A linear response stretchable resistive strain sensor

Abstract

A linear response stretchable resistive strain sensor belongs to the field of wearable sensor technology. It is a three-layer membrane structure, including a stretchable elastic substrate, a middle strain sensitive layer, and a top stretchable elastic package. The nano-conductive material network bonded with trace polymers has a high conductivity close to that of pure nano-conductive materials and enhances the mechanical stability of the conductive network. After the initial stretching, uniform and random cracks are formed to form a stable structure similar to a planar spring. The strain of the object under test drives the change in the size of the air gap in the crack, changes the conductive path, and then changes the resistance. The present invention demonstrates the detection capability of the sensor in the strain range of 0.001% to 100%, hysteresis (1.61%), linear response, sufficiently fast reaction speed and extremely low residual resistance. It also includes stability, insensitivity to pressure and waterproofness, which is suitable for long-term and accurate monitoring of the strain of soft systems such as biological tissues in the medical and health field.

Description

Technical Field

[0001] The present invention belongs to the technical field of wearable sensors, and in particular relates to a linear response stretchable resistive strain sensor. Background Art

[0002] Compared with capacitive, inductive, and magnetic inductive sensing mechanisms, resistive sensors only require simple readout circuits. Resistance measurements are insensitive to magnetic field interference and the dielectric properties of biological tissues / fluids, making them ideal candidates for biomedical and healthcare applications. Traditional resistive strain sensors (including metal foils and semiconductor devices) are widely used and reliable, but are not compatible with applications involving biological tissues / organs, such as the strain range of 0-100% in typical medical and health fields. Material strategies for stretchable resistive strain sensors include intrinsically stretchable conductor materials, stretchable structures composed of non-stretchable conductors, and low-dimensional nanocomposites. Resistive sensors that use geometry to detect strain, such as liquid metals, ionic liquids / gels, and conductive polymers, are generally less sensitive. Resistive sensors based on crack and contact resistance can provide extremely high sensitivity, but their upper limit of strain detection is low, at 2-5%, and they usually face problems such as highly nonlinear response, hysteresis, attenuation, and crack propagation.

[0003] Nanocomposites combine non-conductive polymers with metal nanowires, carbon black, graphene sheets, carbon nanotubes, MXene, etc., and are used for stretchable strain sensors. Nanocomposites have stable structures and good stretchability. However, due to the viscoelastic effect of polymers such as silicone, the reconstruction of fillers during polymer relaxation, and the friction between fillers and polymers, the response recovery speed is slow, the hysteresis is large, and the measurement of small strains is inaccurate. Recent work based on multi-composite materials has further broadened the strain detection range and improved the sensitivity. However, the hysteresis and nonlinearity problems are still not solved. Summary of the invention

[0004] In order to solve at least one of the above-mentioned and other technical problems in the prior art, the present invention provides a linear response stretchable resistive strain sensor, which can accurately measure the strain of the object under test across multiple orders of magnitude, achieve linear response within a wide strain range, solve the hysteresis problem that conventional resistive strain sensors cannot solve, broaden the detection capability of ultra-small strains, and can take into account long-term stability, providing new ideas for the development of resistive strain sensors for medical and health care applications.

[0005] The present invention provides a linear response stretchable resistive strain sensor, comprising:

[0006] a strain-sensitive layer consisting of a network of nano-conductive materials bonded by stretchable polymers;

[0007] a stretchable elastic base layer, located below the strain sensitive layer and bonded to the strain sensitive layer;

[0008] A stretchable elastic encapsulation layer encapsulated above the strain sensitive layer;

[0009] Among them, the strain sensitive layer is based on a network of trace polymer-bonded nano-conductive materials (TPN), which has a conductivity close to that of pure nano-conductive materials. The cracks formed after the initial stretching constitute a stable structure similar to a planar spring, so that the resistance of the strain sensitive layer increases linearly with the increase of strain.

[0010] Beneficial effects:

[0011] According to a specific embodiment of the present invention, a strain sensor based on a trace polymer bonded carbon nanotube (TP-CNT, TracePolymer-Bonded Carbon Nanotube) network is capable of detecting strains spanning five orders of magnitude. Compared with most existing resistive sensors, the TP-CNT sensor has a low hysteresis of 1.61% and a good linear range of 0-100% strain. The sensor has fast response, extremely low detection limit (0.001%), excellent long-term stability, waterproof, pressure insensitivity and biocompatibility. It has a wide adjustable performance range, simple manufacturing, and can be easily customized for various applications, attached to deformable tissues and biomedical devices for healthcare applications. In actual medical application scenarios, such as responding to the challenges of tracheal intubation in different patient conditions, it is difficult for medical staff to assess the sealing contact of the cuff and potential over-pressurization leading to pain or injury. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a basic schematic diagram of a linear response stretchable resistive strain sensor of the present invention;

[0013] Figure 2 A strain sensor based on a micro-silicone bonded carbon nanotube (TP-CNT) network and a manufacturing flow chart thereof according to an embodiment of the present invention;

[0014] Figure 3 The present invention is based on a strain sensor based on a micro-silicone bonded carbon nanotube (TP-CNT) network according to an embodiment of the present invention: (a) is a diagram of its overall structural model; (b) is a photo of the actual object;

[0015] Figure 41 is a strain sensor based on a micro-silicone bonded carbon nanotube (TP-CNT) network according to an embodiment of the present invention: (a) is a schematic diagram of a pure carbon nanotube network and a conductive path, and the corresponding scanning electron microscope image is shown below; (b) is a schematic diagram of a micro-silicone bonded carbon nanotube network and a conductive path, and the corresponding scanning electron microscope image is shown below;

[0016] Figure 5 It is a strain sensor based on a micro-silicone bonded carbon nanotube (TP-CNT) network according to an embodiment of the present invention, and a comparison of the initial resistance values ​​of a control group thereof;

[0017] Figure 6 Schematic diagram of a strain sensor based on a micro-silicone bonded carbon nanotube (TP-CNT) network according to an embodiment of the present invention: (a) before stretching; (b) after stretching 100%; (c) finite element analysis of the TP-CNT network potential distribution diagram.

[0018] Figure 7 The basic characteristics of a strain sensor based on a micro-silicone bonded carbon nanotube (TP-CNT) network according to an embodiment of the present invention are as follows: (a) resistance-strain curve and linear fitting line in the stretching and releasing stage; (b) minimum strain detection limit; (c) maximum strain; (d) performance comparison with other similar sensors;

[0019] Figure 8 This is an embodiment of the present invention, a strain sensor based on a micro-silicone bonded carbon nanotube (TP-CNT) network: (a) comparison of residual resistance after large strain; (b) pressure insensitive characteristics; (c) 10,000 cycle stability;

[0020] Fig. 9 This is a schematic diagram of an embodiment of the present invention, in which a strain sensor based on a trace amount of silicone bonded carbon nanotube (TP-CNT) network is pasted on the surface of a silicone block; (a) a schematic diagram of a silicone block with four sensors integrated on the side, and the result of the four sensors being used as a tilt sensor; (b) the silicone block being tested is immersed in water, and small ripples in different directions generated by a finger lightly touching the water surface at different positions A and B are detected.

[0021] Fig.10 This is a schematic diagram of an embodiment of the present invention, in which a strain sensor based on a micro-silicone bonded carbon nanotube (TP-CNT) network is pasted on the middle part of an endotracheal tube balloon, (a) the endotracheal tube connects the patient's trachea and the ventilator circuit during intubation surgery; (b) the simulation experimental device; (c) the resistance response of the balloon when it is incrementally inflated by 2.5 kPa; (d) the resistance change process of the balloon when it is inflated in an open environment and in a printed trachea with an inner diameter of 25.44 mm, 26 mm, and 26.1 mm, respectively, when the inflation pressure increases from 1.5 kPa to 4 kPa.

[0022] Fig.11 This is a schematic diagram of a strain sensor based on a micro-silicone bonded carbon nanotube (TP-CNT) network for detecting swallowing and breathing coordination according to an embodiment of the present invention, (a) two TP-CNT sensors attached to the Adam's apple and chest can monitor swallowing and breathing coordination; (b) swallowing and breathing signals recorded when a volunteer drinks water; (c) normal swallowing behavior; (d) recorded swallowing signals when drinking water, drinking yogurt, and eating biscuits.

[0023] In the drawings, the meanings of the reference numerals are as follows:

[0024] 1. Stretchable elastic packaging layer;

[0025] 2. Strain sensitive layer;

[0026] 3. Stretchable elastic base layer;

[0027] 4. Conductive path;

[0028] 5. Nano conductive materials;

[0029] 6. Stretchable polymers. DETAILED DESCRIPTION

[0030] Below, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of embodiments of the present invention. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of concepts of the present invention.

[0031] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0032] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0033] In the case of using expressions such as "at least one of A, B, and C, etc.", it should generally be interpreted in accordance with the meaning of the expression generally understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.). In the case of using expressions such as "at least one of A, B, or C, etc.", it should generally be interpreted in accordance with the meaning of the expression generally understood by those skilled in the art (for example, "a system having at least one of A, B, or C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0034] The present invention provides a linear response stretchable resistive strain sensor, which is based on a trace polymer-bonded nano-conductive materials (TPN) network. Figure 1 The figure is a basic schematic diagram of a linear response stretchable resistive strain sensor of the present invention. The inserted figure is an enlarged schematic diagram of a micro-polymer bonded nano-conductive material (TPN) network. The working principle includes:

[0035] Higher aspect ratios for different nanoconductive materials ( Figure 1 5) monomers, providing many electrical contact points, thus achieving good overall conductivity in the three-dimensional network. However, the pure nano-conductive material network cannot stably maintain its shape and will break and peel off when a large strain is applied. However, once the pure nano-conductive material network is stretched by a small amount of stretchable polymer ( Figure 1 6), which can achieve both good mechanical stability and high conductivity close to that of a pure nanoconductive material network. Although almost all the surfaces of the nanoconductive materials are covered by the stretchable polymer, the electrical contact points between the nanoconductive materials remain almost unchanged, thus maintaining high conductivity. Crucially, due to the strain sensitive layer ( Figure 1 The TPN network and its upper and lower stretchable elastic substrate layers ( Figure 1 3) and a stretchable elastic encapsulation layer ( Figure 1 There is a huge gap in stretching capacity between the two layers (see Figure 1). During the pre-stretching process, a stable crack structure similar to a planar spring is generated in the strain sensitive layer. If the maximum strain does not exceed the pre-stretching strain value during actual use, no new cracks will be generated. That is, the strain sensitive layer can maintain long-term dynamic mechanical stability and conductivity, and can restore its original conductivity after the strain is released to zero.

[0036] The above-mentioned spraying process utilizes the nanoscale solvent-driven capillary wetting phenomenon to spontaneously form a TPN network of the strain sensitive layer. The mixed solution of the nanoconductive material and the volatile solvent is ultrasonically treated to obtain a dispersed solution, which is sprayed on the uncured stretchable polymer film. Due to the high pressure and the impact when the sprayed solution reaches the substrate, there are many electrical contact points in close contact between the nanoconductive materials, thus having high conductivity. During the drying process, the volatile solvent evaporates rapidly, spontaneously driving a small amount of uncured polymer into the nanoconductive material network. The infiltrated stretchable polymer will cover the surface of the nanoconductive material monomer and the small gaps between the monomers. After the trace amount of stretchable polymer in the nanoconductive material network is cured, it provides electromechanical bonding between the nanoconductive material monomers to form a stable TPN network of the strain sensitive layer.

[0037] The linear response stretchable resistive strain sensor comprises: a strain sensitive layer ( Figure 1 2 in the figure), made of a stretchable polymer ( Figure 1 The nano-conductive material ( Figure 1 5) network structure; stretchable elastic base layer ( Figure 1 3 in the figure), located below the strain sensitive layer and bonded to the strain sensitive layer; a stretchable elastic packaging layer ( Figure 1 1 in the figure), encapsulated above the strain sensitive layer, wherein the strain sensitive layer has good conductivity close to that of pure nano conductive materials and good mechanical stability. The cracks formed after the initial stretching constitute a stable structure similar to a planar spring, so that the resistance of the strain sensitive layer increases linearly with the increase of strain.

[0038] The preparation process of the above sensors includes:

[0039] Step 1: Place the nano-conductive material ( Figure 1 5) is mixed with a volatile solvent to form a uniform dispersion. The nano-conductive material can be carbon nanotubes, carbon nanorods, metal nanowires, metal organic framework materials, graphene, and MXene.

[0040] Step 2: On the fully cured stretchable elastic base layer ( Figure 1 3), adding a layer of uncured stretchable polymer ( Figure 1 The stretchable polymer may be silicone rubber, polydimethylsiloxane, polyethylene, polypropylene, or polyurethane.

[0041] Step 3: Spray the dispersion evenly on the uncured stretchable polymer, and use a mask to form a conductive network pattern of a specific shape to form a strain sensitive layer. Figure 1The conductive paths in the conductive network pattern are shown ( Figure 1 4).

[0042] Step 4: After the volatile solvent is completely evaporated, leads are added to both ends of the strain sensitive layer. Finally, the whole is covered with a layer of uncured stretchable polymer as a stretchable elastic encapsulation layer, and the stretchable polymer is cured to form a complete strain sensor.

[0043] In the above sensor, the change of the resistance in the strain sensitive layer is determined in the following manner: the strain of the measured object causes the size of the air gap in the crack to change, causing the conductive path in the strain sensitive layer ( Figure 1 The reference numeral 4) in the figure changes, that is, the resistance series-parallel model changes, which in turn causes the resistance in the strain sensitive layer to change.

[0044] Depend on Figure 1 It can be seen that the sensor is a three-layer membrane structure similar to a sandwich, that is, the strain sensitive layer and the stretchable elastic base layer and the stretchable elastic packaging layer on the upper and lower sides thereof constitute a three-layer membrane structure similar to a sandwich.

[0045] The upper surface of the stretchable elastic base layer is interlocked and bonded with the strain sensitive layer, and the lower surface of the stretchable elastic base layer is connected to the object to be measured. The strain of the object to be measured drives the size of the air gap in the crack to change, resulting in a conductive path ( Figure 1 The change of the resistance series-parallel model in the figure (4) causes the change of the resistance in the strain sensitive layer to measure the strain of the object under test. The interlocking bonding refers to the capillary phenomenon driven by the volatile solvent, which spontaneously drives the uncured stretchable polymer to penetrate into the pure nano-conductive material network. When the stretchable polymer is cured, the strain sensitive layer and the stretchable elastic substrate layer are reliably bonded.

[0046] The lower surface of the stretchable elastic packaging layer is bonded to the strain sensitive layer to protect the strain sensitive layer from interference from external water and dust.

[0047] The strain sensor based on a micro-polymer bonded carbon nanotube (TP-CNT) network is capable of detecting strains spanning five orders of magnitude. Compared with most existing resistive sensors, the TP-CNT sensor has a low hysteresis of 1.61% and a good linear range of 0-100% strain. The sensor has fast response, extremely low detection limit (0.001%), excellent long-term stability, waterproof, pressure insensitivity and biocompatibility. It has a wide performance adjustment range, simple manufacturing, and can be easily customized for various applications, attached to deformable tissues and biomedical devices for healthcare applications. In actual medical application scenarios, such as responding to the challenges of tracheal intubation in different patient conditions, it is difficult for medical staff to assess the sealing contact of the cuff and potential over-pressurization leading to pain or injury. Based on this embodiment of the present invention, a balloon with an integrated TP-CNT sensor is developed to accurately measure the inflation state of the balloon, providing a reliable solution for contact state assessment. In addition, in terms of solving dysphagia, this embodiment of the present invention has been proven to have the ability to monitor breathing and swallowing biomechanics, providing a technical solution for patients with dysphagia.

[0048] Figure 2 FIG. 2 shows a specific embodiment of the present invention, that is, a preparation process of a TP-CNT strain sensor. Figure 2 As shown, the process includes the following steps:

[0049] Step 1: mixing carbon nanotubes into isopropanol and dispersing by ultrasonication to obtain a dispersed solution;

[0050] Step 2: Spin-coat liquid silicone rubber on the fully cured base silicone rubber layer as a bonding penetration layer;

[0051] Step 3: Wait for a while at room temperature until the silicone rubber is cross-linked to a semi-viscous state, and then stick the mask on the surface of the semi-cross-linked silicone rubber;

[0052] Step 4: Spray the dispersed solution on the bonding penetration layer through the mask using a spray gun. After each spraying, wait for the isopropyl alcohol to evaporate quickly before continuing the next spraying, and finally obtain the TP-CNT network structure;

[0053] Step 5: Remove the mask and use stretchable conductive silver paste to bond wires at both ends of the TP-CNT. Continue to spin-coat silicone rubber on the TP-CNT for encapsulation and wait for it to completely solidify. Finally, a three-layer membrane structure sensor is formed, such as Figure 3 shown.

[0054] The control group 1 of the above specific embodiment:

[0055] Step 1: dissolving carbon nanotubes in isopropanol and dispersing by ultrasonication to obtain a dispersed solution;

[0056] Step 2: Use a spray gun to spray the carbon nanotube isopropyl alcohol dispersion on the polyimide film substrate through the mask. After each spraying, wait for the isopropyl alcohol to evaporate quickly before continuing the next spraying, and finally obtain a pure carbon nanotube (pure CNT) network structure;

[0057] Step 3: Tear off the mask and use stretchable conductive silver paste to bond leads at both ends of the pure carbon nanotube network structure.

[0058] Control group 2 of the above specific embodiment:

[0059] Step 1: dissolving carbon nanotubes in isopropanol and dispersing by ultrasonic to obtain a dispersion solution; calculating the mass of silicone rubber according to the carbon nanotube filler ratio of 3wt% in the carbon nanotube polymer composite (CPC, CNT-polymer composite), adding it to the dispersion solution, stirring evenly, and obtaining a carbon nanotube-silicone rubber-isopropanol dispersion solution;

[0060] Step 2: Spin-coat liquid silicone rubber on the fully cured base silicone rubber layer as a bonding penetration layer;

[0061] Step 3: Wait for a while at room temperature until the silicone rubber is cross-linked to a semi-viscous state, and then stick the mask on the surface of the semi-cross-linked silicone rubber;

[0062] Step 4: Use a spray gun to spray the above ternary dispersion on the bonding penetration layer through the mask. After each spraying, wait for the isopropyl alcohol to evaporate quickly before continuing the next spraying, and finally obtain the CPC network structure;

[0063] Step 5: Remove the mask and use stretchable conductive silver paste to bond leads at both ends of the CPC;

[0064] Step 6: Continue to spin-coat silicone rubber on CPC and wait for it to cure thoroughly.

[0065] In this specific embodiment of the present invention, the carbon nanotubes may be multi-walled carbon nanotubes (MW-CNTs) having a diameter of 10-20 nm, a length of 10-30 μm, and an aspect ratio of more than 1000. Figure 4 As shown in the scanning electron microscope image below (a), its extremely high aspect ratio provides many electrical contact points between different carbon nanotubes, thereby achieving good overall conductivity in the three-dimensional network. However, the pure carbon nanotube network cannot stably maintain its shape and will crack and peel off when large strain is applied. Once the pure carbon nanotube network is bonded by a trace amount of silicone, it can obtain both good mechanical stability and high conductivity close to that of a pure carbon nanotube network. Although almost all the surfaces of the carbon nanotubes are covered with silicone, the electrical contact points between the carbon nanotubes remain almost unchanged, thereby maintaining high conductivity, which accounts for 41.76% of the conductivity of the pure carbon nanotube network ( Figure 5 ). In addition, the electrical conductivity of TP-CNT is 33.74 times higher than that of carbon nanotube-silicon composite (CPC) (with carbon nanotube filling ratio above the percolation threshold). Crucially, after the pre-stretching process, the TP-CNT network remains mechanically stable and conductive after 100% re-stretching and can recover its original conductivity after strain release to zero.

[0066] The spontaneous infiltration process driven by capillary action can be used to efficiently and reliably prepare TP-CNT networks. Figure 4 As shown in (b), an ultrasonically treated carbon nanotube-isopropyl alcohol (IPA) dispersion is sprayed on an uncured silicone film. Due to the high pressure and the impact when the sprayed solution reaches the substrate, there are many electrical contact points between the CNTs in close contact, resulting in high conductivity. During the drying process, IPA evaporates rapidly, and capillary action automatically drives a small amount of uncured silicone into the carbon nanotube network. The infiltrated silicone covers the surface of the carbon nanotubes and the small gaps between individual carbon nanotubes and carbon nanotube bundles. After cross-linking, the trace amount of silicone in the carbon nanotube network is cured, providing mechanical bonding between the carbon nanotubes to form a stable three-dimensional TP-CNT network.

[0067] A specific example of the present invention, TP-CNT, demonstrates the detection capability of this sensor in the strain range of 0.001% to 100%, with extremely low hysteresis (1.61%), linear response, fast reaction speed and extremely low residual resistance. In addition, it also includes stability of 10,000 cycles, insensitivity to pressure and waterproofness, which is suitable for long-term monitoring of strain in soft systems such as biological tissues. Further examples of tracheal intubation and real-time monitoring of dysphagia have been demonstrated to verify that it can provide stable and reliable measurement results in the field of medical health. These characteristics and effects will be described in further detail below.

[0068] The characteristics of a specific example TP-CNT sensor of the present invention are as follows:

[0069] The sensor is pre-stretched by 120% to fully generate the crack structure. No new cracks will be generated during the subsequent stretching process in the range of 0-100%, and the crack structure remains stable. The silicone of the substrate layer has a tensile strain capacity of at least 400%. Microscopically, because CNT is dominant in TP-CNT, its fracture strain is much smaller than that of the substrate, resulting in cracks that form a stable microstructure similar to a planar spring. Figure 6 This is the sensing principle of the strain sensor based on the micro-silicone bonded carbon nanotube (TP-CNT) network in a specific embodiment of the present invention. Figure 6In (a) and (b), the top is a real picture, the bottom is a scanning electron microscope image of the crack microstructure, and the right is a schematic diagram of the conductive path. (a) is the picture before TP-CNT stretching, (b) is the picture after TP-CNT stretching 100%, and (c) is the finite element analysis of the TP-CNT network potential distribution diagram. When the applied strain increases from 40% to 80%, the number of current lines decreases and the shape becomes distorted, and the resistance value calculated by simulation increases. Before and after the TP-CNT sensor is stretched, the increase in the air gap in the crack changes the conductive path, resulting in a change in the overall equivalent resistance of the nano conductive network. In the strain range of 0-100%, when the stretching speed is 1% L / s, the resistance strain curve of the TP-CNT sensor has an ultra-small hysteresis of 1.61% and a linear response ( Figure 7 (a) in the figure). The TP-CNT sensor has a stable and accurate measurement capability of strain detection from 0.001% to 100%, spanning 5 orders of magnitude. According to the static noise and sensitivity of the resistor, the theoretical minimum detectable strain is 0.0008% ( Figure 7 (b) in the figure). In contrast, the CPC has no significant resistance response even under a strain excitation of 0.026%. Considering unexpected situations in actual scenarios, this device has a maximum detectable strain of more than 300% ( Figure 7 (c) in Figure 1). Comprehensively considering the minimum detectable strain, maximum detectable strain and hysteresis, TP-CNT significantly surpasses other current sensors ( Figure 7 (d) in the figure.

[0070] Resistive stretchable sensors generally have the problem of large residual resistance and poor mechanical stability after large strain excitation. Based on the unique microstructure of TP-CNT, the present invention can basically restore its original conductivity after the strain is released to zero ( Figure 8 (a) in the figure), while the CPC of the control group has significant resistance residual. In complex application scenarios such as medical health, there is often crosstalk between different axes. The sample is subjected to a periodic compression of 2 N perpendicular to the sensor. Compared with the resistance response of the sample when it is stretched by 2% strain, this sensor is insensitive to pressure ( Figure 8 (b) in the figure). From a microscopic perspective, the use of solvent-driven micro-silica gel to infiltrate carbon nanotubes and the additional encapsulation of the outermost layer of TP-CNTs reinforce the interlocking layer between the conductive material and the elastic substrate, thereby enhancing the long-term mechanical stability of the device. The sample was subjected to a 13% strain and repeated for 10,000 cycles ( Figure 8 (c) in the figure). Taking the first cycle as the reference, the resistance peak value attenuated by 7.52% at the 300th cycle, and the resistance curve maintained excellent repeatability afterwards. Compared with similar inventions, the present invention exhibits excellent long-term stability.

[0071] Testing the reliability and waterproofness of the TP-CNT strain sensor of this specific embodiment for use in an actual soft system includes:

[0072] Fig. 9 An embodiment of the present invention shows that a strain sensor based on a micro-silicone bonded carbon nanotube (TP-CNT) network is pasted on the surface of a silicone block to preliminarily verify its reliability and waterproofness on the surface of a soft system, wherein (a) shows a schematic diagram of a silicone block, four sensors integrated on the side, and the result of a tilt sensor; (b) the silicone block under test is immersed in water to detect small ripples in different directions generated by a finger touching the water surface at different positions A and B. Further, the TP-CNT sensors are pasted on the four sides of a silicone block made of silicone rubber, as shown in the model diagram ( Fig. 9 The silicone block was initially mounted on a glass plate and the tilt angle was changed by manual adjustment. The resulting data illustrates the stable relationship between resistance and tilt angle. In the subsequent waterproof test, the block was fixed in a water tank, and the silicone rod was pushed by the weak water waves generated by lightly touching the water surface without touching the silicone rod directly. Fig. 9 In (b), these disturbances are effectively detected by the corresponding resistors, while the response of the adjacent resistors is very small. The experiments preliminarily confirmed that the sensor can accurately detect various strains, respond quickly, and maintain reliable waterproof performance on soft substrates.

[0073] This embodiment is used to improve the intelligence of tracheal intubation in medical health, including:

[0074] Fig.10 According to one embodiment of the present invention, a strain sensor based on a micro-silicone bonded carbon nanotube (TP-CNT) network is attached to the middle of a tracheal intubation balloon to verify its ability to monitor the balloon expansion process and the contact state with the tracheal wall, wherein (a) shows the tracheal intubation connecting the patient's trachea to the ventilator circuit during the intubation operation; (b) shows a simulation experimental device, a 3D printed sleeve simulates human tracheas of different diameters, and a syringe pump inflates the balloon; (c) shows the resistance response when the balloon is incrementally inflated by 2.5 kPa, and when the balloon is in full contact with the tracheal wall, the resistance no longer increases; (d) shows the resistance change process of the balloon when it is inflated in an open environment and in a printed trachea with an inner diameter of 25.44 mm, 26 mm, and 26.1 mm, respectively, when the inflation pressure increases from 1.5 kPa to 4 kPa. The following is a detailed description:

[0075] In the intensive care unit, mechanical ventilation involves delivering oxygen to the lungs through the patient's airways ( Fig.10(a) in the figure). The endotracheal tube connects the patient's airway to the ventilator, and the balloon (endotracheal tube balloon) ensures the airway is sealed and stable, preventing air leakage, preventing the backflow of contaminants, and preventing ventilator-associated pneumonia. The recommended balloon pressure is 20-30 cm (1.96-2.94kPa). Insufficient pressure can cause the balloon to wrinkle or separate from the trachea, allowing fluid or gas to pass; excessive pressure may cause ischemic tracheal injury. Ideally, balloon pressure should be monitored regularly with a manometer. In practice, healthcare providers usually manually assess pressure by squeezing the indicator balloon of the endotracheal tube to maintain optimal contact between the trachea and the balloon, which relies heavily on their experience. Few studies have explored the integration of sensors onto endotracheal tubes, and no studies have specifically focused on balloon air pressure. Due to its ultrathin (200 μm) and stretchable design, accurate small strain detection capability ( Figure 7 (b) in the figure), is not sensitive to pressure ( Figure 8 (b)), waterproof ( Fig. 9 (b)) and excellent biocompatibility, the TP-CNT sensor is very suitable for integration into the balloon ( Fig.10 (b) in the figure). Monitoring the change in balloon diameter can evaluate the contact status between the balloon and the tracheal wall in real time. The experimental setup uses a 3D-printed tube sleeve to simulate the different inner diameters of the human trachea. A syringe pump is controlled to gradually inflate the balloon in steps of 0.18 kPa, simulating the medical scenario of inflating the balloon by a syringe. For example, the inner diameter of the trachea (3D-printed tube) is 26 mm ( Fig.10 In (c)), the balloon pressure continued to increase from 1.5 kPa to 4 kPa, while the recorded resistance stopped increasing when the pressure reached 3.21 kPa, at which point the balloon did not inflate further due to firm contact with the tracheal wall. It is worth noting that the pressure-time curve does not provide information about the balloon inflation or the contact status of the balloon with the tracheal wall, while the resistance-time curve clearly shows the turning point at which medical staff should stop inflating the balloon. Fig.10 As shown in (d), even a small change in wall diameter from 25.44 mm to 26 mm and 26.1 mm results in significant differences in the resistance-pressure curves, indicating the critical pressure required to ensure firm contact. In practice, it is very beneficial to provide medical staff with reliable information on contact status, as patients may have different tracheal wall characteristics. In summary, the TP-CNT sensor-integrated balloon can monitor the contact between the balloon and the tracheal wall in real time, providing a promising solution for improving safety and patient health in medical rehabilitation and mechanical ventilation.

[0076] The TP-CNT strain sensor of this specific embodiment is used for real-time monitoring of dysphagia in the medical field, including:

[0077] Fig.11 This is a schematic diagram of a strain sensor based on a micro-silicone bonded carbon nanotube (TP-CNT) network for detecting swallowing and breathing coordination according to a specific embodiment of the present invention, in order to verify its ability to accurately detect swallowing and breathing processes at the same time, wherein (a) two TP-CNT sensors attached to the Adam's apple and chest can monitor swallowing and breathing coordination, divided into three modes A, B, and C; (b) swallowing and breathing signals are recorded when volunteers drink water; (c) normal swallowing behavior, including type B and type C, occurs at different stages of the respiratory cycle; (d) swallowing signals recorded when drinking water, drinking yogurt, and eating biscuits. Refer to the following Fig.11 Describe in detail:

[0078] Breathing and swallowing are closely linked anatomically. Swallowing begins with protective closure of the airway: the larynx rises and the epiglottis presses down to protect the glottis, followed by controlled closure of the glottis. After swallowing is complete, the larynx returns to its original position, as indicated by the rapid peaking and subsequent descent of the thyroid cartilage (Adam's apple). Swallowing occurs primarily during the second half of the expiratory phase ( Fig.11 In (a), the probability is 75% during the C phase, and during the inspiratory phase ( Fig.11 Stage A in (a), with a probability of 3%), rarely occurs, highlighting the physiological contradiction between inspiration and swallowing. Closure of the glottis during exhalation is essential to protect the airway, while the glottis is in a relaxed state during inspiration, and uncoordinated swallowing may cause aspirated material to enter the trachea instead of the esophagus, increasing the risk of lung infection or death. Therefore, the coordination of swallowing and breathing is crucial. The risk of aspiration pneumonia is significantly higher with solid or semisolid food than with liquid intake. Detection of dysphagia usually requires a modified barium swallow, which carries radiation risks, while respiratory inductance plethysmography is considered the gold standard for assessing breathing. However, these diagnostic methods require specialized hospital equipment and well-trained personnel, so there is a need for easily accessible home-use devices that can be used for early detection and monitoring in complex clinical situations to enhance safety and proactive care.

[0079] Here, we introduce a simple wearable sensing system that can monitor the swallowing and breathing coordination process in real time ( Fig.11 (a) in Figure 1). The first TP-CNT sensor was attached to a healthy male volunteer above the Adam's apple, with the skin and sensor in a pre-stretched state. During swallowing, the Adam's apple first rises and then falls, causing the resistance to first decrease and then increase. The second sensor was attached to a stretchable belt. When the volunteer inhaled, the chest expanded, stretching the sensor and increasing the resistance. The subsequent resistance-time curve is marked as "IN" during inspiration, while the resistance decreases during exhalation, marked as "EX". In the case of swallowing water ( Fig.11 In (b), the data of three swallows were extracted for analysis. Fig.11As shown in (c), we can know the specific stage in the respiratory cycle where each swallow occurs, such as stage B (the transition stage between inhalation and exhalation) and stage C (the middle and late stages of breathing). We can also know the duration of each swallow, and judge the degree of completion of each swallowing action by the amplitude of the swallowing curve. The breathing curve shows that there is a coordinated pause in breathing during each swallow. In addition, swallowing foods of different viscosities is demonstrated: water, yogurt, and chewed biscuits. Swallowing water and yogurt produced similar smooth resistance-time curves, while higher frequency signals were observed when swallowing biscuits ( Fig.11 In summary, this simple wearable sensor system based on TP-CNTs recorded synchronized breathing and swallowing behaviors, providing a potential technical solution for early detection and cost-effective rehabilitation training of high-risk dysphagia patients.

[0080] The specific embodiments of the present invention are described above. However, these embodiments are only for the purpose of illustration, and are not intended to limit the scope of the present invention. Although each embodiment is described above, it does not mean that the measures in each embodiment cannot be used in combination. The scope of the present invention is defined by the attached claims and their equivalents. Without departing from the scope of the present invention, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present invention.

Claims

1. A linear response stretchable resistive strain sensor, characterized in that: include: A strain-sensitive layer (2) composed of a network of nano-conductive materials (5) bonded to a stretchable polymer (6); A stretchable elastic base layer (3) is located below the strain sensitive layer (2) and is bonded to the strain sensitive layer (2); A stretchable elastic packaging layer (1) is packaged above the strain sensitive layer (2); The strain sensitive layer (2) has a conductivity close to that of a pure nano conductive material (5), and cracks formed after the initial stretching form a stable structure similar to a planar spring, so that the resistance of the strain sensitive layer (2) increases linearly with the increase of strain; The preparation process of the sensor is as follows: Step 1: mixing the nano conductive material (5) with a volatile solvent to form a uniform dispersion; Step 2: Adding a layer of uncured stretchable polymer (6) as an adhesive layer on the fully cured stretchable elastic base layer (3); Step 3: spraying the dispersion evenly on the uncured stretchable polymer (6), and forming a specific conductive network pattern using a mask to form a strain sensitive layer (2); Step 4: After the volatile solvent has completely evaporated, leads are added to both ends of the strain sensitive layer (2), and finally the entire layer is covered with a layer of uncured stretchable polymer (6) as a stretchable elastic packaging layer (1) to form a complete strain sensor.

2. A linear response stretchable resistive strain sensor according to claim 1, characterized in that: The process in which the resistance of the strain sensitive layer (2) increases linearly with increasing strain includes: the strain of the measured object causes the size of the air gap in the crack to change, resulting in a change in the conductive path (4), that is, a change in the series-parallel model of resistance, thereby causing the resistance of the strain sensitive layer (2) to change.

3. The linear response stretchable resistive strain sensor according to claim 1, characterized in that: The upper surface of the stretchable elastic base layer (3) is interlocked and bonded to the strain sensitive layer (2), and the lower surface of the stretchable elastic base layer (3) is bonded to the object to be measured. The strain generated in the object to be measured drives the size of the air gap in the crack to change, causing the conductive path (4) to change, that is, the resistance series-parallel model to change, thereby causing the resistance of the strain sensitive layer (2) to change, so as to achieve the measurement of the strain of the object to be measured.

4. The linear response stretchable resistive strain sensor according to claim 1, characterized in that: The lower surface of the stretchable elastic packaging layer (1) is interlocked and bonded to the strain sensitive layer (2).

5. The linear response stretchable resistive strain sensor according to claim 1, characterized in that: The nano-conductive material (5) is at least one of carbon nanotubes, carbon nanorods, metal nanowires, metal organic framework materials, graphene, and MXene.

6. The linear response stretchable resistive strain sensor according to claim 1, characterized in that: The stretchable polymer (6) is at least one of silicone rubber, polydimethylsiloxane, polyethylene, polypropylene, and polyurethane.

7. The linear response stretchable resistive strain sensor according to claim 1, characterized in that: The strain-sensitive layer (2) can be stretched by a maximum of more than 300%.

8. The linear response stretchable resistive strain sensor according to claim 5, characterized in that: The carbon nanotubes are multi-walled carbon nanotubes with a diameter of 10-20 nm, a length of 10-30 μm, and an aspect ratio of more than 1000.

9. The linear response stretchable resistive strain sensor according to claim 1, characterized in that: The volatile solvent is isopropyl alcohol.

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