Preparation method of bionic electronic skin based on PVA / CNF, wearable device and monitoring system

Abstract

The embodiment of the invention discloses a preparation method of bionic electronic skin based on PVA / cellulose nanofiber, wearable equipment and a monitoring system. The preparation method comprises the following steps: uniformly mixing a cellulose nanofiber solution, an MXene colloidal suspension and water to obtain a mixed solution; heating and stirring polyvinyl alcohol, boric acid, glycerol and the mixed solution at 90-95 DEG C to obtain a PCM hydrogel precursor solution; uniformly coating the PCM hydrogel precursor solution to form a film, and performing directional freezing to obtain D-PCM hydrogel; the D-PCM hydrogel is soaked in a mixed solution of a salt solution and glycerin for salting out for at least 6 h, and the DS-PCM hydrogel capable of being used as the bionic electronic skin is obtained. The bionic electronic skin has unique layered pores and excellent air permeability; the anti-swelling performance is improved through a strong hydrogen bond cross-linked network, and the problem that a hydrogel sensor is prone to failure in a humid environment is solved. In addition, the material has various high-sensitivity sensing capabilities, and tiny physiological signals and environment temperature changes can be accurately captured.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible electronic materials, and in particular to a preparation method of PVA / CNF-based bionic electronic skin, a wearable device, and a monitoring system. Background Art

[0002] Personal wearable devices have gained widespread application in health monitoring and information transmission. They enable diverse functions such as health monitoring, exercise monitoring, and biosignal monitoring through a human-machine interface. However, due to the soft nature of most human tissue and the limited flexibility of many current electronic devices, creating a comfortable and stable human-machine interface presents challenges. This flexibility difference directly impacts device performance, making it difficult to accurately and consistently collect physiological signals. Therefore, developing personal wearable devices with compatible human-machine interfaces is crucial.

[0003] Traditional hydrogel materials have good biocompatibility and flexibility, making them good substrate materials for flexible wearable devices. However, their poor electrical conductivity, poor mechanical properties, easy swelling, and insufficient breathability limit the demand for long-term wear. In the existing technology, conductive fillers and cross-linking agents are added to improve electrical conductivity and mechanical properties, but there are still problems such as large thickness, poor breathability, easy water absorption and swelling in humid environments, leading to failure, and mismatch of mechanical modulus of the human-machine interface. Therefore, there is an urgent need to develop a bionic electronic skin material that is ultra-thin, highly breathable, and anti-swelling. Summary of the Invention

[0004] The present invention provides a method for preparing PVA / CNF bionic electronic skin, comprising:

[0005] The cellulose nanofiber (CNF) solution, MXene colloidal suspension and water were uniformly mixed to obtain a mixed solution;

[0006] Polyvinyl alcohol (PVA), boric acid, and glycerol are heated and stirred at 90-95° C. to obtain a PCM hydrogel precursor solution;

[0007] The PCM hydrogel precursor solution is evenly coated into a film and directionally frozen to obtain D-PCM hydrogel;

[0008] The D-PCM hydrogel was immersed in a mixed solution of salt solution and glycerol for salt precipitation for at least 6 hours to obtain the DS-PCM hydrogel that can be used as a bionic electronic skin.

[0009] Further,

[0010] The cellulose nanofiber (CNF) solution is 0.1-3 wt%, the MXene colloidal suspension is 0.1-0.3 wt%, and the mass ratio of cellulose nanofiber to MXene is (1-3):(0.1-0.3).

[0011] Further,

[0012] Add boric acid to the mixed solution, stir evenly, then add polyvinyl alcohol (PVA), heat and stir at 90-95°C for at least 4 hours, then add glycerol, and continue stirring for at least 1 hour to form a PCM hydrogel precursor solution;

[0013] Among them, the mass ratio of polyvinyl alcohol PVA, cellulose nanofiber CNF and MXene is: (1-12): (0.1-3): (0.01-0.3), and more preferably (8-12): (1-2): (0.1-0.3):.

[0014] Further,

[0015] The CNF content in the PCM hydrogel precursor solution is 0.1-3 wt%, preferably 2 wt%; the MXene content is 0.01-3 wt%, preferably 2 wt%, and the concentration is 0.01-3 mg / ml, preferably 2 mg / ml; the PVA content is 8-12 wt%, preferably 10 wt%;

[0016] Further,

[0017] The boric acid content in the PCM hydrogel precursor solution is 0.5-1 wt%, preferably 0.9 wt%; the mass ratio of glycerol to water is 1:(1-9), preferably 1:(2-3), and more preferably 1:3 / 7.

[0018] Further,

[0019] The PCM hydrogel precursor solution is evenly poured on a glass sheet and spin-coated into a film by a one-step spin coating method, wherein the spin coating speed is 300-1000 r / min, preferably 500-600 r / min, the acceleration is 40-200 r / s, preferably 80-100 r / s, and the spin coating time is 10-30 s, preferably 13-16 s.

[0020] Further,

[0021] Directional freezing was performed on a copper plate immersed in liquid nitrogen, and the freeze-thaw process was repeated at least three times, wherein, when freezing, the copper plate was immersed in liquid nitrogen for at least 2 hours, and when thawing, it was taken out and placed at room temperature for at least 2 hours.

[0022] Further,

[0023] During the salting out process, the mass ratio of the salt solution to the glycerol is (0.5-1.5): (0.5-2.4), wherein the salt solution is a disodium citrate solution, a sodium chloride solution, and a disodium sulfate solution, and the concentration of the salt solution is 0.5-1.5 mol / ml.

[0024] The present invention provides a wearable device, which is obtained by processing the PVA / cellulose nanofiber-based bionic electronic skin prepared by the above-mentioned preparation method. The DS-PCM hydrogel can be cut into a suitable shape and then worn.

[0025] The present invention provides a monitoring system comprising the aforementioned wearable device and a monitoring device for collecting physiological signals from the wearable device. The monitoring device can be combined with an electrochemical workstation or other device for physiological signal collection, primarily for motion monitoring and underwater communications.

[0026] The beneficial effects of the embodiments of the present invention are as follows: the DS-PCM bionic electronic skin developed by the present invention achieves an ultra-thin structure (≤126.8±2.1μm) and high tensile strength through a directional freezing-salting-out synergistic strategy. Its unique layered pore design gives the material excellent air permeability (water vapor permeability 2516.7±102.5g·m-2·d-1), far exceeding traditional PDMS-based materials (<200g·m-2·d-1). At the same time, the strong hydrogen bond cross-linking network significantly improves the anti-swelling performance (swelling rate of 141.2% after 7 days of immersion, and tensile strength retention rate of >90±5% on the 7th day compared to the first day), solving the problem of hydrogel sensors being prone to failure in humid environments.

[0027] This material combines multiple high-sensitivity sensing capabilities (strain sensitivity GF = 0.55, temperature coefficient TCR = 3.67% / °C), accurately capturing minute physiological signals (such as breathing and joint movement) and ambient temperature changes, and stably transmitting Morse code underwater. Its ultra-thin and flexible nature allows for seamless skin adhesion, and its bioelectrical signal acquisition signal-to-noise ratio surpasses that of commercial electrodes, providing innovative solutions for wearable healthcare, intelligent interaction, and underwater monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0029] Figure 1 A schematic diagram of a process for preparing DS-PCM hydrogel according to an embodiment of the present invention;

[0030] Figure 2 Scanning electron microscope (SEM) images of PCM and DS-PCM2 hydrogels in Comparative Example 1 and Example 1 of the present invention;

[0031] Figure 3 This is a comparison chart of the air permeability between Comparative Example 1 and Example 1 of the present invention;

[0032] Figure 4 This is a Fourier transform infrared spectrum of the DS-PCM hydrogel in Example 1 of the present invention;

[0033] Figure 5 This is an X-ray photoelectron spectroscopy (XPS) graph of the DS-PCM hydrogel in Example 1 of the present invention;

[0034] Figure 6 The mechanical properties and strain sensitivity test graphs of the hydrogels prepared in Comparative Examples 1-3 and Examples 1-4 of the present invention are shown;

[0035] Figure 7 This is an underwater sensing diagram of the DS-PCM hydrogel in Example 1 of the present invention;

[0036] Figure 8 This is a temperature sensing diagram of the DS-PCM hydrogel in Example 1 of the present invention;

[0037] Figure 9 This is a comparison chart of the electromyographic signal collected by the DS-PCM hydrogel in Example 1 of the present invention and that of a commercial electrode. DETAILED DESCRIPTION

[0038] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0039] Comparative Example 1

[0040] Preparation of PCM ultrathin hydrogel:

[0041] 1. Mix 4 ml of CNF solution, 2.4 ml of MXene, and 2 ml of deionized water and ultrasonicate for 15 min to obtain a mixed solution.

[0042] 2. Add 0.108 g of boric acid to the mixed solution and stir magnetically until completely dissolved. Add 1.2 g of PVA to the above solution and stir at 90 °C until the PVA is fully dissolved. Finally, add 3.6 ml of glycerol and mix evenly to obtain a PCM hydrogel precursor solution.

[0043] 3. Pour the PCM hydrogel precursor solution onto a circular glass slide and spin-coat it at an acceleration of 100 r / s and a rate of 600 r / min for 16 seconds. Place the glass slide with the hydrogel precursor solution in a -40°C freezer for three cycles of freeze-thaw. The resulting product is named PCM hydrogel.

[0044] Comparative Example 2

[0045] Preparation of D-PCM ultrathin hydrogel:

[0046] 1. Mix 4 ml of CNF solution, 2.4 ml of MXene, and 2 ml of deionized water and ultrasonicate for 15 min to obtain a mixed solution.

[0047] 2. Add 0.108 g of boric acid to the mixed solution and stir magnetically until completely dissolved. Add 1.2 g of PVA to the above solution and stir at 90 °C until the PVA is fully dissolved. Finally, add 3.6 ml of glycerol and mix evenly to obtain a PCM hydrogel precursor solution.

[0048] 3. The PCM hydrogel precursor solution was poured onto a circular glass slide and spin-coated at an acceleration of 100 r / s and a rate of 600 r / min for 16 seconds. The glass slide with the precursor solution was placed on a copper sheet immersed in liquid nitrogen at one end and subjected to three cycles of directional freezing. This product was named D-PCM hydrogel.

[0049] Comparative Example 3

[0050] Preparation of S-PCM ultrathin hydrogel:

[0051] 1. Mix 4 ml of CNF solution, 2.4 ml of MXene, and 2 ml of deionized water and ultrasonicate for 15 min to obtain a mixed solution.

[0052] 2. Add 0.108 g of boric acid to the mixed solution and stir magnetically until completely dissolved. Add 1.2 g of PVA to the above solution and stir at 90 °C until the PVA is fully dissolved. Finally, add 3.6 ml of glycerol and mix evenly to obtain a PCM hydrogel precursor solution.

[0053] 3. Pour the PCM hydrogel precursor solution onto a circular glass slide and spin-coat it at an acceleration of 100 r / s and a rate of 600 r / min for 16 seconds. Place the glass slide with the hydrogel precursor solution in a -40°C freezer for three cycles of freeze-thaw. The resulting product is named PCM hydrogel.

[0054] 4. After freeze-thawing, the PCM hydrogel was placed in a 1 mol / L disodium citrate glycerol and water mixed solution for salting out for 6 h and named S-PCM hydrogel.

[0055] Example 1

[0056] Preparation of DS-PCM ultrathin hydrogel:

[0057] 1. Mix 4 ml of CNF solution (6 wt %), 2.4 ml of MXene, and 2 ml of deionized water, and ultrasonicate for 15 min to obtain a mixed solution.

[0058] 2. Add 0.108 g of boric acid to the mixed solution and stir magnetically until completely dissolved. Add 1.2 g of PVA to the above solution and stir at 90 °C until the PVA is fully dissolved. Finally, add 3.6 ml of glycerol and mix evenly to obtain a PCM hydrogel precursor solution.

[0059] 3. Pour the PCM hydrogel precursor solution onto a circular glass slide and spin-coat it at an acceleration of 100 r / s and a rate of 600 r / min for 16 seconds. Place the glass slide with the precursor solution on a copper sheet immersed in liquid nitrogen at one end and perform three cycles of directional freezing.

[0060] 4. After freeze-thawing, the D-PCM hydrogel was placed in a 1 mol / L disodium citrate glycerol and water mixed solution for salting out for 6 h and named DS-PCM hydrogel.

[0061] Example 2-3

[0062] The preparation methods for the DS-PCM hydrogels in Examples 2-3 were the same as those described in Example 1, differing only in the amount of MXene added. The amounts added for each example are shown in Table 1, where the components are expressed in parts by mass. The resulting samples were designated DS-PCMx (where x represents the amount of MXene added). Specifically, the sample obtained in Example 1 was designated DS-PCM, the sample obtained in Example 2 was designated DS-PCM1, and the sample obtained in Example 3 was designated DS-PCM3.

[0063] Table 1. Amount of each component added in hydrogel in Examples 1-3

[0064]

[0065] Sample characterization:

[0066] The samples obtained from Comparative Examples 1-3 and Examples 1-3 were subjected to scanning electron microscopy (SEM) testing, X-ray photoelectron spectroscopy (XPS) testing, Fourier transform infrared spectroscopy (FTIR) testing, mechanical properties and strain sensitivity testing, and bioelectrical signal acquisition testing. The models of the various testing equipment are:

[0067] SEM: ZEISS Gemini 300, Germany;

[0068] XPS: Thermo Fisher Scientific XPS Escalab Xi+;

[0069] FTIR: Thermo Fisher iS50 FTIR, USA;

[0070] Mechanical properties and strain sensitivity testing: Beijing Sinoagg flexible electronics in-situ testing platform Sinoagg FE-350I;

[0071] Bioelectric signal acquisition test: 16-channel physiological signal recording and analysis system BIOPAC MP160.

[0072] Among them, mechanical properties and strain sensitivity test methods:

[0073] The samples obtained from Comparative Examples 1-3 and Examples 1-3 were cut into a size of 10×5 mm, fixed to both ends of the tensile test bench by clamps, and subjected to a force-electricity synchronous tensile test at a rate of 30 mm / min at 25°C and a relative humidity of 60%.

[0074] Bioelectric signal acquisition and testing method:

[0075] The conductive gel on the commercial electrodes was replaced with DS-PCM ultrathin hydrogel, and the replaced electrodes were used as the positive electrode, negative electrode, and GND electrode, respectively. The three electrodes were connected to the forearm and biceps brachii to collect EMG signals.

[0076] SEM, XPS, FTIR test:

[0077] like Figure 1 The figure shows the process flow diagram of preparing DS-PCM in Example 1. The PCM, S-PCM, DS-PCM (same as DS-PCM2 in Example 2), DS-PCM1 and DS-PCM3 prepared in Comparative Examples 1 and 2 and Examples 1-3 were characterized. Figure 2-5 They are SEM images, FTIR spectra, XPS spectra, and mechanical properties and strain sensitivity test graphs.

[0078] The DS-PCM prepared in Example 1 is used as an example for description.

[0079] Depend on Figure 2 The SEM images shown in the figure show that compared with the disordered pores of PCM, the DS-PCM hydrogel has a regularly arranged layered structure with an interlayer spacing of about 2-5 μm. The layers are connected by transversely interpenetrating polymer fibers. The thickness of DS-PCM is 126.8±2.1 μm. Figure 3 As shown in Figure 2, the unique layered structure and ultra-thin thickness make the hydrogel's air permeability reach 2516.7±102.5g·m -2 ·d -1, which is much higher than the average sweat evaporation of the human body (600g·m -2 ·d -1 ).exist Figure 4 The FTIR spectrum of DS-PCM hydrogel shows that the -OH vibration peak is at a lower wavenumber compared with PVA, which indicates that the -OH interaction between the components in the hydrogel is more intense and has more intense inter-molecular chain entanglement. In addition, the intensity of the intramolecular hydrogen bond band of DS-PCM at 1640 cm-1 is stronger than that of PVA, indicating that the molecular chain rearrangement caused by salting out transforms the weak hydrogen bonds between the molecular chains into strong hydrogen bonds. Figure 5 The full XPS spectra of the four materials were depicted. PCM had additional Ti, F, and Na peaks compared to PVA, proving the successful incorporation of MXene and CNF, indicating the successful preparation of DS-PCM hydrogel.

[0080] Mechanical and sensor performance tests:

[0081] The mechanical properties and strain sensitivity of the sample hydrogels obtained in Comparative Examples 1-3 and Examples 1-3 were tested.

[0082] The experimental results show that the mechanical strength of DS-PCM and S-PCM hydrogels after salting out is significantly better than that before salting out. Figure 6 It shows that the addition of 2mg / ml MXene makes the DS-PCM ultrathin hydrogel have the best tensile properties, among which, Figure 6 a is the force-strain diagram of hydrogels with different treatment methods; b is the force-strain diagram of DS-PCMx hydrogel; c is the force-strain diagram of DS-PCM hydrogel after swelling; d is the strain sensitivity and stability test diagram of DS-PCM hydrogel before and after swelling. Figure 6 It can be seen that the mechanical properties of the samples swollen in water for 1, 3, 5, and 7 days did not change significantly compared to the first day, and both small and large strains before and after swelling were highly sensitive. Figure 7 As shown in the figure, due to the good anti-swelling property of DS-PCM ultra-thin hydrogel, it can accurately identify the bending signal of the finger in water and can send Morse code in water. Figure 8 As shown in Figure 3, DS-PCM can respond quickly to temperature changes and has good linearity in cyclic temperature response.

[0083] Bioelectric signal acquisition test:

[0084] Mechanical properties and strain sensitivity tests of the sample hydrogel obtained in Example 1.

[0085] like Figure 9 As shown, Figure 9a is the ECM signal image collected by DS-PCM hydrogel and commercial electrode; b is the ECM signal image collected before and after DS-PCM hydrogel swelling; c is the background noise comparison image, Figure 9 The ECM collected by the DS-PCM ultrathin hydrogel has a potential amplitude comparable to that of commercial electrodes, but with less background noise. Furthermore, after swelling, the DS-PCM hydrogel exhibits more pronounced potential amplitude and background noise, demonstrating that the DS-PCM ultrathin hydrogel can effectively collect bioelectrical signals in humid environments, making it suitable for use on cold nights.

[0086] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing PVA / CNF bionic electronic skin, characterized in that: include: The cellulose nanofiber solution, the MXene colloidal suspension and water are uniformly mixed to obtain a mixed solution; Polyvinyl alcohol, boric acid, glycerol and the mixed solution are heated and stirred at 90-95° C. to obtain a PCM hydrogel precursor solution; The PCM hydrogel precursor solution is evenly coated into a film and directionally frozen to obtain D-PCM hydrogel; The D-PCM hydrogel was immersed in a mixed solution of salt solution and glycerol for salt precipitation for at least 6 hours to obtain the DS-PCM hydrogel that can be used as a bionic electronic skin.

2. The preparation method according to claim 1, characterized in that The cellulose nanofiber solution is 0.1-3 wt%, the MXene colloidal suspension is 0-0.3 wt%, and the mass ratio of cellulose nanofiber to MXene is (0.1-3): (0-0.3).

3. The preparation method according to claim 1, characterized in that Also includes: Add boric acid to the mixed solution, stir evenly, then add polyvinyl alcohol, heat and stir at 90-95°C for at least 4 hours, then add glycerol, and continue stirring for at least 1 hour to form a PCM hydrogel precursor solution; Among them, the mass ratio of polyvinyl alcohol, cellulose nanofibers and MXene is (1-12): (0.1-3): (0.01-0.3).

4. The preparation method according to claim 1, characterized in that The PCM hydrogel precursor solution has a cellulose nanofiber content of 0.1-3 wt%, a MXene content of 0.01-0.3 wt%, and a polyvinyl alcohol content of 8-12 wt%.

5. The preparation method according to claim 1, characterized in that Also includes: The content of boric acid in the PCM hydrogel precursor solution is 0.5-1 wt %; the mass ratio of glycerol to water is 1:(1-9).

6. The preparation method according to claim 1, characterized in that Also includes: The PCM hydrogel precursor solution is evenly poured on a glass sheet and is spin-coated into a film using a one-step spin coating method, wherein the spin coating speed is 300-1000 r / min, the acceleration is 40-200 r / s, and the spin coating time is 10-30 s.

7. The preparation method according to claim 1, characterized in that Also includes: Directional freezing was performed on a copper plate immersed in liquid nitrogen, and the freeze-thaw process was repeated at least three times, wherein, when freezing, the copper plate was immersed in liquid nitrogen for at least 2 hours, and when thawing, it was taken out and placed at room temperature for at least 2 hours.

8. The preparation method according to claim 1, characterized in that Also includes: During the salting-out process, the mass ratio of salt solution to glycerol is (0.5-1.5): (0.5-2.4); The salt solution is disodium citrate solution, sodium chloride solution, and disodium sulfate solution, and the concentration of the salt solution is 0.5-1.5 mol / ml.

9. A wearable device, characterized in that: The PVA / cellulose nanofiber-based bionic electronic skin prepared by the preparation method according to any one of claims 1 to 8 is processed to obtain a wearable device.

10. A monitoring system, characterized in that: include: The wearable device and monitoring device according to claim 9, wherein the monitoring device is used to collect physiological signals of the wearable device.

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