SENSOR PLATFORM AND METHOD OF PREPARING THE SAME

Provided is a sensor platform and a method of preparing the same. The sensor platform may include a hydrogel sheet comprising a net structure; an electrolyte applied to the net structure; and a plurality of electrodes disposed on the hydrogel sheet.

DETAILED DESCRIPTION

FIG. 1is a diagram illustrating an example of a sensor platform100. Referring toFIG. 1, the sensor platform100may include a net structure110, a hydrogel sheet130including an electrolyte120, and a plurality of electrodes140. The net structure110may support the electrolyte120, and may include a material having an insulating property. The net structure110may have a shape that allows ions to travel in a vertical direction with respect to the plane of the hydrogel sheet130and to disallow ions to travel in a horizontal direction with respect to the plane of the hydrogel sheet130. As shown inFIG. 1, the net structure110may be in the form of a rectangular grid. However, the net structure110is not limited to a specific shape, and may include any other shape, such as, for example, a triangular shape, a pentagonal shape, a hexagonal shape, and a circular shape. The net structure110may be made from a member, a fabric, or a mesh having a desired shape. For example, the net structure110may be prepared by printing a micro-cell pattern of a wax or an elastomer on a non-woven fabric, followed by transcription using photopolymerization. Due to a shape of the net structure110, a conductive path may be formed in the vertical direction and electrical isolation may be provided in the horizontal direction to prevent ions from migrating in the horizontal direction with respect to the plane of the hydrogel sheet130. The net structure110may have a non-ionic conductivity to limit an ionic conduction in the horizontal direction with respect to the plane of the hydrogel sheet130, however, the net structure110is not limited in this regard.

The hydrogel sheet130may contain moisture and electrolyte120, and the hydrogel sheet130may be prepared by polymerization of a polymer of high biocompatibility. A hydrophilic polymer, which is used to prepare the hydrogel sheet130may be a natural polymer and may include, but is not limited to, at least one selected from the group consisting of collagen, gelatin, fibril, alginic acid, hyaluronic acid, chitosan, or dextran. A hydrophilic polymer may also be a synthetic polymer and may include, but is not limited to, at least one selected from the group consisting of polyethyleneglycol, poly2-hydroxyethyl methacrylate (PH EMA), poly(N,N-ethylaminoethyl methacrylate), polyacrylic acid (PAAc), polylactide (PLC), polyglycolide (PGA), polycaprolactone (PCL), poly(caprolactonelactide) random copolymer (PCLA), poly(glycolide-co-ε-caprolactone) random copolymer (PCGA), poly(lactic-co-glycolic acid) random copolymer (PLGA), or polyacrylamide.

The electrolyte120, as a biocompatible electrolyte, may include, but is not limited to, at least one selected from the group consisting of potassium chloride (KCl), sodium chloride (NaCl), sodium sulfate (Na2SO4), lithium perchlorate (LiClO4), potassium sulfate (K2SO4), lithium chloride (LiCl), potassium nitrate (KNO3), sodium nitrate (NaNO3), lithium sulfate (Li2SO4), lithium nitrate (LiNO3), sodium perchlorate (NaClO4), or potassium perchlorate (KClO4). The plurality of electrodes140may include, but is not limited to, at least one selected from the group consisting of a metal, a conductive metallic oxide, or a conductive polymer.

The hydrogel sheet130may have an anisotropic ionic conductivity. To transmit bioelectrical signals in the vertical direction effectively, the anisotropic ionic conductivity may be an ability to move ions in the vertical direction of the hydrogel sheet130, while blocking ion movement in the horizontal direction of the hydrogel sheet130.

The anisotropic ionic conductivity may represent impedance less than or equal to 2 kiloohms (kohm) at 10 hertz (Hz) in the vertical direction with respect to the plane of the hydrogel sheet 130 and impedance greater or equal to 10 kohms at 10 Hz in the horizontal direction with respect to the plane of the hydrogel sheet130, when measured between electrodes arranged at a spacing greater than or equal to 5 centimeters (cm), however, the anisotropic ionic conductivity is not limited in this regard. Impedance in a particular direction may be a factor for determining an ionic conductivity. When impedance in the vertical direction with respect to the plane of the hydrogel sheet130is greater than 2 kohms at 10 Hz, a sensitivity for bio-potential measurement may be reduced due to high impedance. The Association for the Advancement of Medical Instrumentation (AAMI) recommends that impedance between two bioelectrodes for electrocardiogram (ECG) measurement be less than or equal to 2 kohms at 10 Hz when the bioelectrodes are attached such that they face one another. When impedance in the horizontal direction with respect to the plane of the hydrogel sheet130is less than 10 kohms at 10 Hz, an electrical shunt may be generated between the two points intended to measure a bio-potential, and may consequently produce an error in the bio-potential measurement.

Accordingly, a high ionic conductivity in the vertical direction with respect to the plane of the hydrogel sheet130and a low ionic conductivity in the horizontal direction with respect to the plane of the hydrogel sheet130may be achieved. The hydrogel sheet130may be attached to a bioelectrical signal measurement device without conducting a special alignment between the hydrogel sheet130and the device, to provide an electrical access over various regions of the human body.

FIGS. 2A and 2Bare diagrams illustrating examples of sensor platforms having a plurality of electrodes disposed at different locations. Although the non-exhaustive examples shown inFIGS. 2A and 2Bshow two electrodes on the hydrogel sheet130, a plurality of electrodes may be used without departing from the spirit and scope of the illustrative examples described.

As shown inFIGS. 2A and 2B, an ionic conductivity is high, at each location, in the vertical direction and is low in the horizontal direction with respect to the plane of the hydrogel sheet130. Thus, even when the plurality of electrodes140are disposed at arbitrary locations in a disordered arrangement on the hydrogel sheet130, bioelectrical signals may be measured at a plurality of regions on a human body without causing an electrical interference between the electrodes140. Unlike a conventional hydrogel sheet, which is prepared individually in alignment with an array of electrodes, the hydrogel sheet130may be applied irrespective of placement of electrodes. Also, the hydrogel sheet130may have a simple structure, making it easy to produce a large area hydrogel sheet. The hydrogel sheet130may also be tailored to an appropriate size and may be applicable irrespective of a type of a bioelectrical signal measurement system.

The hydrogel sheet130may be flexible so as not to cause inconvenience when attached to the human body, however, other types of hydrogel sheets may be used without departing from the spirit and scope of the illustrative examples described.

The hydrogel sheet130may have an adhesive strength to prevent noise due to poor adhesion of the hydrogel sheet130to the human body when the hydrogel sheet130transmits a bioelectrical signal. Also, the adhesive strength of the hydrogel sheet130may be such that it avoids skin damage, pain associated with detachment, and cell death in a skin after long-term application of the hydrogel sheet130. The hydrogel sheet130may have an adhesive strength to the skin greater than or equal to a predetermined level, which does not require the use of a separate adhesive. The adhesive strength of the hydrogel sheet130to the skin may be greater than or equal to about 50 grams per square centimeter (g/cm2), however, other levels of adhesive strength of the hydrogel sheet130to the skin may be used without departing from the spirit and scope of the illustrative examples described.

The sensor platform100may further include a lining to support the hydrogel sheet130. However, the sensor platform100may be used without a lining without departing from the spirit and scope of the illustrative examples described. The lining may protect a surface of the hydrogel sheet130, and may be removed before attaching the hydrogel sheet130to the human body.

FIG. 3is a diagram illustrating an example of a sensor platform200. Referring toFIG. 3, the sensor platform200may include conductive particles210, a hydrogel sheet230including an electrolyte220, and a plurality of electrodes240.

The conductive particles210may allow an ionic conduction in a vertical direction with respect to a plane of the hydrogel sheet230, however, the illustrative examples described are not limited in this regard. The conductive particles210may have an anisotropic ionic conductivity due to a high-density arrangement in the vertical direction with respect to the plane of the hydrogel sheet230.

The conductive particles210may include, but are not limited to, a non-polarizable metal. The non-polarizable metal may include, but is not limited to, metals in Group 1, metals in Group 2, metals in Group 3, mixtures of one or more of these metals, and alloys of one or more of these metals with carbon, silicon, boron, and other metals. The conductive particles210may also include, but are not limited to, a valuable metal such as, for example, silver/silver chloride (Ag/AgCl) or gold (Au), stainless steel, and tungsten. The conductive particles210may also include, but are not limited to, a metal and an insoluble metallic salt of the metal. The conductive particles210may also include, but are not limited to, a non-polarizable metal and an oxide or insoluble metallic salt of the metal. The conductive particles210may also correspond to a core-shell particle, where the core may include a non-polarizable metal and the shell may include an oxide or insoluble metallic salt of the metal. The conductive particles210may also include, but are not limited to, a magnetic metal. When the conductive particles210includes a magnetic metal, vertical arrangement may be enabled, i.e., the conductive particles210may allow an ionic conduction in a vertical direction with respect to a plane of the hydrogel sheet230.

The conductive particles210are not limited to a particular particle as long as the particle has a diameter in a range of about 1 nanometer (nm) to 1,000 micrometer (pm). In another non-exhaustive example, the diameter of the conductive particles210may be about 2 nm to 100 μm, and may correspond to, for example, a particle of a metallic material, a magnetic material, or a magnetic alloy. The metallic material may include, but is not limited to, at least one selected from the group consisting of platinum (Pt), palladium (Pd), Ag, copper (Cu), and Au.

The magnetic material may include, but is not limited to, at least one selected from the group consisting of cobalt (Co), iron (Fe), nickel (Ni), manganese (Mn), gadolinium (Gd), molybdenum (Mo), MM′2O4, and MxOyin which each of M and M′ denotes, independently, Co, Fe, Ni, Mn, zinc (Zn), Gd, or Cr, 0<x=3, and 0<y=5.

The magnetic alloy may include, but is not limited to, at least one selected from the group consisting of cobalt copper (CoCu), cobalt platinum (CoPt), iron platinum (FePt), cobalt samarium (CoSm), nickel iron (NiFe), or nickel iron cobalt (NiFeCo).

The hydrogel sheet230and the electrolyte220may correspond to the hydrogel sheet130and the electrolyte120, respectively. The description of hydrogel sheet130and the electrolyte120is also applicable to the hydrogel sheet230and the electrolyte220, respectively, and thus will not be repeated here.

Similar to the sensor platform including the net structure, the sensor platform230including the conductive particles220may enable measurement of a bioelectrical signal at a plurality of locations on a human body without causing an electrical interference between electrodes. Unlike a conventional hydrogel sheet, which is prepared individually in alignment with an array of electrodes, the hydrogel sheet230may be applied irrespective of placement of electrodes. Also, the hydrogel sheet230may have a simple structure, making it easy to produce a large area hydrogel sheet. The hydrogel sheet230may also be tailored to an appropriate size and may be applicable irrespective of a type of the bioelectrical signal measurement system.

The hydrogel sheet230may be so flexible not to cause inconvenience when attached to the human body, however, other types of hydrogel sheets may be used without departing from the spirit and scope of the illustrative examples described.

The hydrogel sheet230may have an anisotropic ionic conductivity and adhesive strength similar to that of hydrogel sheet130. The anisotropic ionic conductivity and adhesive strength of hydrogel sheet130are described above, and thus will not be repeated here. The sensor platform200may further include a lining to support the hydrogel sheet230. The lining for sensor platform200may be similar to the lining for sensor platform100, which is described above, and thus will not be repeated here.

FIG. 4is a diagram illustrating an example of a method of preparing a sensor platform. The operations inFIG. 4may be performed in the sequence and manner as shown, although the order of some operations may be changed or some of the operations omitted without departing from the spirit and scope of the illustrative examples described. Many of the operations shown inFIG. 4may be performed in parallel or concurrently. The description ofFIGS. 1-3is also applicable toFIG. 4, and thus will not be repeated here.

Referring toFIG. 4, in410, a net structure may be disposed on a lining. The net structure may be disposed on the lining to support the hydrogel sheet on the lining and to protect a surface of the hydrogel sheet.

In420, a hydrogel sheet including the net structure may be formed by applying a mixed solution including an electrolyte onto the lining such that the electrolyte is disposed among the net structure. The mixed solution including the electrolyte may include a biocompatible electrolyte, a monomer, a cross-linker, and a photoinitiator. In a non-exhaustive example, the biocompatible electrolyte, the monomer, the cross-linker, and the photoinitiator may be added to the mixed solution before introducing the mixed solution onto the lining.

The cross-linker may be used to prepare a hydrogel sheet having appropriate mechanical properties, such as, for example, a desired tensile strength. The cross-linker may include, but is not limited to, a compound having an aldehyde group at a terminal, for example, polyaldehydes such as ethylene glycol dimethyl acrylate, triethanolamine (TEOA), glutaraldehyde, dialdehyde starch, and succinate aldehyde.

The photoinitiator may be used to induce the photopolymerization of the monomer, and may include, but is not limited to, 2,2-dimethoxy-2-phenylacetophenone (DMPA), 2-hydroxy-2-methylpropipphenone (HOMPP), and Irgacure 2959.

The mixed solution including the electrolyte may further include a chain extender, and the chain extender may include, but is not limited to, hexamethylenediamine, m-phenylenediamine, and combinations thereof.

In430, the hydrogel sheet may be cured. The curing may be carried out using thermal cure or ultraviolet (UV) cure.

In440, the plurality of electrodes may be formed on the hydrogel sheet. The plurality of electrodes may be disposed at an arbitrary location, rather than at a uniform spacing, to acquire a bioelectrical signal stably irrespective of placement of the electrodes.

FIG. 5is a diagram illustrating an example of a method of preparing a sensor platform. The operations inFIG. 5may be performed in the sequence and manner as shown, although the order of some operations may be changed or some of the operations omitted without departing from the spirit and scope of the illustrative examples described. Many of the operations shown inFIG. 5may be performed in parallel or concurrently. The description ofFIGS. 1-4is also applicable toFIG. 5, and thus will not be repeated here.

Referring toFIG. 5, in510, a mixed solution including an electrolyte with a conductive particles may be prepared by mixing the mixed solution including the electrolyte with the conductive particles.

The mixed solution including the electrolyte may include, but is not limited to, a biocompatible electrolyte, a monomer, a cross-linker, and a photoinitiator.

In520, the hydrogel sheet may be formed by applying the mixed solution including the conductive particles onto the lining.

In530, the conductive particles may be arranged in the vertical direction with respect to the plane of the hydrogel sheet. As a non-exhaustive example, when the conductive particles includes a magnetic metal, the conductive particles may be arranged in the vertical direction with respect to the plane of the hydrogel sheet in the presence of a magnetic field formed using magnetic properties.

In540, the applied mixed solution may be cured. The curing may be carried out using thermal cure or UV cure.

In550, a plurality of electrodes may be formed on the hydrogel sheet. The plurality of electrodes may be disposed at an arbitrary location, rather than at a uniform spacing, to acquire a bioelectrical signal stably irrespective of placement of the electrodes.

FIG. 6is a diagram illustrating an example of use of a sensor platform in a biosignal measurement system. Referring toFIG. 6, the biosignal measurement system may be formed by disposing a sensor platform300on a skin310and by coupling a biosignal measurement device320onto the sensor platform300. The sensor platform300may correspond to a sensor platform including a net structure according to a non-exhaustive example, and a sensor platform including a conductive particles according to another non-exhaustive example. The following non-exhaustive examples are only provided for illustrative purposes only and do not limit the scope of the disclosure in any way.

In a non-exhaustive example, a net structure is placed on a lining, and a mixed solution including a monomer, a cross-linker, a photoinitiator, a moisturizer, and water is applied onto the net structure. A hydrogel sheet including the net structure is formed after removing the excess mixed solution. The excess mixed solution is removed by rolling a roller over the applied mixed solution and another lining is placed on the mixed solution. The prepared hydrogel sheet is placed in a UV curer and cured for fifteen minutes.

A biosignal measurement device is prepared by contacting a flexible printed circuit board (FPCB) having three electrode patterns with the prepared hydrogel sheet at both sides. Using the prepared biosignal measurement device, impedance between the electrodes is measured.

FIG. 7is a diagram illustrating an example of impedance properties of a biosignal measurement device with three electrodes arranged at a spacing of 5 cm. When an electrode for testing was adhered to an opposite surface of the hydrogel sheet for each electrode of the sensor platform, it was found that impedance between each electrode pair was 200 ohms at 10 Hz sufficiently lower than AAMI standard of 2 kohms. Also, it was found that impedance between adjacent electrodes on the same horizontal plane included in the sensor platform was 20 times or more higher at 1 Hz and 100 times or more higher at 10 Hz than impedance between electrodes facing one another. It was found from this impedance difference that the hydrogel sheet had an anisotropic ionic conductivity.

In another non-exhaustive example, a mixed solution including conductive particles is prepared by mixing a mixed solution including a monomer, a cross-linker, a photoinitiator, a moisturizer, and water, with particles in which silver chloride is formed on a surface of a silver-plated nickel particles. The mixed solution including the conductive particles is applied on a lining. A hydrogel sheet is formed after removing an excess mixed solution. The excess mixed solution is removed by rolling a roller over the applied mixed solution with another lining put on the mixed solution. The particles in which silver chloride are formed on the surface of the silver-plated nickel particles are arranged in a vertical direction with respect to a plane of the hydrogel sheet. The hydrogel sheet is placed in a UV curer and cured for fifteen minutes.

Impedance of the biosignal measurement device formed from the hydrogel sheet is measured. Impedance between electrodes facing one another was 220 ohms at 10 Hz, sufficiently lower than the AAMI standard of 2 kohms. Also, it was found that impedance between adjacent electrodes on the same horizontal plane was 18 times or more higher at 1 Hz and 120 times or more higher at 10 Hz than impedance between electrodes facing one another. It was also found from this impedance difference that the hydrogel sheet including the conductive particles had an anisotropic ionic conductivity of an effective level.