Multi-scale interface ionic gel / leather ionic skin as well as preparation method and application thereof

Abstract

The invention discloses a multi-scale interface ionic gel / leather ionic skin and a preparation method and application thereof.According to the method, an ionic gel precursor solution is immersed into a leather skeleton, in-situ polymerization is conducted in collagen fiber gaps of the leather skeleton to form ionic gel, a solvent is replaced with ionic liquid, and the multi-scale interface ionic gel / leather ionic skin is obtained. Therefore, the ionic gel / leather ionic skin with high toughness, stretchability, puncture resistance and uniform conductivity is developed. A physical interlocking structure of an ionic gel matrix and a leather skeleton is macroscopically formed through in-situ polymerization; mesoscopically, gaps among collagenous fibers are uniformly filled with ionic gel, and the collagenous fibers are tightly embedded in a polymer network of the gel through a phase separation mechanism; microscopically, rich hydrogen bonds can be formed between functional groups on the surface of the collagenous fiber and the ionic gel, so that the problems of weak interaction force between the flexible ionic gel and a leather skeleton and non-uniform dispersion of the ionic gel are effectively solved, and a wide application prospect is provided for continuous monitoring of physiological signals.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional polymer materials, and relates to a multi-scale interfacial ionic gel / leather ionic skin, a preparation method thereof, and an application thereof. Background Art

[0002] In the past few decades, the rapid development of skin-like flexible electronic technology has greatly promoted the progress of continuous health monitoring technology. Traditional electronic skin mainly relies on electron transfer to conduct electrical signals. Although it meets the requirements of conductivity and certain flexibility, its complex manufacturing process makes it unable to meet more requirements, such as comfort and multi-modal sensing modes. Ionic skin technology realizes mechanical / thermal signal response through ion migration, successfully simulates the sensing mechanism of biological skin, and opens up a new path for wearable medical monitoring. Natural leather, as a green biomass material, has excellent toughness, durability, and biocompatibility. The dense collagen fibers form a unique hierarchical network structure of leather, providing an ideal skeleton material for constructing an ionic skin with natural skin sensing functions. Ionic liquids have significant advantages such as low melting point, low volatility, and strong ionic conductivity. Ionic gels composed of polymer networks and ionic liquids are ideal candidate materials for constructing ionic skins. Combining ionic gels with leather skeletons is expected to achieve ionic skins with unique ionic conductivity and mechanical properties. However, due to the large difference in their mechanical strengths (for example, the mechanical strength of flexible ionic gels is 0.16 - 2 MPa, while that of leather is 9.6 - 19 MPa), the interaction force between flexible ionic gels and leather skeletons is weak, resulting in easy separation of these two components under large deformations. At the same time, existing preparation methods are difficult to overcome the limitation of uniformly dispersing ionic gels in leather matrices. The above problems affect the conductive uniformity, structural integrity, functional reliability, and long-term durability of ionic skins, restricting their practical applications in fields such as health monitoring and intelligent wear. Therefore, the key to developing leather ionic skins lies in effectively combining soft ionic gels with hard leather skeletons, and uniformly dispersing ionic gels inside leather, so as to improve the mechanical properties and sensing properties of ionic skins. Summary of the Invention

[0003] Aiming at the problems existing in the prior art, the present invention provides a multi-scale interfacial ionic gel / leather ionic skin, its preparation method and application. By immersing a leather skeleton in an ionic gel precursor solution, in-situ polymerization is carried out in the gaps of the collagen fibers of the leather skeleton to form an ionic gel, realizing the encapsulation of the collagen fibers by the gel, and preparing the ionic gel / leather ionic skin, so as to solve the technical problems of weak interaction force between the flexible ionic gel and the leather skeleton and uneven dispersion of the ionic gel in the prior art. Based on this, an ionic gel / leather ionic skin with high toughness, stretchability, puncture resistance and uniform conductivity is developed. The multi-modal sensor based on the ionic skin has excellent strain, temperature and respiration multi-modal sensing performance, providing a broad application prospect for continuous monitoring of physiological signals.

[0004] The present invention is realized by the following technical solutions:

[0005] A preparation method of a multi-scale interfacial ionic gel / leather ionic skin, comprising the following steps:

[0006] S1: Add acrylamide, N,N'-methylenebisacrylamide and ammonium persulfate to a polyvinyl alcohol solution in sequence for mixing treatment to obtain a gel precursor solution;

[0007] S2: Immerse the leather in the gel precursor solution and carry out a free radical polymerization reaction to obtain a leather-based hydrogel;

[0008] S3: Place the leather-based hydrogel in an ionic liquid for solvent replacement to prepare the ionic gel / leather ionic skin.

[0009] Preferably, the mass ratio of polyvinyl alcohol to acrylamide is 1:(4 - 12).

[0010] Preferably, the time for adding acrylamide, N,N'-methylenebisacrylamide and ammonium persulfate to the polyvinyl alcohol solution in sequence for mixing treatment is 1 - 1.5 h.

[0011] Preferably, the thickness of the leather is 1 - 1.4 mm.

[0012] Preferably, the temperature of the free radical polymerization reaction is 50 - 60 °C and the time is 4 - 6 h.

[0013] Preferably, the mass ratio of the leather-based hydrogel to the ionic liquid is 1:(3 - 5).

[0014] Preferably, the ionic liquid is 1-butyl-3-methylimidazolium tetrafluoroborate.

[0015] Preferably, the time for solvent replacement is 1 - 6 h.

[0016] A multi-scale interfacial ion gel / leather ion skin is prepared by the above method; the tensile strength of the ion skin is 3.47-8.92 MPa, and the toughness is 1.33-3.13 MJ m -3 , and the conductivity is 0.04-0.30 S m -1 .

[0017] A multi-mode wearable flexible sensor includes the above multi-scale interfacial ion gel / leather ion skin.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects:

[0019] The present invention discloses a preparation method of a multi-scale interfacial ion gel / leather ion skin. First, a uniform precursor solution (including polyvinyl alcohol (PVA) polymer, acrylamide (AAm) monomer, ammonium persulfate (APS) initiator, and a small amount of N,N′-methylenebisacrylamide (MBAA) crosslinking agent) is in-situ polymerized in a leather skeleton to prepare a PVA-PAM / Leather composite material. During the gelation process, the precursor solution penetrates into the gaps between the leather collagen fibers, and thermal initiation causes the in-situ polymerization of the AAm monomer. Therefore, the viscoelastic polymer network composed of intertwined PVA and PAM chains can be in-situ polymerized deep inside the leather skeleton to form uniform ion transport channels; subsequently, solvent replacement is carried out using an ionic liquid, and the osmotic pressure gradient and phase separation mechanism can cause the volume contraction of the PVA-PAM polymer chains in the collagen fibers, enhancing the interaction and entanglement between the collagen fibers and the PVA-PAM polymer chains, thereby forming a strong interfacial bond between the PVA-PAM / IL ion gel matrix and the leather skeleton, and obtaining a PVA-PAM / IL / Leather (VMIL) ion skin composed of PVA-PAM / IL ion gel encapsulating collagen fibers. In the ion gel / leather ion skin prepared by the present invention, the ionic liquid acts as a conductive medium and fills the structural voids of the polymer network to form stable ion transport channels, and these ion transport channels allow ions to freely migrate under the action of an electric field, thereby achieving stable and uniform conductivity.

[0020] In a second aspect, the present invention effectively improves the mechanical properties of the ionic skin through multi-scale interface design. Specifically, the present invention conducts multi-scale interface design at the macroscopic, mesoscopic, and microscopic levels. At the macroscopic level, the physical interlocking of the PVA-PAM / IL ionic gel matrix and the leather skeleton is introduced to form a stable composite structure. This structure not only enhances the mechanical properties of the material but also provides support for the uniform distribution of ions. At the mesoscopic level, the ionic gel is filled into the rich gaps between collagen fibers to form continuous ionic channels, which ensure the uniform migration of ions in the gel and provide guarantee for conductivity. At the microscopic level, the hydrogen bond interaction between the functional groups suspended on the surface of collagen fibers and the PVA and PAM polymer chains enhances the binding force between the ionic gel and the leather skeleton. Due to the poor compatibility between the PAM polymer chain and the imidazolium-based ionic liquid, rich hydrogen bonds are generated between the polymer chain and the functional groups of collagen fibers, forming a phase separation domain. At the same time, this microscopic interaction also contributes to the uniform distribution and migration of ions. The present invention ensures the uniform distribution and migration of ions in the gel based on multi-scale interface design, thereby achieving uniform conductivity and effective improvement of internal mechanical forces, especially the high binding force (5.24 N) between the two components. Finally, an ionic gel / leather ionic skin with high toughness, stretchability, puncture resistance, and uniform conductivity is prepared.

[0021] In a third aspect, the present invention also discloses a multi-mode wearable flexible sensor, which includes a multi-scale interface ionic gel / leather ionic skin multi-mode sensor in the present invention. The ionic skin has excellent strain, temperature, and respiration multi-mode sensing performance, providing broad application prospects for continuous monitoring of physiological signals. Therefore, the ionic skin constructs a multi-mode sensor integrating mechanical and temperature sensing functions to simulate natural tactile and temperature stimuli. In addition, it can also be used as a sensing unit for an intelligent continuous motion system to real-time monitor and distinguish the angles of fine finger movements through wireless transmission, so as to conduct health assessment on specific populations that need continuous monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0023] Figure 1 It is a flowchart for preparing the ionic gel / leather ionic skin in Embodiment 1 of the present invention;

[0024] Figure 2Tensile stress-strain diagram of the PVA-PAM gel prepared in Experimental Examples 1-3 of the present invention;

[0025] Figure 3 Test results of the interaction force between the ionic gel matrix and the leather skeleton in the leather-based hydrogel prepared in Example 1 of the present invention;

[0026] Figure 4 Stress-strain curve of the scale interface design ionic gel / leather ion skin prepared in Example 1 of the present invention.

[0027] Figure 5 Comparison results of stress, Young's modulus and toughness of the ion skin prepared with different solvent replacement times in Examples 1-4 and Comparative Example 1 of the present invention;

[0028] Figure 6 Test results of the puncture resistance of the ionic gel / leather ion skin prepared in Example 1 of the invention.

[0029] Figure 7 Conductivity of the ion skin prepared with different solvent replacement times in Examples 1-4 and Comparative Example 1 of the invention.

[0030] Figure 8 Change in relative resistance of the ionic gel / leather ion skin prepared in Example 1 of the invention from 25°C to 70°C during testing.

[0031] Figure 9 Change in relative resistance with time when the temperature of the ionic gel / leather ion skin prepared in Example 1 of the invention rises from 36.5°C to 37.5°C, with a temperature increase of 0.1°C.

[0032] Figure 10 Monitoring human body temperature diagram of the ionic gel / leather ion skin prepared in Example 1 of the invention, where a is the resistance change curve during simulated human body fever, and b is the resistance change curve during breathing;

[0033] Figure 11 Tensile strain-relative resistance change rate of the ionic gel / leather ion skin prepared in Example 1 of the invention;

[0034] Figure 12 Monitoring human body movement diagram of the ionic gel / leather ion skin prepared in Example 1 of the invention, where a is the resistance change rate-time curve at different finger bending angles, b is the resistance change rate-time curve when frowning, and c is the resistance change rate-time curve when swallowing;

[0035] Figure 13 Relationship diagram between joint bending angle and arc length;

[0036] Figure 14It is the integration of the ion gel / leather ion skin prepared in Invention Example 1 with the intelligent system. After testing the bending by 90° through wireless transmission, a photo of the index finger and the corresponding data window of the remote monitoring system are obtained;

[0037] Figure 15 It is the relationship between the actual bending angle and the calculated bending angle of the ion gel / leather ion skin prepared in Invention Example 1 at different bending angles;

[0038] Figure 16 It is the angle and relative resistance change of the joint movement tested by the ion gel / leather ion skin prepared in Invention Example 1;

[0039] Figure 17 It is the change diagram of the relative resistance and time of the index finger bending tested by the ion gel / leather ion skin prepared in Invention Example 1. Detailed implementation mode

[0040] To enable those skilled in the art to understand the features and effects of the present invention, the following is a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning understood by those skilled in the art for the present invention. In case of conflict, the definition in this specification shall prevail.

[0041] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall not limit the scope of the present invention in any way, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0042] In this article, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are only for the sake of simplicity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values within the range (including integers and fractions).

[0043] In this article, unless otherwise specified, "comprising", "including", "containing", "having" or similar terms cover the meanings of "consisting of" and "consisting essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A only comprises a".

[0044] In this article, for the sake of concise description, all possible combinations of the technical features in each embodiment or example are not described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered as the scope described in this specification.

[0045] Such as Figure 1As shown in the figure, the present invention provides a preparation method of a multi-scale interface ionic gel / leather ionic skin, comprising the following steps:

[0046] S1: Add 1 g of polyvinyl alcohol to 40 g of water, stir at 60 - 70 °C for 1 - 2 h to obtain a polyvinyl alcohol solution; sequentially add acrylamide, N,N'-methylenebisacrylamide, and ammonium persulfate to the polyvinyl alcohol solution, and perform mixing treatment for 1 - 1.5 h to obtain a uniform gel precursor solution;

[0047] The mass ratio of the polyvinyl alcohol to acrylamide is 1:(4 - 12), preferably 1:8;

[0048] Furthermore, the mass ratio of the acrylamide, N,N'-methylenebisacrylamide, and ammonium persulfate is (4 - 12):(0.0024 - 0.0072):(0.0039 - 0.0117), preferably 8:0.0048:0.0079.

[0049] S2: Immerse the leather in the gel precursor solution, and carry out a free radical polymerization reaction at 50 - 60 °C for 4 - 6 h to effectively gelify the gel precursor solution and obtain a leather-based hydrogel;

[0050] Specifically, immerse the leather in the gel precursor solution. A specific embodiment can be to pour the precursor solution into a mold with leather. The mold selects a silicone gasket with a thickness of 2 - 6 mm, and the thickness of the leather is preferably 1 - 1.4 mm, which can improve the mechanical properties of the gel.

[0051] S3: Place the leather-based hydrogel in an ionic liquid for solvent replacement for 1 - 6 h, preferably 4 h, to prepare the ionic gel / leather ionic skin. The mass ratio of the leather-based hydrogel to the ionic liquid is 1:(3 - 5).

[0052] The ionic liquid is preferably 1-butyl-3-methylimidazolium tetrafluoroborate.

[0053] The present invention also discloses a multi-scale interface ionic gel / leather ionic skin prepared by the above method. The tensile strength of the multi-scale ionic gel / leather ionic skin is 3.47 - 8.92 MPa, and the toughness is 1.33 - 3.13 MJ m -3 and the conductivity is 0.04 - 0.30 S m -1 .

[0054] Meanwhile, the present invention also discloses a wearable flexible sensor comprising the above multi-scale interface ionic gel / leather ionic skin.

[0055] The present invention discloses a uniform and stable polyvinyl alcohol (PVA)-polyacrylamide (PAM) / ionic liquid ([BMIM][BF4]) ion gel / leather (VMIL) ionic skin. The principle is that the PVA-PAM hydrogel is in-situ polymerized within the interstitial spaces of the leather framework collagen fibers and then replaced with the [BMIM][BF4] ionic liquid solvent. The osmotic pressure gradient can cause the volume contraction of the PVA-PAM polymer chains in the collagen fibers, enhancing the interaction and entanglement between the collagen fibers and the PVA-PAM polymer chains, thereby forming a firm interfacial bond between the PVA-PAM / IL ion gel matrix and the leather framework. At the same time, cations and anions can be evenly dispersed in the networks of the PVA-PAM / IL ion gel matrix and the leather framework. In particular, due to the poor compatibility between the PAM polymer chains and the imidazolium-based ionic liquid, rich hydrogen bonds are generated between the polymer chains and the functional groups of the collagen fibers, forming a phase separation domain. The final VMIL ionic skin exhibits excellent mechanical properties and conductive uniformity in multiple dimensions: (1) At the macroscopic level, the physical interlocking of the PVA-PAM / IL ion gel and the leather framework provides a continuous conductive channel for ion transport; (2) At the mesoscopic scale, the PVA-PAM / IL ion gel forms a firm and seamless interfacial bond in the gaps between the collagen fibers; (3) At the microscopic scale, the dense hydrogen bonds enhance the binding between the ion gel matrix and the leather framework. In particular, the binding force (5.24 N) between the two components is very high. Therefore, the VMIL ionic skin has high toughness, stretchability, and uniform conductivity. The ionic skin has excellent strain, temperature, and respiration multimodal sensing properties, providing broad application prospects for continuous monitoring of physiological signals.

[0056] Therefore, the VMIL ionic skin can be used to construct a multimodal sensor integrating mechanical sensing and temperature sensing functions to simulate natural tactile and temperature stimuli. In addition, it can also be used as a sensing unit for an intelligent continuous motion system to real-time monitor and distinguish the angles of fine finger movements through wireless transmission, so as to conduct health assessments on specific populations that require continuous monitoring.

[0057] The following further elaborates the present invention in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0058] Conventional instruments and equipment in the art are used in the following examples. For the experimental methods without specific conditions noted in the following examples, they are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer. Various raw materials are used in the following examples. Unless otherwise specified, commercially available products are used, and their specifications are the conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0059] Experimental Example 1

[0060] The preparation of a PVA-PAM gel includes the following steps:

[0061] (1) Preparation of the hydrogel precursor solution: Disperse 1 g of polyvinyl alcohol (purchased from Aladdin, product number 9002-89-5) in 40 g of water, and successively add 8 g of acrylamide (purchased from Kermel, product number 79-10-7), 0.0048 g of N,N'-methylenebisacrylamide (purchased from Macklin, product number 7447-41-8), and 0.0072 g of ammonium persulfate (purchased from Kermel, product number 328-50-7). Among them, ammonium persulfate is used as the initiator, and stir at room temperature for 1 h to obtain the PVA-PAM hydrogel precursor solution;

[0062] (2) Preparation of the PVA-PAM hydrogel: Pour the PVA-PAM hydrogel precursor solution into a mold, and then place it in an oven at 55 °C for 5 h to obtain the PVA-PAM hydrogel.

[0063] Experimental Example 2

[0064] The difference between this experimental example and Experimental Example 1 is that the mass ratio of polyvinyl alcohol to acrylamide is 1:4.

[0065] Experimental Example 3

[0066] The difference between this experimental example and Experimental Example 1 is that the mass ratio of polyvinyl alcohol to acrylamide is 1:12.

[0067] Figure 2 The tensile stress-strain diagram of the PVA-PAM gel prepared in Experimental Examples 1-3 of the present invention. As can be seen from the figure, when the weight ratio of PVA to PAM (R VA ) is different, the PVA-PAM hydrogel exhibits different mechanical properties. As can be seen from the figure, compared with R VA = 1:12 (tensile property 810.88%, tensile strength 0.12 MPa, toughness 0.55 MJ m -3 , 0.053 MPa) and 1:4 (tensile property 1254.59%, tensile strength 0.042 MPa, toughness 0.23 MJ m -3 , 0.005 MPa), RVA The PVA / PAM hydrogel with a ratio of 1:8 has more excellent stretchability (1009.28%), tensile strength (0.13 MPa) and toughness (0.58 MJ m -3 , 0.005 MPa).

[0068] Example 1

[0069] This example provides a multi-scale interface design ion gel / leather ion skin, whose breaking strength is 8.32 MPa; the toughness is 3.13 MJ / m 3 .

[0070] In this example, the tensile properties of the ion skin were tested in accordance with GB1040-92, and the same applies to the other examples.

[0071] The multi-scale interface design ion gel / leather ion skin is obtained by the following preparation method, and the preparation method includes the following steps:

[0072] (1) Preparation of the hydrogel precursor solution: Disperse 1 g of polyvinyl alcohol (purchased from Aladdin, product number 9002-89-5) in 40 g of water, and sequentially add 8 g of acrylamide (purchased from Kermel, product number 79-10-7), 0.0048 g of N,N'-methylenebisacrylamide (purchased from Macklin, product number 7447-41-8) and 0.0072 g of ammonium persulfate (purchased from Kermel, product number 328-50-7). Among them, ammonium persulfate is used as an initiator, and stir at room temperature for 1 h to obtain the PVA-PAM hydrogel precursor solution;

[0073] (2) Preparation of the leather-based hydrogel: Pour the PVA-PAM hydrogel precursor solution into a mold with leather (a mold composed of two glass plates, a piece of leather and a rubber ring), and then place it in an oven at 55 °C for 5 h to obtain the leather-based hydrogel;

[0074] (3) Preparation of the ion skin: Remove the leather-based hydrogel from the mold and soak it in 1-butyl-3-methylimidazolium tetrafluoroborate for 4 h. After soaking, obtain the PVA-PAM / IL / Leather ion skin, abbreviated as VMIL ion skin, that is, the ion gel / leather ion skin.

[0075] Example 2

[0076] This example provides a multi-scale interface ion gel / leather ion skin, whose breaking strength is 5.10 MPa; the toughness is 1.72 MJ m -3 .

[0077] In this example, the test standard for the ion skin is GB1040-92, and the same applies to the other examples.

[0078] The ionic skin is obtained by the following preparation method, and the preparation method includes the following steps:

[0079] (1) Preparation of hydrogel precursor solution: Disperse 1 g of polyvinyl alcohol (purchased from Aladdin, product number 9002 - 89 - 5) in 40 g of water, and sequentially add 8 g of acrylamide (purchased from Comin, product number 79 - 10 - 7), 0.0048 g of N,N’-methylenebisacrylamide (purchased from Macklin, product number 7447 - 41 - 8) and 0.0072 g of ammonium persulfate (purchased from Comin, product number 328 - 50 - 7) initiator, and stir at room temperature for 1 h to obtain the PVA - PAM hydrogel precursor solution;

[0080] (2) Preparation of leather - based hydrogel: Pour the PVA - PAM hydrogel precursor solution into a mold with leather (a mold composed of two glass plates, one piece of leather and a rubber ring), and then place it in an oven at 55 °C for 5 h to obtain the leather - based hydrogel;

[0081] (3) Preparation of ionic skin: Remove the leather - based hydrogel from the mold and soak it in 1 - butyl - 3 - methylimidazolium tetrafluoroborate for 1 h to prepare the ionic gel / leather ionic skin.

[0082] Example 3

[0083] This example provides a multi - scale interface - designed ionic gel / leather ionic skin, whose fracture strength is 6.62 MPa; the toughness is 2.36 MJ m -3 .

[0084] In this example, the test standard for the ionic skin is GB1040 - 92, and the same applies to the other examples.

[0085] The ionic skin is obtained by the following preparation method, and the preparation method includes the following steps:

[0086] (1) Preparation of hydrogel precursor solution: Disperse 1 g of polyvinyl alcohol (purchased from Aladdin, product number 9002 - 89 - 5) in 40 g of water, and sequentially add 8 g of acrylamide (purchased from Comin, product number 79 - 10 - 7), 0.0048 g of N,N’-methylenebisacrylamide (purchased from Macklin, product number 7447 - 41 - 8) and 0.0072 g of ammonium persulfate (purchased from Comin, product number 328 - 50 - 7) initiator, and stir at room temperature for 1 h to obtain the PVA - PAM hydrogel precursor solution;

[0087] (2) Preparation of leather-based hydrogel: Pour the PVA-PAM hydrogel precursor solution into a mold with leather (a mold composed of two glass plates, one piece of leather and a rubber ring), and then place it in an oven at 55 °C for 5 h to obtain the leather-based hydrogel;

[0088] (3) Preparation of ionic skin: Remove the leather-based hydrogel from the mold and soak it in 1-butyl-3-methylimidazolium tetrafluoroborate for 2 h to prepare the ionic gel / leather ionic skin.

[0089] Example 4

[0090] This example provides a multi-scale interface design ionic gel / leather ionic skin with a fracture strength of 8.92 MPa; the toughness is 2.67 MJ m -3 .

[0091] In this example, the test standard for the ionic skin is GB1040-92, and the same applies to the other examples.

[0092] The ionic skin is obtained by the following preparation method, and the preparation method includes the following steps:

[0093] (1) Preparation of hydrogel precursor solution: Disperse 1 g of polyvinyl alcohol (purchased from Aladdin, product number 9002-89-5) in 40 g of water, and sequentially add 8 g of acrylamide (purchased from Kermel, product number 79-10-7), 0.0048 g of N,N'-methylenebisacrylamide (purchased from Macklin, product number 7447-41-8) and 0.0072 g of ammonium persulfate (purchased from Kermel, product number 328-50-7) initiator, and stir at room temperature for 1 h to obtain the PVA-PAM hydrogel precursor solution;

[0094] (2) Preparation of leather-based hydrogel: Pour the PVA-PAM hydrogel precursor solution into a mold with leather (a mold composed of two glass plates, one piece of leather and a rubber ring), and then place it in an oven at 55 °C for 5 h to obtain the leather-based hydrogel;

[0095] (3) Preparation of ionic skin: Remove the leather-based hydrogel from the mold and soak it in 1-butyl-3-methylimidazolium tetrafluoroborate for 6 h to prepare the ionic gel / leather ionic skin.

[0096] Comparative Example 1

[0097] The difference from Example 1 is that in step (3), no soaking is carried out, that is, the prepared leather-based hydrogel is not subjected to ionic liquid replacement.

[0098] To reveal the strong interfacial bonding between the ionic gel matrix and the leather skeleton in this application, a pull-out test was carried out on the leather-based hydrogel prepared in Example 1 of the present invention, and the force required to pull out the collagen fiber bundle from the ionic gel matrix (fixed embedding depth of 10 mm) was recorded. The test results are shown in Figure 3 . As can be seen from the figure, the maximum tensile force of the VMIL ionic skin is 5.24 N, which means that there is a strong adhesive force between the PVA-PAM / IL ionic gel matrix and the leather skeleton in the VMIL ionic skin.

[0099] Example 5

[0100] A preparation method of a multi-scale interfacial ionic gel / leather ionic skin includes the following steps:

[0101] S1: Add 1 g of polyvinyl alcohol to 40 g of water, stir at 60 °C for 2 h to obtain a polyvinyl alcohol solution; sequentially add 4 g of acrylamide, 0.0024 g of N,N'-methylenebisacrylamide, and 0.0039 g of ammonium persulfate to the polyvinyl alcohol solution, and perform a mixing process for 1 h to obtain a uniform gel precursor solution;

[0102] S2: Immerse the leather with a thickness of 1 mm in the gel precursor solution, and carry out a free radical polymerization reaction at 50 °C for 6 h to effectively gelify the gel precursor solution and obtain a leather-based hydrogel;

[0103] S3: Place the leather-based hydrogel in 1-butyl-3-methylimidazolium tetrafluoroborate for solvent replacement for 1 h to prepare the ionic gel / leather ionic skin, and the mass ratio of the leather-based hydrogel to the ionic liquid is 1:3.

[0104] The tensile strength of the multi-scale ionic gel / leather ionic skin prepared in this example is 3.51 MPa, and the toughness is 1.37 MJ m -3 , and the conductivity is 0.07 S m -1 .

[0105] Example 6

[0106] A preparation method of a multi-scale interfacial ionic gel / leather ionic skin includes the following steps:

[0107] S1: Add 1 g of polyvinyl alcohol to 40 g of water, stir at 70 °C for 1 h to obtain a polyvinyl alcohol solution; sequentially add 12 g of acrylamide, 0.0072 g of N,N'-methylenebisacrylamide, and 0.0117 g of ammonium persulfate to the polyvinyl alcohol solution, and perform a mixing process for 1.5 h to obtain a uniform gel precursor solution;

[0108] S2: Immerse the leather with a thickness of 1.4 mm in the gel precursor solution, and carry out a free radical polymerization reaction at 60 °C for 4 h to effectively gelify the gel precursor solution, thereby obtaining a leather-based hydrogel;

[0109] S3: Place the leather-based hydrogel in 1-butyl-3-methylimidazolium tetrafluoroborate for solvent replacement for 6 h to prepare the ion gel / leather ion skin, and the mass ratio of the leather-based hydrogel to the ionic liquid is 1:5.

[0110] The tensile strength of the multi-scale ion gel / leather ion skin prepared in this example is 8.54 MPa, and the toughness is 2.95 MJ m -3 , and the conductivity is 0.21 S m -1 .

[0111] Example 7

[0112] A preparation method of a multi-scale interfacial ion gel / leather ion skin includes the following steps:

[0113] S1: Add 1 g of polyvinyl alcohol to 40 g of water, stir at 65 °C for 1.5 h to obtain a polyvinyl alcohol solution; sequentially add 10 g of acrylamide, 0.006 g of N,N'-methylenebisacrylamide, and 0.0097 g of ammonium persulfate to the polyvinyl alcohol solution, and carry out a mixing process for 1 h to obtain a uniform gel precursor solution;

[0114] S2: Immerse the leather with a thickness of 1.2 mm in the gel precursor solution, and carry out a free radical polymerization reaction at 55 °C for 5 h to effectively gelify the gel precursor solution, thereby obtaining a leather-based hydrogel;

[0115] S3: Place the leather-based hydrogel in 1-butyl-3-methylimidazolium tetrafluoroborate for solvent replacement for 4 h to prepare the ion gel / leather ion skin, and the mass ratio of the leather-based hydrogel to the ionic liquid is 1:4.

[0116] The tensile strength of the multi-scale ion gel / leather ion skin prepared in this example is 5.62 MPa, and the toughness is 2.01 MJ m -3 , and the conductivity is 0.17 S m -1 .

[0117] Figure 4 This is the stress-strain curve of the scale interface design ion gel / leather ion skin prepared in Example 1 of the present invention. As can be seen from the figure, the VMIL ion skin has high fracture strength performance.

[0118] Figure 5This is the comparison result of the stress, Young's modulus, and toughness of the ion skins prepared with different solvent replacement times in Examples 1-4 of the present invention and Comparative Example 1. As can be seen from the figure, immersing the PVA-PAM / Leather composite material in the ionic liquid can form VMIL ion skins with different mechanical properties, which specifically depend on the soaking time. By adjusting the soaking time (0-6 hours), especially the sample with a soaking time of 4h shows the maximum tensile strength (8.32 MPa), Young's modulus (2.77 MPa), and the highest toughness (3.13 MJ m -3 ) ( Figure 3 d, e), which exceed twice that of the PVA-PAM / Leather composite material (3.47 MPa, 1.29 MPa, 1.32 MJ m -3 ) at a tensile strain of 80%. In the case of a longer ionic liquid exchange time (such as 6h), the Young's modulus slightly increases to 3.54 MPa, and the tensile strain decreases to 70%. This is because an excessive amount of ionic liquid will cause the PVA-PAM network in the VMIL ion epidermis to become dense and the collagen fibers to become tight, thereby reducing its flexibility and ductility. These results indicate that an excessive amount of ionic liquid will weaken the mechanical properties of the VMIL ion epidermis, and the best mechanical properties (8.32 MPa fracture stress, 3.13 MJ m -3 toughness, 2.77 MPa Young's modulus, and 80% tensile strain) appear at the critical point of a soaking time of 4h.

[0119] Figure 6 This is the test result of the puncture resistance of the ion gel / leather ion skin prepared in Example 1 of the invention. As can be seen from the figure, the regions composed of dense polymer entanglements and the tight interlocking between polymer chains and collagen fibers in the VMIL ion skin generate high tensile stress and toughness. Therefore, this VMIL ion epidermis not only has sufficient stretchability to conformally deform with human tissues but also has sufficient toughness to resist mechanical damage, such as punctures that usually cause equipment failure.

[0120] Figure 7 This is the conductivity of the ion skins prepared with different solvent replacement times in Examples 1-4 of the present invention and Comparative Example 1. As can be seen from the figure, the conductivity of the VMIL ion skin is mainly related to the anions and cations in the ionic liquid and the continuous ion conduction path provided by the PVA-PAM / IL ion gel interconnection network that penetrates into the leather skeleton. After soaking for 4h, the highest conductivity of the VMIL ion skin is 0.3 S m -1 .

[0121] Figure 8is the change in relative resistance of the ion gel / leather ion skin prepared in Example 1 of the present invention when the test temperature ranges from 25 °C to 70 °C. The calculation formula for the temperature coefficient of resistance (TCR) is TCR = (R T -R0) / ΔT, where R T and R0 are the instantaneous resistances of the VMIL ion skin at a certain temperature (T) and the reference temperature (25 °C), respectively. As can be seen from the figure, the VMIL ion skin has the best temperature sensitivity (TCR = -2.23% °C -1 ) in the range of 25 - 40 °C, showing a negative temperature-sensitive characteristic due to the enhanced mobility of ions at high temperatures.

[0122] Figure 9 is the change in relative resistance with time when the temperature of the ion gel / leather ion skin prepared in Example 1 of the present invention rises from 36.5 °C to 37.5 °C, and the temperature increase is 0.1 °C. As can be seen from the figure, the VMIL ion skin can capture slight temperature changes as low as 0.1 °C, having high resolution.

[0123] Body temperature, as an important vital sign, its real-time change reflects a person's health condition, especially for infants who cannot accurately express their feelings. Here, a "simulated fever" is simulated on the forehead of the model using a heat source, and the instantaneous temperature before and after the "simulated fever" is recorded by an infrared thermal imaging camera. Figure 10 is the human body temperature monitoring diagram using the ion gel / leather ion skin prepared in Example 1 of the present invention. Among them, a is the resistance change curve when simulating human body fever. As can be seen from the figure, the |ΔR / R0| value of the VMIL ion skin can quantitatively display the body temperature, and the response at a normal forehead temperature of 36.5 °C is 0%. In contrast, when the temperature rises to 40 °C, the response increases sharply to about 6.97%. A highly distinguishable temperature resolution (3.5 °C) is observed in a relatively narrow human body temperature range. In addition, a reversible response can be accurately obtained during the process of reducing fever. The infrared thermal imager reacts almost simultaneously, indicating that the VMIL ion skin is sufficient to accurately monitor the human body temperature. Therefore, this kind of VMIL ion skin has the potential to timely monitor the human body temperature, especially the body temperature of infants who cannot accurately describe their own health conditions, and warn and avoid the risks of some related diseases. b is the resistance change curve during breathing. When the volunteer breathes normally at a frequency of 20min -1 on the VMIL ion skin attached to the eustachian tube, obvious relative resistance changes will occur during the cyclic inhalation and exhalation processes. The output signal deviation in each cycle can be ignored, indicating high repeatability and stability. This significant responsiveness of the VMIL ion skin to continuous breathing makes it promising for the intensive care of comatose patients.

[0124] Figure 11is the tensile strain - relative resistance change rate of the ion gel / leather ion skin prepared in Invention Example 1; as can be seen from the figure, with the increase of strain, two stages of linear change of GF are observed (R 2 ≥0.99). In the first stage (0 - 65% strain), GF is 0.68, and in the second stage (65% - 80% strain), GF is 1.12. Among them, GF, that is, Gauge Factor, is a parameter used to quantify the relationship between the relative change rate of resistance and strain when the material is subjected to tensile strain. GF is an important index for evaluating the performance of strain sensors, which reflects the sensitivity of the material to deformation.

[0125] Figure 12 is the human motion monitoring diagram of the ion gel / leather ion skin prepared in Invention Example 1 of the present invention. Among them, a is the resistance change rate - time curve when the finger bends at different angles, b is the resistance change rate - time curve when frowning, and c is the resistance change rate - time curve when swallowing. The sensors are respectively fixed on the index finger, wrist and elbow of the volunteer to monitor various joint movements of the upper limb. Since the ion skin has excellent mechanical stretchability and flexibility, it has good compliance with the human skin when the limb undergoes large deformations. As the bending angle of the finger increases from 0° to 90°, the sensor is gradually stretched. The resulting increase in resistance accurately reflects the bending angle of the finger ( Figure 12 a). When the bending angle of the finger remains unchanged, the change in resistance is consistent, showing excellent repeatability, stability and fast response ability. For facial expressions, such as frowning, the ion skin shows obvious electrical signal fluctuations ( Figure 12 b). In the actions of facial expressions, the relative resistance change shows a similar and stable peak shape. In addition, the sensor shows significant potential in capturing throat actions (such as swallowing) and can be displayed in the form of a characteristic signal pattern ( Figure 12 c). The swallowing action is repeated multiple times, and there is no obvious change in the signal wave. These results prove that the VMIL ion skin can be used as a wearable sensor to detect large and minor human activities.

[0126] The VMIL ion skin prepared in the present invention has excellent mechanical properties and excellent strain sensing ability. It can be integrated with intelligent systems through wireless transmission to continuously monitor the bent index finger. Its excellent strain sensing ability enables it to accurately and sensitively capture the bending degree of the index finger. The system consists of several modules, including VMIL ion skin, microcontroller unit, Bluetooth, power supply and mobile terminal.

[0127] Figure 13It is a relationship diagram between the joint bending angle and the arc length. As can be seen from the figure, the bending angle (α) of the index finger can be expressed as α = (|R - R0|·L0) / (R0·GF·r), where r is the radius of the bent index finger; L0 and L are the circumferences of the index finger before and after bending respectively; and GF is the strain sensitivity of the VMIL ion skin.

[0128] Figure 14 It is the integration of the ion gel / leather ion skin prepared by using Invention Example 1 with the intelligent system. After testing the bending of 90° through wireless transmission, a photo of the index finger and the corresponding data window of the remote monitoring system are shown.

[0129] Figure 15 It is the relationship between the actual bending angle and the calculated bending angle of the ion gel / leather ion skin prepared by Invention Example 1 at different bending angles. As can be seen from the figure, for different ΔR / R0 values, there is a good linear relationship and consistency between different actual bending angles and the calculated angles reported by the system.

[0130] Figure 16 It is the angle and relative resistance change of the joint movement tested by the ion gel / leather ion skin prepared by Invention Example 1 and Figure 17 It is a change diagram of the relative resistance and time of the index finger bending tested by the ion gel / leather ion skin prepared by Invention Example 1, which can show that the system has stable and reversible sensing performance during operation. Therefore, this VMIL ion skin integrated with the intelligent system is expected to record the resistance change at different bending angles of the index finger in real time through wireless transmission. It will provide important guidance for doctors and caregivers to timely understand the health status of high-specificity populations that need continuous monitoring.

[0131] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a multi-scale interface ion gel / leather ion skin, characterized in that: The following steps are involved: S1: adding acrylamide, N,N'-methylenebisacrylamide and ammonium persulfate to a polyvinyl alcohol solution in sequence for mixing to obtain a gel precursor solution; S2: soaking the leather in the gel precursor solution and performing a free radical polymerization reaction to obtain a leather-based hydrogel; S3: placing the leather-based hydrogel in an ionic liquid for solvent replacement to prepare the ionic gel / leather ionic skin.

2. The method for preparing a multi-scale interface ion gel / leather ion skin according to claim 1, characterized in that: The mass ratio of the polyvinyl alcohol to acrylamide is 1:(4-12).

3. The method for preparing a multi-scale interface ion gel / leather ion skin according to claim 1, characterized in that: Acrylamide, N,N'-methylenebisacrylamide and ammonium persulfate are sequentially added to the polyvinyl alcohol solution and mixed for 1 to 1.5 hours.

4. The method for preparing a multi-scale interface ion gel / leather ion skin according to claim 1, characterized in that: The leather has a thickness of 1 to 1.4 mm.

5. The method for preparing a multi-scale interface ion gel / leather ion skin according to claim 1, characterized in that: The temperature of the free radical polymerization reaction is 50-60° C. and the time is 4-6 hours.

6. The method for preparing a multi-scale interface ion gel / leather ion skin according to claim 1, characterized in that: The mass ratio of the leather-based hydrogel to the ionic liquid is 1:(3-5).

7. The method for preparing a multi-scale interface ion gel / leather ion skin according to claim 1, characterized in that: The ionic liquid is 1-butyl-3-methylimidazolium tetrafluoroborate.

8. The method for preparing a multi-scale interface ion gel / leather ion skin according to claim 1, characterized in that: The solvent replacement time is 1 to 6 hours.

9. A multi-scale interface ion gel / leather ion skin, characterized in that: The ionic skin is prepared by the method according to any one of claims 1 to 8; the tensile strength of the ionic skin is 3.47 to 8.92 MPa, and the toughness is 1.33 to 3.13 MJ m -3 , conductivity is 0.04~0.30Sm -1 .

10. Use of the multi-scale interface ion gel / leather ion skin described in claim 9 in preparing a multi-mode wearable flexible sensor.

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