Bio-based Ultrathin Melanin-Silk Nanofiber Electronic Device with Carbon Nanomaterial Coating for Multi-Signal Applications

Abstract

The present invention applies melanin-introduced silk nanofibers to a skin-attachable electronic device, enabling seamless bonding with the skin for health monitoring and medical applications. The electronic device is a thin, lightweight, and highly breathable device that attaches comfortably to the skin without causing irritation. Unlike conventional rigid probes, this flexible and skin-friendly electronic device platform can continuously and non-invasively track key biological signals, including skin moisture status and electrophysiological activity, making it ideal for real-time diagnosis and personalized healthcare.

Description

Technology Field

[0001] The present invention relates to a biomaterial-based ultrathin melanin-silk nanofiber electronic device with a carbon nanomaterial coating for multi-signal applications. Background Technology

[0003] Extensive research is being conducted on epidermal electronic systems used for the detection of bioelectronic signals and drug delivery for human-machine interface-based personalized healthcare. Furthermore, studies are underway to utilize these devices in multifunctional bio-applications that feature minimal invasiveness due to mechanical deformation of biological tissues, biocompatibility, and stable electrical performance.

[0004] Epidermal electronic systems can provide advantages in clinical diagnosis, treatment, and human-machine interfaces, and have the advantage of being able to operate in a real-time, continuous, and non-invasive manner.

[0005] To date, these epidermal electronic devices have been manufactured using flexible polymer substrates as an alternative to rigid and brittle materials that are difficult to apply in vivo. However, there are limitations in meeting the demand for low-cost, biocompatible, deformable, and skin-type-improving systems.

[0006] To address these issues, research on skin electronic devices manufactured using materials with excellent biocompatibility is actively underway. However, the technology to utilize these materials as active materials by imparting semiconductor properties to their fundamentally electrically insulating characteristics has not yet been realized.

[0007] Korean Patent Publication No. 10-2020-0075720 is a patent relating to an electronic device attachable to the skin and a method for manufacturing the same. However, the said patent uses a polymer material as a flexible material and does not describe an electronic device for skin attachment using a material with excellent biocompatibility. Furthermore, it does not describe the imparting of the aforementioned semiconductor properties. The problem to be solved

[0009] The present invention applies melanin-introduced silk nanofibers to a skin-attachable electronic device, enabling seamless bonding with the skin for health monitoring and medical applications. The electronic device is a thin, lightweight, and highly breathable device that attaches comfortably to the skin without causing irritation. Unlike conventional rigid probes, the flexible and skin-friendly electronic device can continuously and non-invasively track key biological signals, including skin moisture status and electrophysiological activity, making it ideal for real-time diagnosis and personalized healthcare. means of solving the problem

[0011] The present invention comprises a support layer including silk nanofibers; and

[0012] It includes a carbon nanomaterial layer formed on the above-mentioned support layer,

[0013] The present invention provides an electronic device for skin attachment in which melanin is distributed on the surface and / or internal matrix of the above silk nanofiber.

[0015] In addition, the present invention comprises the step of forming nanofibers by electrospinning a silk solution;

[0016] A step of forming a support layer by immersing the above nanofibers in a melanin solution; and

[0017] A method for manufacturing an electronic device for skin attachment is provided, comprising the step of forming a carbon nanomaterial layer by coating a carbon nanomaterial on the above-mentioned support layer. Effects of the invention

[0019] The skin-attachable electronic device according to the present invention is an innovative wearable bioelectronic platform that enables advancements in non-invasive diagnostic, human-machine interaction, and therapeutic applications, and can provide continuous real-time health monitoring while seamlessly aligning with biological, mechanical, and electrical properties.

[0020] The ultra-thin and porous silk nanofiber mat for skin-attachable electronic devices offers superior water vapor permeability compared to commercial bandages, allowing it to maintain a tight fit without skin irritation even during prolonged use. By combining silk nanofibers, melanin, and graphene, a multifunctional electronic device platform is realized, which enables energy harvesting utilizing the triboelectric properties of silk nanofibers, respiration sensor functions, and electrophysiological signal measurement with a high signal-to-noise ratio (SNR).

[0021] These electronic devices possess multifunctional characteristics and can provide functions such as monitoring skin moisture status through changes in skin impedance, detecting ultraviolet rays through changes in photoconductivity, and generating energy using triboelectric nanogenerator (TENG) technology.

[0022] Specifically, it is utilized as an advanced wearable medical device capable of continuous health monitoring, early diagnosis of diseases, and real-time therapeutic intervention, and can be applied to prosthetic limbs, robotics, and augmented reality through seamless communication between biological systems and electronic devices. Additionally, it can be applied in the sports and fitness fields to monitor hydration status, electrolyte balance, and physical performance during activities. Furthermore, it can be applied as a wearable sensor utilizing sensitivity to changes in hydration and UV exposure, and can enhance the sustainability of portable devices by expanding energy harvesting capabilities to power low-power wearable electronic devices. Brief explanation of the drawing

[0024] Figure 1 shows the fabrication process of an electronic device for skin attachment. Figure 2 shows the change in current according to changes in melanin concentration and immersion time. Figure 3 shows the effect of temperature while melanin is doped into silk nanofibers. Figure 4 shows an SEM image of an electronic device for skin attachment. Figure 5 shows the results of measuring the electrical conductivity of an electronic device for skin attachment. Figure 6 shows the FTIR spectrum of the melanin-introduced SNF mat as the melanin concentration increases. Figure 7 shows the FTIR spectra of an untreated SNF mat, a melanin-introduced SNF mat, and a graphene / melanin-introduced SNF mat. Figure 8 shows stress-strain curves showing the maximum tensile strength, tensile modulus, and elongation at fracture of an untreated SNF mat, a melanin-introduced SNF mat, and a graphene / melanin-introduced SNF mat. Figure 9 shows the moisture loss and the resulting water vapor permeability when air permeability is investigated using various membranes. Figure 10 is a schematic diagram of measuring skin impedance while the electronic irradiation is attached to pig skin, showing the measurement results when the pig skin is in a dry state and a wet state, respectively. Figure 11 shows the photoresponse characteristics of an electronic device according to UV LED power density. Figure 12 is a schematic diagram illustrating the triboelectric mechanism in a graphene / melamine-introduced SNF mat. Figure 13 shows the open-circuit voltage (Voc) and short-circuit current (Isc) of a graphene / melamine-introduced SNF mat. Figure 14 shows the measurement results of the average voltage and power density of a graphene / melamine-introduced SNF mat according to various resistances. Figure 15 shows the current-time (CT) curve of the current changing as humidity increases in a melanin-introduced SNF mat-based humidity sensor. Figure 16 shows a schematic diagram of a mask integrated with a melanin-introduced SNF mat for respiration monitoring, along with a humidity sensing mechanism. Additionally, current-time (CT) curves were recorded when exhaling and inhaling using the mask. Figure 17 shows electrocardiogram (ECG) signals comparing an electronic device platform and a commercial gel electrode in a resting state and after physical activity. Specific details for implementing the invention

[0025] Throughout the invention, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0026] Throughout the invention, the description "A and / or B" means "A or B, or A and B".

[0027] The present invention comprises a support layer including silk nanofibers; and

[0028] The present invention relates to an electronic device for skin attachment comprising a carbon nanomaterial layer formed on the above-described support layer. Melanin is distributed on the surface and / or internal matrix of the silk nanofiber.

[0029] The skin-attachable electronic device of the present invention is an ultra-thin and flexible electronic device capable of detecting, transmitting, and / or processing biosignals by being directly attached to the surface of the skin. The electronic device is a multi-functional platform capable of simultaneously performing humidity detection and electrophysiological monitoring, and can be applied to next-generation biomedical and wearable healthcare applications. The electronic device according to the present invention is designed to conform to the curves and fine movements of the skin, minimizes foreign body sensation or mechanical irritation even when worn for a long time, and can be used by being directly attached to the skin without a separate strap or fastening means.

[0030] The electronic device of the present invention may also be referred to as an electronic tattoo due to its thin and flexible characteristics.

[0032] Hereinafter, the skin-attachable electronic device of the present invention will be described in more detail.

[0033] In the present invention, the support layer is a layer that comes into contact with and adheres to the skin, and comprises silk nanofibers. The silk nanofibers can provide strong adhesion, biocompatibility, and flexibility.

[0034] In one embodiment, the silk enables close adhesion to the skin by allowing hydroxyl groups (-OH) and amine groups (-NH₂) to interact with functional groups on the skin surface through van der Waals bonding. This allows the support layer to be stably attached even to uneven surfaces.

[0035] In one embodiment, the silk may be silk fibroin. Silk fibroin may be a protein extracted from the silkworm cocoon Bombyx mori. Silk fibroin is an eco-friendly material with high light transmittance and biodegradability. Due to its high glycine specific gravity, it has excellent adhesion to metals and possesses the characteristic of being able to change into various forms, such as an amorphous structure, an alpha-helix structure, and a crystalline beta-sheet structure.

[0036] In one embodiment, the silk nanofibers may have a porous matrix structure by having a plurality of silk nanofibers intertwine to form a network. In the present invention, this can be expressed as an internal matrix.

[0037] In one embodiment, the average diameter of the silk nanofiber may be 100 to 1,000 nm. The lower limit of the diameter may be 150 nm or more, or 200 nm or more, and the upper limit may be 800 nm or less, 500 nm or less, 400 nm or less, or 350 nm or less.

[0038] In the present invention, melanin is distributed on the surface and / or within the matrix of the silk nanofibers. Melanin is a natural pigment that exhibits broadband light absorption and electron-ion mixed conductivity, supporting biological functions such as photoprotection and free radical scavenging. The unique properties of melanin, such as moisture-dependent conductivity, photoconductivity, and amorphous semiconductor characteristics, make it suitable for bioelectronic applications. Melanin-incorporated silk nanofibers exhibit excellent humidity sensing capabilities as their conductivity changes significantly depending on moisture content.

[0039] In one embodiment, melanin can be introduced by penetration and diffusion into the internal matrix structure of the silk nanofiber. The melanin can be non-uniformly and locally distributed on the surface of the silk nanofiber and / or within the matrix.

[0040] In one embodiment, the weight ratio of silk nanofiber to melanin may be 1:0.0005 to 1:0.05. The lower limit of the melanin content may be 0.0005 parts by weight or more and 0.001 parts by weight or more per 1 part by weight of silk nanofiber, and the upper limit may be 0.05 or less, 0.045 or less, or 0.04 or less. Within the above content range, the effect of introducing melanin can be maximized, and aggregation does not occur.

[0041] Optimized melanin introduction concentrations can improve electrical performance while maintaining biocompatibility. Furthermore, applying melanin to electronic devices enables electrophysiological signal measurements with a signal-to-noise ratio (SNR) similar to that of commercial gel electrodes. This melanin introduction concentration is related to the optical transmittance of the electronic device, and increasing the introduction amount can increase mechanical elasticity.

[0042] In one embodiment, the thickness of the support layer may be 5 to 10 μm.

[0043] In the present invention, a carbon nanomaterial layer is formed on the support layer. Melanin improves electrical conductivity but is not sufficient for performing skin impedance measurement and electrophysiological signal measurement. Therefore, this can be supplemented by forming a carbon nanomaterial layer as an electrode material on the support.

[0044] In one embodiment, the carbon nanomaterial may be graphene or carbon nanotubes.

[0045] In one embodiment, the carbon nanomaterial may be graphene. Unlike metal-based electrodes, graphene has high electrical and thermal conductivity, which can provide reliable performance even under extreme conditions. The graphene coating can ensure stability during deformation by providing optimized electrical conductivity while maintaining skin adhesion and the ultra-thin characteristics of the electronic device.

[0046] In the present invention, through a combination of silk nanofibers, melanin, and graphene, it is possible to manufacture an electronic device that possesses excellent electrical, optical, and mechanical properties and mimics the natural properties of skin.

[0047] The carbon nanotubes can be uniformly coated on the surface of a support to form a smooth and continuous graphene layer without aggregation or coating non-uniformity. This uniform distribution plays a crucial role in maintaining stable electrical conductivity and efficient charge transfer within the silk nanofiber matrix, thereby enabling reliable electrophysiological signal detection. The resulting ultrathin electronic device offers advantages such as biocompatibility, deformability, and skin adhesion, and can overcome the limitations of existing materials, such as silver and gold nanowires (e.g., oxidation, corrosion, and high cost).

[0048] In one embodiment, the thickness of the carbon nanomaterial layer may be 20 to 25 μm. Electrical conductivity can be controlled by adjusting the coating amount of the carbon nanomaterial layer, and mechanical elasticity can be improved as the coating amount increases. Such improvement may be attributed to the excellent mechanical reinforcement effect of the carbon nanomaterial, uniform dispersion, and the formation of hydrogen bonds with the support layer.

[0049] In the present invention, the electronic device for skin attachment may have a size and shape suitable for attachment to the skin depending on the purpose of use.

[0050] The aforementioned electronic device possesses multifunctional characteristics and features excellent biocompatibility, mechanical durability, and strong skin adhesion. Being ultra-thin and highly breathable, it effectively facilitates sweat evaporation, thereby preventing skin irritation during prolonged wear. It monitors skin moisture status through changes in skin impedance, detects ultraviolet rays through changes in photoconductivity, generates energy using triboelectric nanogenerator (TENG) technology, and functions as a respiration sensor and heart rate monitor, enabling real-time health monitoring. Furthermore, its porous structure allows for sweat evaporation, which can prevent bacterial proliferation.

[0051] Furthermore, the ultrathin structure of the electronic device enhances close contact with the skin's microtopography, maximizing intermolecular interactions and enabling stable adhesion without the need for conductive gels or additional adhesives. During the initial attachment process, a small amount of water softens the nanofiber matrix to facilitate close contact with the skin; once the water evaporates, van der Waals forces act as the primary adhesion mechanism, allowing for prolonged attachment while maintaining flexibility and breathability. The electronic device can maintain a stable attachment even under mild sweating and natural skin movements, making it suitable for long-term, non-invasive bioelectronic applications.

[0053] In addition, the present invention relates to a method for manufacturing the aforementioned electronic device for skin attachment.

[0054] The skin-attachable electronic device according to the present invention can be manufactured through the following steps:

[0055] (S1) A step of forming nanofibers by electrospinning a silk solution;

[0056] (S2) A step of forming a support layer by immersing the nanofibers in a melanin solution; and

[0057] (S3) A step of forming a carbon nanomaterial layer by coating carbon nanomaterials on the support layer.

[0058] The description of the above silk, nanofibers, melanin, carbon nanomaterials, etc. is as described above in the electronic device for skin attachment.

[0059] In the present invention, step (S1) is a step of forming nanofibers by electrospinning a silk solution.

[0060] In one embodiment, the silk solution contains silk, and the silk may be silk fibroin.

[0061] In one embodiment, the solvent of the silk solution may be water. Here, water refers to water commonly used in experiments or manufacturing, and may include, for example, purified water, distilled water, ultrapure water, etc.

[0062] In one embodiment, the content of silk in the silk solution may be 2 to 10 weight% or 4 to 8 weight% relative to the silk solution.

[0063] In one embodiment, the above step may electrospun a mixed solution of a silk solution and a polymer solution. The polymer solution is used to increase the viscosity of the electrospinning solution and can impart surface tension suitable for electrospinning.

[0064] The above polymer may be selected from the group consisting of polyethylene oxide (PEO), nylon, polycarbonate, and polyurethane.

[0065] The solvent of the polymer solution may be water, formic acid, dichloromethane, dimethylformamide (DMF), or a mixture thereof. Additionally, the content of the polymer in the polymer solution may be 1 to 10 weight% or 3 to 7 weight% relative to the polymer solution.

[0066] In one embodiment, electrospinning can be performed for 1 to 10 hours or 4 to 8 hours at a voltage of 5 to 30 kV or 10 to 20 kV, a speed of 10 to 50 μL / min, and a speed of 20 to 40 μL / min. If conditions are not met, there is a problem in that nanofibers are not formed or accumulate in the nozzle and are not spun.

[0067] In the present invention, the thickness of the nanofiber can be controlled by adjusting the electrospinning time. In one embodiment, the thickness of the electrospun nanofiber may be 5 to 10 μm. If the thickness falls outside this range, the nanofiber may break or the thickness uniformity may decrease during the electrospinning process, which may reduce production efficiency.

[0068] In the present invention, step (S2) is a step of forming a support layer by immersing the nanofibers prepared in step (S1) in a melanin solution.

[0069] In one embodiment, the solvent of the melanin solution may be water, NH₄OH, or a mixture thereof.

[0070] In one embodiment, the content of melanin in the melanin solution may be 0.05 to 5 weight%. If it exceeds 5 weight%, the repulsive force decreases, causing partial aggregation and potentially limiting dispersion. Additionally, the optical transmittance of the electronic device can be controlled by adjusting the degree of melanin introduction.

[0071] In one embodiment, melanin can be uniformly introduced into the nanofibers by immersion. Specifically, melanin molecules can diffuse and be immobilized into the silk nanofiber matrix. Melanin can easily penetrate into the silk nanofiber matrix and subsequently crystallize the silk molecule bonds to stably immobilize the melanin. Specifically, crystallization of the silk nanofibers can be induced through methanol treatment after step (S2) to stably immobilize the melanin.

[0072] In one embodiment, the immersion time in the melanin solution may be 10 minutes to 36 hours, or 30 minutes to 24 hours. The level of melanin introduction can be controlled by adjusting the time.

[0073] In the present invention, step (S3) is a step of forming a carbon nanomaterial layer by coating a carbon nanomaterial on a support layer.

[0074] In one embodiment, the carbon nanomaterial may be graphene, specifically few-layered graphene.

[0075] In one embodiment, the content of carbon nanomaterial in the carbon nanomaterial solution may be 0.05 to 3 weight%.

[0076] In one embodiment, the solvent in the carbon nanomaterial solution may be water, methanol, ethanol, or a mixture thereof.

[0077] In one embodiment, the carbon nanomaterial solution may additionally include a surfactant to prevent aggregation. That is, a solution can be prepared by using a surfactant to prevent aggregation of graphene composed of several layers and then dispersing it.

[0078] The above surfactant may be sodium lauryl sulfate (SLS).

[0079] In one embodiment, a carbon nanomaterial layer can be formed by applying a carbon nanomaterial solution onto a support and then drying it.

[0080] In one embodiment, when using graphene, if the graphene layer becomes excessively thick, the air permeability of the electronic device may be reduced, so a single graphene coating may be applied. Through this, an open graphene network structure can be maintained without significantly blocking the porosity of the nanofiber. The graphene may be partially distributed as particles within the porous structure of the nanofiber.

[0082] In the present invention, by applying an optimized manufacturing method, high water vapor and oxygen permeability is provided to satisfy the essential conditions for skin-attached bioelectronic applications, while simultaneously contributing to preventing tissue irritation or discomfort.

[0084] The present invention will be explained in detail below through the following examples. However, the following examples are merely illustrative of the present invention, and the scope of the present invention is not limited to the following examples.

[0086] Examples

[0087] Figure 1 shows the process of manufacturing an electronic device for skin attachment according to the present invention.

[0089] Preparation Example 1. Fabrication of an electronic device for skin attachment

[0090] (1) Fabrication of silk nanofiber mats

[0091] First, a silk solution was prepared. Specifically, an aqueous solution of approximately 6 wt% silk pyrophosphate was prepared using silk protein extracted from the cocoon of the house silkworm (*Bombyx Mori*).

[0092] An aqueous silk fibroin solution was mixed with a 5 wt% polyethylene oxide (PEO; molecular weight 900,000, Sigma-Aldrich) solution in a 1:1 volume ratio and homogeneously mixed using a vortex mixer. The silk / PEO mixture was injected into a 10 mL Leur-lock syringe (Henke-Ject, Germany) equipped with a 25G steel needle and mounted on an electrospinning device (NanoNC, ESR200R2D, Korea). Electrospinning was performed with the needle tip positioned 15 cm away from a collection device wrapped in aluminum foil, using a glass slide attached to the collection device with Scotch tape as the substrate. The process was carried out for 6 hours at a voltage of 12 kV and a flow rate of 30 μL / min. Subsequently, the silk nanofiber mat was separated from the substrate to fabricate a flexible template.

[0094] (2) Melanin introduction

[0095] Melanin powder (Sigma Aldrich) was dissolved in a 0.15 M NH₄OH solution to prepare stable solutions of desired concentrations (0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, and 4 wt%). The silk nanofiber mat prepared in (1) was immersed in the melan solution for various times (30 minutes, 1 hour, 2 hours, 4 hours, 8 hours, 12 hours, 16 hours, 20 hours, and 24 hours) to precisely control the doping level.

[0096] After immersion, the silk nanofiber mat was treated with methanol to induce crystallization of the silk protein and insolubilize the fibers. It was air-dried at room temperature for 12 hours.

[0098] (3) Formation of a graphene coating layer

[0099] 1 mg of expanded graphite was microwaved for 30 seconds to produce worm-shaped graphene (WLG), which was then dispersed in a 33 wt% hydrogen peroxide (H₂O₂) solution and sonicated for 15 minutes. Subsequently, the dispersion was further microwaved for approximately 60 seconds to exfoliate it into hydrophobic graphene (FLG). It was then dried in a 100°C vacuum oven for 1 hour.

[0100] 1 mg of FLG was added to a solution in which 10 mg of sodium lauryl sulfate (SLS) was dissolved in 1 mL of methanol, and the mixture was sonicated for 3 hours. To increase viscosity, 5 mg of PEO was added, and the mixture was continuously stirred for 7 days. The prepared graphene ink was uniformly applied to a melanin-introduced silk nanofiber mat using a brush, and then air-dried at room temperature for 4 hours to fabricate a skin-attachable electronic device.

[0102] Hereinafter, the mat manufactured in (1) can be described as an untreated SNF mat, the mat manufactured in (2) as a melanin-introduced SNF mat, and the mat manufactured in (3) as a graphene / melanin-introduced SNF mat or an electronic device.

[0104] [characteristic]

[0105] The surface morphology and structural characteristics of the skin-attachable electronic device were analyzed using a field emission scanning electron microscope (FE-SEM; FC-SM40, Hitachi).

[0106] Chemical bonding between graphene, melanin, and SNF mats was analyzed using Fourier transform infrared spectroscopy (FTIR; Nicolet iS50, Thermo Scientific, USA).

[0107] Tensile properties were evaluated using a universal testing machine (UTM; Shimadzu, Kyoto, Japan) according to ASTM D882 at a crosshead speed of 0.1 mm / min. The size of the specimens used for the tensile test was approximately 5 mm × 30 mm.

[0108] Electrical characteristics, including IV characteristics and CT characteristics, were measured using a Keithley 2400 Source Measure Unit (SMU). To facilitate the application of electrical signals, a fine copper wire (Nilaco, CU111267) was bonded to the surface of the specimen using silver paste.

[0109] A UV LED with a wavelength of 365 nm (Thor Labs, USA) was used for light detection measurements.

[0110] Electrical impedance characteristics were analyzed using an LCR meter (4263B, Agilent Technologies, Kobe, Hyogo, Japan). Impedance was measured at different frequencies of 100 Hz, 120 Hz, 1 kHz, 10 kHz, 20 kHz, and 100 kHz. To ensure measurement accuracy, the LCR meter was calibrated according to the manufacturer's standard procedures.

[0111] Five different specimens were used for statistical analysis, and all measurements were performed at room temperature.

[0113] Experimental Example 1. Evaluation of the effect of melanin on electrical performance

[0114] The effect of melanin on the electrical performance of electronic devices was investigated.

[0115] Melanin was introduced into silk nanofibers using melanin solutions of various concentrations (0.1 wt% to 4 wt%). When the concentration of melanin exceeded 5 wt%, partial aggregation occurred in the solution due to a decrease in repulsion, which limited the uniform dispersion of melanin.

[0116] The electrical characteristics of electronic devices were evaluated according to melanin concentration during immersion times ranging from 0.5 to 24 hours. Electrical conductivity is important for improving signal sensitivity while minimizing background noise and instability. Current was measured using specimens measuring 1 cm × 1 cm, and electrical connections were formed by applying silver paste.

[0117] Figure 2 shows the change in current according to changes in melanin concentration and immersion time.

[0118] As shown in Figure 2, it can be observed that the current increases as the immersion time increases and tends to stabilize after about 20 hours. In particular, under the 24-hour immersion condition, the current increased from about 0.1 nA to about 11.4 nA as the melanin concentration increased.

[0119] Through this, it can be confirmed that an immersion time of 24 hours and a melanin concentration of 4 wt% are optimal specimen preparation conditions for securing the maximum current to improve signal acquisition performance.

[0120] In addition, Figure 3 shows that the resistance value remains constant within the error range due to the influence of temperature while immersed in the melamine solution.

[0121] The ultrathin characteristics of the electronic device were confirmed by mass measurements of 1 cm × 1 cm specimens. Specifically, the untreated SNF mat exhibited a mass of approximately 3.5 mg, the melanin-introduced SNF mat approximately 3.8 mg, and the graphene / melanin-introduced SNF mat approximately 4.1 mg, corresponding to an area density of approximately 4100 μg / cm². These values ​​are significantly lower than those of previously reported epidermal E-tattoos. Such lightweight properties can enable perceptible operation on the skin surface.

[0123] Figure 4 shows SEM images of an untreated SNF mat, a melanin-introduced SNF mat, and a graphene / melanin-introduced SNF mat.

[0124] The untreated SNF mat forms a network or matrix structure in which nanofibers with a diameter of approximately 200 to 350 nm are interconnected, and it can be confirmed that melanin is uniformly deposited within the porous matrix of the melanin-introduced SNF mat. Graphene is uniformly coated on the surface, forming a conductive layer while partially filling some pores. Cross-sectional SEM analysis confirms that the graphene / melanin-introduced SNF mat has an ultrathin thickness of approximately 30 μm.

[0125] Figure 5 shows the results of measuring the electrical conductivity of an electronic device.

[0126] The electrical conductivity was measured to be approximately 0.12 S / cm, confirming its suitability for electrical applications.

[0127] To further evaluate the skin attachment stability and adhesion strength of the electronic device, a peel test was performed by applying adhesive tape to the attached electronic device and then removing it (not shown). As a result, the electronic device remained on the skin even after multiple repetitions of attachment and peeling. This confirms strong adhesion and durability suitable for long-term monitoring.

[0128] In addition, the electronic device maintains structural and functional integrity even under mechanical deformation such as elongation, compression, and torsion, and the change in resistance over 50 repeated cycles was less than 8% (not shown). These results demonstrate that the electronic device possesses excellent stability and functionality as a bioelectronic skin system for advanced applications.

[0130] Experimental Example 2. Evaluation of Chemical Interactions of Skin-Attached Electronic Devices

[0131] The chemical interactions between graphene, melanin, and silk nanofibers were analyzed using Fourier Transform Infrared Spectroscopy (FTIR).

[0132] Figure 6 shows the FTIR spectra of a melanin-introduced SNF mat as the melanin concentration increases, and Figure 7 shows the FTIR spectra of an untreated SNF mat, a melanin-introduced SNF mat, and a graphene / melanin-introduced SNF mat.

[0133] As shown in the figure, the pure silk protein contained in the silk nanofibers exhibits several characteristic peaks as follows: approximately 3300 cm⁻¹ -¹ Broad absorption peak in the vicinity (NH stretching vibration of the amide group), approximately 1620 cm⁻¹ - ¹(Amide I, C=O stretching vibration), approx. 1515 cm - ¹(Amide II, NH bending vibration), and about 1230 cm - ¹(Amide III, CN stretching vibration).

[0134] In the case of the melanin-introduced SNF mat, no distinct new peaks were observed; however, systematic peak shifts were observed as the melanin concentration increased, suggesting that the melanin was uniformly dispersed without aggregation. These systematic peak shifts in the FTIR spectrum demonstrate that the melanin is stably attached to the SNF mat. In particular, the shift of the amide peak to a lower wavenumber region implies that the hydrogen bonding interactions between melanin and the silk fibroin matrix were strengthened.

[0135] Silk fibroin contains functional groups such as hydroxyl groups (-OH), carboxyl groups (-COOH), and amide groups (-CONH-), which can form strong hydrogen bonds with amine, hydroxyl, and carboxyl groups present in melanin. These interactions stabilize melanin within the nanofiber structure, thereby preventing the shedding of melanin even under dynamic conditions.

[0136] After graphene coating, approximately 1770 cm - ¹ and 1900 cm - An additional peak corresponding to the C=O stretching vibration was observed in ¹. In addition, due to the high concentration of graphene, the intrinsic peak of melanin was somewhat suppressed, and the shift toward lower wavenumbers suggests an interaction between the π-electron system of graphene and the aromatic group of melanin.

[0138] UV-visible (UV-vis) spectroscopy was additionally used to evaluate the binding interactions between melanin and the silk nanoparticle matrix (not shown). The untreated SNF mat exhibited light transmittance of approximately 23.7% at 400 nm (visible region) and approximately 27.4% at 800 nm (near-infrared, NIR region). When 0.1 wt% melanin was introduced, the transmittance decreased to approximately 10.9% at 400 nm and approximately 25.3% at 800 nm. As the melanin concentration increased, the transmittance decreased sharply, and for 4 wt% melanin, it decreased to approximately 0.5% at 400 nm and approximately 0.7% at 800 nm.

[0139] This significant reduction in transmittance is attributed to the light absorption characteristics of melanin, scattering by the nanofiber structure, and the optical properties of silk. These results suggest that the present platform is suitable for UV and visible light blocking applications.

[0141] Experimental Example 3. Evaluation of Mechanical Properties of Skin-Attached Electronic Devices

[0142] Tensile properties were analyzed by measuring the stress-strain curves of the untreated SNF mat, the melanin-introduced SNF mat, and the graphene / melanin-introduced SNF mat.

[0143] Figure 8 shows stress-strain curves showing the maximum tensile strength (UTS), tensile modulus (TM), and elongation at fracture of an untreated SNF mat, a melanin-introduced SNF mat, and a graphene / melanin-introduced SNF mat.

[0144] The untreated SNF mats were measured to have a UTS of 0.39 MPa and a TM of 0.51 MPa. With the introduction of melanin, UTS and TM increased, and at a melanin concentration of 4 wt%, they improved to 0.67 MPa and 1.14 MPa, respectively.

[0145] Meanwhile, elongation at break decreased as melanin concentration increased, which is because the elasticity and flexibility of the fibers were reduced due to the stiffness of melanin. Additionally, melanin aggregates formed under high-concentration conditions disrupted the molecular structure of silk, forming stress concentration points that induced premature breakage.

[0146] After graphene coating, UTS and TM increased significantly to 1.20 MPa and 4.2 MPa, respectively. This improvement is attributed to the excellent mechanical reinforcement effect of graphene, uniform dispersion, and the formation of interfacial hydrogen bonds between melanin and SNF, which improved stress distribution and reduced defects. Strong intermolecular interactions further enhanced stiffness and rigidity, resulting in a tendency for elongation at break to decrease.

[0148] For the long-term imperceptible use of electronic devices, the breathability of the device is very important and can be evaluated by measuring the water vapor transmission rate (WVTR). The WVTRs of untreated SNF mats, melanin-introduced SNF mats, and graphene / melanin-introduced SNF mats with the same thickness (approx. 30 μm) were compared with the WVTRs of commercial films such as Parafilm (thickness approx. 50 μm) and Band-Aid (thickness approx. 50 μm).

[0149] Figure 9 shows the moisture loss and the resulting WVTR when air permeability is investigated using various membranes.

[0150] Due to the introduction of melanin, the WVTR is 3191 g·m- ²·d - 2311 g·m at ¹ - ²·d - It decreased to ¹. In this regard, it is necessary to emphasize that graphene coating plays a key role in maintaining air permeability. That is, excessive deposition of graphene can impede permeability by making the structure dense.

[0151] To optimize graphene deposition on melanin-introduced SNF mats, the number of coating passes was systematically varied, with a 5-hour interval between each coating to allow the graphene ink to dry sufficiently. The WVTR of a single-coated mat was approximately 1783 g·m². - ²·d - It was measured as ¹. On the other hand, when graphene coating is repeated additionally, a denser graphene network is formed by layered stacking, and the WVTR is approximately 693 g·m - ²·d - It decreased to 1.

[0152] In particular, all WVTR values ​​of the single-coated electronic devices were measured to be higher than the WVTR of commercial band-aids. Based on this, the condition of applying a single graphene coating to the mat was selected as the optimal condition for electronic device fabrication. It is possible to maintain an open graphene network structure without significantly blocking the porosity of the nanofibers.

[0153] This optimized structure provides high water vapor and oxygen permeability, meeting the essential requirements for skin-attached bioelectronic applications while contributing to the prevention of tissue irritation or discomfort.

[0155] Experimental Example 4. Evaluation of Electrical Characteristics of Skin-Attached Electronic Devices

[0156] Based on high water vapor permeability (WVTR), excellent electrical conductivity, skin compatibility, and an ultra-thin design, the electronic device enables continuous monitoring of skin moisture status without hindering transdermal water loss or causing discomfort during prolonged use.

[0157] The humidity-dependent conductivity of melanin plays a key role in impedance measurement, making it a suitable material for detecting skin moisture levels. A schematic diagram of an electronic device attached to the skin for skin moisture monitoring is shown in FIG. 10, illustrating how it adheres closely to the skin by van der Waals forces.

[0158] The graphene layer serves as an electrode providing high electrical conductivity during use, while also contributing to improving the mechanical durability of the platform.

[0159] To evaluate the moisture sensing capability of the platform, electronic devices were attached to pig skin as models, and impedance was measured under different alternating current (AC) bias frequency conditions. As shown in the lower graph of Figure 10, impedance measurements were performed in wet and dry states.

[0160] In wet conditions, OH - and H3 + Water molecules containing O ions enhanced electrical conductivity at the electrode-skin interface, making charge transfer more efficient. Under 100 Hz conditions, the impedance of the electronic device in the wet state was measured to be 6.8 ± 1.52 kΩ, whereas in the dry state, the impedance increased significantly to 52.6 ± 5.4 kΩ due to a decrease in conductivity and capacitance. In both states, the impedance showed a tendency to decrease as the frequency increased, which is consistent with previously reported results.

[0161] In addition, the results of measuring the change in impedance over time during the skin drying process (not shown) showed a tendency for the impedance to increase, confirming that the platform can effectively detect moisture differences beneath the skin.

[0162] The negative correlation between impedance and skin moisture demonstrates that this platform has the ability to effectively monitor skin moisture status and confirms its potential for real-world applications for skin health assessment.

[0164] Experimental Example 5. Evaluation of Monitoring of Skin-Attached Electronic Devices

[0165] Due to the hygroscopic nature of melanin, environmental humidity can affect skin moisture measurement results. To ensure accurate monitoring in real-world applications, a calibration equation was derived to compensate for this influence.

[0166] To this end, electronic devices were placed on a glass slide, and impedance at 100 Hz was measured under different environmental humidity conditions. This was used as a control experiment to evaluate and correct for interference caused by environmental humidity. Subsequently, with the electronic device platform attached to pig skin maintained at a stable moisture level of approximately 40%, impedance measurements were performed while varying the ambient humidity.

[0167] The impedance value exhibited a linear relationship with relative humidity (%RH); accordingly, a correction equation (Appendix-A) was derived by applying linear regression analysis. The above correction process was configured to estimate the expected dry impedance value under each humidity condition and, based on this, compensate for the influence of environmental humidity, thereby isolating only the impedance response resulting from actual skin moisture changes.

[0168] Furthermore, the introduction of melanin extends the platform's capabilities beyond skin moisture monitoring to include ultraviolet (UV) detection, which is attributed to melanin's unique light-responsive properties. Prolonged exposure to ultraviolet rays can have adverse effects on skin health, leading to sunburn, premature aging, and an increased risk of skin cancer. By integrating melanin, the platform gains real-time UV monitoring capabilities, enabling users to track UV exposure levels and take preventive measures to protect their skin.

[0169] To evaluate this possibility, a melanin-introduced SNF mat equipped with two silver paste electrodes was exposed to an LED light source with a wavelength of 365 nm. Throughout the experiment, the size of the melanin-introduced SNF mat was maintained at 1 cm × 1 cm, and photocurrent was measured in a lateral configuration.

[0170] To evaluate the real-time response characteristics to UV irradiation, current-time (CT) curves were recorded following the repetitive on-off switching of the UV-LED. The melanin-introduced SNF mat exhibited distinct UV response characteristics, with a pronounced increase in current upon UV irradiation. Furthermore, the output current increased in proportion to the power density of the UV-LED.

[0171] The response characteristics of the melanin-SNF membrane-based photodetector were calculated using the following formula:

[0172]

[0173] Here, I_ON and I_OFF represent the current measured when the specimen is exposed to a UV LED and under dark conditions, respectively. As shown in Fig. 11, the photodetector is approximately 0.53 mW·cm² -It exhibited excellent linearity with a sensitivity of 2. This linear response implies that the melanin-introduced SNF mat-based photodetector effectively converts ultraviolet light into an electrical signal, suggesting that it is a promising candidate for flexible UV photodetector applications.

[0174] The fast response characteristics are attributed to efficient photon absorption and rapid photoexcitation of charge carriers, whereas the relatively slow recovery characteristics are attributed to environmental factors such as delays in charge recombination, surface trapping, and adsorption / desorption of molecules. Furthermore, intrinsic properties of the nanofibers such as charge mobility and surface defects, thermal effects, and the gradual relaxation process to the reference state also act as factors that extend the recovery time. These results demonstrate that the membrane has the potential to serve as a UV photodetector providing efficient charge carrier generation, linear sensitivity, and stable response characteristics, proving its suitability for various optoelectronic applications.

[0176] Figure 12 schematically shows the structure and charge generation mechanism of a triboelectric nanogenerator (TENG) using a graphene / melamine-introduced SNF mat.

[0177] To harvest energy, a TENG structure was applied comprising a PDMS film and a graphene / melamine-introduced SNF mat as the friction layer. It was observed that charge moves due to the difference in electron affinity between the PDMS and the mat upon contact, and electron movement through an external circuit is induced by the potential difference formed during the separation process. An alternating current electrical signal is generated following these repetitive contact-separation operations, confirming that mechanical stimulation can be converted into electrical energy.

[0178] Figure 13 shows the response characteristics over time of the open-circuit voltage (Voc) and short-circuit current (Isc) measured during TENG operation.

[0179] With repetitive tapping motions, Voc of several hundred volts and Isc of microamperes are generated periodically, confirming the reproducibility and stability of the output signal. This demonstrates that the graphene / melamine-incorporated SNF mat is an effective material for self-generated energy conversion and shows its potential as a self-generating energy harvesting platform capable of generating stable electrical output without an external power source.

[0180] In addition, Figure 14 shows the average open-circuit voltage and output power density characteristics of the TENG according to changes in external load resistance.

[0181] As the load resistance increases, the output voltage tends to increase and then saturate in the high-resistance region, and it can be confirmed that the maximum power density appears under specific load conditions. In this system, a maximum power density of several mW / cm² is achieved under a load of approximately 1 MΩ, which suggests that practical energy storage and driving applications are possible as a non-contact self-generating energy harvesting device.

[0183] Experimental Example 6. Evaluation of the Applicability of Skin-Attached Electronic Devices

[0184] One of the interesting properties of melanin is that its electrical conductivity can be regulated by moisture levels, which is directly related to the potential for electronic devices to be applied as humidity sensors. The humidity sensing performance of melanin-introduced SNFs was evaluated by measuring electric current under conditions of relative humidity (RH) in the range of 2–75% and a constant temperature of 25°C. To ensure statistical reliability, measurements were performed using five different sensors.

[0185] As shown in Fig. 15, a trend of increasing current was observed with increasing humidity (left graph), and different behaviors were observed in the low humidity region (2–11%) and the high humidity region (23–75%) (right graph). In the low humidity region, the current increased linearly with a sensitivity of approximately 0.79 ± 0.04 nA / % RH, which is attributed primarily to electron conduction driven by the semiconductor properties of melanin. In this range, moisture adsorption is limited, resulting in the presence of only isolated water molecules, which consequently restricts proton conduction. Conversely, in the region exceeding 11% RH, the current increased sharply, exhibiting a sensitivity of approximately 1.73 ± 0.13 nA / % RH. This is interpreted as being due to the formation of hydrogen bond networks by adsorbed water molecules, which enables efficient proton hopping according to the Grotthuss mechanism. Melanin provides active proton exchange sites and further amplifies this process by increasing electron conductivity through doping by water molecules.

[0186] Through this dual conduction mechanism (electron conduction and proton conduction), the rapid response characteristics of the sensor in high humidity regions can be confirmed.

[0188] To investigate repeatability characteristics, specimens were exposed to 75% RH conditions for 10 consecutive cycles. Melanin-doped SNFs exhibited sufficient repeatability. The response time (τ) and recovery time (τ) of the melanin-introduced SNF mat-based humidity sensor were measured to be approximately 0.38 seconds and 0.52 seconds, respectively, during the transition between 2% RH and 75% RH (not shown). These ultrafast kinetic characteristics are attributed to the synergistic effect between the porous SNF structure and the hygroscopicity of melanin, which enables rapid adsorption and desorption of water molecules. This ensures a rapid change in conductivity upon changes in humidity.

[0189] Furthermore, the high specific surface area and the low energy barrier for water molecule desorption further enhance these kinetics. Due to its ultrathin structure and uniform melanin distribution, the sensor exhibited a consistent response-recovery cycle with almost no hysteresis, demonstrating stable repetitive operation characteristics.

[0190] To evaluate the practical feasibility of humidity sensors for environmental monitoring, a long-term stability test was conducted under 75% RH conditions. Response time, recovery time, and current values ​​were monitored for two weeks for five humidity sensors based on melanin-introduced SNF mats. As a result, response time and recovery time varied within a range of approximately 15%, while current fluctuation was observed at a level of about 10% after two weeks. These fluctuations are attributed to structural and environmental factors affecting material stability. Specifically, structural (morphological) changes in the silk nanofiber matrix and changes in hydrogen bonding interactions between melanin and silk fibroin can affect charge transfer and diffusion characteristics. Furthermore, prolonged exposure to high-humidity environments and fluctuations in the surrounding environment may induce microstructural fatigue or minor oxidation, potentially contributing to changes in sensor performance.

[0191] Nevertheless, despite these fluctuations, the response and recovery times of the melamine-introduced SNF mat-based humidity sensor remain significantly superior to values ​​reported in the literature, demonstrating that this sensor is a reliable platform for long-term humidity sensing applications.

[0192] The rapid response and recovery characteristics of the melanin-introduced SNF mat-based humidity sensor make it suitable for real-time respiration monitoring. To verify this, the sensor was integrated into a mask (Fig. 16) to detect changes in humidity occurring during nose breathing. During exhalation, the sensor's current response increased due to high humidity, whereas during inhalation, the current response decreased as humidity levels dropped due to dry air. Meanwhile, slight hysteresis was observed due to insufficient detachment time between breaths and repeated exposure to high humidity, but this did not have a significant impact on overall performance. These results demonstrate that the sensor has promising potential for medical respiration monitoring applications.

[0194] The electrocardiogram (ECG) monitoring performance of the melanin-introduced SNF mat was evaluated by comparing its electrical signal acquisition capability with that of a commercial Ag / AgCl gel electrode. The electrical conductivity enhanced by melanin introduction and the excellent adhesion characteristics of the electronic device, which conforms to the skin's microtopography, significantly improve ECG signal acquisition performance.

[0195] To compare the effects, ECG signals recorded using a melanin-introduced SNF mat and a conventional Ag / AgCl gel electrode are presented in Fig. 17, respectively. Under steady-state conditions, the signal-to-noise ratio (SNR) of the electronic device was measured to be approximately 25.12 dB, which is similar to the level of approximately 23.58 dB of the Ag / AgCl electrode. This demonstrates that the electronic device can acquire high-quality ECG signals without the need for conductive gel or additional adhesives. This performance is consistent with previously reported SNR values ​​for dry AgNWs / PDMS electrodes and flexible conductive fabrics, reaffirming that the electronic device acquires high-quality ECG signals. Furthermore, the high porosity and mechanical flexibility of the electronic device enable stable and continuous contact with the skin, ensuring accurate cardiac monitoring in which the PQRST waveform, essential for clinical diagnosis, is clearly distinguishable.

[0196] To emphasize the importance of introducing melanin, comparative ECG measurements were also performed using an electronic device that does not contain melanin (not shown). As a result, the SNR decreased to approximately 19.85 dB, which clearly demonstrates that the introduction of melanin is essential for effective signal acquisition.

[0197] Overall, graphene / melanin-incorporated SNF mats serve as a gel-free alternative to conventional ECG electrodes, offering advantages such as equivalent or superior signal fidelity, enhanced skin adhesion, and reduced risk of irritation, thereby demonstrating practical utility for clinical bioelectronic applications.

[0199] These results demonstrate that the electronic device is a multifunctional platform capable of simultaneously performing humidity sensing and electrophysiological monitoring, and show high potential for next-generation biomedical and wearable healthcare applications.

Claims

Claim 1 An electronic device for skin attachment comprising a support layer including silk nanofibers; and a carbon nanomaterial layer formed on the support layer, wherein melanin is distributed on the surface and / or internal matrix of the silk nanofibers. Claim 2 An electronic device for skin attachment according to claim 1, wherein the average diameter of the silk nanofiber is 100 to 1,000 nm. Claim 3 An electronic device for skin attachment according to claim 1, wherein the weight ratio of silk nanofiber to melanin is 1:0.0005 to 0.

05. Claim 4 An electronic device for skin attachment according to claim 1, wherein the thickness of the support layer is 5 to 10 μm. Claim 5 In claim 1, the carbon nanomaterial is a skin-attachable electronic device that is graphene or carbon nanotube. Claim 6 An electronic device for skin attachment according to claim 1, wherein the thickness of the carbon nanomaterial layer is 20 to 25 μm. Claim 7 A method for manufacturing an electronic device for skin attachment, comprising the steps of: forming nanofibers by electrospinning a silk solution; forming a support layer by immersing the nanofibers in a melanin solution; and forming a carbon nanomaterial layer by coating a carbon nanomaterial on the support layer. Claim 8 A method for manufacturing a skin-attachable electronic device, wherein, in claim 7, the step of forming nanofibers is electrospinning a mixed solution of a silk solution and a polymer solution. Claim 9 A method for manufacturing an electronic device for skin attachment according to claim 7, wherein electrospinning is performed for 1 to 10 hours at a voltage of 5 to 30 kV and a rate of 10 to 50 μL / min. Claim 10 A method for manufacturing an electronic device for skin attachment according to claim 7, wherein the melanin content in the melanin solution is 0.1 to 4 weight% and the immersion time in the melanin solution is 10 minutes to 36 hours. Claim 11 A method for manufacturing an electronic device for skin attachment according to claim 7, wherein the carbon nanomaterial content in the carbon nanomaterial solution is 0.05 to 3 weight%.

Images