CN115198512A

CN115198512A - Propolis and silk fibroin composite membrane based on MXene and preparation method and application thereof

Info

Publication number: CN115198512A
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: 2022-10-18
Anticipated expiration: 2042-07-18
Also published as: CN115198512B

Abstract

The invention discloses a preparation method of a propolis silk fibroin composite membrane based on MXene, which comprises the following steps: 1) Preparing an SF solution: taking silk fibroin, and preparing 19-21wt% SF solution 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 an SF/EEP composite solution: mixing SF solution and EEP solution uniformly to obtain SFEEP complex 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 substance, and air drying to obtain the composite membrane. The composite film has good antibacterial property and conductivity, wide induction range (1 kPa-50 kPa) and outstanding stability.

Description

Propolis and 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 as well as a preparation method and application thereof.

Background

Silk Fibroin (SF) is a natural protein fiber, has good biocompatibility, degradability and excellent mechanical properties, thus having great attraction in flexible electronic products, and also has good flexibility, being easy to be attached to the skin, improving the hard form of the traditional sensor, and further meeting the requirements of flexible wearable sensors.

Transition metal carbides and nitrides (MXenes) are an emerging family with excellent properties, including high electrical conductivity, good hydrophilicity, large specific surface area, etc. MXene is produced by selective etching of the "A" layer from the MAX phase and can be represented by the general formula Mn +1XnTx, where M represents an early transition metal (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 composite film is sprayed on the composite film, so that the conductivity of the composite film is effectively improved, and the unique performance of the composite film enables the composite film to show great potential in the preparation and application of strain sensors.

With the development of semiconductor and internet of things technologies, flexible wearable sensors have good application prospects in the fields of personal wearable electronic equipment, human-computer interaction, intelligent robots and the like, and have attracted great research interests due to the superior real-time sensing capability, high integration potential and portability of the sensors. In particular, the flexible wearable sensor plays an important role in the personal wearable electronic device, and can effectively capture the physiological parameters of the human body and convert the physiological parameters into electronic signals, thereby realizing the monitoring of the health of the human body. Human health monitoring mainly includes pulse sensation analysis, acoustics, swallowing, and finger movement. The flexible wearable strain sensor has a 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 the limitation of the sensor, is beneficial to realizing remote and movable monitoring, screening and prevention and health monitoring of diseases, and can be beneficial to normalization and family monitoring of human health monitoring. Therefore, the method also has good application prospect and market value. Although applications based on human bodies are considered, bacteria, fungi and the like may have negative effects on human health when the sensor is used for a long time, so that a wearable flexible sensor with excellent antibacterial effect and excellent conductivity is needed.

Disclosure of Invention

The invention aims to solve 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 silk fibroin concentration of 19-21wt% by using formic acid as a solvent;

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

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

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

6) Spraying a conductive substance: spraying the prepared GR dispersion liquid on the dried composite fiber film, and spraying the MXene thin-layer dispersion liquid after drying; spraying 3-5ml of conductive substance solution in total per 7-9 cm of the composite fiber film, wherein the volume ratio of the GR dispersion liquid to the MXene thin-layer dispersion liquid is 1: 2.5-3.5; and (3) drying to obtain the MXene-based propolis silk fibroin composite membrane.

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

The volume ratio of the SF solution to the EEP solution in step 3) is 100: 0.9-1.1 or 100: 1.

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

The concentration of the GR dispersion liquid or the MXene thin-layer dispersion liquid in the step 5) is 2.4-2.6mg/ml or 2.5mg/ml; the MXene is Ti ₃ C ₂ Tx。

And 6) spraying 3.5-4.5ml or 4ml of total conductive substance solution per 7-9 cm or 8 cm of composite fiber membrane, wherein the volume ratio of the GR dispersion liquid to the 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 silkworm cocoons as raw materials through the following method: cutting silkworm cocoon into pieces with Na ₂ CO ₃ Degumming the solution, washing with water, drying to obtain degummed fibroin, mixing the degummed fibroin with formic acid and CaCl ₂ Mixing, stirring to dissolve, centrifuging, collecting supernatant, drying, soaking in water to remove Ca ²⁺ And (3) carrying out plasma to prevent the conductive particles from influencing the measurement of the resistance value of the composite membrane after spraying the conductive substance, and then drying to obtain the silk fibroin for preparing the SF solution.

The invention further aims to provide a propolis and silk fibroin composite membrane based on MXene, 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 and is prepared by adopting the preparation method of any one of the materials.

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

Preferably, the flexible electronic device is a flexible wearable strain sensor.

The invention has the beneficial effects that:

(1) The propolis is adopted to increase the antibacterial property of the silk fibroin membrane, experimental research shows that the fiber inside the membrane is broken due to the excessive addition of the EEP, so that the mechanical property of the composite membrane is remarkably reduced, and experiments show that the proper propolis addition not only ensures that the composite membrane has good antibacterial property, but also ensures good mechanical property. 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 proper SF and EEP concentration in the SF-EEP composite solution and the electrostatic spinning process are found out, so that the fibers obtained by spinning are smooth and have proper diameters.

(3) The invention adopts silk fibroin and propolis for blending, and then adopts spraying GR and MXene (Ti) ₃ C ₂ Tx and Nb ₂ CTx), the conductivity of which is obviously enhanced by conductive substances GR and Ti ₃ C ₂ Tx and Nb ₂ Comparison of CTx found using GR-Ti ₃ C ₂ The conductive material of Tx collocation has the best conductivity and sensitivity.

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

Drawings

FIG. 1 is a flow chart of a preparation method of the SF/EEP/GR/MXene composite membrane of the invention.

FIG. 2 is a SEM surface morphology representation of SF/EEP films.

FIG. 3 is a graph showing the results of mechanical property tests of SF composite films.

FIG. 4 shows the total amount of SF/EEP/GR/Ti used for different conductive materials ₃ C ₂ Rate of change of resistance of the Tx composite film.

FIG. 5 shows the difference GR and Ti ₃ C ₂ SF/EEP/GR/Ti prepared with Tx usage ₃ C ₂ Resistance change rate of the Tx composite film.

FIG. 6 shows the total amount of SF/EEP/GR/Nb used for different conductive materials ₂ The rate of change of resistance of the CTx composite film.

FIG. 7 shows different GR and Nb ₂ SF/EEP/GR/Nb prepared by CTx using amount ₂ The rate of change in resistance of the CTx composite film.

FIG. 8 shows different total amounts of conductive material and different GR and Ti ₃ C ₂ SF/EEP/GR/Ti prepared with Tx usage ₃ C ₂ Maximum resistance change rate error analysis chart of Tx composite film.

FIG. 9 shows different total amounts of conductive material and different GR and Nb ₂ SF/EEP/GR/Nb prepared by CTx using amount ₂ And (3) a maximum resistance change rate error analysis diagram of the CTx composite film.

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

FIG. 11 is SF/EEP/GR/Ti ₃ C ₂ And (3) a repeated cyclic response experimental result chart of different tension loading-unloading of the Tx composite membrane.

FIG. 12 is SF/EEP/GR/Ti ₃ C ₂ And (3) an error analysis chart of the result of the repeated cyclic response experiment of loading and unloading of different tensile forces of the Tx composite membrane.

FIG. 13 is SF/EEP/GR/Ti ₃ C ₂ And (3) testing the sensitivity of the Tx composite membrane under different tensile forces.

FIG. 14 is SF/EEP/GR/Ti ₃ C ₂ And (5) testing the circulating durability of the Tx composite membrane at 25 kPa.

Fig. 15 is a graph showing changes in air permeability of an SF composite membrane with time.

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 compoundingAnd (5) testing the bacteriostatic circle of the membrane.

FIG. 18 shows SF/EEP/GR/Ti at different degrees of finger flexion ₃ C ₂ Response behavior of Tx complex film sensors.

FIG. 19 is the chart of SF/EEP/GR/Ti in wrist flexion ₃ C ₂ Tx complex film sensor response.

FIG. 20 shows SF/EEP/GR/Ti at elbow flexion ₃ C ₂ Tx complex film sensor response.

FIG. 21 is the SF/EEP/GR/Ti curve of the knee ₃ C ₂ Tx complex film sensor response.

Detailed Description

The invention is further illustrated by the following examples, which are not intended to be limiting.

The experimental procedures in the following examples are all conventional procedures unless otherwise specified; the biological and chemical reagents used are all conventional reagents in the field and are all commercially available if no special indication is given.

Example 1

1. Preparation of flexible SF/EEP/GR/MXene wearable strain sensor

The method comprises the steps of adding a propolis solution with good antibacterial property into a silk fibroin solution with good biocompatibility, enhancing the antibacterial property and flexibility of a film through the interaction of the propolis solution and the silk fibroin solution, preparing the composite film by adopting an electrostatic spinning method, spraying MXene and GR on the surface of the composite film to improve the conductivity of the composite film, and carrying out operation steps as shown in figure 1.

1. Preparation of Silk Fibroin (SF) solution

(1) Cleaning: taking 15 silkworm cocoons with uniform size, cutting each silkworm cocoon into 4 pieces, placing into a beaker filled with a proper amount of ultrapure water, placing into an ultrasonic cleaning instrument, ultrasonically cleaning for 8min at the power of 100Hz, taking out the silkworm cocoons, and washing impurities on the surfaces of the silkworm cocoons by running water.

(2) And (3) drying: and (3) putting 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: 4.24g of Na ₂ CO ₃ Solid adding 2L electricityPreparing 0.02M Na in ultrapure water with resistivity of 18.25M omega cm ₂ CO ₃ And (3) solution. Na is charged by an electric furnace with a power of 1000W ₂ CO ₃ Heating the solution to boiling, at which time, pouring Na into the silkworm cocoon ₂ CO ₃ Stirring in the solution to degum for 45min.

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

(5) Preparing an SF solution: taking out degummed silk fibroin and dissolving in formic acid and CaCl ₂ In the method, the reagent ratio is formic acid stock solution and solid CaCl ₂ And (3) drying the fibroin, wherein the mass ratio of the dried fibroin is = 10: 1: 2.5, and stirring by a magnetic stirrer for 4h until the fibroin is completely dissolved.

(6) Centrifuging: after the fibroin is completely dissolved, the solution is centrifuged for 20min in a centrifuge with the working parameter of 9000rpm and 4 ℃, and the supernatant is collected.

(7) And (3) drying: the supernatant was placed in a petri dish and allowed to dry overnight.

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

(9) Preparing a high-concentration SF solution: taking the dried SF and formic acid solution (adopting formic acid stock solution) to prepare SF solution with different concentrations of 16wt% -22 wt%, and marking as solution I.

2. Preparation of propolis (EEP) solution

Taking appropriate amount of propolis, adding 0.5g propolis into 5ml 70% ethanol solution, dissolving for 3 hr, and taking EEP solution after completely dissolving.

Propolis is a sticky solid jelly formed by mixing plant resin collected by worker bees with secretions such as jawbone and cerifera, and the like, and the raw propolis used in the embodiment is purchased from Anxin bee industry Co., ltd (Yunnan).

3. Preparation of SF/EEP composite solution

Adding 0.05ml, 0.1ml and 0.2ml of EEP solution into 10ml of solution I respectively, magnetically stirring for 4h, and standing for 24h for later use after the EEP solution is completely mixed with the SF solution to obtain the SF/EEP composite solution. 0.05ml, 0.1ml and 0.2ml of EEP solution are added into the SF/EEP composite solution respectively, and the concentration of the EEP solution in the SF/EEP composite solution is calculated to be 0.5wt%, 1wt% and 2wt%.

4. Preparation of SF/EEP composite fiber film material

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

5. Preparation of the sensor

Preparing a conductive substance solution: graphene (GR, graphene) and MXene (Ti) were used in this study ₃ C ₂ Tx and Nb ₂ CTx) as a conductive substance, comparing sensors prepared using GR alone as a conductive substance and using both GR and MXene as conductive substances, and also comparing Ti ₃ C ₂ Tx and Nb ₂ CTx performance of sensors made with two different mxenes as conductive substances.

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

GR was prepared with NMP (N-methylpyrrolidone) as a 2.5mg/ml GR dispersion and MXene was prepared with deionized water as a 2.5mg/ml thin layer dispersion of titanium carbide (Ti) 2.5mg/ml ₃ C2 Tx) MXene thin layer dispersion was used as it is as a commercial product, nb ₂ CTx dispersion was prepared by itself. When spraying two kinds of conductive matter, firstly spraying GR dispersion liquid, after drying, spraying MXene componentAnd (4) dispersing.

And cutting off a membrane with the size of 2cm x 4cm after the fiber membrane is completely dried, spraying a conductive substance solution onto the silk fibroin/propolis composite membrane by using a spray gun, placing at a natural temperature, and drying to form a membrane to obtain the high-density flexible SF/EEP/GR/MXene wearable strain sensor.

2. Properties of SF/EEP film

(1) Surface micro-topography characterization

The SF/EEP composite fiber film (SF/EEP film for short) prepared by the electrostatic spinning technology is composed of a large amount of nano fibers. In order to meet the requirements of practical application, the SF/EEP film needs to have structural characteristics such as porosity, uniform diameter of nanofibers, and flat surface, which enable the SF/EEP film to develop into a flexible substrate with good air permeability. Therefore, the microscopic morphology of the surface of the SF/EEP film is observed by adopting the SEM in the research so as to optimize various process parameters of electrostatic spinning. The operation steps are as follows: and (3) cutting the SF/EEP film into a rectangular sample of 1cm multiplied by 1cm, carrying out gold spraying treatment on the sample, fixing the sample on a scanning base with the surface facing upwards, and finally carrying out SEM observation on the sample.

In FIG. 2, plots (a 1) - (a 3) are the surface morphology at 10k magnification of pure SF nanofiber membranes (without EEPs) at concentrations of 18,20 and 22wt%, respectively; (b1) - (b 3) the surface morphology of the SF/EEP film at a magnification of 10k times, with EEP concentrations of 0.5%,1% and 2%, respectively, at an SF concentration of 20 wt%; (c1) The surface morphology of SF/EEP films with the electrostatic spinning voltage of 16,18 and 20kV under the magnification of 10k times when the SF concentration on (c 3) is 20wt% and the EEP concentration is 1%; (d1) - (d 3) is the surface morphology of SF/EEP film at magnification factor of 5k, with SF concentration of 20wt%, EEP concentration of 1%, and voltage of 18kV, and electrostatic spinning jet velocities of 0.004,0.006 and 0.008ml/min, respectively.

When the concentration of the electrospun SF is 18wt% or less, the obtained fiber has too many droplets to make the surface of the SF/EEP film uneven, and the diameter of the nanofiber is not uniform (a 1 in FIG. 2), which may cause more difficult-to-solve problems in the subsequent process of spraying the conductive material. At an SF concentration of 22wt%, due to the excessively high viscosity of the solution, "beads" or "filaments" appear between the fibers during electrospinning (a 3 in FIG. 2), and the needle is easily clogged, making the entire spinning process difficult. As shown in a2 in fig. 2, the fiber diameter obtained from the SF solution with 20wt% is uniform (518 ± 10 nm), the inside has pores with proper size and the network structure characteristics of cross winding between fibers, which provides the former base for the functions of air permeability of the subsequent composite membrane and the stability of the membrane after spraying the conductive substance. Therefore, the present study conducted the study fixing the concentration of SF in the range of 18wt% to 22 wt%.

As shown in FIGS. 2b1-b2, the EEP with low concentration has low technical requirement on electrostatic spinning, the obtained fiber has uniform diameter (528 +/-5 nm), and the network structure of the SF/EEP film is obvious. However, when the EEP concentration reaches 2%, the obtained fiber has extremely non-uniform diameter and disordered internal structure (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 nanofibers are bent, and the pores inside the scaffold are large, which is not favorable for subsequent spraying of conductive substances. However, when the external high voltage is increased to 18kV, the diameter of the nanofiber tends to be uniform, and the diameter of the fiber is continuously reduced and gradually becomes non-uniform even if the fiber is broken due to the fact that the voltage is continuously increased to 20 kV. The external voltage reaches the electric field intensity required by the inherent viscosity of the solution, so that the fiber diameter is uniform and the network structure is clear; however, when the voltage continues to increase above the electric field strength required for the inherent viscosity of the solution, the fibers are pulled apart between the needle and the receiving plate, resulting in a disordered internal structure and adversely affecting the mechanical properties of the SF/EEP.

As shown in FIGS. 2d1-d3, when the injection speed of electrospinning is 0.004ml/min, there are "filaments" around the fibers and the diameter is small, which is not favorable for the subsequent spraying of the conductive material. When the injection rate was increased to 0.006ml/min, the fibers were smooth and of suitable diameter. When the injection speed is increased to 0.008ml/min, the fiber diameter and the internal porosity are increased sharply, and the SF/EEP film has undesirable performance indexes.

From the above results and analysis, it can be known that the structure of the SF/EEP film and the diameter of the nanofibers can be controlled by changing the electrostatic spinning process parameters, and through experimental investigation, the electrostatic spinning process parameters of the present study are selected as the SF concentration of 20wt%, the EEP concentration of not higher than 1%, the applied voltage of 18kV, and the jet velocity of 0.006ml/min.

(2) Mechanical Properties

SF is known to have a series of advantages such as high mechanical strength and easy processing. In the case of SF/EEP membranes, compliance with many properties of the skin is one of its conditions. The present invention uses a universal tester to perform tensile testing on SF/EEP films containing 18% SF, 20% SF, 0.5% EEP, 20% SF 1% EEP, 20% SF 2% EEP, respectively. To investigate the effect of EEP addition on the mechanical properties of SF films. The specific operation is as follows: the SF/EEP film was cut into a rectangular sample of 20 cm. Times.10 cm, and the sample was fixed to a jig of a universal tester to be subjected to a tensile test, and the thickness a of the sample was measured by a vernier caliper. In the process, the tensile speed of the universal tester is 100mm/min, UTS (universal mechanical tester) is calculated by formula (2), and the stress-strain curve is directly obtained by testing of the universal tester.

The results of the tests are shown in FIG. 3, and indicate that the SF was 18% at a stress of 2.92 (+ -0.13) MPa;20% increase in SF stress to 3.98 (+ -0.23) MPa; and the flexibility thereof becomes better with the increase of the SF concentration, so 20% SF is selected for experiments. When 0.5% EEP was added, the stress was 3.79 (+ -0.45) MPa, because the influence on SF was small because the propolis content was small; when adding 1% of EEP, the stress can reach 4.87 (+ -0.19) MPa, improving the flexibility of SF, and when the content of EEP is increased to 2%, the stress is only 2.79 (+ -0.41) MPa, which is because the increased content of EEP leads to the breakage of fibers in the membrane, and the mechanical property of the composite membrane is reduced. Therefore, experiments were carried out using 20-volume SF 1-volume EEP.

Through the experiment, the SF/EEP composite fiber membrane prepared by selecting the SF/EEP composite solution with the weight percent of SF 20 percent and the weight percent of EEP solution 1 percent is finally determined to be used for preparing the subsequent sensor, 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 that conductive substances are sprayed on the SF/EEP film, the composite film has a porous nanofiber network structure which can provide large specific surface area, sufficient roughness and elasticity, the conductive substances are uniformly distributed in gaps of the film, and the distance between the conductive substances is increased by means of stretching, bending and the like, so that the resistance of the material is changed. The resistance change rate is calculated in the manner shown in formula (1).

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

GR and MXene with different contents are sprayed on films with the size of 2cm x 4cm, and when the films are bent by 180 degrees, the optimal proportioning is found by comparing the resistance change rates. Since MXenes are a large class of 2D Transition Metal Carbides (TMC), nitrides and carbonitrides, MXenes have the general formula Mn +1XnTx, where M is a transition metal (Ti, zr, nb, V, ta, cr, etc.), X is carbon or nitrogen, and n =1,2, 3 or 4,tx indicates the surface functionalization of the two-dimensional sheet by various groups such as fluorine, oxygen and hydroxyl. The MXene series have developed rapidly over the past few years and experiments have demonstrated over 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 there are many other theoretical structures. Current experiments have demonstrated Ti ₃ C ₂ Tx has high conductivity and mechanical properties, so this study was done 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 carry out the next experiment.

Taking different volumes of GR dispersion with concentration of 2.5mg/ml and MXene (Ti) with concentration of 2.5mg/ml ₃ C ₂ Tx) dispersion experiments were performed, 3ml GR and 3ml Ti, as shown in FIG. 4 ₃ C ₂ The resistance change rate of the Tx sensor is about 13 (± 2)%; 2ml GR and 2ml Ti ₃ C ₂ The resistance change rate of the Tx sensor is about 40 (± 2)%; 1ml GR and 1ml Ti ₃ C ₂ The resistance change rate of the Tx sensor is about 17 (± 2)%; the total volume of the sprayed conductive substance was finally determined to be 4ml. Spray coating 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 resistance change rate of the Tx sensor is about 7 (± 0.92)%; 2ml GR and 2ml Ti ₃ C ₂ The resistance change rate of the Tx sensor is about 40 (± 2)%; 3ml of Ti ₃ C ₂ The resistance change rates of the Tx and 1ml GR sensors were about 100 (+ -3.8)%.

Taking 2.5mg/ml GR and 2.5mg/ml MXene (Nb) in different volumes ₂ CTx) from FIG. 6, 3ml GR and 3ml Nb ₂ The rate of change of resistance of the CTx sensor was about 12 (± 1.4)%; 2ml GR and 2ml Nb ₂ The rate of change of resistance of the CTx sensor was about 17 (± 1.14)%; 1ml GR and 1ml Nb ₂ The rate of change of resistance of the CTx sensor was about 15 (± 2)%; it was verified at this time that the rate of change of the sensor resistance was indeed the greatest when 4ml of conductive material was sprayed, excluding contingency. As shown in FIG. 7, 3ml GR and 1ml Nb ₂ The resistance change rate of the CTx sensor was about 7 (± 0.92)%; 2ml GR and 2ml Nb ₂ The rate of change of resistance of the CTx sensor was about 17 (± 1.14)%; 1ml GR and 3ml Nb ₂ The resistance change rate of the CTx sensor was about 40 (± 5)%.

FIG. 8 and FIG. 9 show the respective concentrations of Ti ₃ C ₂ Tx and different Nb concentrations ₂ The rate of change of resistance of the CTx sensor was analyzed for errors. At the same time, the resistance change rate was measured when only 4ml GR was sprayed, and as shown in FIG. 10, the sensor resistance change rate was about 4.2 (+ -0.2)%, when GR was fully sprayed. And due to Ti ₃ C ₂ Tx and Nb ₂ The solvent of CTx is water, and the totally-sprayed MXene cannot be subjected to subsequent experiments because the SF composite film becomes wrinkled and brittle when meeting water, so that the resistance change rate of the totally-sprayed MXene is not researched in the experiments. Verified that 1ml GR and 3ml Ti are sprayed ₃ C ₂ The rate of change of the sensor resistance at Tx is the largest. From the above, it can be seen that the same content of Ti ₃ C ₂ The resistance change rate of the Tx composite film is higher than that of sprayed Nb ₂ A composite film of CTx. Therefore, 1ml GR and 3ml Ti were sprayed ₃ C ₂ The combination of Tx was subjected to the next experiment.

The conductive material (1 ml GR and 3ml Ti) is sprayed ₃ C ₂ Tx) was attached 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 is measured under different tensile forces and is divided into three regions, 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 three areas of low voltage, medium voltage and high voltage are 0.4, 3 and 1.5 respectively, which are attributed to the change of the distance between the conductive substances during the stretching process, and the conductive substances are uniformly distributed among the holes and the gaps through spraying due to the porous holes and the gaps on the composite film, and the distance between the conductive substances is increased once the tensile force is applied to the sensor. When a small force (1 kPa-7 kPa) is applied, the distance between the conductive substances is increased slightly, the resistance change rate is small, and the linear slope is small; when the applied tension is increased (10 kPa-20 kPa), the unstretched state is maximized, the distance between the conductive materials is increased greatly, the rate of change in resistance is increased, and the linear slope is also increased; when a greater internal force is applied, the distance between the conductive substances increases, but the slope decreases because the stretching range is maximized. Therefore, the sensor has good sensitivity, and the low-voltage, medium-voltage and high-voltage areas tend to be linear.

(2) The different tensile load-unload repetitive cycle responses of the sensor are shown in fig. 11 and 12, and it can be clearly observed that the sensor shows a wide sensing range (1 kPa-50 kPa) and good stability. FIG. 14 shows a graph based on SF/EEP/GR/Ti ₃ C ₂ The outstanding stability of the Tx composite sensor, after 100 compression loading-unloading cycles of 0 to 25kPa, the sensing response remains stable without obvious decrease, indicating that the human motion monitoring is reliable and stableAnd the potential for fixed and long-term service.

4. Performance of the sensor

(1) Air permeability

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 characteristic of adjusting and keeping the temperature and humidity balance. Conventional flexible polymeric substrates, such as PDMS, are generally impermeable and permeable to air, which can cause skin discomfort. The air permeability of the SF nanocomposite fiber membranes was evaluated by a water vapor transmission index test. A polymer film was used to cover a bottle containing 20g of purified water. And the open bottle, PDMS film covered bottle, pure SF nanofiber membrane (20% SF electrospun fiber membrane) covered bottle and SF/EEP/GR/Ti ₃ C ₂ Tx film (SF 20wt%, EEP solution 1wt% prepared SF/EEP film spray coated with 1ml GR and 3ml Ti ₃ C ₂ Tx manufactured) the covered bottles were placed in an environment at a temperature of 37 c and 20% relative humidity for comparison. The way WVTR is calculated is shown in equation (3).

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

Results are shown in fig. 15, where the PDMS film covered bottle, almost 85% of water remained in the bottle after being left at 37 ℃ and 20% humidity for 192h, the bottle covered with pure SF nanofiber film having a higher water vapor transmission rate than the bottle covered with PDMS film, and GR and Ti were introduced into the SF nanofiber film ₃ C ₂ After Tx, the air permeability of the composite membrane does not change much compared to that of the pure SF membrane.

(2) Biocompatibility

Based on SF/EEP/GR/Ti ₃ C ₂ The Tx strain sensor is directly placed on human skin and used for monitoring human health, and the biocompatibility and toxicity of the Tx strain sensor have important significance. The growth of NIH3T3 fibroblasts was tested by CCK-8 assay as an evaluationJudging SF/EEP/GR/Ti ₃ C ₂ Criteria for biocompatibility of sensors of Tx nanocomposites. Using a mixture containing pure SF nanofiber membranes (20% of SF electrospun fiber membranes) and SF/EEP/GR/Ti ₃ C ₂ The morphology and number of NIH3T3 fibroblasts cultured in the Tx composite membrane soak solution are almost the same as those of the blank control group, as shown in FIG. 16, which shows that SF/EEP/GR/Ti ₃ C ₂ The Tx composite membrane has good biocompatibility.

(3) Antibacterial property

By solid plate culture, according to the grouping (white: pure SF nanofiber membrane (20% SF electrospun fiber membrane), black: SF/EEP/GR/Ti ₃ C ₂ Tx composite membrane) the treated sample was attached to the surface of a medium full of staphylococcus aureus, the test surface was facing down, and pressed gently to bring the sample into full contact with the medium, and the petri dish was placed in a 37 ℃ incubator for 24h. After the culture was completed, the cells were taken out and photographed with a general camera and the size of the zone of inhibition was measured with a ruler, and the number of repetitions was 3.

The result of the bacteriostatic zone test shows that: the black sample has obvious antibacterial effect on staphylococcus aureus. The organic extract EEP originated from the black sample containing bee production has good antibacterial performance, and when the organic extract EEP is introduced into the silk fibroin composite membrane, excellent antibacterial effect can be achieved, long-term use of the sensor is facilitated, and the result is shown in figure 17 and table 1.

TABLE 1 zone of inhibition diameter

Example 2 application example-for monitoring human Activity

The flexible strain sensor comprises a substrate layer and a sensing layer, wherein the substrate 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 A Tx layer, wherein the lower sensing layer contacts the base layer. Because of high sensitivity and high response speed, the sensor is a reliable and potential real-time full-range human motion detection device.

1. Flexible strain sensor for detecting finger bending

The flexible strain sensor is arranged on the knuckle of the index finger of a person and connected to an electrochemical workstation to measure the motion signal of the flexible strain sensor in the state of bending and straightening relaxation of the finger. The bending angles of the fingers are respectively 15 degrees, 30 degrees, 45 degrees and 90 degrees, when the fingers are bent, the sensor rapidly reacts to the stretching action, 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 is straightened, the distance between the conductive substances in the sensor can be well restored to the initial state, and the resistance can be well restored to the initial value at the moment. As shown in fig. 18, when the finger was bent 15 °, the sensor resistance change rate was about 4 (± 0.5)%; when the finger is bent by 30 degrees, the rate of change of the sensor resistance is about 6.5 (+ -0.2)%; when the finger is bent at 45 °, the rate of change of the sensor resistance is about 11.5 (± 0.5)%; when the finger is bent by 90 °, the rate of change of the sensor resistance is about 27 (± 0.7)%. As described above, as the bending angle increases, the resistance increases during bending, and the resistance change rate further increases. The finger is repeatedly bent and straightened, 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 bending of wrist, elbow and knee

The flexible strain sensor is arranged on the wrist, elbow and knee joint of a person, and is connected to an electrochemical workstation to measure the motion signals of the flexible strain sensor in the wrist bending and straightening relaxing states. The response principle is consistent with the finger bending and stretching principle. As shown in fig. 19, 20, 21, the rate of change of the sensor resistance was about 78 (± 2)%, when the wrist was bent 90 °; when the elbow bends 90 °, the rate of change of the sensor resistance is approximately 128 (+ -2)%; (the rate of change of resistance of the sensor at this time is greater than the previous 180 degrees of bending of the sensor because the previous sensor was only bent and not in tension; when the sensor was applied to the elbow, the sensor was not only bent but also in tension when the elbow was bent.) this rate of change of resistance of the sensor was about 55 (± 5)% when the knee was bent at 45 degrees.

As can be seen from the above examples, the sensor has great significance for detecting physical rehabilitation training and treating muscle injuries. Therefore, this strain sensor has great potential in medical diagnosis and monitoring care.

Claims

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

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

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

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

2. The production method according to claim 1, characterized in that: SF solution with the silk fibroin concentration of 19.5-20.5wt% or 20wt% is prepared in the step 1); step 2) dissolving propolis in 65-75% or 67-72% or 70% ethanol solution, wherein the concentration of propolis in EEP solution is 0.09-0.11g/ml or 0.1g/ml.

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

4. The method of claim 1, wherein: the electrostatic spinning in the step 4) has the following technological parameters: spinning voltage is 17.5kV to 18.5kV or 18kV, solution injection speed is 0.0055ml/min to 0.0065ml/min or 0.006ml/min, and spinning distance is 15cm.

5. The production method according to claim 1, characterized in that: the concentration of the GR dispersion liquid or the MXene thin-layer dispersion liquid in the step 5) is 2.4-2.6mg/ml or 2.5mg/ml; the MXene is Ti ₃ C ₂ Tx。

6. The method of claim 1, wherein: and 6) spraying 3.5-4.5ml or 4ml of total conductive substance solution per 7-9 cm or 8 cm of composite fiber membrane, wherein the volume ratio of the GR dispersion liquid to the MXene thin-layer dispersion liquid is 1: 2.7-3.3 or 1: 3.

7. The method of claim 1, wherein: the silk fibroin in the step 1) is prepared by taking silkworm cocoons as raw materials through the following method: cutting silkworm cocoon into pieces with Na ₂ CO ₃ Degumming the solution, washing with water, drying to obtain degummed fibroin, mixing the degummed fibroin with formic acid and CaCl ₂ Mixing, stirring to dissolve, centrifuging, collecting supernatant, drying, soaking in water to remove Ca ²⁺ And (3) carrying out plasma to prevent the conductive particles from influencing the measurement of the resistance value of the composite membrane after spraying the conductive substance, and then drying to obtain the silk fibroin for preparing the SF solution.

8. An MXene-based propolis silk fibroin composite membrane is 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 the MXene-based propolis silk fibroin composite membrane of claim 8 in the preparation of flexible electronic devices.

10. Use according to claim 9, characterized in that: the flexible electronic device is a flexible wearable strain sensor.