopotential to the extent dictated by the physiological requirements and constraints of the animal. It would thereby be possible to also record the biopotentials of a being other than the user (10).

[0051] Various embodiments of the invention may include biopotential acquisition from different living beings to the extent described above. For example, in case it is required to acquire an electrocardiogram from a subject as part of a polygraph test, this data can be collected using the electrode on the glove component of the present invention.

[0052] In various other embodiments of the invention, said biopotential circuit comprises particular additional functionalities. For example, according to an embodiment, the biopotential circuit may be configured to provide continuous data exchange with a remote computer / machine and to establish a wired or wireless connection for this purpose. Moreover, it may be configured to share in real time the biopotential data it continuously obtains throughout this connection, with said remote computer / machine. This remote machine may be to a braincomputer interface or a human-machine interaction device, or it may be configured to regularly feed biopotential data to enable the present invention to be used with augmented / artificial reality applications.

[0053] According to an embodiment of the invention, a wearable biopotential acquisition device (20) is proposed, comprising a primary component (21) and a secondary component (22), textile electrodes disposed in said components (21 , 22) and a connection component (23) capable of connecting said components. According to an embodiment, said primary component (21) is textile armband, preferably having a rectangular shape, adapted to be applied to the upper arm of a user (10). According to at least one embodiment, said secondary component (22) is a textile in the form of a glove adapted to be applied to the hand of a user (10), wherein the textile forming said secondary component (22) comprises multiple finger units creating a glove form and a graphene electrode associated with at least one of said finger units, and the preferably rectangular textile armband constituting said primary component (21) comprises two graphene electrodes and a data processing unit.

[0054] According to an embodiment of the invention, said data processing unit is configured to implement at least one signal-to-noise ratio improvement application.

[0055] According to an embodiment of the invention, the main material of the primary (21), secondary (22) and connection (23) components is selected from the group comprising cotton fabric, bamboo fabric, and polyester fabric.

[0056] According to an embodiment of the invention, the resistance of said graphene electrodes is in the range of 0.5 kQ to 1 kQ.

[0057] According to an embodiment of the invention, said secondary component (22) comprises at least one second graphene electrode associated with another finger unit.

[0058] According to an embodiment of the invention, said data processing unit is configured to establish a wired or wireless connection with a remote computer. According to at least one embodiment, said data processing unit is configured to exchange biopotential data in realtime via a wired or wireless connection with a remote computer.

Claims

CLAIMS1) A wearable biopotential acquisition device (20) comprising a primary component (21) and a secondary component (22), textile electrodes disposed in said components (21 , 22) and a connection component (23) capable of connecting said components, characterized in that: said primary component (21) is a textile armband, preferably having a rectangular shape, adapted to be applied to the upper arm of a user (10), said secondary component (22) is a textile in the form of a glove adapted to be applied to the hand of a user (10), the textile in the form of a glove constituting said secondary component (22) comprises multiple finger units creating a glove form and a graphene electrode associated with at least one of said finger units, and the preferably rectangular textile armband constituting the primary component (21) comprises two graphene electrodes and a data processing unit.2) A wearable biopotential acquisition device (20) according to claim 1 , wherein said data processing unit is configured to implement at least one signal-to-noise ratio improvement application.3) A wearable biopotential acquisition device (20) according to claim 1 , wherein the main material of the primary (21), secondary (22) and connection (23) components is selected from the group comprising cotton fabric, bamboo fabric, and polyester fabric.4) A wearable biopotential acquisition device (20) according to any one of the preceding claims, wherein said graphene electrodes have a resistance in the range of 0.5 kQ to 1 kQ.5) A wearable biopotential acquisition device (20) according to any one of the preceding claims, wherein said secondary component (22) comprises at least one second graphene electrode associated with another finger unit.6) A wearable biopotential acquisition device (20) according to any one of the preceding claims, wherein said data processing unit is configured to establish a wired or wireless connection with a remote computer.7) A wearable biopotential acquisition device (20) according to claim 6, wherein said data processing unit is configured to exchange biopotential data in real-time via a wired or wireless connection with a remote computer.

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