CN115198512B

CN115198512B - Propolis silk fibroin composite membrane based on MXene, and preparation method and application thereof

Info

Publication number: CN115198512B
Application number: CN202210842935.9A
Authority: CN
Inventors: 陈龙聪; 樊艳莉; 刘改琴; 熊兴良; 江奇锋; 杨家琦
Original assignee: Chongqing Medical University
Current assignee: Chongqing Medical University
Priority date: 2022-07-18
Filing date: 2022-07-18
Publication date: 2023-07-28
Anticipated expiration: 2042-07-18
Also published as: CN115198512A

Abstract

The invention discloses a preparation method of a propolis silk fibroin composite membrane based on MXene, which comprises the following steps: 1) Preparing SF solution: preparing SF solution with the concentration of 19-21wt% by adopting formic acid; 2) Preparing a propolis EEP solution: the concentration of propolis in EEP solution is 0.08-0.12g/ml; 3) Preparing SF/EEP composite solution: uniformly mixing SF solution and EEP solution to obtain SF/EEP composite solution; 4) Preparing an SF/EEP composite fiber film: preparing a composite fiber film by adopting electrostatic spinning; 5) Preparing a conductive substance solution: preparing GR dispersion liquid and MXene thin layer dispersion liquid, wherein MXene is Ti ₃ C ₂ Tx or Nb ₂ CTx; 6) Spraying conductive substances, and airing to obtain the composite film. The composite film has good antibacterial property and conductivity, wide sensing range (1 kPa-50 kPa) and outstanding stability.

Description

Propolis silk fibroin composite membrane based on MXene, and preparation method and application thereof

Technical Field

The invention belongs to the technical field of biological materials, and particularly relates to a propolis silk fibroin composite membrane based on MXene, and a preparation method and application thereof.

Background

Silk Fibroin (SF) is a natural protein fiber, has good biocompatibility, degradability and excellent mechanical properties, so that the silk fibroin has great attraction in flexible electronic products, has good bending property, is easy to attach to skin, improves the rigid form of a traditional sensor, and meets the requirements of a flexible wearable sensor.

Transition metal carbides and nitrides (mxnes) are an emerging family with excellent properties including high electrical conductivity, good hydrophilicity, large specific surface area, etc. MXene is produced by selectively etching an "a" layer from a MAX phase and may be represented by the general formula mn+1xntx, where M represents early transition metals (e.g., ti, sc, cr, and Mo), X represents C and/or N, tx represents a surface functional group (e.g., -O, -OH, or-F), and n=1, 2, or 3. The conductive performance of the composite film is effectively improved by spraying the composite film on the composite film, and the unique performance of the composite film makes the composite film have great potential in the preparation and application of strain sensors.

With the development of the technologies of semiconductors and the Internet of things, the flexible wearable sensor has good application prospects in the fields of personal wearable electronic equipment, man-machine interaction, intelligent robots and the like, and has attracted great research interests due to the excellent real-time sensing capability, high integration potential and portability. In particular, the flexible wearable sensor plays an important role in the personal wearable electronic device, and can effectively capture physiological parameters of a human body and convert the physiological parameters into electronic signals, so that the human health is monitored. Human health monitoring mainly includes pulse sensory analysis, acoustics, swallowing, and finger movement. The flexible wearable strain sensor has good application prospect in the field of human health monitoring due to the advantages of light weight, flexible application scene and the like, breaks the limitation of monitoring places and conditions, is beneficial to realizing remote and movable monitoring, screening prevention and health monitoring of diseases, and can be beneficial to normalization and family of human health monitoring. Therefore, the method also has good application prospect and market value. Although applications based on the human body are considered, bacteria, fungi, etc. may be generated for the long-term use of the sensor and negatively affect the health of the human body, and thus there is a need for a wearable flexible sensor having excellent antibacterial effect and excellent electrical conductivity.

Disclosure of Invention

The invention aims at solving the problems and provides a preparation method of a propolis silk fibroin composite membrane based on MXene, which comprises the following steps:

1) Preparing SF solution: taking silk fibroin, and preparing SF solution with the concentration of 19-21wt% by taking formic acid as a solvent;

2) Preparing a propolis EEP solution: dissolving propolis in 65-100% ethanol solution to obtain EEP solution, wherein the concentration of propolis in EEP solution is 0.08-0.12g/ml;

3) Preparing SF/EEP composite solution: uniformly mixing SF solution and EEP solution to obtain SF/EEP composite solution, wherein the volume ratio of the SF solution to the EEP solution is 100:0.8-1.2;

4) Preparing an SF/EEP composite fiber film: preparing SF/EEP composite solution into a composite fiber film by adopting electrostatic spinning, wherein the electrostatic spinning process parameters are as follows: the spinning voltage is 17 kV-19 kV, the solution injection speed is 0.005 ml/min-0.007 ml/min, and the spinning distance is 14-16cm; drying the composite fiber film for later use after spinning is completed;

5) Preparing a conductive substance solution: GR dispersion with concentration of 2.2-2.8mg/ml is prepared by NMP, MXene thin-layer dispersion with concentration of 2.2-2.8mg/ml is prepared by deionized water, and the MXene is Ti ₃ C ₂ Tx or Nb ₂ CTx；

6) Spraying conductive substances: taking an air-dried composite fiber film, spraying the prepared GR dispersion liquid, and spraying the MXene thin-layer dispersion liquid after air drying; spraying according to the total amount of 3-5ml of conductive substance solution sprayed on each 7-9 square meters cm of composite fiber film, wherein the volume ratio of GR dispersion liquid to MXene thin layer dispersion liquid is 1:2.5-3.5; and (3) airing to obtain the propolis silk fibroin composite membrane based on MXene.

Preparing SF solution with concentration of silk fibroin of 19.5-20.5wt% or 20wt% in the step 1); in step 2), the propolis is dissolved in 65-75% or 67-72% or 70% ethanol solution, and the concentration of the propolis in EEP solution is 0.09-0.11g/ml or 0.1g/ml.

In the step 3), the volume ratio of SF solution and EEP solution is 100:0.9-1.1 or 100:1.

The electrostatic spinning process parameters in the step 4) are as follows: the spinning voltage is 17.5 kV-18.5 kV or 18kV, the solution injection speed is 0.0055 ml/min-0.0065 ml/min or 0.006ml/min, and the spinning distance is 15cm.

The GR dispersion or the MXene thin layer dispersion in step 5) had a concentration of 24-2.6mg/ml or 2.5mg/ml; the MXene is Ti ₃ C ₂ Tx。

In step 6), the total amount of 3.5-4.5ml or 4ml of the conductive substance solution is sprayed per 7-9 square meter cm or 8 square meter cm of the composite fiber film, wherein the volume ratio of GR dispersion liquid to MXene thin layer dispersion liquid is 1:2.7-3.3 or 1:3.

The silk fibroin in the step 1) is prepared by adopting cocoons as raw materials through the following method: na for shearing silkworm cocoons ₂ CO ₃ Degumming with solution, washing with water, drying to obtain degummed silk fibroin, and mixing degummed silk fibroin with formic acid and CaCl ₂ Mixing and stirring until dissolved, centrifuging to obtain supernatant, drying, and removing Ca from the dried solid ²⁺ And (3) plasma to prevent conductive particles from affecting measurement of the resistance value of the composite film after spraying the conductive substances, and drying to obtain the silk fibroin for preparing the SF solution.

The invention also provides an MXene-based propolis silk fibroin composite membrane, which comprises a silk fibroin composite fiber membrane containing antibacterial substance propolis and a conductive layer grafted on the fiber membrane, wherein the conductive layer is made of GR and MXene by the preparation method of any one of the above materials.

The final object of the invention is to provide the application of the propolis silk fibroin composite membrane based on MXene in the preparation of flexible electronic devices.

Preferably, the flexible electronics is a flexible wearable strain sensor.

The beneficial effects of the invention are as follows:

(1) The antibacterial property of the silk fibroin film is increased by adopting propolis, and experimental research shows that the excessive addition of EEP can lead to the rupture of fibers in the film, so that the mechanical property of the composite film is obviously reduced, and the experiment finds out the proper addition of propolis, thereby ensuring that the composite film has good antibacterial property and good mechanical property. The addition of the propolis can well enhance the antibacterial property and the flexibility of the composite film, can effectively prevent the formation of bacteria and fungi on the surface of the skin, and is beneficial to the long-term use of the sensor. The composite membrane has good biocompatibility.

(2) The SF and EEP concentration and the electrostatic spinning technology in the proper SF-EEP composite solution are found out, so that the fiber obtained by spinning is smooth and has proper diameter.

(3) The invention adopts silk fibroin and propolis to blend, and then adopts GR and MXene (Ti ₃ C ₂ Tx and Nb ₂ CTx), the conductivity of the material is obviously enhanced by the preparation process of the conductive materials GR and Ti ₃ C ₂ Tx and Nb ₂ CTx comparison, found that GR-Ti was used ₃ C ₂ The conductive material of the Tx match has the best conductivity and sensitivity.

(4) Experiments prove that the propolis silk fibroin composite membrane based on MXene prepared by the method has wide induction range (1 kPa-50 kPa) and outstanding stability.

Drawings

FIG. 1 is a flow chart of a method for preparing the SF/EEP/GR/MXene composite film of the present invention.

FIG. 2 is an SEM surface morphology characterization of SF/EEP films.

Fig. 3 is a graph of the results of mechanical property testing of SF composite films.

FIG. 4 is a graph of SF/EEP/GR/Ti for various total amounts of conductive material ₃ C ₂ Resistivity change rate of Tx composite film.

FIG. 5 shows the GR and Ti differences ₃ C ₂ SF/EEP/GR/Ti prepared by Tx usage ₃ C ₂ Resistivity of the Tx composite film.

FIG. 6 is a graph of SF/EEP/GR/Nb for various total amounts of conductive material ₂ Resistivity change rate of CTx composite film.

FIG. 7 is a graph of GR and Nb ₂ SF/EEP/GR/Nb prepared by CTx usage amount ₂ Resistivity change rate of CTx composite film.

FIG. 8 shows the total amount of different conductive materials and GR, ti ₃ C ₂ SF/EEP/GR/Ti prepared by Tx usage ₃ C ₂ Maximum resistivity error analysis plot for Tx composite film.

FIG. 9 shows the total amount of different conductive materials and GR, nb ₂ SF/EEP/GR/Nb prepared by CTx usage amount ₂ Maximum resistance change rate error of CTx composite filmDifference analysis chart.

FIG. 10 shows the rate of change of the SF/EEP/GR composite film resistance when the conductive material was sprayed with only 4ml GR.

FIG. 11 is SF/EEP/GR/Ti ₃ C ₂ Results of repeated cyclic response experiments of Tx composite films with different tensile loading-unloading forces.

FIG. 12 is SF/EEP/GR/Ti ₃ C ₂ Error analysis chart of the results of repeated cyclic response experiments of different tensile loading-unloading of Tx composite films.

FIG. 13 is SF/EEP/GR/Ti ₃ C ₂ The sensitivity test experiment results of the Tx composite film under different tensile forces.

FIG. 14 is SF/EEP/GR/Ti ₃ C ₂ Results of cycle durability test at Tx composite film 25 kPa.

Fig. 15 is a graph of permeability versus time for SF composite films.

FIG. 16 is SF/EEP/GR/Ti ₃ C ₂ Tx composite membrane biocompatibility test results.

FIG. 17 is SF/EEP/GR/Ti ₃ C ₂ Tx composite film inhibition zone test results.

FIG. 18 is SF/EEP/GR/Ti at different finger bending levels ₃ C ₂ Response of Tx composite film sensor.

FIG. 19 is SF/EEP/GR/Ti during wrist bending ₃ C ₂ Tx composite membrane sensor response.

FIG. 20 is SF/EEP/GR/Ti during elbow bending ₃ C ₂ Tx composite membrane sensor response.

FIG. 21 is SF/EEP/GR/Ti at knee bending ₃ C ₂ Tx composite membrane sensor response.

Detailed Description

The invention is further illustrated, but is not limited, by the following examples.

The experimental methods in the following examples are conventional methods unless otherwise specified; the biological and chemical reagents used, unless otherwise specified, are all conventional in the art and are commercially available.

Example 1

1. Preparation of Flexible SF/EEP/GR/MXene wearable Strain sensor

The invention adds propolis solution with good antibacterial property into silk fibroin solution with good biocompatibility, enhances the antibacterial property and flexibility of the film by the interaction of the propolis solution and the silk fibroin solution, prepares the composite film by adopting an electrostatic spinning method, improves the conductivity of the composite film by spraying MXene and GR on the surface of the composite film, and has the operation steps shown in figure 1.

1. Preparation of Silk Fibroin (SF) solution

(1) Cleaning: taking 15 domestic cocoons with uniform size, cutting each cocoon into 4 pieces, placing into a beaker with proper amount of ultrapure water, placing into an ultrasonic cleaner, ultrasonically washing for 8min at 100Hz power, taking out cocoons, and flushing surface impurities with running water.

(2) And (3) drying: placing the cleaned silkworm cocoons into a culture dish, and drying the silkworm cocoons in a constant-temperature drying oven at 60 ℃ for at least 3 hours to realize thorough drying.

(3) Degumming: will be 4.24g Na ₂ CO ₃ The solid was added to 2L of ultrapure water having a resistivity of 18.25 M.OMEGA.cm to prepare Na having a concentration of 0.02M ₂ CO ₃ A solution. Na was fed to an electric furnace with a power of 1000W ₂ CO ₃ Heating the solution to boil, at this time, pouring the silkworm cocoon into Na ₂ CO ₃ And (5) degumming the solution for 45min under stirring.

(4) Cleaning: after degumming, transferring the degummed silk fibroin into a beaker filled with ultrapure water, ultrasonically cleaning for 5-10min at a power of 100Hz, taking out the degummed silk fibroin, repeatedly flushing with ultrapure water to thoroughly remove residual sericin, wringing the residual sericin, placing the residual sericin into a culture dish, and naturally drying overnight. The next day, the mixture was dried in a constant temperature oven at 60℃for 4 hours.

(5) Preparing SF solution: taking out degummed silk fibroin and dissolving in formic acid and CaCl ₂ Wherein the ratio of the reagent is formic acid stock solution to solid CaCl ₂ The mass ratio of silk fibroin after drying=10:1:2.5, and the magnetic stirrer was stirred for 4 hours until silk fibroin was completely dissolved.

(6) And (3) centrifuging: after complete dissolution of the silk fibroin, the dissolution solution was centrifuged in a centrifuge with working parameters of 9000rpm at 4 ℃ for 20min, and the supernatant was collected.

(7) And (3) drying: the supernatant was placed in a petri dish and dried naturally overnight.

(8) Soaking in water: immersing the dried SF in ultra-pure water for one day, taking out after the supernatant in the culture dish turns white, putting the culture dish into a 50 ℃ oven, and drying.

(9) Preparing a high-concentration SF solution: and (3) preparing SF (sulfur hexafluoride) solution with different concentration of 16-22 wt% from the dried SF and formic acid solution (formic acid stock solution), and recording as solution I.

2. Preparation of propolis (EEP) solution

Taking a proper amount of propolis raw rubber, adding 0.5g of propolis into 5ml of 70% ethanol solution, dissolving for 3 hours, and recording as EEP solution after complete dissolution.

Propolis is a viscous solid jelly formed by mixing plant resin collected by worker bees with secretions such as palate glands, wax glands and the like, and the propolis used in the embodiment is purchased from the safe hive company (Yunnan).

3. Preparation of SF/EEP composite solution

And respectively adding 0.05ml, 0.1ml and 0.2ml of EEP solution into 10ml of solution I, magnetically stirring for 4 hours, and standing for 24 hours for standby to obtain the SF/EEP composite solution. SF/EEP composite solution of 0.05ml, 0.1ml and 0.2ml EEP solution is added respectively, and the concentration of EEP solution in the SF/EEP composite solution is 0.5wt%, 1wt% and 2wt%.

4. Preparation of SF/EEP composite fiber film material

Sucking the SF/EEP composite solution prepared in the third step into a medical injector, connecting the injector and a needle, setting injection speed, connecting a high-voltage power supply anode to a spinning stainless steel needle, connecting an aluminum foil with a negative electrode, selecting a receiving device, setting spinning parameters of 16 kV-20 kV in spinning voltage, adjusting the injection speed (namely jet speed) of the solution to 0.004 ml/min-0.008 ml/min and the spinning distance to 15cm, starting spinning, and after finishing spinning, turning off the power supply to carefully tear off the aluminum foil from the receiving device. And (3) standing at room temperature for 2 days, drying the fiber film, removing the solvent remained on the fiber film, transferring the dried fiber film into a sample bag, writing a label, and placing into a dryer for storage for later use.

5. Preparation of the sensor

Preparing a conductive substance solution: the present study used Graphene (GR, graphene) and MXene (Ti ₃ C ₂ Tx and Nb ₂ CTx) as a conductive material, compared to sensors prepared with GR alone as a conductive material and with both GR and MXene as conductive materials, also compared to Ti ₃ C ₂ Tx and Nb ₂ CTx performance of two different MXene as conductive material prepared sensors.

Ti ₃ C ₂ CAS number of Tx: 12363-89-2, nb ₂ CTx CAS number 12069-94-2.

GR was prepared as a GR dispersion at a concentration of 2.5mg/ml using NMP (N-methylpyrrolidone), and MXene was prepared as a MXene thin layer dispersion at a concentration of 2.5mg/ml using deionized water, wherein 2.5mg/ml of titanium carbide (Ti ₃ The C2 Tx) MXene thin layer dispersion is commercially available and used as it is, nb ₂ CTx dispersions were prepared on their own. When the GR and the MXene conductive substances are sprayed, the GR dispersion liquid is sprayed first, and then the MXene dispersion liquid is sprayed after the GR dispersion liquid is dried.

After the fiber film is completely dried, cutting a film with the size of 2cm x 4cm, spraying a conductive substance solution onto the silk fibroin/propolis composite film by adopting a spray gun, placing the film at a natural temperature, and after the film is dried, obtaining the high-density flexible SF/EEP/GR/MXene wearable strain sensor.

2. Performance of SF/EEP film

(1) Surface microtopography characterization

The SF/EEP composite fiber film (SF/EEP film for short) prepared by the electrostatic spinning technology is composed of a large number of nanofibers. In order to meet the requirements of practical applications, SF/EEP films need to have structural characteristics such as porosity, uniform diameter of nanofibers, smooth surface, etc., which enable them to develop into flexible substrates with good breathability. Therefore, the study adopts SEM to observe the microscopic morphology of the SF/EEP film surface so as to optimize various technological parameters of electrostatic spinning. The operation steps are as follows: the SF/EEP film is cut into rectangular samples with the length of 1cm multiplied by 1cm, the samples are subjected to metal spraying treatment, the surfaces of the samples are upwards fixed on a scanning base, and finally SEM observation is carried out on the samples.

In FIG. 2, graphs (a 1) - (a 3) are the surface morphology of pure SF nanofiber membranes (without EEP) at 10 k-times magnification at concentrations of 18,20 and 22wt%, respectively; (b1) - (b 3) at an SF concentration of 20wt%, the surface morphology of the SF/EEP film at a magnification of 10k times was 0.5%,1% and 2% respectively; (c1) - (c 3) SF/EEP film having an SF concentration of 20wt% and an EEP concentration of 1% and electrospinning voltages of 16,18 and 20kV, respectively, had a surface morphology at a magnification of 10k times; (d1) - (d 3) is the surface morphology of SF/EEP films having SF concentration of 20wt% and EEP concentration of 1% and electrospinning jet velocity of 0.004,0.006 and 0.008ml/min, respectively, at 5 k-times magnification at 18 kV.

When the concentration of the electrospun SF is 18wt% or less, the resulting fibers have excessive droplets to make the SF/EEP film surface uneven, and the diameter of the nanofibers is not uniform (a 1 in FIG. 2), which may cause more problematic problems in the subsequent spraying of the conductive material. On the other hand, when the SF concentration is 22wt%, the viscosity of the solution is too high, so that "beads" or "filaments" are formed between the fibers during the electrospinning (a 3 in FIG. 2), and the needle is extremely liable to be blocked, making the whole spinning process difficult. As shown in fig. 2 a2, the fiber diameter obtained from 20wt% SF solution is uniform (518±10 nm), and the inside has pores of proper size and network structure characteristics of cross winding between fibers, which can provide a pre-foundation for the air permeability of the subsequent composite film and the stability of the film after spraying conductive material. Thus, the present study conducted a study with the concentration of SF fixed in the range of 18wt% to 22 wt%.

As shown in FIGS. 2b1-b2, the technical requirement of the low-concentration EEP on the electrostatic spinning is not high, the diameter of the obtained fiber is uniform (528+/-5 nm), and the network structure of the SF/EEP film is obvious. However, when the EEP concentration reaches 2%, the fiber diameter obtained is extremely uneven, the internal structure is disturbed (FIG. 2b 3), and the needle connected to the high-voltage device is easily clogged during the preparation process, and the electrospinning process is difficult to perform.

As shown in fig. 2c1-c3, when the applied external high voltage is 16kV, the obtained nanofiber is bent, and the internal pore of the bracket is large, which is not beneficial to the subsequent spraying of conductive substances. However, when the external high voltage is increased to 18kV, the diameter of the nanofiber has a uniform trend, and the voltage is continuously increased to 20kV so that the diameter of the fiber is continuously reduced, and the fiber is gradually uneven and even broken. The external voltage reaches the electric field strength required by the intrinsic viscosity of the solution, so that the fiber diameter is uniform, and the network structure is clear; however, when the voltage continues to increase to an electric field strength higher than that required for the intrinsic viscosity of the solution, the fibers are broken between the needle and the receiving plate, causing disorder of the internal structure and adversely affecting the mechanical properties of SF/EEP and the like.

As shown in FIGS. 2d1-d3, when the injection speed of the electrospinning is 0.004ml/min, the filaments appear around the fibers and have smaller diameters, which is disadvantageous for the subsequent spraying of the conductive substance. When the injection speed is increased to 0.006ml/min, the fiber is smooth and has a proper diameter. When the injection speed was continuously increased to 0.008ml/min, the fiber diameter and the internal pores were rapidly increased at this time, and various performance indexes of the SF/EEP film at this time were not ideal.

From the above results and analysis, the structure of the SF/EEP film and the diameter of the nanofibers can be controlled by changing the process parameters of the electrospinning, and experimental finding shows that the SF concentration is 20wt%, the EEP concentration is not higher than 1%, the applied voltage is 18kV, and the jet velocity is 0.006ml/min as the process parameters of the electrospinning in the present study.

(2) Mechanical properties

SF is known to have a number of advantages, such as high mechanical strength, ease of processing, etc. In the case of SF/EEP films, compliance with many characteristics of the skin is one of its conditions. The invention adopts a universal tester to respectively carry out tensile test on SF/EEP films containing 18 percent SF film, 20 percent SF 0.5 percent EEP, 20 percent SF 1 percent EEP and 20 percent SF 2 percent EEP. To investigate the effect of EEP addition on SF film mechanical properties. The specific operation is as follows: the SF/EEP film was cut into rectangular samples of 20cm by 10cm and fixed to a jig of a universal tester for tensile testing, and the sample thickness a was measured by vernier calipers. In the process, the stretching speed of the universal testing machine is 100mm/min, UTS (universal mechanical testing machine) is calculated by a formula (2), and a stress-strain curve is directly obtained by testing by the universal testing machine.

The test results are shown in FIG. 3, and the results show that the stress of 18% SF reaches 2.92 (+ -0.13) MPa; the stress of 20% SF is improved to 3.98 (+ -0.23) MPa; and the flexibility of the SF is improved along with the increase of SF concentration, so 20% SF is selected for experiments. When 0.5% EEP is added, the stress is 3.79 (+ -0.45) MPa, at this time, because the content of propolis is less, the effect on SF is not great; when adding 1% EEP, the stress can reach 4.87 (+ -0.19) MPa, the flexibility of SF is improved, and when the EEP content is increased to 2%, the stress is only 2.79 (+ -0.41) MPa, because the content of EEP is increased, the fiber inside the membrane is broken, and the mechanical property of the composite membrane is reduced. Therefore, 20% SF 1% EEP was finally selected for the experiment.

Through the experimental finding, the SF/EEP composite fiber membrane prepared by SF 20wt% and EEP solution 1wt% is finally determined to be used for the subsequent sensor preparation, and the adopted electrostatic spinning process parameters are as follows: the applied voltage was 18kV and the jet velocity was 0.006ml/min.

3. Optimization of sensors

The sensing mechanism of the strain sensor is to spray conductive substances on the SF/EEP film, and the porous nanofiber network structure of the composite film can provide large specific surface area, enough roughness and elasticity, so that the conductive substances are uniformly distributed in the gaps of the film, and the distance between the conductive substances is increased by stretching, bending and other means, so that the change of the material resistance is caused. The resistance change rate is calculated as shown in the formula (1).

Wherein R represents real-time resistance; r is R ₀ Representing the initial resistance; the unit of the rate of change of resistance is (%).

Different amounts of GR and MXene were sprayed onto a film of size 2cm by 4cm and were bent 180℃to find out by comparing the rate of change of the electrical resistanceTo the optimal proportion. Since MXene is a broad class of 2D Transition Metal Carbides (TMC), nitrides and carbonitrides, MXenes has the general formula mn+1xntx, where M is a transition metal (Ti, zr, nb, V, ta, cr, etc.), X is carbon or nitrogen, n=1, 2, 3 or 4, tx represents the surface functionalization of a two-dimensional sheet layer by various groups such as fluorine, oxygen and hydroxyl. In the last few years, the MXene series has been rapidly evolving, and experiments have demonstrated more than 30 different stoichiometric structures, such as Ti ₃ C ₂ Tx、Ti ₂ CTx、Nb ₂ CTx、Nb ₄ C ₃ Tx、V ₂ CTx and Mo ₂ TiC ₂ Tx, and many other theoretical structures exist. Current experiments have demonstrated that Ti ₃ C ₂ Tx has high conductivity and mechanical properties, so this study was conducted by spraying Ti ₃ C ₂ Tx (two-dimensional nano titanium carbide dispersion) and Nb ₂ Comparison of CTx (niobium carbide dispersion) to verify this theory and to conduct the next experiment.

GR dispersion with concentration of 2.5mg/ml and MXene (Ti) with concentration of 2.5mg/ml were taken in different volumes ₃ C ₂ Tx) dispersion, shown in FIG. 4, 3ml GR and 3ml Ti ₃ C ₂ The resistivity of the Tx sensor was about 13 (±2)%; 2ml GR and 2ml Ti ₃ C ₂ The resistivity of the Tx sensor was about 40 (±2)%; 1ml GR and 1ml Ti ₃ C ₂ The resistivity of the Tx sensor was about 17 (±2)%; the total volume of the sprayed conductive material was finally determined to be 4ml. Spraying 1ml GR and 3ml Ti respectively ₃ C ₂ Tx and 3ml GR and 1ml Ti ₃ C ₂ Tx, as shown in FIG. 5, 3ml GR and 1ml Ti ₃ C ₂ The resistivity of the Tx sensor was about 7 (±0.92)%; 2ml GR and 2ml Ti ₃ C ₂ The resistivity of the Tx sensor was about 40 (±2)%; 3ml Ti ₃ C ₂ The resistivity of Tx and 1ml GR sensors is about 100 (+ -3.8)%.

GR with concentration of 2.5mg/ml and MXene (Nb) with concentration of 2.5mg/ml are taken in different volumes ₂ CTx), shown in fig. 6, 3ml gr and 3ml Nb ₂ The rate of change of the resistance of the CTx sensor is about 12 (±1.4)%; 2ml GR and 2ml Nb ₂ Resistance of CTx sensorThe rate of change was about 17 (+ -1.14)%; 1ml GR and 1ml Nb ₂ The rate of change of resistance of CTx sensor is about 15 (±2)%; at this time, it was verified that the rate of change of the sensor resistance was indeed the largest when 4ml of the conductive substance was sprayed, excluding contingencies. As shown in FIG. 7, 3ml GR and 1ml Nb ₂ The rate of change of resistance of CTx sensor is about 7 (±0.92)%; 2ml GR and 2ml Nb ₂ The rate of change of resistance of CTx sensor is about 17 (±1.14)%; 1ml GR and 3ml Nb ₂ The resistivity of CTx sensors varies by about 40 (±5)%.

FIGS. 8 and 9 show the respective concentrations of Ti ₃ C ₂ Tx and different concentrations Nb ₂ The rate of change of resistance of the CTx sensor is analyzed for errors. The rate of change of resistance when only 4ml GR was sprayed was also measured, and as shown in FIG. 10, the rate of change of sensor resistance when GR was sprayed entirely was about 4.2 (+ -0.2%). And due to Ti ₃ C ₂ Tx and Nb ₂ The solvent of CTx is water, and the fully sprayed MXene is crumpled and brittle when the SF composite film is exposed to water, so that subsequent experiments cannot be carried out, and the resistance change rate of the fully sprayed MXene is not studied in the experiment. Verified, 1ml GR and 3ml Ti are sprayed ₃ C ₂ The rate of change of sensor resistance at Tx is the largest. From the above, it is clear that the same content of Ti ₃ C ₂ The resistivity change rate of the Tx composite film is higher than that of the spray Nb ₂ CTx composite membrane. Therefore, the study uses spraying of 1ml GR and 3ml Ti ₃ C ₂ Combinations of Tx were subjected to the next experiment.

The sprayed conductive material (1 ml GR and 3ml Ti ₃ C ₂ Tx) is connected to a universal mechanical tester and coupled to an electrochemical workstation to study the characteristics of the sensor:

(1) As the tensile force increases, the rate of change of resistance also increases. As shown in FIG. 13, the sensitivity of the sensor under different tensile forces was measured and divided into three areas, a low pressure range (1 kPa-7 kPa), a medium pressure range (10 kPa-20 kPa), and a high pressure range (30 kPa-50 kPa). The slopes of the low, medium and high voltage areas are 0.4, 3 and 1.5, respectively, due to the distance between the conductive substances during stretching, which increases once tension is applied to the sensor due to the relatively uniform distribution of the conductive substances between the holes and gaps by spraying due to the very holes and gaps in the composite film. When a smaller force (1 kPa-7 kPa) is applied, the distance between conductive substances increases less, and the rate of change of resistance is smaller at this time, so the linear slope is also smaller; when the applied tensile force increases (10 kPa-20 kPa), the distance between the conductive substances increases greatly because it is not stretched to the maximum, and at this time, the rate of change of the resistance becomes large, so the linear slope is also large; when a larger internal force is applied, the distance between the conductive substances increases, but the slope decreases because the stretching range has reached a maximum. Therefore, the sensor has good sensitivity, and the areas of low voltage, medium voltage and high voltage tend to be linear.

(2) The sensor shows a wide sensing range (1 kPa-50 kPa) and good stability as clearly observed from the different tension load-unload repeated cycling responses of the sensor as shown in fig. 11, 12. FIG. 14 shows SF/EEP/GR/Ti based ₃ C ₂ The outstanding stability of the sensor of the Tx composite, after 100 compression load-unload cycles of 0 to 25kPa, the sensing response remained stable with no significant drop, indicating the potential for reliable, stable and long-term service of human motion monitoring.

4. Sensor performance

(1) Air permeability properties

The air permeability refers to the function of the base material for exchanging air and moisture between the skin and the environment, and has the characteristics of adjusting and keeping temperature and humidity balance. Conventional flexible polymeric substrates, such as PDMS, are generally impermeable to air and breathable, which can lead to skin discomfort. The air permeability of the SF nanocomposite fiber membrane was evaluated by a water vapor transmission index test. The polymer film was used to cover a bottle containing 20g of purified water. And covering bottle with open bottle, PDMS film, pure SF nanofiber film (20% SF electrostatic spinning fiber film), SF/EEP/GR/Ti film ₃ C ₂ Tx film (SF 20wt%, EEP solution 1wt% SF/EEP film prepared was sprayed with 1ml GR and 3ml Ti ₃ C ₂ Tx) the overlay bottles were subjected to comparison at 37 ℃ and 20% relative humidity. The manner of calculation of WVTR is shown in equation (3).

Wherein W is ₀ 、W _t Respectively weighing the system before and after incubation (g); t is the length of the time interval (h); WVTR has a unit of (gm ^-2 day ^-1 )。

As shown in FIG. 15, after being left at 37℃and 20% humidity for 192 hours, the PDMS film-covered bottle, in which almost 85% of water was kept, was covered with a pure SF nanofiber film having a higher water vapor permeability than the PDMS film-covered bottle, and GR and Ti were incorporated into the SF nanofiber film ₃ C ₂ After Tx, the air permeability of the composite film does not change much compared to that of a pure SF film.

(2) Biocompatibility of

Due to SF/EEP/GR/Ti-based ₃ C ₂ The Tx strain sensor is directly placed on human skin for human health monitoring, and the biocompatibility and toxicity of the Tx strain sensor are of great significance. The growth of NIH3T3 fibroblasts is tested by CCK-8 test method as a judgment of SF/EEP/GR/Ti ₃ C ₂ Standard for the biocompatibility of the sensor of Tx nanocomposite. With a nanofiber membrane containing pure SF (20% SF electrospun fiber membrane) and SF/EEP/GR/Ti ₃ C ₂ The morphology and number of NIH3T3 fibroblasts cultured with the Tx composite membrane soak were almost identical to those of the blank, as shown in FIG. 16, demonstrating SF/EEP/GR/Ti ₃ C ₂ The Tx composite film has good biocompatibility.

(3) Antibacterial property

Adopting solid plate culture method, grouping (white: pure SF nanofiber membrane (20% SF electrospun fiber membrane), black: SF/EEP/GR/Ti) ₃ C ₂ Tx composite film) the treated sample was attached to the surface of a medium full of Staphylococcus aureus, with the test face down, and gently pressed to bring the sample into full contact with the medium, and the petri dish was placed in a constant temperature incubator at 37℃for 24 hours. After the cultivation is completed, taking out, taking a picture by using a common camera, and measuring the size of the inhibition zone by using a ruler, wherein the repetition number is 3.

The test result of the inhibition zone shows that: the black sample has obvious antibacterial effect on staphylococcus aureus. The black sample contains the organic extract EEP produced by bees, has good antibacterial performance, and can achieve excellent antibacterial effect by introducing the EEP into a silk fibroin composite membrane, thereby being beneficial to long-term use of the sensor, and the results are shown in figure 17 and table 1.

TABLE 1 diameter of inhibition zone

Example 2 application example- -use for monitoring human Activity

The flexible strain sensor comprises a basal layer and a sensing layer, wherein the basal layer is an SF/EEP film, the lower layer of the sensing layer is a GR layer, and the upper layer of the sensing layer is Ti ₃ C ₂ And a Tx layer, wherein the sensing layer lower layer contacts the base layer. The sensor is reliable and has potential real-time full-range human motion detection equipment due to high sensitivity and high response speed.

1. Flexible strain sensor for detecting finger bending

The flexible strain sensor is mounted on the joint of the index finger of a person and connected to the electrochemical workstation to measure the movement signals of the finger in the bending and unbending states. The bending angles of the fingers are 15 degrees, 30 degrees, 45 degrees and 90 degrees respectively, when the fingers are bent, the sensor rapidly reacts to stretching actions, and the resistance value is obviously increased to a stable value due to the change of the distance between the conductive substances; when the finger straightens, the distance between the conductive substances in the sensor can be better restored to the initial state, and the resistance can be better restored to the initial value. As shown in fig. 18, when the finger is bent by 15 °, the sensor resistance change rate is about 4 (±0.5%; when the finger is bent by 30 degrees, the change rate of the sensor resistance is about 6.5 (+ -0.2)%; when the finger is bent by 45 degrees, the change rate of the sensor resistance is about 11.5 (+ -0.5)%; when the finger is bent by 90 °, the sensor resistance change rate is about 27 (+ -0.7)%. As is clear from the above, as the bending angle increases, the resistance increases during bending, and the rate of change of the resistance increases further. The finger repeatedly bends and straightens, and the response curve can keep a certain stability, which indicates that the sensor has a certain stability and repeatability.

2. Flexible strain sensor for detecting wrist, elbow and knee bending

The flexible strain sensor is installed on the wrist, elbow and knee joint of a person, and is connected to an electrochemical workstation to measure the motion signals of the wrist in the bending and stretching states. The response principle is consistent with the finger bending and stretching principle. As shown in fig. 19, 20, 21, when the wrist is bent by 90 °, the sensor resistance change rate is about 78 (±2)%; when the elbow is bent by 90 °, the sensor resistivity is about 128 (+ -2)%; (when the sensor is bent 180 DEG more than before, because the sensor is just bent and not in tension; when the sensor is attached to the elbow, the sensor is not only bent but also in tension when the elbow is bent.) the rate of change of the sensor resistance when the knee is bent 45 DEG is about 55 (+ -5)%.

From the above examples, the sensor has important significance for detecting physical rehabilitation training and treating muscle injury. Therefore, this strain sensor has great potential in medical diagnosis and monitoring care.

Claims

1. The preparation method of the propolis silk fibroin composite membrane based on MXene is characterized by comprising the following steps:

2. The method of manufacturing according to claim 1, characterized in that: preparing SF solution with concentration of silk fibroin of 19.5-20.5wt% in the step 1); in step 2), the propolis is dissolved in 65-75% ethanol solution, and the concentration of the propolis in EEP solution is 0.09-0.11g/ml.

3. The method of manufacturing according to claim 1, characterized in that: in the step 3), the volume ratio of SF solution to EEP solution is 100:0.9-1.1.

4. The method of manufacturing according to claim 1, characterized in that: the electrostatic spinning process parameters in the step 4) are as follows: the spinning voltage is 17.5 kV-18.5 kV, the solution injection speed is 0.0055 ml/min-0.0065 ml/min, and the spinning distance is 15cm.

5. The method of manufacturing according to claim 1, characterized in that: the concentration of GR dispersion or MXene thin layer dispersion in step 5) is 2.4-2.6mg/m; the MXene is Ti ₃ C ₂ Tx。

6. The method of manufacturing according to claim 1, characterized in that: in step 6), the total amount of 3.5-4.5ml of conductive substance solution is sprayed on each 7-9 square meter cm of composite fiber film, wherein the volume ratio of GR dispersion liquid to MXene thin layer dispersion liquid is 1:2.7-3.3.

7. The method of manufacturing according to claim 1, characterized in that: the silk fibroin in the step 1) is prepared by adopting cocoons as raw materials through the following method: na for shearing silkworm cocoons ₂ CO ₃ Degumming with solution, washing with water, drying to obtain degummed silk fibroin, and mixing degummed silk fibroin with formic acid and CaCl ₂ Mixing and stirring until dissolved, centrifuging to obtain supernatant, drying, and removing Ca from the dried solid ²⁺ And (3) plasma to prevent conductive particles from affecting measurement of the resistance value of the composite film after spraying the conductive substances, and drying to obtain the silk fibroin for preparing the SF solution.

8. An MXene-based propolis silk fibroin composite membrane, characterized in that: the silk fibroin composite fiber film comprises a silk fibroin composite fiber film containing antibacterial substance propolis and a conductive layer grafted on the fiber film, wherein the conductive layer is made of GR and MXene, and is prepared by the preparation method of any one of claims 1 to 7.

9. Use of an MXene-based propolis silk fibroin composite film of claim 8 in the preparation of a flexible electronic device.

10. The use according to claim 9, characterized in that: the flexible electronics is a flexible wearable strain sensor.