Design and preparation method of flexible sensing array for plantar pressure monitoring

Abstract

The invention relates to a design and preparation method of a flexible sensing array for plantar pressure monitoring, and the structure of the flexible sensing array for plantar pressure monitoring comprises a first sensing unit and a second sensing unit. The first sensing unit is applied to a first phalanx area, a second phalanx area, a third phalanx area, a fourth phalanx area, a fifth phalanx area, a heel inner side area and a heel outer side area; the second sensing unit is applied to a first metatarsal bone area, a second metatarsal bone area, a third metatarsal bone area, a fourth metatarsal bone area, a fifth metatarsal bone area and a middle foot area, complete expression of plantar pressure information is achieved by optimizing the size, the number and the distribution of the sensing units, and the problems that an existing sensor is low in resolution ratio and insufficient in plantar pressure information expression are effectively solved. The quasi homogeneous material interface of the sensor is enhanced based on a swelling process, and the interface stability and reliability of the sensor are improved; the preparation method of the sensing array for plantar pressure monitoring has the advantages of low cost, easiness in batch preparation and easiness in large-area expansion.

Description

Technical Field

[0001] The invention belongs to the technical field of flexible sensors, and in particular relates to a design of a flexible sensor array for monitoring plantar pressure and a preparation method thereof. Background Art

[0002] Over the past few decades, with the improvement of people's living standards and quality of life, electronic products in the field of human health monitoring have attracted a large number of researchers. The knee joint is the earliest degenerated, most damaged and unhealable joint in the human body. It is estimated that the number of relevant patients in my country is more than 50 million, and authoritative data show that 80% of patients with knee pain are due to degenerative lesions of the knee joint. Once they are sick, they will experience symptoms such as knee pain and swelling, limited movement, and even limb disability, which seriously affects the health of the whole people. Studies have shown that the severity of knee joint diseases directly affects the gait of patients when walking, which will eventually be reflected in the distribution of plantar pressure. Therefore, monitoring the distribution of plantar pressure can understand the gait information of the human body and provide athletes and rehabilitation patients with precise and individualized exercise intervention and rehabilitation guidance. By reducing the parts that bear pressure and adopting appropriate exercise methods, the risk of knee cartilage degeneration can be reduced and the rehabilitation process can be promoted.

[0003] Existing devices based on electronic and sensor technology for measuring plantar pressure are mainly divided into two categories: platform type and wearable insoles. Platform monitoring equipment can provide accurate and detailed measurement data, but the equipment is expensive, large in size, and has limited usage scenarios, limited to laboratory and hospital environments. At the same time, the non-portability of such systems also makes it impossible to monitor plantar pressure signals in real time and unable to feedback current information, so their application is very limited. Nowadays, with the development of smart medical care and the improvement of people's awareness of health management, medical scenarios are gradually shifting to families, and patient rehabilitation requires frequent and real-time monitoring of movement postures. Therefore, wearable pressure insoles are more convenient in comparison, and can also carry out remote, automated, and professional screening assessments and rehabilitation training, which greatly facilitates people's lives.

[0004] However, in the current research on the pattern design of plantar pressure array, the sensor units are basically distributed in a small and sparse density, and the number of sensor units is within 20-50. The spatial resolution of pressure perception is low, and the information expressed is only the basic pressure state of a normal person when walking, which makes it difficult to carry out deeper applications such as disease diagnosis (such as Figure 1 Furthermore, most existing sensors are bonded using glue during integration ( Figure 2 As shown in the figure) or mechanical combination (direct hot pressing), the reliability is insufficient and it is easy to fail during walking or exercise, which will have a certain impact on the stability of the device and it is difficult to meet the requirements of long-term monitoring. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a design of a flexible sensor array for plantar pressure monitoring and a preparation method thereof.

[0006] The structural design of the flexible sensor array for plantar pressure monitoring described in the present invention optimizes the size, number and distribution of the sensor units according to the plantar pressure distribution characteristics of the human body during walking or exercise, thereby achieving complete expression of plantar pressure information; the present invention greatly improves the interface reliability of the sensor through heterogeneous interface enhancement technology, so that it can stably output accurate plantar pressure distribution signals under human movement, meeting the needs of long-term monitoring.

[0007] The technical solution adopted by the present invention is:

[0008] A flexible sensor array for monitoring plantar pressure, the sensor array comprising a first sensor unit and a second sensor unit;

[0009] The first sensor unit is applied to the first phalanx area, the 2nd to 5th phalanx areas, the medial heel area and the lateral heel area;

[0010] The second sensing unit is applied to the first metatarsal region, the second metatarsal region, the third metatarsal region, the fourth metatarsal region, the fifth metatarsal region and the midfoot region.

[0011] The single point side length of the first sensing unit is 4-8.5 mm, and the spacing is 1-3 mm;

[0012] The single point side length of the second sensing unit is 9-15 mm, and the spacing is 1-4 mm;

[0013] The total number of the first sensing units and the second sensing units is 120-160.

[0014] Further, the flexible sensor array for monitoring plantar pressure also includes a third sensor unit and a fourth sensor unit, and the third sensor unit and the fourth sensor unit are applied to the arch area;

[0015] The side length of the third sensing unit is 20-35 mm, the side length of the fourth sensing unit is 20-30 mm, and the distance between the third sensing unit and the fourth sensing unit is 1-7 mm.

[0016] The method for preparing the flexible sensor array for plantar pressure monitoring comprises the following steps:

[0017] (1) Preparation of TPU solution

[0018] Dissolve TPU particles in DMF solvent to obtain a TPU solution;

[0019] (2) Preparation of Conductive Particle Dispersion

[0020] The dispersant PVP is added to the DMF solvent and fully dissolved under stirring conditions; then the conductive particles are added to the above solution, and after stirring and ultrasonic treatment, a conductive particle dispersion is obtained;

[0021] (3) Preparation of pressure-sensitive slurry

[0022] The TPU solution obtained in step (1) and the conductive particle dispersion obtained in step (2) are fully mixed and concentrated by heating to obtain a conductive polymer composite slurry with a relatively high viscosity;

[0023] (4) Preparation of pressure-sensitive composite film

[0024] The conductive polymer composite slurry obtained in step (3) is coated on a substrate, heated and cured to form a film, and then the film is peeled off from the substrate to obtain a pressure-sensitive composite material film;

[0025] (5) Preparation of interdigitated electrode array

[0026] Based on the designed interdigital electrode array pattern, the first silver paste is printed and coated on the flexible substrate through mask printing. After curing, the solder resist green oil is screen printed and coated at the lead intersection. After UV curing to form insulation, the second silver paste is printed and coated. After heating and curing, the interdigital electrode array is obtained.

[0027] (6) Integration of plantar pressure sensor array

[0028] The pressure-sensitive composite material film obtained in step (4) is cut to obtain a plurality of pressure-sensitive composite material film units so as to be adapted to the corresponding positions of the interdigitated electrode array; the plurality of pressure-sensitive composite material film units and the interdigitated electrode array are first immersed in a non-polar solvent, and then the pressure-sensitive composite material film units and the interdigitated electrode array obtained in step (5) are hot-pressed and integrated to obtain the plantar pressure sensor array.

[0029] Among them, the lead crossing refers to: the two leads on the left and right parts of the forked electrode are on the same plane. Therefore, when forming a forked electrode array, all the left leads in the array are connected to form column electrodes, and all the right leads are connected to form row electrodes. There must be a crossing part between the row and column electrodes, which is the lead crossing.

[0030] In step (1), the mass ratio of the TPU particles to the DMF solvent is 1:5.

[0031] In step (2), the mass ratio of the dispersant PVP, the conductive particles and the DMF solvent is 1:7.5:1500;

[0032] The conductive particles are a mixture of CNTs and CB in a mass ratio of (0.6-1):(0-2); preferably, the conductive particles are a mixture of CNTs and CB in a mass ratio of 0.8:0.2.

[0033] In step (3), the mass ratio of TPU in the obtained TPU solution to the conductive particles in the obtained conductive particle dispersion is (88-99):(1-12);

[0034] The solvent was evaporated by heating in a 60°C water bath to 80%.

[0035] In step (4), the temperature for heating and curing is 80°C;

[0036] In step (5), the flexible substrate is a TPU substrate, the UV curing time is 10 seconds, and the heating curing temperature is 80°C.

[0037] In step (6), the plurality of pressure-sensitive composite film units and the interdigitated electrode array are first immersed in cyclohexane at 60-100° C. for 0.5-2 h. 。

[0038] The application of the flexible sensor array for plantar pressure monitoring in flexible wearable devices.

[0039] Among them, TPU can also be replaced by any polymer material, such as polydimethylsiloxane, PDMS; polyimide, PI; epoxy resin, EPOXY, etc.

[0040] The inventors of the present application have discovered in long-term research that the existing sensor arrays used for wearable plantar pressure distribution monitoring have the following deficiencies: ① Low spatial resolution: The spatial resolution of the sensor array in the pressure insole is low, and the distribution of the sensor units cannot accurately and completely express the pressure information of the plantar, and cannot provide characteristic information with reference value for the diagnosis of injuries and diseases; ② Poor reliability of the sensor: Most sensor interfaces are combined using adhesives, which have weak adhesion. In actual application scenarios, the bonding will become unstable due to the addition of external forces, and there is a risk of structural stratification, which will lead to structural failure of the sensor and affect the long-term stable use of the device.

[0041] The present invention has the following specific beneficial effects:

[0042] The flexible sensor array for monitoring plantar pressure of the present invention comprises a first sensor unit and a second sensor unit; the first sensor unit is applied to the first metatarsal area, the second to fifth metatarsal areas, the medial heel area and the lateral heel area; the second sensor unit is applied to the first metatarsal area, the second metatarsal area, the third metatarsal area, the fourth metatarsal area, the fifth metatarsal area and the midfoot area. The structural design is based on the plantar pressure distribution characteristics of the human body during walking or exercise, and the size, number and distribution of the sensor units are optimized, so as to achieve complete expression of plantar pressure information, and effectively solve the problem of low resolution of existing sensors and insufficient expression of plantar pressure information; furthermore, based on the swelling process, the sensor quasi-homogeneous material is achieved. Interface enhancement, that is, by using a non-polar solvent (preferably cyclohexane) to heat and swell the pressure-sensitive composite material film and the TPU substrate printed with electrodes, the molecular chains on the surfaces of the two films can be activated and moved, and physical cross-linking points are generated inside the molecular chains. Then, by means of hot pressing, the external field temperature and pressure are used to generate physical cross-linking between the molecular chains on the surfaces of the two films, thereby realizing stable integration of the flexible pressure sensor interface, improving the interface stability and reliability of the sensor, and solving the problem of structural failure of the sensor due to large differences in chemical components. In addition, the present invention proposes a method for preparing a sensor array for plantar pressure monitoring, which has the advantages of low cost, easy batch preparation, and easy large-area expansion. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0044] Figure 1 The sensor array design for plantar pressure monitoring reported in the prior art is shown; wherein ac is reported in the prior art, and d is a commercially available plantar pressure insole product;

[0045] Figure 2 It is a schematic diagram showing the use of double-sided tape for sensor integration in the prior art;

[0046] Figure 3 The figure shows the pattern design of the flexible sensor array for monitoring plantar pressure of the present invention; wherein a is the position distribution, and b is the interdigital electrode array;

[0047] Figure 4 The display is the CAD design drawing of the array electrode; a is the overall pattern; b is the interdigital electrode array and the row electrode pattern; c is the insulating layer pattern; d is the column electrode pattern;

[0048] Figure 5 The figure shows a physical picture of the flexible sensor array for monitoring plantar pressure according to Example 1 of the present invention; wherein a is a physical picture of a part of the flexible electrode, b is a picture of the detection thickness of 388 μm, and c is a picture of the whole body;

[0049] Figure 6 The figure shows the interface bonding stability test of the flexible sensor array described in Example 1 of the present invention; wherein a is the current response before and after bending 1500 times, and b is the nearly 3000 cycle test before and after bending 1500 times;

[0050] Figure 7 Shown are the actual picture and cycle stability of commercial pressure insoles; a is the actual picture, b is the cycle stability;

[0051] Figure 8 It shows the contour map of plantar pressure when the heel touches the ground, the whole foot stands, and the forefoot touches the ground in three typical support phases, as well as the whole foot touches the ground in a sitting state; among which, a is the pressure insole of the present application, and b is the domestic pressure insole;

[0052] Fig. 9 The display shows the plantar pressure distribution diagram of domestic commercial plantar pressure insoles in three typical support phases: heel contact, full foot standing, forefoot contact, and full foot contact in sitting position;

[0053] Fig.10 Shown is the comparison of bonded / non-bonded interface microstructures under bending, torsion, and tension conditions;

[0054] Fig.11 Schematic diagram showing the mechanism of interface enhancement achieved by the swelling method. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work. DETAILED DESCRIPTION

[0057] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0058] Example 1

[0059] According to the pressure distribution characteristics of the human foot, the foot can be divided into 10 areas: the first toe bone area (Toe1, T 1 ), Toe 2-5, T 2-5 ), Meta 1, Metatarsal 1 1 ), Meta 2, Metatarsal region 2 ), Meta 3, Metatarsal 3 ), Meta 4, Metatarsal 4 ), Meta 5, Metatarsal 5 5 ), midfoot (MF), heel medial (HM), heel lateral (HL). Taking the anterior cruciate ligament (ACL) rupture knee disease as an example, by investigating the plantar pressure distribution characteristics of related patients, it was found that the pressure distribution of the whole foot, T 2-5 The average peak pressure of the inner and outer sides of the heel was significantly lower than that of the uninjured side and the normal group, and the decrease in HM and HL was more significant, so the resolution was higher. 3 >M 2 >M 4 >HM>HL>M 1 >M 5 >T 1 >MF>T 2-5 ) and the pressure change rate between the damaged side and the undamaged side (T 2-5 >HM>T 1 >HL>M 4 >MF>M 1 >M 5 >M 2 ), thereby designing the flexible sensor array for plantar pressure monitoring described in this embodiment.

[0060] like Figure 3 As shown, this embodiment provides a pressure insole with a length of 261mm and a maximum width of 101mm. The flexible sensor array for plantar pressure monitoring described in this embodiment includes a first sensor unit and a second sensor unit; the total number of the first sensor unit and the second sensor unit is 130. The first sensor unit has a single point length of 7mm and a spacing of 2.5mm, and is mainly used in the first metatarsal area (T 1 ), 2nd to 5th phalanges (T 2-5 ), the medial heel area (HM) and the lateral heel area (HL); the single point side length of the second sensor unit is 10mm, the spacing is 3mm, and it is mainly used in the first metatarsal area (M 1 ), the second metatarsal region (M2 ), the third metatarsal region (M 3 ), the fourth metatarsal region (M 4 ), the fifth metatarsal region (M 5 ) and midfoot area (MF).

[0061] Since there is no obvious pressure change in the arch area of ​​a normal foot during movement, no special design is made in the arch area. However, some flatfoot patients are also taken into consideration. Therefore, as a preferred embodiment, larger sensor units are added to the arch area: a third sensor unit and a fourth sensor unit. The side length of the third sensor unit is 30 mm, the side length of the fourth sensor unit is 22 mm, and the distance between the third sensor unit and the fourth sensor unit is 5 mm.

[0062] The method for preparing the flexible sensor array for plantar pressure monitoring comprises the following steps:

[0063] (1) Preparation of TPU solution

[0064] The weighed DMF solution was placed on a magnetic stirrer, TPU particles were added according to a mass ratio of TPU:DMF = 1:5, and heated and stirred at 60°C until there were no particles in the solution, i.e., the solution was completely dissolved, to obtain a TPU solution;

[0065] (2) Preparation of Conductive Particle Dispersion

[0066] The dispersant PVP was added into the DMF solvent according to the proportion (m PVP :m DMF =1:1500), and stir magnetically until completely dissolved; then the composite conductive particles (CNTs and CB are mixed at m CNTs :m CB =0.6:0.4 mixture) was added to the above solution, the mass ratio of PVP, composite conductive particles and DMF was 1:7.5:1500; after stirring at a speed of 800 rpm with a magnetic stirrer for 30 minutes, ultrasonic cell disruptor was used at 80% power for 2 hours to fully disperse the conductive particles in DMF to obtain a conductive particle dispersion;

[0067] (3) Preparation of pressure-sensitive slurry

[0068] The TPU solution obtained in step (1) is mixed with the conductive particle dispersion obtained in step (2), wherein the mass ratio of TPU to composite conductive particles is 88:12, and after stirring at a speed of 800 rpm for 2 hours using a magnetic stirrer, about 80% of the solvent is evaporated at 60° C. by heating in a water bath to obtain a conductive polymer composite slurry with a relatively high viscosity;

[0069] (4) Preparation of pressure-sensitive composite film

[0070] The conductive polymer composite slurry obtained in step (3) is scraped onto a glass plate by a scraper, the glass plate is placed on a heating table, heated at 80° C. to form a film, and finally the film is peeled off from the glass plate to obtain a pressure-sensitive composite material film;

[0071] (5) Preparation of interdigitated electrode array

[0072] The flexible substrate TPU is ultrasonically cleaned with deionized water and alcohol, and then dried with nitrogen gas. A drawing of the interdigital electrode array is drawn using a drawing software, and the dried substrate is mask-printed with silver paste using a customized patterned screen through a screen printer. After curing, the lead intersection is screen-printed with a layer of solder resist green oil after the first printing and UV-cured for 10 seconds for the purpose of insulation, and then silver paste is printed on the top for connection. After curing at 80°C on a heating table, the interdigital electrode array can be obtained.

[0073] The specific operation of mask printing silver paste is as follows: fix the customized patterned screen (also called screen printing plate) on the screen printer, apply silver paste in front of the pattern, control the ink coating knife to cover the entire pattern area with silver paste at a speed of 100mm / min (values ​​can be taken in the range of 50-400mm / min), and then control the printing knife to print the electrode at a speed of 100mm / min (values ​​can be taken in the range of 50-400mm / min) and a printing pressure of 40N with a screen printing spacing of 1.2mm, that is, the spacing between the screen and the printing table is 1.2mm (values ​​can be taken in the range of 0.4-1.5mm). After that, the electrode is cured at a temperature of 80℃ (values ​​can be taken in the range of 60-120℃) for about half an hour.

[0074] The specific operation of screen printing and coating solder resist green oil is as follows: fix the customized patterned screen on the screen printer, apply solder resist green oil in front of the pattern, control the ink coating knife to cover the solder resist green oil to the entire pattern area at a speed of 100mm / min (the value can be within the range of 50-400mm / min), and then control the printing knife to print the insulating layer at a speed of 100mm / min (the value can be within the range of 50-400mm / min), a printing pressure of 40N, and a screen printing spacing of 1.2mm, that is, the spacing between the screen and the printing table is 1.2mm (the value can be within the range of 0.4-1.5mm).

[0075] The specific operation of printing silver on the insulating layer is as follows: fix the customized screen printing plate on the screen printing machine, apply silver paste in front of the pattern, control the ink coating knife to cover the entire pattern area with silver paste at a speed of 100mm / min (50-400mm / min), and then control the printing knife to print the electrode at a speed of 100mm / min (50-400mm / min), a printing pressure of 40N, and a screen printing spacing of 1.2mm, that is, the spacing between the screen plate and the printing table is 1.2mm (0.4-1.5mm). After that, the electrode is cured at a temperature of 80℃ (60-120℃) for about half an hour.

[0076] The above three printing patterns are all different, such as Figure 4 As shown, first, the silver electrode in Figure b is printed and cured, then the solder resist green oil insulating layer in Figure c is printed and cured, and finally the column electrode in Figure d is printed. After curing, the entire interdigitated electrode array pattern can be obtained, that is, Figure a.

[0077] (6) Integration of plantar pressure sensor array

[0078] The pressure-sensitive composite material film obtained in step (4) is cut into suitable sizes by using a femtosecond laser printing system to obtain a plurality of pressure-sensitive composite material film units, so as to be able to fit the positions corresponding to the interdigital electrode array; the TPU substrate printed with the interdigital electrode array and the pressure-sensitive composite material film units of different sizes are placed in cyclohexane (C 6 H 12 ) solvent for 1.5 h (under 80° C.), and then the pressure-sensitive composite film unit is placed at a position corresponding to the interdigital electrode array (such as Figure 3 ), hot pressing was performed at 80°C and 0.7MPa pressure, and the device surface was packaged with PI to obtain an integrated flexible plantar pressure sensor array. Figure 5 Shown is a physical picture of the flexible plantar pressure sensor array.

[0079] Example 2

[0080] This embodiment provides a method for preparing a flexible sensor array for plantar pressure monitoring, which differs from Embodiment 1 only in that: when preparing the conductive particle dispersion in step (2), the composite conductive particles are composed of a mixture of CNTs and CB in a mass ratio of 0.8:0.2; when preparing the pressure-sensitive slurry in step (3), the mass ratio of TPU in the TPU solution to the composite conductive particles in the conductive particle dispersion is 91:9.

[0081] Example 3

[0082] This embodiment provides a method for preparing a flexible sensor array for monitoring plantar pressure, which is different from the embodiment 1 only in that: when preparing the conductive particle dispersion in step (2), the composite conductive particles are a mixture of CNTs and CB in a mass ratio of 1:2; when preparing the pressure-sensitive slurry in step (3), the mass ratio of TPU in the TPU solution to the composite conductive particles in the conductive particle dispersion is 99:1. In step (6), hot pressing is performed at 80°C and 2MPa.

[0083] Experimental example

[0084] 1. Bending performance test

[0085] A systematic bending performance test was performed on the flexible sensor array prepared in Example 1 to verify its interface stability and overall function.

[0086] The current response test of the flexible sensor array under different pressures was carried out before and after bending 1500 times. The results are as follows: Figure 6 As shown in a. As can be seen from the figure, the current response of the sensor array after bending cycles under the same pressure is relatively stable, and the current gradually increases with the increase of pressure; in addition, it can be clearly seen that under the same pressure, the current response of the sensor array after bending 1500 times is higher than the current before bending. The reason may be that the sensor array is subjected to lateral strain during the bending process, and the conductive materials in the pressure-sensitive material are spaced in the normal direction and even contact each other, which increases the conductive path and the current. However, in general, the increase in current is within an acceptable range, which also proves the interface stability of the sensor.

[0087] 2. Cycle stability performance test

[0088] The cyclic stability test of the flexible sensor array prepared in Example 1 can reflect its reliability and durability in practical applications. The specific test results are as follows Figure 6 As shown in b.

[0089] It can be clearly observed from the figure that after 1500 bending tests, the current response of the sensor array increased slightly when it was subjected to nearly 3000 cycles of impact. This may be related to the structural fine-tuning of the material under repeated stress and the changes in interface interactions. Long-term bending may cause the polymer chain segments to rearrange, thereby affecting the current conduction path. By comparing the cyclic stability data before and after bending, it is found that the current response of the interface-enhanced sensor after the bending test is not much different from the current response before bending. Specifically, ΔI / I 0 The values ​​of are all kept at about 9, which indicates that the sensor array can maintain its current response relatively stably after repeated bending and impact. This result further proves the effectiveness of the enhanced interface design.

[0090] For further comparison, we purchased domestic commercial plantar pressure insoles (such as Figure 7 a), the pressure insole adopts a 6-row*4-column array design, consisting of 18 independent sensing units in total. The current response results after nearly 3000 cycles of impact under the same pressure are as follows Figure 7 As shown in b. It can be clearly seen from the figure that the current is relatively stable before 4000s, while the current of the sensor array has a significant change of first decreasing and then increasing at nearly 4500s and 5500s, and the durability is average.

[0091] 3. Wearable testing

[0092] A healthy volunteer (25-year-old female) wearing a right foot insole was tested in three typical support phases during walking, corresponding to heel contact, full foot standing, forefoot contact, and sitting. Based on the resistance changes of 130 sensor units, the plantar pressure distribution map in these four states was drawn through contour lines. The specific results are as follows: Figure 8 As shown in a. From the figure, we can see that the pressure insole can accurately identify three typical support phase gaits in the walking state. In addition, when comparing the two states of full-foot standing and full-foot sitting, we can clearly see that the pressure distribution position is roughly the same, but there is a significant difference in the pressure size. This difference further strongly proves the precise perception ability of the pressure insole in different postures, and fully demonstrates the accurate gait recognition ability of the pressure insole, which is of vital significance for subsequent related research and actual disease prevention and rehabilitation applications.

[0093] The purchased domestic pressure insoles were tested for wearability. Similarly, the plantar pressure distribution in four states was tested: heel contact, full foot standing, forefoot contact, and sitting. The results are as follows: Figure 8 As shown in b, the numbers in each part of the figure represent the weight (unit: gram) received by each sensor unit.

[0094] By comparing the two, it can be seen that in the contour map of the heel contact stage, the pressure area displayed by the commercial insole is larger than that of the pressure insole described in the present application. The reason is that the resolution of the commercial insole is lower, and the entire heel is composed of only 4 sensor units, while the pressure insole described in the present application is composed of 33 sensor units, which is larger in number and density, so it can accurately identify the pressure distribution within the heel area.

[0095] In the full-foot standing stage, the pressure insole prepared by the present application can identify the pressure position of the entire foot, especially the arch of the foot, which is subject to less pressure. However, from the contour map of the commercial insole, no pressure is detected at the arch of the foot. Fig. 9 As can be seen in the figure, the pressure insole is2-5 No pressure was detected in the forefoot and the junction between the forefoot and the arch, indicating that the commercial pressure insole lacks the ability to detect small pressures. At the same time, in the forefoot position, the graphics displayed in the contour map are more angular, which also shows that the commercial insole outputs insufficient data and the resolution of the sensor unit is low. When the whole foot is in a sitting position, the pressure insole described in this application can detect a plantar pressure distribution diagram that is similar to the pressure distribution when the whole foot is standing and only has a numerical difference, while the commercial insole cannot detect the plantar pressure, once again indicating that the commercial pressure insole lacks the ability to detect small pressures, and further highlights the large-range characteristics of the pressure insole prepared in this study. More importantly, for the application scenarios of plantar pressure insoles, taking ACL disease as an example, after the patient becomes ill, the load on the whole foot is significantly reduced on the injured side of the feet compared to the non-injured side, and the pressure in most plantar partitions is reduced. If the small pressure on the affected side cannot be detected, it will be meaningless for assisting disease prevention and rehabilitation. In addition, as mentioned before, the sole of the foot is usually divided into ten zones, and the pressure of patients and normal people in different zones is significantly different. If the resolution of the sensor unit cannot meet the requirements, the pressure distribution of similar areas cannot be distinguished, which is also of little use for disease assessment and prevention. In summary, the plantar pressure sensor array prepared in this application has great application potential for future disease assessment, prevention and rehabilitation.

[0096] 4. Interface bonding performance test

[0097] The interfaces of the experimental group and the control group were bent, stretched and twisted, and the interface bonding was compared using confocal scanning electron microscopy (SEM). Fig.10 As shown in the figure (the bonding interface in the figure refers to the interface connection through the swelling method, which is the experimental group; the non-bonding interface refers to the interface without any treatment, which is the control group). It can be found that: the bonding interface is very strong under the external force condition, while the non-bonding interface is delaminated under the external force, indicating that the interface bonding is fragile. Among them, the schematic diagram of the mechanism of achieving interface enhancement by swelling method is shown in Fig.11 shown.

[0098] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A flexible sensor array for monitoring plantar pressure, characterized in that: The sensor array comprises a first sensor unit and a second sensor unit; The first sensor unit is applied to the first phalanx area, the 2nd to 5th phalanx areas, the medial heel area and the lateral heel area; The second sensing unit is applied to the first metatarsal region, the second metatarsal region, the third metatarsal region, the fourth metatarsal region, the fifth metatarsal region and the midfoot region.

2. The flexible sensor array for monitoring plantar pressure according to claim 1, characterized in that: The single point side length of the first sensing unit is 4-8.5 mm, and the spacing is 1-3 mm; The single point side length of the second sensing unit is 9-15 mm, and the spacing is 1-4 mm; The total number of the first sensing units and the second sensing units is 120-160.

3. The flexible sensor array for monitoring plantar pressure according to claim 1, characterized in that: It also includes a third sensor unit and a fourth sensor unit, wherein the third sensor unit and the fourth sensor unit are applied to the arch area; The side length of the third sensing unit is 20-35 mm, the side length of the fourth sensing unit is 20-30 mm, and the distance between the third sensing unit and the fourth sensing unit is 1-7 mm.

4. The method for preparing the flexible sensor array for plantar pressure monitoring according to any one of claims 1 to 3, characterized in that: The steps include: (1) Preparation of TPU solution Dissolve TPU particles in DMF solvent to obtain a TPU solution; (2) Preparation of Conductive Particle Dispersion The dispersant PVP is added to the DMF solvent and fully dissolved under stirring conditions; then the conductive particles are added to the above solution, and after stirring and ultrasonic treatment, a conductive particle dispersion is obtained; (3) Preparation of pressure-sensitive slurry The TPU solution obtained in step (1) and the conductive particle dispersion obtained in step (2) are fully mixed and concentrated by heating to obtain a conductive polymer composite slurry with a relatively high viscosity; (4) Preparation of pressure-sensitive composite film The conductive polymer composite slurry obtained in step (3) is coated on a substrate, heated and cured to form a film, and then the film is peeled off from the substrate to obtain a pressure-sensitive composite material film; (5) Preparation of interdigitated electrode array Based on the designed interdigital electrode array pattern, the first silver paste is printed and coated on the flexible substrate through mask printing. After curing, the solder resist green oil is screen printed and coated at the lead intersection. After UV curing to form insulation, the second silver paste is printed and coated. After heating and curing, the interdigital electrode array is obtained. (6) Integration of plantar pressure sensor array The pressure-sensitive composite material film obtained in step (4) is cut to obtain a plurality of pressure-sensitive composite material film units so as to be adapted to the corresponding positions of the interdigitated electrode array; the plurality of pressure-sensitive composite material film units and the interdigitated electrode array are first immersed in a non-polar solvent, and then the pressure-sensitive composite material film units and the interdigitated electrode array obtained in step (5) are hot-pressed and integrated to obtain the plantar pressure sensor array.

5. The method for preparing a flexible sensor array for monitoring plantar pressure according to claim 4, characterized in that: In step (1), the mass ratio of the TPU particles to the DMF solvent is 1:

5.

6. The method for preparing a flexible sensor array for monitoring plantar pressure according to claim 4, characterized in that: In step (2), the mass ratio of the dispersant PVP, the conductive particles and the DMF solvent is 1:7.5:1500; The conductive particles are a mixture of CNTs and CB in a mass ratio of (0.6-1):(0-2); preferably, the conductive particles are a mixture of CNTs and CB in a mass ratio of 0.8:0.

2.

7. The method for preparing a flexible sensor array for monitoring plantar pressure according to claim 4, characterized in that: In step (3), the mass ratio of TPU in the obtained TPU solution to the conductive particles in the obtained conductive particle dispersion is (88-99):(1-12); The solvent was evaporated by heating in a 60°C water bath to 80%.

8. The method for preparing a flexible sensor array for monitoring plantar pressure according to claim 4, characterized in that: In step (4), the temperature for heating and curing is 80°C; In step (5), the flexible substrate is a TPU substrate, the UV curing time is 10 seconds, and the heating curing temperature is 80°C.

9. The method for preparing a flexible sensor array for monitoring plantar pressure according to claim 4, characterized in that: In step (6), the plurality of pressure-sensitive composite film units and the interdigitated electrode array are first immersed in cyclohexane at 60-100° C. for 0.5-2 h. 。 10. Application of the flexible sensor array for monitoring plantar pressure according to any one of claims 1 to 4 or the flexible sensor array for monitoring plantar pressure prepared by the method according to any one of claims 5 to 9 in flexible wearable devices.

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