Design of flexible sensor array for plantar pressure monitoring and method for manufacturing the same

Abstract

This invention relates to the design and fabrication method of a flexible sensor array for plantar pressure monitoring. The flexible sensor array includes a first sensing unit and a second sensing unit. The first sensing unit is applied to the 1st metatarsal region, the 2nd-5th metatarsal regions, the medial heel region, and the lateral heel region. The second sensing unit is applied to the 1st metatarsal region, the 2nd metatarsal region, the 3rd metatarsal region, the 4th metatarsal region, the 5th metatarsal region, and the midfoot region. By optimizing the size, number, and distribution of the sensing units, complete representation of plantar pressure information is achieved, effectively solving the problem of low resolution and insufficient representation of plantar pressure information in existing sensors. A swelling process is used to enhance the interface of the quasi-homogeneous materials of the sensor, improving the interface stability and reliability of the sensor. The fabrication method of the plantar pressure monitoring sensor array of this invention has the advantages of low cost, easy mass production, and easy large-area expansion.

Description

Technical Field

[0001] This invention belongs to the field of flexible sensor technology, specifically relating to the design and fabrication method of a flexible sensor array for plantar pressure monitoring. Background Technology

[0002] Over the past few decades, with the improvement of people's living standards and demands for quality of life, electronic products in the field of human health monitoring have attracted a large number of researchers. The knee joint is the first joint in the human body to degenerate, suffers the most damage, and is unable to heal. It is estimated that there are over 50 million related patients in my country, and authoritative data shows that 80% of knee pain patients have knee joint degenerative diseases. Once afflicted, symptoms such as knee pain and swelling, limited mobility, and even limb disability will occur, seriously affecting the health of the entire population. Research shows that the severity of knee joint disease directly affects the patient's gait, which is ultimately reflected in the distribution of plantar pressure. Therefore, monitoring plantar pressure distribution can provide gait information, offering precise and individualized exercise interventions and rehabilitation guidance for athletes and rehabilitation patients. By reducing pressure-bearing areas and adopting appropriate exercise methods, the risk of knee cartilage degeneration can be reduced, and the rehabilitation process can be promoted.

[0003] Existing devices for measuring plantar pressure based on electronic and sensor technologies mainly fall into two categories: platform-type and wearable insoles. Platform-type monitoring devices can provide accurate and detailed measurement data, but they are expensive, bulky, and have limited application scenarios, confined to laboratory and hospital environments. Furthermore, their lack of portability prevents them from monitoring plantar pressure signals in real time and providing current information, severely limiting their applications. With the development of smart healthcare and increased awareness of health management, medical settings are gradually shifting to the home. Patient rehabilitation requires frequent and real-time monitoring of movement postures. Therefore, wearable pressure insoles are more convenient and can facilitate remote, automated, and professional screening, assessment, and rehabilitation training, greatly simplifying people's lives.

[0004] However, current research on plantar pressure array pattern design primarily focuses on low and sparse sensor unit density, with the number of sensor units typically ranging from 20 to 50. This results in low spatial resolution of pressure sensing, conveying only basic pressure states during normal walking, hindering deeper applications such as disease diagnosis. Figure 1 (As shown). Furthermore, most existing sensors are bonded together using adhesive during integration (as shown). Figure 2 The method of mechanical combination (direct hot pressing) or as shown is not reliable enough and is prone to failure during walking or movement, which will have a certain impact on the stability of the device and make it difficult to meet the requirements of long-term monitoring. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, this invention provides a design and fabrication method for a flexible sensor array for plantar pressure monitoring.

[0006] The structural design of the flexible sensor array for plantar pressure monitoring described in this invention optimizes the size, number, and distribution of the sensing units based on the plantar pressure distribution characteristics of the human body during walking or exercise, thereby achieving a complete representation of plantar pressure information. This invention significantly improves the interface reliability of the sensor through heterogeneous interface enhancement technology, enabling it to stably output accurate plantar pressure distribution signals under human movement conditions, meeting the needs of long-term monitoring.

[0007] The technical solution adopted in this invention is as follows:

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

[0009] The first sensing unit shown is applied to the first metatarsal bone region, the second-to-fifth metatarsal bone regions, the medial heel region, and the lateral heel region;

[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 4-8.5mm, and the spacing is 1-3mm;

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

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

[0014] Furthermore, the flexible sensor array for plantar pressure monitoring also includes a third sensing unit and a fourth sensing unit, which are applied to the arch area of ​​the foot.

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

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

[0017] (1) Preparation of TPU solution

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

[0019] (2) Preparation of conductive particle dispersion

[0020] The dispersant PVP was added to the DMF solvent and dissolved completely under stirring. Then, the conductive particles were added to the solution, and after stirring and ultrasonic treatment, a conductive particle dispersion was 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 thoroughly mixed and concentrated by heating to obtain a conductive polymer composite slurry with high viscosity.

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

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

[0025] (5) Fabrication of interdigitated electrode array

[0026] Based on the designed interdigitated electrode array pattern, a first silver paste mask printing coating is performed on a flexible substrate. After curing, solder resist green oil is screen printed at the lead intersection. After UV curing to form insulation, a second silver paste printing coating is performed. After heat curing, the interdigitated electrode array is obtained.

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

[0028] The pressure-sensitive composite film obtained in step (4) is cut to obtain multiple pressure-sensitive composite film units, which can be adapted to the corresponding positions of the interdigital electrode array. First, the multiple pressure-sensitive composite film units and the interdigital electrode array are immersed in a non-polar solvent, and then the pressure-sensitive composite film units and the interdigital electrode array obtained in step (5) are hot-pressed together to obtain the foot pressure sensing array.

[0029] The term "lead intersection" refers to the fact that the two leads of the left and right parts of the interdigitated electrode are on the same plane. Therefore, to form an interdigitated electrode array, all the left leads in the array are connected to form a column electrode, and all the right leads are connected to form a row electrode. There must be a crossover between the row and column electrodes, which is the intersection of the lead.

[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, conductive particles, and 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 between the TPU in the obtained TPU solution and the conductive particles in the obtained conductive particle dispersion is (88-99):(1-12);

[0034] Heating in a 60℃ water bath causes 80% of the solvent to evaporate.

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

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

[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 hours. 。

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

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

[0040] The inventors of this application have discovered through long-term research that existing sensor arrays for wearable plantar pressure distribution monitoring have the following shortcomings: 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 surface, thus failing to provide valuable feature information for the diagnosis of injuries and diseases; ② Poor sensor reliability: Most sensor interfaces are bonded using adhesives, which have weak adhesion. In practical applications, the bonding may become unstable due to the addition of external forces, posing a risk of structural delamination, leading to sensor structural failure and affecting the long-term stable use of the device.

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

[0042] The flexible sensor array for plantar pressure monitoring described in this invention comprises a first sensing unit and a second sensing unit. The first sensing unit is applied to the first metatarsal region, the second-to-fifth metatarsal regions, the medial heel region, and the lateral heel region. 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. The structural design optimizes the size, number, and distribution of the sensing units based on the plantar pressure distribution characteristics during walking or exercise, thereby achieving a complete representation of plantar pressure information and effectively solving the problem of low resolution and insufficient representation of plantar pressure information in existing sensors. Furthermore, a quasi-homogeneous material for the sensor is achieved based on a swelling process. Interface enhancement involves heating and swelling the pressure-sensitive composite film and the TPU substrate with printed electrodes using a non-polar solvent (preferably cyclohexane). This activates the molecular chains on the surfaces of both films, creating physical cross-linking points within the chains. Then, through hot pressing, the external temperature and pressure induce physical cross-linking between the molecular chains on the surfaces of the two films, achieving stable integration of the flexible pressure sensor interface. This improves the sensor's interface stability and reliability, and solves the problem of structural failure caused by significant differences in chemical composition. Furthermore, this invention proposes a method for fabricating a sensor array for plantar pressure monitoring, which offers advantages such as low cost, ease of mass production, and large-area scalability. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 The image shows a sensor array design for plantar pressure monitoring as reported in the prior art; where ac represents existing literature reports and d represents commercially available plantar pressure insole products.

[0045] Figure 2 This diagram illustrates the use of double-sided adhesive for sensor integration in existing technologies.

[0046] Figure 3 The diagram shows the pattern design of the flexible sensor array for plantar pressure monitoring described in this invention; where a is the position distribution and b is the interdigital electrode array.

[0047] Figure 4 The diagram shows the CAD design of the array electrodes; where a is the overall pattern; b is the interdigitated electrode array and row electrode pattern; c is the insulating layer pattern; and d is the column electrode pattern.

[0048] Figure 5 The image shown is a physical diagram of the flexible sensor array for plantar pressure monitoring described in Embodiment 1 of the present invention; wherein, a is a partial physical diagram of the flexible electrode, b is a detection thickness of 388μm, and c is an overall diagram;

[0049] Figure 6 The diagram shows the interface bonding stability detection of the flexible sensing array described in Embodiment 1 of the present invention; where a is the current response before and after 1500 bends, and b is the nearly 3000 cycle test before and after 1500 bends.

[0050] Figure 7 The images shown are of commercially available compression insoles and their cyclic stability; where a is the actual product image and b is the cyclic stability.

[0051] Figure 8 The diagram shows the plantar pressure contours for three typical support phases: heel strike, full foot standing, and forefoot strike, as well as for a seated full foot strike position; where a is the pressure insole of this application and b is a domestically produced pressure insole.

[0052] Figure 9 The diagram shows the plantar pressure distribution of domestically produced commercial plantar pressure insoles under three typical support phases: heel strike, full foot standing, and forefoot strike, as well as in a sitting position with the entire foot on the ground.

[0053] Figure 10 The microstructure comparison of adhesive / non-adhesive interfaces is shown under bending, torsion and tension conditions.

[0054] Figure 11 The diagram shows a schematic of the mechanism by which the swelling method enhances the interface. Attached Figure Description

[0056] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Detailed Implementation

[0057] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0058] Example 1

[0059] Based on the pressure distribution characteristics of the human foot, the sole can be divided into 10 regions: the first metatarsal region (T1), the second-to-fifth metatarsal regions (T2-T5), and the third-to-fifth metatarsal regions (T1-T1). 2-5 The plantar pressure distribution is divided into five regions: Meta 1 (M1), Meta 2 (M2), Meta 3 (M3), Meta 4 (M4), Meta 5 (M5), Midfoot (MF), Heel Medial (HM), and Heel Lateral (HL). Taking anterior cruciate ligament (ACL) ruptured knee disease as an example, a survey of plantar pressure distribution characteristics in relevant patients revealed that the entire foot and T1 on the side of ACL injury... 2-5 The average peak pressure on the inner and outer sides of the heel was significantly lower than that on the uninjured side and in the normal group, with the decrease in HM and HL being more significant, thus providing higher resolution. The pressure distribution in different areas of the sole was comprehensively assessed (M3>M2>M4>HM>HL>M1>M5>T1>MF>T). 2-5 ) and the magnitude of the rate of pressure change between the damaged and undamaged sides (T) 2-5 >HM>T1>HL>M4>MF>M1>M5>M2), 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 foot pressure monitoring described in this embodiment includes a first sensing unit and a second sensing unit; the total number of the first and second sensing units is 130. The first sensing unit shown has a single-point side length of 7mm and a spacing of 2.5mm, and is mainly applied to the first metatarsal region (T1) and the second-to-fifth metatarsal regions (T2-T3). 2-5 The first sensing unit has a single-point side length of 10mm and a spacing of 3mm, and is mainly applied to the first metatarsal region (M1), the second metatarsal region (M2), the third metatarsal region (M3), the fourth metatarsal region (M4), the fifth metatarsal region (M5), and the midfoot region (MF).

[0061] Since there is no significant pressure change in the arch area of ​​a normal foot during exercise, no special design is made in the arch area. However, considering some patients with flat feet, as a preferred implementation, a larger sensing unit is added to the arch area: a third sensing unit and a fourth sensing unit. The side length of the third sensing unit is 30mm, the side length of the fourth sensing unit is 22mm, and the distance between the third sensing unit and the fourth sensing unit is 5mm.

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

[0063] (1) Preparation of TPU solution

[0064] Place the weighed DMF solution on a magnetic stirrer, add TPU particles according to the mass ratio of TPU:DMF = 1:5, and heat and stir at 60°C until there are no particles in the solution, that is, completely dissolved, to obtain a TPU solution.

[0065] (2) Preparation of conductive particle dispersion

[0066] The dispersant PVP was added to the DMF solvent in a specific ratio (m PVP :m DMF =1:1500), stir magnetically until completely dissolved; then add the composite conductive particles (CNTs and CB according to m CNTs :m CB A mixture of PVP, composite conductive particles, and DMF (components of 0.6:0.4) was added to the above solution. The mass ratio of PVP, composite conductive particles, and DMF was 1:7.5:1500. The mixture was stirred at 800 rpm for 30 minutes using a magnetic stirrer, and then sonicated at 80% power for 2 hours using an ultrasonic cell disruptor to fully disperse the conductive particles into the DMF, thus obtaining 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. After stirring at 800 rpm for 2 hours using a magnetic stirrer, about 80% of the solvent is evaporated at 60°C by water bath heating to obtain a conductive polymer composite slurry with high viscosity.

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

[0070] The conductive polymer composite slurry obtained in step (3) is coated onto a glass plate using a film scraper. The glass plate is placed on a heating table and heated to 80°C to solidify into a film. Finally, the film is peeled off from the glass plate to obtain a pressure-sensitive composite film.

[0071] (5) Fabrication of interdigitated electrode array

[0072] The flexible TPU substrate is ultrasonically cleaned with deionized water and alcohol, and then dried with nitrogen gas. The interdigitated electrode array is drawn using graphic design software, and the dried substrate is screen-printed with silver paste using a customized patterned screen printing machine. After curing, a layer of solder resist green oil is screen-printed and UV-cured at the lead intersections after the first printing to provide insulation. Then, silver paste is printed on top for connection. After curing at 80°C on a heating table, the interdigitated electrode array is obtained.

[0073] The specific operation of mask printing silver paste is as follows: A customized patterned screen (also known as a screen printing plate) is fixed on the screen printing machine. Silver paste is applied in front of the pattern. The inking blade is controlled to cover the entire pattern area with silver paste at a speed of 100 mm / min (values ​​within the range of 50-400 mm / min are acceptable). Then, the printing blade is controlled to print electrodes at a speed of 100 mm / min (values ​​within the range of 50-400 mm / min), a printing pressure of 40 N, and a screen printing pitch of 1.2 mm, that is, the distance between the screen and the printing table is 1.2 mm (values ​​within the range of 0.4-1.5 mm are acceptable). Afterward, the electrodes are cured at a temperature of 80℃ (values ​​within the range of 60-120℃ are acceptable) for about half an hour.

[0074] The specific operation of screen printing solder resist coating is as follows: Fix the customized patterned screen onto the screen printing machine, apply solder resist in front of the pattern, control the inking blade to cover the entire pattern area with solder resist at a speed of 100mm / min (values ​​within the range of 50-400mm / min), and then control the printing blade to print the insulating layer at a speed of 100mm / min (values ​​within the range of 50-400mm / min), a printing pressure of 40N, and a screen printing pitch of 1.2mm, that is, the distance between the screen and the printing table is 1.2mm (values ​​within the range of 0.4-1.5mm).

[0075] The specific operation for printing silver on the insulating layer is as follows: A customized screen printing plate is fixed on the screen printing machine. Silver paste is applied in front of the pattern. The inking blade is controlled to cover the entire pattern area with silver paste at a speed of 100 mm / min (a value within the range of 50-400 mm / min is acceptable). Then, the printing blade is controlled to print electrodes at a speed of 100 mm / min (a value within the range of 50-400 mm / min), a printing pressure of 40 N, and a screen printing pitch of 1.2 mm (i.e., the distance between the screen and the printing table is 1.2 mm (a value within the range of 0.4-1.5 mm is acceptable). The electrodes are then cured at 80℃ (a value within the range of 60-120℃ is acceptable) for approximately half an hour.

[0076] The three printed patterns are all different, such as Figure 4As 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 interdigital electrode array pattern, i.e., Figure a, can be obtained.

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

[0078] The pressure-sensitive composite film obtained in step (4) is cut into appropriate sizes using a femtosecond laser printing system to obtain multiple pressure-sensitive composite film units that can be adapted to the corresponding positions of the interdigitated electrode array; the TPU substrate with the interdigitated electrode array and the pressure-sensitive composite film units of different sizes are then printed on cyclohexane (C6H4O4). 12 Immerse the pressure-sensitive composite film unit in a solvent for 1.5 hours (at 80°C), and then place it at the position corresponding to the interdigitated electrode array (e.g., Figure 3 The device is hot-pressed at 80℃ and 0.7MPa pressure, and then its surface is encapsulated with PI to obtain an integrated flexible plantar pressure sensor array. Figure 5 The image shown is a physical diagram of a flexible plantar pressure sensing array.

[0079] Example 2

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

[0083] Experimental Example

[0084] 1. Bending performance test

[0085] The flexible sensing array prepared in Example 1 was subjected to a systematic bending performance test to verify its interface stability and overall function.

[0086] The current response of the flexible sensor array under different pressures was compared before and after 1500 bending cycles. The results are as follows: Figure 6 As shown in Figure a, the current response of the sensor array after bending cycles under the same pressure is relatively stable, and the current gradually increases with increasing pressure. It is also evident that, under the same pressure, the current response of the sensor array after 1500 bends is slightly higher than before bending. This may be because the sensor array experiences lateral strain during bending, causing the conductive materials in the pressure-sensitive material to decrease in the normal direction and even come into contact, thus increasing the conductive path and current. However, overall, the increase in current is within an acceptable range, thus demonstrating the interface stability of the sensor.

[0087] 2. Cyclic stability performance test

[0088] Cyclic stability testing was performed on the flexible sensor array prepared in Example 1, which reflects its reliability and durability in practical applications. Specific test results are as follows: Figure 6 As shown in b.

[0089] As clearly observed in the figure, after 1500 bending tests, the current response of the sensor array showed a slight increase after nearly 3000 cyclic impacts. This may be related to the structural fine-tuning of the material under repeated stress and changes in interfacial interactions. Prolonged bending may cause the polymer chain segments to rearrange, thus affecting the current conduction path. By comparing the cyclic stability data before and after bending, it was found that the current response of the sensor after bending tests was not significantly different from that before bending. Specifically, the value of ΔI / I0 remained at approximately 9, indicating that the sensor array can maintain its current response relatively stably after repeated bending and impacts. This result further proves the effectiveness of the enhanced interface design.

[0090] To further compare, we purchased domestically produced commercial foot pressure insoles (such as...) Figure 7 a) This pressure insole uses a 6-row x 4-column array design, consisting of a total of 18 independent sensing units. After nearly 3000 cyclic impacts under the same pressure, the current response results are as follows: Figure 7 As shown in b, the current is relatively stable before 4000s, but the current of the sensor array shows a significant change of first decreasing and then increasing around 4500s and 5500s, indicating that its durability is average.

[0091] 3. Wearable testing

[0092] A healthy volunteer (25-year-old female) wearing a right insole was tested during walking in three typical support phases: heel strike, full-foot stance, forefoot strike, and a seated position. Based on the resistance changes of 130 sensor units, the plantar pressure distribution in these four states was mapped using contour lines. Specific results are shown below. Figure 8 As shown in figure a, the pressure insole accurately identifies three typical support phases of gait during walking. Furthermore, comparing the full-foot standing and seated full-foot landing positions, we can clearly see that while the pressure distribution is roughly the same, the pressure magnitude differs significantly. This difference further strongly demonstrates the pressure insole's accurate sensing capability under different postures, fully showcasing its accurate gait recognition ability. This is of crucial significance for subsequent related research and practical disease prevention and rehabilitation applications.

[0093] Wearable testing was conducted on the purchased domestically produced pressure insoles. Similarly, the plantar pressure distribution was tested in four states: heel strike, full-foot standing, forefoot strike, and sitting. The results are as follows: Figure 8 As shown in Figure b, the numbers in each part of the figure represent the weight (unit: grams) experienced by each sensing unit.

[0094] A comparison of the two shows that, in the contour map of the heel contact phase, the commercial insole displays a larger pressure area than the pressure insole described in this application. This is because the commercial insole has a lower resolution, with only 4 sensing units constituting the entire heel, while the pressure insole described in this application consists of 33 sensing units, which is more numerous and denser, thus enabling accurate identification of the pressure distribution within the heel area.

[0095] During the full-foot standing phase, the pressure insole prepared in this application can identify the pressure points across the entire foot, especially in areas like the arch where pressure is relatively low. However, contour maps of commercially available insoles do not detect pressure at the arch. Figure 9 As can be seen in the image, this pressure insole is located in the T... 2-5No pressure was detected at the forefoot and arch junction, indicating that this commercially available pressure insole lacks the ability to detect low-pressure areas. Furthermore, the contour plot at the forefoot shows sharp edges, further suggesting insufficient data output and low sensor resolution. When the entire foot is on the ground in a seated position, the pressure insole described in this application can detect a plantar pressure distribution similar to that of a standing insole, differing only in numerical value. The commercially available insole, however, cannot detect plantar pressure, again demonstrating its lack of ability to detect low-pressure areas and highlighting the large-range characteristics of the pressure insole developed in this study. More importantly, considering the application scenario of plantar pressure insoles, taking ACL disease as an example, after the onset of the disease, the load on the injured side of both feet is significantly reduced compared to the uninjured side, and the pressure in most plantar regions decreases. If the low-pressure areas on the affected side cannot be detected, it will be meaningless for assisting in disease prevention and rehabilitation. Furthermore, as mentioned earlier, the sole of the foot is typically divided into ten zones, and the pressure in different zones differs significantly between patients and healthy individuals. If the resolution of the sensing unit is insufficient, pressure distribution in similar areas cannot be distinguished, thus offering little benefit for disease assessment and prevention. In conclusion, the plantar pressure sensing array prepared in this application has enormous application potential for future disease assessment, prevention, and rehabilitation.

[0096] 4. Interface integration performance testing

[0097] The interface between the experimental and control groups was subjected to bending, stretching, and torsion operations. The interfacial bonding was compared using confocal scanning electron microscopy (SEM). The results are as follows: Figure 10 As shown in the figure (the bonded interface refers to the interface connection achieved through the swelling method, representing the experimental group; the non-bonded interface refers to the interface without any treatment, representing the control group), it can be observed that the bonded interface exhibits very strong interfacial bonding under external force, while the non-bonded interface shows delamination under external force, indicating weak interfacial bonding. The schematic diagram of the mechanism by which the swelling method enhances the interface is shown below. Figure 11 As shown.

[0098] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for fabricating a flexible sensor array for plantar pressure monitoring, characterized in that, Includes the following steps: (1) Preparation of TPU solution TPU particles were dissolved in DMF solvent to obtain a TPU solution; (2) Preparation of conductive particle dispersion The dispersant PVP was added to the DMF solvent and dissolved completely under stirring. Then, the conductive particles were added to the solution, and after stirring and ultrasonic treatment, a conductive particle dispersion was obtained. (3) Preparation of pressure-sensitive slurry The TPU solution obtained in step (1) and the conductive particle dispersion obtained in step (2) are thoroughly mixed and concentrated by heating to obtain a conductive polymer composite slurry with high viscosity. (4) Preparation of pressure-sensitive composite film The conductive polymer composite slurry obtained in step (3) is coated on the substrate, heated and cured into a film, and then the film is peeled off from the substrate to obtain the pressure-sensitive composite film. (5) Fabrication of interdigital electrode array Based on the designed interdigitated electrode array pattern, a first silver paste mask printing coating is performed on a flexible substrate. After curing, solder resist green oil is screen printed at the lead intersection. After UV curing to form insulation, a second silver paste printing coating is performed. After heat curing, the interdigitated electrode array is obtained. (6) Integration of plantar pressure sensor array Cut the pressure-sensitive composite film obtained in step (4) to obtain multiple pressure-sensitive composite film units so that they can be adapted to the corresponding positions of the interdigital electrode array; first, immerse the multiple pressure-sensitive composite film units and the interdigital electrode array in a non-polar solvent, and then heat-press the pressure-sensitive composite film units and the interdigital electrode array obtained in step (5) to obtain the foot pressure sensing array.

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

5.

3. The method for fabricating a flexible sensor array for plantar pressure monitoring according to claim 1, characterized in that, In step (2), the mass ratio of the dispersant PVP, conductive particles, and 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).

4. The method for fabricating a flexible sensor array for plantar pressure monitoring according to claim 3, characterized in that, The conductive particles are a mixture of CNTs and CB in a mass ratio of 0.8:0.

2.

5. The method for fabricating a flexible sensor array for plantar pressure monitoring according to claim 1, characterized in that, In step (3), the mass ratio between the TPU in the obtained TPU solution and the conductive particles in the obtained conductive particle dispersion is (88-99):(1-12). Heating in a 60℃ water bath causes 80% of the solvent to evaporate.

6. The method for fabricating a flexible sensor array for plantar pressure monitoring according to claim 1, characterized in that, In step (4), the heating and curing temperature is 80℃; In step (5), the flexible substrate is a TPU substrate, the UV curing time is 10s, and the heating curing temperature is 80℃.

7. The method for fabricating a flexible sensor array for plantar pressure monitoring according to claim 1, characterized in that, In step (6), the multiple pressure-sensitive composite film units and the interdigitated electrode array are first immersed in cyclohexane at 60-100℃ for 0.5-2h.

8. The flexible sensor array for plantar pressure monitoring prepared by the method according to any one of claims 1-7, characterized in that, The sensing array includes a first sensing unit and a second sensing unit; The first sensing unit shown is applied to the first metatarsal bone region, the second-to-fifth metatarsal bone regions, the medial heel region, and the lateral heel region; 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.

9. The flexible sensor array for plantar pressure monitoring according to claim 8, characterized in that, The single-point side length of the first sensing unit is 4-8.5mm, and the spacing is 1-3mm; The single-point side length of the second sensing unit is 9-15mm, and the spacing is 1-4mm; The total number of the first sensing unit and the second sensing unit is 120-160.

10. The flexible sensor array for plantar pressure monitoring according to claim 8, characterized in that, It also includes a third sensing unit and a fourth sensing unit, which are applied to the arch area of ​​the foot; The third sensing unit has a side length of 20-35mm, the fourth sensing unit has a side length of 20-30mm, and the distance between the third and fourth sensing units is 1-7mm.

11. A flexible wearable pressure insole, characterized in that, This includes a flexible sensor array for plantar pressure monitoring prepared by the method according to any one of claims 1-7 or a flexible sensor array for plantar pressure monitoring according to any one of claims 8-10.

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