GB2610906A

GB2610906A - Bio-based full-fibre self-powered multifunctional electronic skin and preparation method thereof

Info

Publication number: GB2610906A
Application number: GB2209875.0A
Authority: GB
Inventors: Wang Xuechuan; Yue Ouyang; Liu Xinhua; Hou Mengdi; Zheng Manhui; Lv Lihong
Original assignee: Shaanxi University of Science and Technology
Current assignee: Shaanxi University of Science and Technology
Priority date: 2021-09-18
Filing date: 2022-07-05
Publication date: 2023-03-22
Also published as: GB202209875D0; CN114190923A; CN114190923B

Abstract

A bio-based full-fibre self-powered multifunctional electronic skin and a preparation method thereof are provided. The electronic skin comprises: a pressure sensitive layer based on a triboelectric generator (TENG) having a positive friction layer 5, collagen aggregate sponge 6, and negative friction layer 7; a temperature sensitive layer 3; a humidity sensitive layer 1; and an electrode layer 2. The temperature sensitive layer 3 uses electrospun collagen aggregate nanofibres functionally modified preferably with poly(3,4-ethylenedioxythiophene) polystyrene sulphonate and multi-walled carbon nanotube (MWCNT). The humidity sensitive layer 1 uses electrospun collagen aggregate nanofibres functionally modified preferably with acidified carbon nanotube (ACNT) and glycerol. The negative friction layer 7 may be made of electrospun polyvinyl alcohol/polyvinylidene fluoride composite nanofibres, while the positive friction layer 5 may be made of electrospun collagen aggregate nanofibres. The collagen aggregates may be prepared from pigskin, cowhide, sheepskin or fish skin. The pressure sensitive layer may convert mechanical energy into electrical energy using the power management system LTC3588-1.

Description

BIO-BASED FULL-FIBRE SELF-POWERED MULTIFUNCTIONAL ELECTRONIC

SKIN AND PREPARATION METHOD THEREOF

TECHNICAL FIELD OF THE INVENTION

[0001] The present disclosure relates to the technical field of electronic skin manufacturing, and in particular, to a bio-based full-fibre self-powered multifunctional electronic skin and a preparation method thereof.

BACKGROUND TO THE INVENTION

[0002] The skin, as a part of a human body that is most targeted at the above problems, can realize the self-powering function through a triboelectric nanogenerator (TENG). The multi-level structure provides multi-functionality and provides sensitive pressure, humidity, and temperature responsiveness, so as to develop a self-powered multifunctional electronic skin having sensitive responsiveness to various stimuli. In addition, in order to achieve good physiological experience and wearing comfort when the electronic skin is attached to the skin surface, easily degradable biomaterials such as collagen can be used to provide good biocompatibility, and nanofibres can be prepared using the electrospinning technology. The full-fibre structure achieves its good air permeability, and based on the above characteristics, the electronic skin can be widely used in the fields of medical treatment and wearable devices.

[0003] Large organs can not only protect the human body from environmental hazards, but also sense the temperature, pressure and vibration of the external environment in time. In the era of Internet of Things, the electronic skin can surpass human senses in function and sensitivity, which makes it a basic data acquisition device, and it is widely used in the fields of artificial limbs, intelligent robots, wearable devices, and health monitoring systems. For practical application of electronic skin materials, sensitivity, self-powering capability, biocompatibility, air permeability, flexibility, lightness, and cost-effectiveness need to be evaluated. However, so far, few electronic skins integrating these characteristics have been reported [0004] The electronic skins are complex arrays of flexible sensors that realize information collection by converting various environmental stimuli (including temperature, humidity, and pressure) into real-time and visual electronic pulses. Recently, the electronic skins have been endowed with diverse special functions, such as electroluminescence, self-healing, shape memory effect, fire prevention, water resistance, and heat transfer. Despite the continuous improvement and optimization of the above multiple functions, the electronic skins that can truly mimic human skin and its multiple functions for optimal integration are very rare. At present, most electronic skins can only detect one external stimulus, and some electronic skins can detect multiple stimuli, but the sensitivity is insufficient, which is characterized by small detection range, slow response, and long recovery time, thereby greatly limiting their practical application. For example, in specific positions of artificial limbs such as fingertips, in order to detect various stimuli responses of the human skin, a variety of sensors with different functions shall work together. However, the arrangement of sensors with different functions on the plane will cause signal loss in different tiny areas, which is obviously fatal in high-precision applications. In addition, the installation of more sensors will also lead to higher manufacturing costs.

[0005] In previous studies, by designing and modifying the structure of the material, such as designing the concave-convex structure of the material surface by mimicking pyramids or natural skin, the positive and negative electrode materials can obtain a larger contact area under the same pressure, thereby improving the sensitivity. However, this method often requires etching or mold inversion, resulting in a complex production process and expensive manufacturing. In addition, the multifunctional electronic skin cannot be fully powered by traditional batteries due to the contamination caused by battery electrolytes which often poses a health hazard and the inconvenience of battery replacement, charging, and recycling. Although it has been reported that some self-powered electronic skins can be closely attached to the skin to effectively collect biomechanical energy, they are mostly produced with sealed or slightly toxic polymer films such as fluororubber, polydimethylsiloxane or other dense semiconductor films (for example, GaAs, Ti02, and Zn0). These materials may cause skin discomfort, especially after prolonged contact with the human skin, and even cause itching and inflammation. Therefore, it is worth exploring the construction of an electronic skin with highly air-permeable and biocompatible materials as substrates.

SUMMARY OF THE INVENTION

[0006] In order to overcome the above-mentioned deficiencies of the prior art, an objective of the present disclosure is to provide a bio-based full-fibre self-powered multifunctional electronic skin and a preparation method thereof, and a biodegradable multifunctional dual-structure self-powered electronic skin is prepared in a simple manner. The electronic skin is prepared with a three-dimensional (3D) network spatial structure and a bead chain structure, which increases an effective contact area of positive and negative friction layers in a self-generating pressure sensitive layer, and can collect mechanical energy more effectively while sensitively detecting pressure. Through a triboelectric acquisition management system, the collected biomechanical energy can be effectively converted into electrical energy for physiological signals such as temperature and humidity. In addition, a delicate 3D porous structure and microscopic convex structure of a humidity sensitive layer and the adsorption-desorption properties of collagen to moisture ensure the sensitivity to humidity and extremely low short hysteresis. In addition, the unique biological properties of collagen aggregates provide good biocompatibility and biodegradability, while the multi-layer nanofibre structure prepared by electrospinning achieves high air permeability of the electronic skin. These extraordinary functions show that with the help of multi-analysis statistical analysis methods, the recognition and detection of complex human motion and manipulation actions can be realized, and the multi-functional flexible sensor can be more widely used in intelligent robots, health monitoring, and human motion monitoring. [0007] To achieve the above objective, the present disclosure adopts the following technical solution: [0008] A bio-based full-fibre self-powered multifunctional electronic skin includes a pressure sensitive layer, a temperature sensitive layer, a humidity sensitive layer, an electrode layer, a positive friction layer in a self-generating pressure sensitive layer, a collagen aggregate sponge, and a negative friction layer in the self-generating pressure sensitive layer.

[0009] The pressure sensitive layer based on a TENG integrates detection functions of acquiring human mechanical energy and human pressure. When the pressure sensitive layer is stimulated by pressure, the positive and negative friction layers in the self-generating pressure sensitive layer generate a potential difference due to a contact-separation effect externally represented as an alternating current (AC) signal.

[0010] The temperature sensitive layer uses electrospun collagen aggregate nanofibres as a base material, and through functional modification, the collagen aggregate nanofibres have conductivity, temperature sensitivity, and high heat exchange efficiency. When a temperature changes, an electrical performance or potential of the temperature sensitive layer changes to generate an electrical signal.

[0011] The humidity sensitive layer uses electrospun collagen aggregate nanofibres as a base material, and through functional modification, the collagen aggregate nanofibres have conductivity, hygroscopicity, and high humidity sensitivity. When humidity changes, moisture absorption of the humidity sensitive layer causes an electrical performance or potential of the humidity sensitive layer to change to generate an electrical signal.

[0012] The electrode layer is arranged between the temperature sensitive layer and the humidity sensitive layer, and is connected to the temperature sensitive layer and the humidity sensitive layer respectively, and an alternative power supply is a supercapacitor storing a current generated by the pressure sensitive layer after being processed by a power management system LTC3588-1.

[0013] Further, the pressure sensitive layer may be assembled by a negative friction layer of polyvinyl alcohollpolyvinylidene fluoride nanofibres, a positive friction layer of collagen aggregate nanofibres, and an elastic collagen aggregate sponge under a synergistic action of a 3D network spatial structure and a microscopic bead chain structure prepared by electrospinning. [0014] Further, collagen aggregates may be prepared from any one of pigskin, cowhide, sheepskin, and fishskin.

[0015] Further, the pressure sensitive layer may acquire mechanical energy of an applied external force while detecting the pressure, convert the mechanical energy into electrical energy using the power management system LTC3588-1, and store the electrical energy.

[0016] Further, the temperature sensitive layer may be a porous nanofibre film with high temperature exchange efficiency prepared by electrospinning from collagen aggregates subjected to functional modification after being doped with poly(3,4-ethylenedioxythiophene) polystyrene sulfonatc and multi-walled carbon nanotube (MWCNT) composite conductive materials. [0017] Further, the humidity sensitive layer may be obtained by dispersing an acidified carbon nanotube (ACNT) conductive substrate in collagen aggregates as a matrix to obtain conductivity, and conducting modification with glycerol to enhance hygroscopicity.

[0018] Further, a method for preparing the humidity sensitive layer may be to prepare a nanofibre film with a 3D porous structure and a microscopic convex structure with high moisture absorption-desorption properties from a material through electrospinning.

[0019] A preparation method of a bio-based full-fibre self-powered multifunctional electronic skin includes the following steps: [0020] preparing a uniformly mixed polyvinyl alcohol/polyvinylidene fluoride solution, and preparing a negative friction layer having a high specific surface area and air passage rate with a 3D network spatial structure and microscopic bead chains by electrospinning; [0021] preparing a positive friction layer having a high specific surface area and air passage rate from a collagen aggregate solution by electrospinning; [0022] preparing an elastic collagen aggregate sponge from a collagen aggregate solution by freeze-drying, and assembling a pressure sensitive layer; [0023] adding poly(3,4-ethylenedioxythiophene) polystyrene sulfonate and MWCNTs to a collagen aggregate solution for uniform mixing, and electrospinning to obtain a temperature sensitive layer; [0024] spraying conductive graphite on a surface of the temperature sensitive layer to obtain a spiral electrode; and [0025] adding an ACNT conductive substrate material and glycerol to a collagen aggregate solution for uniform mixing, and electrospinning to obtain a structural humidity sensitive layer. [0026] Further, in the negative friction layer of polyvinyl alcohoUpolyvinylidene fluoride nanofibres. polyvinyl alcohol and polyvinylide,ne fluoride may have a mass ratio of (O-20):(O- 20). In the temperature sensitive layer, the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, the MWCNTs, and collagen aggregates may have a mass ratio of (0-1):(0-1):(1-15). In the humidity sensitive layer, ACNTs and collagen aggregates may have a mass ratio of (0-1): (1-15).

[0027] Further, the method may include the following steps: [0028] (1) preparation of the negative friction layer of polyvinyl alcohol/polyvinylidene fluoride: dissolving polyvinyl alcohol in dcionized water at 80-100°C. and stirring for 1-3 h to obtain a solution with a concentration of 0-18 wt.%; then adding 0-20 wt.% polyvinylidene fluoride powder, and stirring for 10-30 h to obtain 0-18 wt.% uniform dispersion of polyvinyl alcohol/polyvinylidene fluoride; fixing a copper mesh on a collector 10-20 cm away from a needle, and uniformly covering the copper mesh with polyvinyl alcohol/polyvinylidene fluoride nanofibres; electrospinning with an electrospinning machine at a feed rate of 0.1-5 int1i1 under certain spinning conditions; and finally, drying a sample in an oven at 30-70°C for 1-6 h to remove a residual solvent; [0029] (2) preparation of the positive friction layer of collagen aggregates and assembly of the self-generating pressure sensitive layer: dissolving 5-20 wt.% collagen aggregates in hexafluoroisopropanol, and stirring at 30-50°C for 10-40 min; electrospinning at a feed rate of 0.1-5 mL.11-1 and an applied voltage of 5-40 kV under certain environmental conditions, fixing the copper mesh on the collector 5-40 cm away from the needle, and drying a sample in the oven at 30-90°C for 1-20 h to remove a residual solvent; drying a 20-40 wt.% aqueous solution of the collagen aggregates in a freeze dryer for 2-48 h until a sponge is formed, and cutting the sponge into rings with a thickness of 0.05-0.2 mm; and assembling the collagen aggregates, polyvinyl alcohol/polyvinylidene fluoride, and the collagen aggregate sponge into the self-generating pressure sensitive layer; [0030] (3) preparation of the temperature sensitive layer: adding 0.1-5 wt.% MWCNTs to 0.1-5 wt.% aqueous dispersion of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, conducting ultrasonic dispersion for mixing for 0.1-5 h, adding 5-20 wt.% collagen aggregates, stirring at 30-80°C for 2-20 h, and finally drying at 30-80°C for later use; stirring a collagen aggregate modifier at 30-80°C for 1-10 h and dissolving the collagen aggregate modifier in hexafluoroisopropanol, adding a 0-5 wt.% water repellant sodium methylsiliconate, and continuing to stir for 2-30 h to obtain a uniformly mixed spinning solution; placing the assembled self-generating pressure sensitive layer on the collector, placing the prepared collagen aggregate spinning solution in a plastic syringe, and placing the needle 5-40 cm away from the collector; maintaining a voltage in a range of 5-40 kV and controlling a feed rate in a range of 0.1-5 mL.11-1; and drying an obtained sample at 30-80°C for 1-10 h to remove a residual solvent, then placing the sample on a platform, and spraying graphite on the sample with a spray gun to form a cross electrode, thereby providing a sample (a); [0031] (4) preparation of the humidity sensitive layer: dispersing 0.1-5 wt.% ACNTs in deionized water by ultrasonic treatment for 0.1-5 h, adding 5-20 wt.% collagen aggregates, stirring at 30-80°C for 0.5-30 h, and drying in the vacuum oven for 1-15 h to obtain a homogeneous mixture; stirring a 5-20 wt.% collagen aggregate/ACNT mixture at 30-50°C for 110 h and dissolving the mixture in hexafluoroisopropanol, adding 0-10 wt.% glycerol, stirring at a high speed for 1-48 h, and then placing a mixture into the syringe of the spinning machine; keeping the sample (a) attached to the collector and 5-40 cm away from the needle, controlling the voltage in a range of 5-40 kV, and keeping certain environmental conditions: a temperature of 30-70°C and humidity of 10-80% RI-I; and drying an obtained sample in the oven at 30-70°C for 1-10 h to remove a residual solvent; and [0032] (5) assembly of the electronic skin: connecting positive and negative electrodes of the self-generating pressure sensitive layer to an input port of the power management system LTC3588-1 to collect energy generated by motion; connecting an output terminal of an energy management circuit and the cross electrode of the electronic skin through a tubing to be used as an energy source for humidity and temperature detection; and closely attaching the prepared electronic skin to human skin to sensitively acquire pressure, temperature, and humidity information.

[0033] Compared with the prior art, the present disclosure has the following beneficial effects. [0034] (1) In the present disclosure, the prepared TENG collects the mechanical energy generated by the human body, and converts it into the electrical energy for storage, which is used as the energy source for other sensing elements in the sensor, replacing the traditional lithium battery.

[0035] (2) The structure of the electronic skin prepared by the present disclosure enables it to have relatively high pressure, humidity, and temperature sensitivity and detection range, as well as excellent responsiveness and cycle performance.

[0036] (3) The full-nanofibre electronic skin prepared by the present disclosure has high air permeability, thereby ensuring the comfort of wearing and attaching.

[0037] (4) The electronic skin achieves excellent responsiveness to pressure, humidity, and temperature, integrates advantages of intelligence, multifunctionality, flexibility, sensitivity, air permeability, biocompatibility, and biodegradability, and can be used as an intelligent electronic skin in the fields of intelligent robots, skin, and medical health detection.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG. 1 is a schematic cross-sectional structural diagram of a self-powered multifunctional sensor of the present disclosure, [0039] where 1-humidity sensitive layer, 2-spiral electrode, 3-temperature sensitive layer, 4-copper mesh, 5-positive friction layer in self-generating pressure sensitive layer, 6-collagen aggregate sponge, and 7-negative friction layer in self-generating pressure sensitive layer; [0040] FIG. 2 shows a scanning electron microscope (SEM) of a cross-section of the self-powered multifunctional sensor and a planar microstructure of different functional layers of the present disclosure; [0041] FIG. 3 shows a power generation and sensing mechanism of a self-generating pressure sensitive layer in the self-powered multifunctional sensor of the present disclosure; [0042] where 1 shows that the positive and negative friction layers are completely separated, 2 shows that the positive and negative friction layers are gradually contacted, 3 shows that the positive and negative friction layers are completely contacted, and 4 shows that the positive and negative friction layers are gradually separated; [0043] FIG. 4 shows an increase mechanism of an effective contact area of positive and negative friction layers when a bead chain structure in the self-generating pressure sensitive layer of the self-powered multifunctional sensor of the present disclosure is under stress; [0044] where I -positvc friction layer, 2-nagative friction layer; [0045] FIG. 5 shows signal output of the self-generating pressure sensitive layer of the self-powered multifunctional sensor of the present disclosure when different external forces are applied; [0046] FIG. 6 shows an effective power and voltage of the self-generating pressure sensitive layer of the self-powered multifunctional sensor of the present disclosure under different external resistances; [0047] FIG. 7 is a schematic diagram of a power management system LTC3588-1 of the self-powered multifunctional sensor of the present disclosure; [0048] FIG. 8 shows output signals of a temperature sensitive layer in the self-powered multifunctional sensor of the present disclosure at different temperatures, with an interior being sensitivity of the temperature sensitive layer to temperature; and [0049] FIG. 9 shows output signals of a humidity sensitive layer in the self-powered multifunctional sensor of the present disclosure under different humidity, with an interior being sensitivity of the humidity sensitive layer to humidity.

[0050] Reference numerals in FIG. 1: 1-humidity sensitive layer, 2-spiral electrode, 3-temperature sensitive layer, 4-copper mesh, 5-positive friction layer in self-generating pressure sensitive layer, 6-collagen aggregate sponge, and 7-negative friction layer in self-generating pressure sensitive layer.

DETAILED DESCRIPTION OF THE INVENTION

[0051] The present disclosure will be described in detail below in conjunction with examples. [0052] With reference to FIG. 1, FIG. 5, FIG. 8, and FIG. 9, this patent discloses a preparation method of a bio-based full-fibre self-powered multifunctional electronic skin, which is different from the current conventional sensor materials, and is characterized in that a bio-inspired multifunctional electronic skin with multi-layer nanofibres is constructed based on a triboelectric generator, which can convert human mechanical enemy into electrical energy to detect external stimuli such as pressure, temperature, and humidity. Polyvinyl alcohol and polyvinylidene fluoride nanofibres in a negative friction layer prepared by clectrospinning have a macroscopic 3D network spatial structure and a microscopic bead chain structure, a porous structure of collagen aggregate nanofibres in a positive electrode layer, and a tentacle structure of an upper humidity sensitive layer. The electronic skin achieves excellent responsiveness to pressure, humidity, and temperature. The electronic skin integrates advantages of intelligence, multifunctionality, flexibility, sensitivity, air permeability, and biocompatibility, and paves the way for intelligent electronic skins in the fields of intelligent robots, skin, and medical health detection.

[0053] With reference to FIG. 1, a multifunctional flexible sensor based on skin collagen aggregates according to the present disclosure includes three functional layers, namely, self-generating pressure sensitive layers 4 to 7, a temperature sensitive layer 3, and a humidity sensitive layer I. The self-generating pressure sensitive layer includes: collagen aggregate nanofibres 5 as a positive friction layer, polyvinyl alcohol/polyvinylidene fluoride nanofibres 7 with a 3D network spatial structure and an internal bead chain structure in a negative friction layer, a conductive copper mesh 4 as an electrode layer, and an elastic collagen aggregate sponge 6.

[0054] With reference to FIG. 2, from an SEM of a cross-section of the multifunctional electronic skin, a multi-layer structure can be clearly observed. In addition, FIG. 2B shows the collagen aggregate nanofibres as the positive friction layer. FIG. 2C shows the polyvinyl alcohol/polyvinylidene fluoride nanofibres 7 with a 3D network spatial structure and an internal bead chain structure in the negative friction layer. FIG. 2D shows collagen aggregates/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate/MWCNT nanofibres as the temperature sensitive layer. FIG. 2E shows a humidity sensitive layer composed of collagen a22re2ates/ACNT nanofibres mimicking a 3D porous structure and a microscopic convex structure. The delicate structural properties of the electronic skin are demonstrated from the SEM in FIG. 2 in conjunction with FIG. A and FIG. 10.

[0055] With reference to FIG. 3, the self-generating pressure sensitive layer in the multifunctional flexible sensor based on skin collagen aggregates according to the present disclosure is based on a contact-separation model in the TENG. In a contact separation process of the positive and negative friction layers subjected to an external force, a generated potential is externally displayed as an AC voltage. After calculation, the magnitude of the external force applied in real time can be obtained, and it can be stored in a capacitor or battery after being processed by a power management system to provide energy sources for other functional layers. [0056] With reference to FIG. 4, the positive and negative friction layers in the self-generating pressure sensitive layer in the multifunctional flexible sensor based on skin collagen aggregates according to the present disclosure are obtained by adjusting the clectrospinning process to obtain nanofibres with a bead chain structure and a porous structure. Compared with ordinary smooth membranes, the nanofibres have a larger relative contact area, which can greatly improve the sensitivity of the self-generating pressure sensitive layer to the external force and the effective output power.

[0057] FIG. 5 to FIG. 6 shows voltage output of the self-generating pressure sensitive layer in the multifunctional flexible sensor based on skin collagen aggregates according to the present disclosure with different areas (1 x I cm2, 2x2 cm2, 3x3 cm2, 4x4 cm2, and 5x5 cm2) under an external force of 135 kPa. The output voltage of the self-generating pressure sensitive layer with an area of 5x5 cm2 is 235 V. and the output voltage of the self-generating pressure sensitive layer with an area of lx1 cm2 is 25 V. Taking lx1 cm2 as a standard size of the electronic skin, the effective output power is 75 mW-m-2 when an external resistance is 55 MO.

[0058] With reference to FIG. 7 and FIG. 10, the power management system used in the multifunctional flexible sensor based on skin collagen aggregates according to the present disclosure is LTC3588-1, which is configured to collect a current generated when the (pressure sensitive) layer is stimulated by an external force, and is used for the temperature sensitive and humidity sensitive layers.

[0059] With reference to FIG. 8 to FIG. 9, the temperature sensitive layer in the multifunctional flexible sensor based on skin collagen aggregates according to the present disclosure has good linearity (R2=0.99) and temperature sensitivity (TCR=0.0075°C-1) in a range of 27-55°C. The humidity sensitive layer has good linearity and sensitivity in a range of 25-55% RH.

[0060] The friction (pressure sensitive) layer in the present example can be prepared by using a positive friction layer based on skin collagen and a negative friction layer based on polyvinyl alcohol/polyvinylidene fluoride. This material can be prepared by the following method: collagen aggregates are dissolved in hexafluoroisopropanol and electrospun to obtain a positive friction layer, a mixed aqueous solution of polyvinyl alcohol/polyvinylidene fluoride is electrospun to prepare a negative friction layer, a freeze-dried sponge of collagen aggregates is used as a separation layer, a conductive copper mesh is used as an electrode layer, and layer-bylayer assembly is conducted.

[0061] The characteristic of the obtained material is that the positive friction layer is prepared by electrospinning natural skin collagen with a 3D network structure as a matrix, and amino acid residues in the collagen aggregates provide positive polarity. The negative friction layer is prepared by electrospinning polyvinyl alcohol/polyvinylidene fluoride materials. By controlling the spinning conditions, a full-fibre film with a 3D network spatial structure and an internal bead chain structure is prepared, and a composite material of polyvinyl alcohol and vinylidene fluoride provides extremely strong negative polarity. The excellent elasticity of the freeze-dried collagen sponge enables the positive and negative friction layers to be quickly separated after the self-generating pressure sensitive layer is removed by the external force. The conductive copper mesh has good conductivity for current conduction and has no effect on the air permeability of the electronic skin.

[0062] The temperature sensitive layer in the present example requires the sensitivity of the material to the temperature and the heat exchange rate of the material itself. Therefore, the temperature sensitive material in the present example can be prepared by the following method: dispersion of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate/ACNT composite conductive substrate materials and a water repellant sodium methylsiliconate are dropwise added to a collagen solution, stirred well and dried at a room temperature, and dissolved in hexatluoroi sopropanol and electrospun.

[0063] The characteristics of the obtained material are that the natural skin collagen is used as the matrix, and the temperature sensitive material poly(3,4-ethylenedioxythiophene) polystyrene sulfonate/carbon nanotube (CNT) composite conductive substrate dispersed in the matrix is used to improve the conductivity of the material, making it temperature sensitive. The full-fibre structure can provide sufficient heat exchange channels to improve heat exchange efficiency and reduce response and hysteresis time.

[0064] The humidity sensitive layer in the present example requires the sensitivity of the material to the humidity and the moisture absorption-desorption properties of the material itself. Therefore, the humidity sensitive material in the present example can be prepared by the following method: dispersion of ACNT composite conductive substrate materials and a hydrophilic agent glycerol are dropwise added to a collagen solution, stirred well and dried at a room temperature, and dissolved in hexafluoroisopropanol and electrospun.

[0065] The characteristic of the obtained material is that the natural skin collagen with 10 adsorption-desorption properties is used as the matrix, and the moisture-sensitive ACNT conductive substrate dispersed in the matrix is used to improve the conductivity of the material, making it humidity sensitive. The full-fibre structure, as well as the 3D porous structure and the microscopic convex structure can provide sufficient moisture exchange channels to improve humidity sensitivity and reduce response and hysteresis time.

[0066] The electrode layer 2 is arranged between the temperature sensitive layer and the humidity sensitive layer, and is connected to the temperature sensitive layer and the humidity sensitive layer respectively, and its external power supply is an output voltage of the self-generating pressure sensitive layer collected mid stored by the power management system when stimulated by an external force. The electrode selected for the electrode layer 2 is preferably a spiral electrode.

[0067] Example I

[0068] (1) Preparation of a negative friction layer of polyvinyl alcohol/polyvinylidene fluoride: polyvinyl alcohol was dissolved in deionized water at 80°C, and stirred for 3 h to obtain a solution with a concentration of 18 wt.%. Then 1 wt.% polyvinylidene fluoride powder was added, and stirred for 10 h to obtain 19 wt.% uniform dispersion of polyvinyl alcohol/polyvinylidene fluoride. A copper mesh was fixed on a collector 10 cm away from a needle, and uniformly covered with polyvinyl alcohol/polyvinylidene fluoride nanofibres. An electrospinning machine worked at a feed rate of 1 mL.11-1 under certain spinning conditions. Finally, a sample was dried in an oven at 30°C for 6 h to remove a residual solvent.

[0069] (2) Preparation of the positive friction layer of collagen aggregates and assembly of the self-generating pressure sensitive layer: 5 wt.% collagen aggregates were dissolved in hexatluoroisopropanol, and stirred at 30°C for 40 min. Electrospinning was conducted at a feed rate of 1 mL.11-1 and an applied voltage of 10 kV under certain environmental conditions. The copper mesh was fixed on the collector 10 cm away from the needle. A sample was dried in the oven at 30°C for 6 h to remove a residual solvent. A 20 wt.% aqueous solution of the collagen aggregates was dried in a freeze dryer for 12 h until a sponge was formed, and the sponge was cut into rings with a thickness of 0.05 mm. The collagen aggregates, polyvinyl alcohol/polyvinylidene fluoride, and the collagen aggregate sponge were assembled into the self-generating pressure sensitive layer.

[0070] (3) Preparation of the temperature sensitive layer: 0.1 wt.% MWCNTs were added to 0.1 wt.% aqueous dispersion of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate. Ultrasonic dispersion was conducted for mixing for 1 h. 5 wt.% collagen aggregates were added, stirred at 30°C for 20 h, and finally dried at 30°C for later use. A collagen aggregate modifier was stirred at 30°C for 60 min and dissolved in hexafluoroisopropanol. A 0.1 wt.% water repellant sodium methylsiliconate was added. Stirring was continued for 2 h to obtain a uniformly mixed spinning solution. The assembled self-generating pressure sensitive layer was placed on the collector. The prepared collagen aggregate spinning solution was placed in a plastic syringe. The needle was placed 10 cm away from the collector. A voltage was maintained at 10 kV and a feed rate was 1 mL-h-1 An obtained sample was dried at 30°C for 6 h to remove a residual solvent, and then placed on a platform. Graphite was sprayed on the sample with a spray gun to form a cross electrode, thereby providing a sample (a).

[0071] (4) Preparation of the humidity sensitive layer: 0.1 wt.% ACNTs were dispersed in deionized water by ultrasonic treatment for 0.5 h. 5 wt.% collagen aggregates were added, and stirred at 30°C for 30 h and dried in the vacuum oven for 5 h to obtain a homogeneous mixture. A 5 wt.% collagen aggrcgate/ACNT mixture was stirred at 30°C for 40 min and dissolved in hexafluoroisopropanol. 0.5 wt.% glycerol was added, and stirred at a high speed for 12 h. Then a mixture was placed into the syringe of the spinning machine. The sample (a) was kept attached to the collector and 10 cm away from the needle. The voltage was controlled at 8 kV, and certain environmental conditions were kept: a temperature of 30°C and humidity of 10% RU. An obtained sample was dried in the oven at 30°C for 6 h to remove a residual solvent.

[0072] (5) Assembly of the electronic skin: positive and negative electrodes of the self-generating pressure sensitive layer were connected to an input port of the power management system LTC3588-1 to collect energy generated by motion. An output terminal of an energy management circuit and the cross electrode of the electronic skin were connected through a tubing to be used as an energy source for humidity and temperature detection. The prepared electronic skin was closely attached to human skin to sensitively acquire pressure, temperature, and humidity information.

[0073] Example II

[0074] (1) Preparation of a negative friction layer of polyvinyl alcohol/polyvinylidene fluoride: polyvinyl alcohol was dissolved in deionized water at 90°C, and stirred for 5 h to obtain a solution with a concentration of 9 wt.%. Then 9 wt.% polyvinylidene fluoride powder was added, and stirred for 20 h to obtain 18 wt.% uniform dispersion of polyvinyl alcohollpolyvinylidene fluoride. A copper mesh was fixed on a collector 15 cm away from a needle, and uniformly covered with polyvinyl alcohoUpolyvinylidene fluoride nanofibres. An electrospinning machine worked at a feed rate of 1.5 inL.11-1 under certain spinning conditions. Finally, a sample was dried in an oven at 50°C for 3 h to remove a residual solvent.

[0075] (2) Preparation of the positive friction layer of collagen aggregates and assembly of the self-generating pressure sensitive layer: 10 wt.% collagen aggregates were dissolved in hexafluoroisopropanol. and stirred at 40°C for 30 min Electrospinning was conducted at a feed rate of 2 mL41-1 and an applied voltage of 15 kV under certain environmental conditions. The copper mesh was fixed on the collector 15 cm away from the needle. A sample was dried in the oven at 50°C for 3 h to remove a residual solvent. A 30 wt.% aqueous solution of the collagen aggregates was died in a freeze dryer for 36 h until a sponge was formed, and the sponge was cut into rings with a thickness of 0.1 mm. The collagen aggregates, polyvinyl alcohol/polyvinylidene fluoride, and the collagen aggregate sponge were assembled into the self-generating pressure sensitive layer.

[0076] (3) Preparation of the temperature sensitive layer: 0.25 wt.% MWCNTs were added to aqueous dispersion of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (2 wt.%). Ultrasonic dispersion was conducted for mixing for 2 h. 10 wt.% collagen aggregates were added, stirred at 40°C for 10 h, and finally dried at 50°C for later use. A collagen aggregate modifier was stirred at 40°C for 40 mm and dissolved in hexafluoroisopropanol. A 2 wt.% water repellant sodium methylsiliconate was added. Stirring was continued for 15 h to obtain a unifomily mixed spinning solution. The assembled self-generating pressure sensitive layer was placed on the collector. The prepared collagen aggregate spinning solution was placed in a plastic syringe. The needle was placed 15 cm away from the collector. A voltage was maintained within 15 kV and a feed rate was controlled within 2 mL41-1 An obtained sample was dried at 50°C for 4 h to remove a residual solvent, and then placed on a platform. Graphite was sprayed on the sample with a spray gun to form a cross electrode, thereby providing a sample (a).

[0077] (4) Preparation of the humidity sensitive layer: 1 wt.% ACNTs were dispersed in deionized water by ultrasonic treatment for 1 h. 9 wt.% collagen aggregates were added, and stirred at 40°C for 20 h and dried in the vacuum oven for 10 h to obtain a homogeneous mixture. A 10 wt.% collagen aggregatc/ACNT mixture was stirred at 40°C for 30 min and dissolved in hexafluoroisopropanol. 4 wt.% glycerol was added, and stirred at a high speed for 35 h. Then a mixture was placed into the syringe of the spinning machine. The sample (a) was kept attached to the collector and 15 cm away from the needle. The voltage was controlled within 15 kV, and certain environmental conditions were kept: a temperature of 40°C and humidity of 50% RH. An obtained sample was dried in the oven at 50°C for 3 h to remove a residual solvent.

[0078] (5) Assembly of the electronic skin: positive and negative electrodes of the self-generating pressure sensitive layer were connected to an input port of the power management system LTC3588-1 to collect energy generated by motion. An output terminal of an energy management circuit and the cross electrode of the electronic skin were connected through a tubing to be used as an energy source for humidity and temperature detection. The prepared electronic skin was closely attached to human skin to sensitively acquire pressure, temperature, and humidity information.

[0079] Example Ill

[0080] (1) Preparation of a negative friction layer of polyvinyl alcohol/polyvinylidene fluoride: polyvinyl alcohol was dissolved in deionized water at 100°C. and stirred for 1 h to obtain a solution with a concentration of 1 wt.%. Then 17 wt.% polyvinylidene flumide powder was added, and stirred for 10-30 h to obtain 18 wt.% uniform dispersion of polyvinyl alcohol/polyvinylidene fluoride. A copper mesh was fixed on a collector 20 cm away from a needle, and uniformly covered with polyvinyl alcohol/polyvinylidene fluoride nanofibrcs. An electrospinning machine worked at a feed rate of 2 mL.11-1 under certain spinning conditions. Finally a sample was dried in an oven at 70°C for 1 h to remove a residual solvent.

[0081] (2) Preparation of the positive friction layer of collagen aggregates and assembly of the self-generating pressure sensitive layer: 18 wt.% collagen aggregates were dissolved in hexafluoroisopropanol, and stirred at 50°C for 10 mm Electrospinning was conducted at a feed rate of 3 mUtil and an applied voltage of 30 kV under certain environmental conditions. The copper mesh was fixed on the collector 30 cm away from the needle. A sample was dried in the oven at 70°C for 1 h to remove a residual solvent. A 40 wt.% aqueous solution of the collagen aggregates was dried in a freeze dryer for 48 h until a sponge was formed, and the sponge was cut into rings with a thickness of 0.2 mm. The collagen aggregates, polyvinyl alcohol/polyvinylidene fluoride, and the collagen aggregate sponge were assembled into the self-generating pressure sensitive layer.

[0082] (3) Preparation of the temperature sensitive layer: 0.5 wt.% MWCNTs were added to 5 wt.% aqueous dispersion of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate. Ultrasonic dispersion was conducted for mixing for 3 h. 18 wt.% collagen aggregates were added, stirred at 50°C for 2 h, and finally dried at 70°C for later use. A collagen aggregate modifier was stirred at 50°C for 10 min and dissolved in hexafluoroisopropanol. A 5 wt.% water repellant sodium methylsiliconate was added. Stirring was continued for 30 h to obtain a unifmmly mixed spinning solution. The assembled self-generating pressure sensitive layer was placed on the collector. The prepared collagen aggregate spinning solution was placed in a plastic syringe. The needle was placed 30 cm away from the collector. A voltage was maintained at 30 kV and a feed rate was controlled at 3 mL-11-1 An obtained sample was dried at 70°C for 1 h to remove a residual solvent, and then placed on a platform. Graphite was sprayed on the sample with a spray gun to form a cross electrode, thereby providing a sample (a).

[0083] (4) Preparation of the humidity sensitive layer: 2 wt.% ACNTs were dispersed in deionized water by ultrasonic treatment for 2 h. 18 wt.% collagen aggregates were added, and stirred at 60°C for 0.5 h and dried in the vacuum oven for 15 h to obtain a homogeneous mixture. A collagen aggregate/ACNT mixture was stirred at 50°C for 10 min and dissolved in hexafluoroisopropanol to prepare a 20 wt.% solution. 10 wt.% glycerol was added, and stirred at a high speed for 48 it Then a mixture was placed into the syringe of the spinning machine. The sample (a) was kept attached to the collector and 20 cm away from the needle. The voltage was controlled within 25 kV, and certain environmental conditions were kept: a temperature of 50°C and humidity of 60% RH. An obtained sample was dried in the oven at 70°C for 1 h to remove a residual solvent.

[0084] (5) Assembly of the electronic skin: positive and negative electrodes of the self-generating pressure sensitive layer were connected to an input port of the power management system LTC3588-1 to collect energy generated by motion. An output terminal of an energy management circuit and the cross electrode of the electronic skin were connected through a tubing to be used as an energy source for humidity and temperature detection. The prepared electronic skin was closely attached to human skin to sensitively acquire pressure, temperature, and humidity information.

Claims

CLAIMSI. A bio-based full-fibre self-powered multifunctional electronic skin, comprising a pressure sensitive layer, a temperature sensitive layer, a humidity sensitive layer, an electrode layer, a positive friction layer in a self-generating pressure sensitive layer, a collagen aggregate sponge, and a negative friction layer in the self-generating pressure sensitive layer, wherein the pressure sensitive layer based on a triboelectric nanogenerator (TENG) integrates detection functions of acquiring human mechanical energy and human pressure; and when the pressure sensitive layer is stimulated by pressure, the positive and negative friction layers in the self-generating pressure sensitive layer generate a potential difference due to a contact-separation effect externally represented as an alternating current (AC) signal; the temperature sensitive layer uses electrospun collagen aggregate nanofibres as a base material, and through functional modification, the collagen aggregate nanofibres have conductivity, temperature sensitivity, and high heat exchange efficiency; and when a temperature changes, an electrical performance or potential of the temperature sensitive layer changes to generate an electrical signal; the humidity sensitive layer uses electrospun collagen aggregate nanofibres as a base material, and through functional modification, the collagen aggregate nanofibres have conductivity, hygroscopicity, and high humidity sensitivity; and when humidity changes, moisture absorption of the humidity sensitive layer causes an electrical performance or potential of the humidity sensitive layer to change to generate an electrical signal; and the electrode layer is arranged between the temperature sensitive layer and the humidity sensitive layer, and is connected to the temperature sensitive layer and the humidity sensitive layer respectively, and an alternative power supply is a supercapacitor storing a current generated by the pressure sensitive layer after being processed by a power management system LTC3588-1.
2. The bio-based full-fibre self-powered multifunctional electronic skin according to claim 1, wherein the pressure sensitive layer is assembled by a negative friction layer of polyvinyl alcoholipolyvinylidene fluoride nanofibres, a positive friction layer of collagen aggregate nanofibres, and an elastic collagen aggregate sponge under a synergistic action of a three-dimensional (3D) network spatial structure and a microscopic bead chain structure prepared by electrospinning.
3. The bio-based full-fibre self-powered multifunctional electronic skin according to claim 2, wherein collagen aggregates are capable of being prepared from any one of pigskin, cowhide, sheepskin, and fishskin.
4. The bio-based full-fibre self-powered multifunctional electronic skin according to claim 1, wherein the pressure sensitive layer acquires mechanical energy of an applied external force while detecting the pressure, converts the mechanical energy into electrical energy using the power management system LTC3588-1, and stores the electrical energy.
5. The bio-based full-fibre self-powered multifunctional electronic skin according to claim I. wherein the temperature sensitive layer is a porous nanofibrc film with high temperature exchange efficiency prepared by electrospinning from collagen aggregates subjected to functional modification after being doped with poly(3,4-ethylenedioxythiophene) polystyrene sulfonate and multi-walled carbon nanotube (MWCNT) composite conductive materials.
6. The bio-bascd full-fibre self-powered multifunctional electronic skin according to claim 1, wherein the humidity sensitive layer is obtained by dispersing an acidified carbon nanotube (ACNT) conductive substrate in collagen aggregates as a matrix to obtain conductivity, and conducting modification with glycerol to enhance hygroscopicity.
7. The bio-based full-fibre self-powered multifunctional electronic skin according to claim 6, wherein a method for preparing the humidity sensitive layer is to prepare a nanofibre film with a 3D porous structure and a microscopic convex structure with high moisture absorption-desorption properties from a material through clectrospinning.
8. A preparation method of a bio-based full-fibre self-powered multifunctional electronic skin, comprising the following steps: preparing a uniformly mixed polyvinyl alcohol/polyvinylidene fluoride solution, and preparing a negative friction layer having a high specific surface area and air passage rate with a 3D network spatial structure and microscopic bead chains by electrospinning; preparing a positive friction layer having a high specific surface area and air passage rate from a collagen aggregate solution by electrospinning, preparing an elastic collagen aggregate sponge from a collagen aggregate solution by freeze-drying, and assembling a pressure sensitive layer; adding poly(3,4-ethylenedioxythiophene) polystyrene sulfonate and MWCNTs to a collagen aggregate solution for uniform mixing, and electrospinning to obtain a temperature sensitive layer; spraying conductive graphite on a surface of the temperature sensitive layer to obtain a spiral electrode; and adding an ACNT conductive substrate material and glycerol to a collagen aggregate solution for uniform mixing, and electrospinning to obtain a structural humidity sensitive layer.
9. The preparation method of a bio-based full-fibre self-powered multifunctional electronic skin according to claim 8, wherein in the negative friction layer of polyvinyl alcohol/polyvinylidene fluoride nanofibres, polyvinyl alcohol and polyvinylidene fluoride have a mass ratio of (0-20):(0-20); in the temperature sensitive layer, the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, the MWCNTs, and collagen aggregates have a mass ratio of (0-1):(0-1):(1-15); and in the humidity sensitive layer, ACNTs and collagen aggregates have a mass ratio of (0-1):(1-15).
10. The preparation method of a bio-based full-fibre self-powered multifunctional electronic skin according to claim 8, comprising the following steps: (1) preparation of the negative friction layer of polyvinyl alcohol/polyvinylidene fluoride: dissolving polyvinyl alcohol in deionized water at 80-100°C, and stirring for 1-3 h to obtain a solution with a concentration of 0-18 wt.%; then adding 0-20 wt.% polyvinylidene fluoride powder, and stirring for 10-30 h to obtain 0-18 wt.% uniform dispersion of polyvinyl alcohol/polyvinylidene fluoride; fixing a copper mesh on a collector 10-20 cm away from a needle, and uniformly covering the copper mesh with polyvinyl alcohol/polyvinylidene fluoride nanofibres; electrospinning with an electrospinning machine at a feed rate of 0.1-5 nth.h-1 under certain spinning conditions; and finally, drying a sample in an oven at 30-70°C for 1-6 h to remove a residual solvent; (2) preparation of the positive friction layer of collagen aggregates and assembly of the self-generating pressure sensitive layer: dissolving 5-20 wt.% collagen aggregates in hexafluoroisopropanol, and stirring at 30-50°C for 10-40 min; electrospinning at a feed rate of 0.1-5 mL.11-1 and an applied voltage of 5-40 kV under certain environmental conditions, fixing the copper mesh on the collector 5-40 cm away from the needle, and drying a sample in the oven at 30-90°C for 1-20 h to remove a residual solvent; drying a 20-40 wt.% aqueous solution of the collagen aggregates in a freeze dryer for 2-48 h until a sponge is formed, and cutting the sponge into rings with a thickness of 0.05-0.2 mm; and assembling the collagen aggregates, polyvinyl alcohol/polyvinylidene fluoride, and the collagen aggregate sponge into the self-generating pressure sensitive layer; (3) preparation of the temperature sensitive layer: adding 0.1-5 wt.% MWCNTs to 0.1-5 wt.% aqueous dispersion of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, conducting ultrasonic dispersion for mixing for 0.1-5 h, adding 5-20 wt.% collagen aggregates, stirring at 30-80°C for 2-20 h, and finally drying at 30-80°C for later use; stirring a collagen aggregate modifier at 30-80°C for 1-10 h and dissolving the collagen aggregate modifier in hexafluoroisopropanol, adding a 0-5 wt.% water repellant sodium methylsiliconate, and continuing to stir for 2-30 h to obtain a uniformly mixed spinning solution; placing the assembled self-generating pressure sensitive layer on the collector, placing the prepared collagen aggregate spinning solution in a plastic syringe, and placing the needle 5-40 cm away from the collector; maintaining a voltage in a range of 5-40 kV and controlling a feed rate in a range of 0.1-5 inL.11-1; and drying an obtained sample at 30-80°C for 1-10 h to remove a residual solvent, then placing the sample on a platform, and spraying graphite on the sample with a spray gun to form a cross electrode, thereby providing a sample (a); (4) preparation of the humidity sensitive layer: dispersing 0.1-5 wt.% ACNTs in deionized water by ultrasonic treatment for 0.1-5 h, adding 5-20 wt.% collagen aggregates, stirring at 3080°C for 0.5-30 h, and drying in the vacuum oven for 1-15 h to obtain a homogeneous mixture; stirring a 5-20 wt.% collagen aggregate/ACNT mixture at 30-50°C for 1-10 h and dissolving the mixture in hexafluoroisopropanol, adding 0-10 wt.% glycerol, stirring at a high speed for 1-48 h, and then placing a mixture into the syringe of the spinning machine; keeping the sample (a) attached to the collector and 5-40 cm away from the needle, controlling the voltage in a range of 5-40 kV, and keeping certain environmental conditions: a temperature of 30-70°C and humidity of 10-80% RI-I; and drying an obtained sample in the oven at 30-70°C for 1-10 h to remove a residual solvent; and (5) assembly of the electronic skin: connecting positive and negative electrodes of the self-generating pressure sensitive layer to an input port of the power management system LTC3588-1 to collect energy generated by motion; connecting an output terminal of an energy management circuit and the cross electrode of the electronic skin through a tubing to he used as an energy source for humidity and temperature detection; and closely attaching the prepared electronic skin to human skin to sensitively acquire pressure, temperature, and humidity information.