Wearable flexible PPG equipment assembly method and equipment for foot microcirculation monitoring

Abstract

The invention relates to the field of wearable equipment, and discloses a wearable flexible PPG equipment assembly method for foot microcirculation monitoring, which comprises the following steps: mixing flexible substrate raw materials, pouring into a mold, and curing to obtain a flexible substrate; activating the surface of the flexible substrate to obtain an activated flexible substrate; designing a conductive circuit for electrically connecting the LED and the photoelectric detector on the activated flexible substrate; performing hydrophilic surface treatment on the flexible substrate with the conductive circuit to obtain a hydrophilic flexible substrate; an LED, a photoelectric detector and a wire are installed at preset positions on the hydrophilic flexible substrate and packaged through a packaging material, and a circuit packaging layer is obtained; a packaging protection layer is additionally arranged outside the circuit packaging layer, a vent hole is reserved in the skin contact surface, and a packaged probe is obtained; and curing the packaged probe to ensure that the packaging layer is fully formed and is firmly combined with the hydrophilic flexible substrate. The flexible wire of the invention enables the device to adapt to the dynamic activity of the foot.

Description

Technical Field

[0001] The present invention relates to the field of wearable devices, and in particular to an assembly method and device of a wearable flexible PPG device for monitoring foot microcirculation. Background Art

[0002] Photoplethysmography (PPG) technology is a non-invasive monitoring method that measures changes in blood volume in tissues through photoelectric sensors. It is widely used to measure physiological parameters such as heart rate, blood oxygen saturation, and blood flow. In the existing technology, PPG devices are usually used for static measurement sites such as fingers and wrists. However, in dynamic environments and foot microcirculation monitoring with high flexibility requirements, traditional devices have significant limitations in signal acquisition and data transmission, making it difficult to meet the accuracy requirements of real-time dynamic monitoring.

[0003] With the high incidence of chronic diseases such as diabetic foot and peripheral neuropathy, the demand for foot microcirculation monitoring in clinical applications is increasing. As one of the areas with the most concentrated peripheral blood vessels in the human body, the foot has the characteristics of a complex microcirculatory system, small blood flow, and sensitive blood flow changes, which puts higher requirements on the sensitivity and wearing comfort of monitoring equipment. However, existing PPG devices face many challenges in practical applications, mainly including:

[0004] Rigidity limitation of signal acquisition probe: The signal acquisition probe of traditional PPG equipment is usually packaged with hard materials, including light-emitting diode (LED) and photodiode (Photodiode) components. Such rigid packaged probes are difficult to fit the surface of the foot, resulting in unstable signals and noise interference due to unstable wearing or displacement during exercise when monitoring foot microcirculation. In addition, the hard probe may also cause pressure on the skin, affecting local blood flow, thereby causing deviations in the measurement results.

[0005] Insufficient flexibility of data transmission wires: In the prior art, data transmission wires are mostly made of rigid or low-flexibility materials, which are easily restricted by foot movement, affecting the reliability of data transmission. In dynamic monitoring environments, such as gait analysis and sports rehabilitation, the rigidity of the wires will limit the wearing position and posture of the device, resulting in data loss or signal distortion. At the same time, the friction between the wires and the skin may cause discomfort, affecting the patient's wearing experience and not conducive to long-term monitoring.

[0006] Insufficient compatibility of data recording modules: The data recording modules of existing PPG devices are mostly designed as independent devices, which are difficult to achieve real-time communication with mobile terminals, resulting in delayed acquisition and analysis of monitoring data. For foot microcirculation monitoring applications that require real-time feedback, such as diabetic foot ulcer risk assessment and postoperative rehabilitation progress monitoring, the data transmission method of traditional devices is difficult to meet clinical needs. In addition, the lack of convenient data synchronization and remote monitoring functions also limits the application potential of the device in home care and telemedicine.

[0007] Poor wearing comfort: Traditional PPG devices are usually not designed with the special needs of foot microcirculation monitoring in mind. The rigidity of the probe and wires has an adverse effect on wearing comfort and fit, especially when worn for a long time (such as daily monitoring of diabetic patients). This poor comfort problem not only affects patient compliance, but may also interfere with local blood flow, thereby affecting the accuracy of the measurement data.

[0008] Based on the above background, there is an urgent need for an innovative PPG device that can improve the flexibility of the signal acquisition probe and the retractability of the wire, enhance the wearing comfort of the device and the stability of signal acquisition, so that it can obtain high-quality signal data in the dynamic environment of foot microcirculation monitoring, thereby providing more reliable support for application scenarios such as chronic disease management and sports rehabilitation. Summary of the invention

[0009] The main purpose of the present invention is to solve the problem that the timing signal separation effect in the prior art is not ideal. A wearable flexible PPG device assembly method for foot microcirculation monitoring, the PPG device includes a flexible substrate, a probe, and a wire, the probe is fixed to the flexible substrate, the wire is used to transmit the data of the probe, the probe includes an LED and a photodetector, and the assembly method includes the following steps:

[0010] Mixing the raw materials of the flexible substrate, pouring them into a mold and curing them to obtain the flexible substrate;

[0011] Performing activation treatment on the surface of the flexible substrate to obtain an activated flexible substrate;

[0012] On the activated flexible substrate, a conductive circuit is designed for electrical connection between the LED and the photodetector, and the conductive circuit is used for connection of the internal circuit of the probe;

[0013] Performing hydrophilic surface treatment on a flexible substrate having a conductive circuit to obtain a hydrophilic flexible substrate;

[0014] Installing LEDs, photodetectors, and wires at predetermined positions on a hydrophilic flexible substrate, and encapsulating them with encapsulation materials to obtain a circuit encapsulation layer;

[0015] A packaging protection layer is added outside the circuit packaging layer, and a vent hole is reserved on the skin contact surface to obtain a packaged probe;

[0016] The encapsulated probe is cured to ensure that the encapsulation layer is fully formed and firmly bonded to the hydrophilic flexible substrate.

[0017] The flexible substrate raw material is a PDMS substrate or a PU substrate.

[0018] The conductive circuit preparation method is: AgNW ink is coated on a flexible substrate using a spraying or printing technique, and silver nanowires are deposited in an interlaced manner by a mask method according to a circuit pattern designed on the substrate material to form a conductive circuit.

[0019] The conductive circuit preparation method comprises: engraving microchannels on a flexible substrate, and injecting liquid gallium-indium alloy into the channels to form a conductive circuit.

[0020] The conductor is a carbon nanotube fiber conductor, and the preparation method is: PDMS prepolymer and curing agent are mixed in a ratio of 10:1, coated on carbon nanotube fibers, and then cured at 60° C. for 30 minutes to obtain the carbon nanotube fiber conductor.

[0021] The wire is a liquid metal microfluidic wire, and the preparation method is: using laser etching technology to carve microchannels with a diameter of 100-200 microns on PDMS, injecting gallium-indium alloy liquid metal into these microchannels to form a conductive path, and encapsulating the microchannels with another layer of PDMS to obtain the liquid metal microfluidic wire.

[0022] The wire also includes a protective layer, which is made of medical silica gel.

[0023] The activation treatment is to use oxygen plasma or UV / Ozone to activate the surface of the flexible substrate.

[0024] The assembly method also includes a mechanical interlocking design step:

[0025] Tiny holes or grooves are etched on the flexible substrate, and the size and distribution of the holes are precisely controlled by laser etching technology, so that the packaging material can penetrate into the surface of the flexible substrate during curing to form a mechanical interlocking structure.

[0026] The present invention also relates to a wearable flexible PPG device obtained by the aforementioned assembly method.

[0027] The present invention has the following beneficial effects:

[0028] 1. Higher signal acquisition stability: By using flexible materials to encapsulate the signal acquisition probe, it can fit closely to the surface of the foot, ensuring the quality of signal acquisition in a dynamic environment. This improvement makes the device particularly suitable for dynamic monitoring of foot microcirculation, with higher sensitivity and stability.

[0029] 2. Higher wearing comfort: The flexible wire design enables the device to adapt to the dynamic activities of the foot, reducing the discomfort caused by the rigidity of the wire. The flexibility of the wire and the application of biocompatible materials further enhance the wearing comfort, especially for long-term continuous wear, improving user compliance.

[0030] 3. More ergonomic design: The probe and wire of this device are made of biocompatible materials, which reduces friction and pressure on the skin, enhances the safety and comfort of wearing, and ensures that users will not feel discomfort during long-term wearing. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic diagram of an assembly method of a wearable flexible PPG device for foot microcirculation monitoring provided in an embodiment of the present invention.

[0032] Figure 2 Schematic diagram and scanning electron microscope image of carbon nanotube films for stretchable transistors.

[0033] Figure 3 Schematic diagram of the use of a wearable flexible PPG device for foot microcirculation monitoring. DETAILED DESCRIPTION

[0034] The terms "first", "second", "third", "fourth", etc. (if any) in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "including" or "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0035] Disadvantages of existing technology

[0036] In the field of foot microcirculation monitoring, existing PPG (photoplethysmography) devices face the following significant disadvantages:

[0037] 1. Rigid design of signal acquisition probe: Traditional PPG devices mostly use hard materials to encapsulate signal acquisition probes, which makes it difficult to fit the surface curve of the foot and is easily disturbed by motion artifacts during dynamic monitoring. This rigid design makes the device unstable when worn on the foot, the signal acquisition quality is poor, and it is easily affected by movement, causing noise interference and measurement errors.

[0038] 2. Insufficient flexibility of the wire affects the wearing experience: The wires of existing PPG devices are usually made of rigid or low-flexibility materials, which limits the flexibility of the device in dynamic foot monitoring. In the scenarios of gait analysis and motion monitoring, the lack of flexibility of the wires leads to discomfort when wearing, and data transmission is easily affected in a dynamic environment, resulting in signal interruption or distortion, which in turn affects the reliability of the monitoring data.

[0039] 3. Poor wearing comfort affects compliance: The design of traditional PPG devices does not take into account the special monitoring needs of the feet. The rigid probe and wire design have an adverse effect on the wearer's comfort, especially when worn for a long time, which can easily cause discomfort, making it difficult for the wearer to monitor continuously for a long time, affecting the user compliance of the device.

[0040] In view of the shortcomings of the above-mentioned prior art, the purpose of this patent is to provide an improved wearable flexible PPG device specifically for dynamic monitoring of foot microcirculation to improve signal acquisition quality, data transmission stability and wearing comfort. The specific purposes include:

[0041] 1. Improve the stability and sensitivity of signal acquisition: By encapsulating the signal acquisition probe with flexible materials, the probe can fit closely to the curved surface of the foot, reducing signal instability and noise interference caused by movement, thereby achieving high-quality PPG signal acquisition.

[0042] 2. Improve the flexibility and wearing comfort of the wire: The highly flexible and biocompatible wire design enables the device to adapt to the dynamic activities of the foot, which not only improves the stability of data transmission, but also significantly improves the wearing comfort, making it suitable for long-term monitoring needs.

[0043] Enhance the wearing comfort of the device and improve user compliance: Through the application of flexible and biocompatible materials, ensure the comfort of the device when worn for a long time, reduce friction and pressure on the skin, and improve user wearing compliance. It is especially suitable for daily monitoring of patients with chronic diseases such as diabetic foot.

[0044] For ease of understanding, the specific process of the embodiment of the present invention is described below. Figure 1 and 3 A first embodiment of a wearable flexible PPG device assembly method for foot microcirculation monitoring in an embodiment of the present invention includes:

[0045] The PPG device comprises a flexible substrate, a probe, and a wire, wherein the probe is fixed to the flexible substrate, the wire is used to transmit data of the probe, the probe comprises an LED and a photodetector, and the assembly method comprises the following steps:

[0046] Mixing the raw materials of the flexible substrate, pouring them into a mold and curing them to obtain the flexible substrate;

[0047] Performing activation treatment on the surface of the flexible substrate to obtain an activated flexible substrate;

[0048] On the activated flexible substrate, a conductive circuit is designed for electrical connection of the LED and the photodetector;

[0049] Performing hydrophilic surface treatment on a flexible substrate having a conductive circuit to obtain a hydrophilic flexible substrate;

[0050] Installing LEDs, photodetectors, and wires at predetermined positions on a hydrophilic flexible substrate, and encapsulating them with encapsulation materials to obtain a circuit encapsulation layer;

[0051] A packaging protection layer is added outside the circuit packaging layer, and a vent hole is reserved on the skin contact surface to obtain a packaged probe;

[0052] The encapsulated probe is cured to ensure that the encapsulation layer is fully formed and firmly bonded to the hydrophilic flexible substrate.

[0053] The details are as follows:

[0054] Part 1: Probe Modification

[0055] The focus of the probe modification is to integrate the LED and photodetector into a flexible, stretchable and biocompatible substrate material to ensure the comfort of the device on the skin and its sensitivity to biological signals. To achieve this goal, we will use the following materials and technologies and explain in detail the design and fabrication process of each step.

[0056] 1. Base material selection and processing

[0057] 1.1 Material selection:

[0058] Polydimethylsiloxane (PDMS): PDMS is highly flexible and biocompatible, suitable for skin adhesion. PDMS can be prepared from commercially available materials, such as Sylgard 184 (Dow Corning). The material is transparent and stretchable, suitable for measuring optical signals. The PDMS substrate provides a soft, conformable support for LEDs and photodetectors.

[0059] Polyurethane (PU): PU has excellent mechanical properties and breathability. Mediprene (provided by Hexpol) is recommended, a medical-grade PU material suitable for wearable devices attached to the skin. The properties of PU enable it to maintain fit on skin areas of different shapes.

[0060] Processing method:

[0061] 1. Preparation of PDMS substrate: Mix PDMS prepolymer and curing agent in a ratio of 10:1, pour into the mold, and use the spin coating process to prepare a film with a thickness of 100-200 microns. Then, bake at 60°C for 1 hour to cure and obtain a soft PDMS substrate. The film thickness can be adjusted as needed to adapt to different skin parts.

[0062] 1. PU substrate preparation: PU film is prepared by hot pressing. The PU material is heated to 60-80°C and pressed into a 100-300 micron thick film in a mold. The PU film has better elasticity and can be used in areas that require higher stretchability.

[0063] 1.2 Selection and processing of conductive materials

[0064] Material selection:

[0065] Mixing with silver Nanowire (AgNWs): AgNWs have high conductivity and mechanical flexibility. It is recommended to use the silver nanowire dispersion provided by Sigma-Aldrich in the United States, or directly use the AgNW ink developed by the Institute of Materials Research and Engineering (IMRE) in Singapore. AgNWs form a conductive circuit on a flexible substrate to connect LEDs and photodetectors.

[0066] Liquid Metal Nanoparticles (LMNPs) gallium-indium alloys (LMNPs represented by gallium (Ga), indium (In), or their eutectic, EGaIn): (provided by Indium Corporation, USA) can be used to prepare conductive and stretchable electrodes and connecting wires. They will not break during bending and stretching and can maintain stable conductive properties.

[0067] 1.2 Processing method:

[0068] 1.2.1 Silver nanowire circuit fabrication: AgNW ink is applied to a PDMS or PU substrate using spraying or printing techniques. First, a circuit pattern is designed on the substrate, and then silver nanowires are deposited in an interlaced manner using a masking method to form a conductive network. The accuracy of the circuit can be fine-tuned using a laser ablation process to ensure accurate docking with the electrodes of the LED and photodetector.

[0069] 1.2.2 Liquid metal wire fabrication: Microchannels are engraved on the PDMS substrate, and then liquid gallium-indium alloy is injected into these channels to form conductive paths. Liquid metal is fluid and can adapt to the bending and stretching of the substrate.

[0070] 1.3 Packaging materials and processes

[0071] Material selection:

[0072] Ecoflex (Smooth-On): Ecoflex is a transparent, soft silicone material that is highly elastic and biocompatible. It can wrap around the entire probe and circuitry, providing protection while maintaining flexibility.

[0073] In addition to the flexible polymer material, the signal acquisition probe may also be made of other flexible, thin materials, such as thermoplastic elastomer (TPE), medical grade silicone, or flexible rubber, to achieve the purpose of closely fitting the surface of the foot.

[0074] Processing method:

[0075] 1.3.1 Encapsulation process: On the prepared PDMS or PU substrate, the LED and photodetector are attached to the predetermined position. The probe surface is coated with Ecoflex with a thickness of about 100-200 microns to protect the internal circuits and components. Then, it is cured at 80°C for 30 minutes. After encapsulation, the probe surface is smooth and can be comfortably attached to the skin.

[0076] The packaging structure of the signal acquisition probe can be designed to be adjustable, for example, using a retractable structure or elastic straps, so that the probe can automatically adjust its fit according to different foot sizes and shapes, thereby adapting to the needs of different wearers.

[0077] It can be designed as a replaceable probe module to achieve flexible replacement of multiple probes, such as using a fitted probe during dynamic activities and a traditional hard probe during static measurements, to enhance the applicability of the equipment.

[0078] 1.3.2 Signal hole design: On the packaging layer, a signal detection hole is reserved for the photodetector to ensure the penetration and reception quality of the optical signal. The Ecoflex layer can be precisely cut using laser engraving technology to form a small hole.

[0079] Part II: Transformation of wires

[0080] The wire modification is designed to be flexible, stretchable, and biocompatible to ensure that the wire does not affect signal transmission when it fits the skin and during dynamic walking. To achieve this goal, we will use the latest materials and technologies for modification. The following is a detailed design plan.

[0081] 2.1 Selection and preparation of flexible wire materials

[0082] The wire needs to maintain stable conductivity when bent and stretched, while also having good biocompatibility and comfort. To this end, we can choose the following materials:

[0083] Material selection:

[0084] Carbon Nanotubes (CNT) fibers: Carbon nanotubes have excellent conductivity and stretchability and can be used to make highly flexible wires. It is recommended to use carbon nanotube fiber materials from the National Institute for Materials Science (NIMS) in Japan or Carbon Solutions in the United States. These materials not only have excellent conductivity, but also their nanoscale structure can be tightly combined with the elastomer substrate to form a stretchable wire.

[0085] Figure 2(h): Schematic diagram and scanning electron microscope image of carbon nanotube film for stretchable transistors, scale bar: 200nm; (Ref: Long G, Jin W, Xia F, Wang Y, Bai T, Chen X, Liang X, Peng LM, Hu Y. Carbonnanotube-based flexible high-speed circuits with sub-nanosecond stagedelays. Nat Commun. 2022Nov 8; 13(1): 6734. doi: 10.1038 / s41467-022-34621-x. PMID: 36347889; PMCID: PMC9643494.); (i): Intrinsically stretchable transistor array based on carbon nanotubes (Ref: Wang S, Xu J, Wang W, Wang GN, Rastak R, Molina-Lopez F, Chung JW, Niu S, Feig VR, Lopez J, Lei T, Kwon SK,Kim Y,Foudeh AM,Ehrlich A,Gasperini A,Yun Y,Murmann B,Tok JB,Bao Z.Skin electronics from scalable fabrication of an intrinsically stretchable transistor array.Nature.2018Mar 1;555(7694):83-88.doi:10.1038 / nature25494.Epub 2018Feb 19.PMID:29466334.).

[0086] Liquid metal (gallium-indium alloy, EGaIn): Liquid metal has fluidity and high conductivity, making it an ideal material for making flexible wires. Gallium-indium alloy materials provided by the US Indium Corporation can be used and embedded in elastomers to prepare stretchable microfluidic wires.

[0087] Wireless signal transmission alternative: In the wire design, in addition to highly flexible materials, the physical wire connection can be completely removed, and wireless Bluetooth, Wi-Fi, etc. can be used to directly transmit signals to the data recording module to achieve a completely wireless design, thereby further improving wearing comfort and eliminating the restrictions of wires on the wearer.

[0088] Embedded wire design: The wire can be designed to be embedded in wearable socks or flexible protective gear, so that the wire is integrated with the fabric, reducing the exposure and interference of the wire to the outside, while improving the aesthetics and concealment of the wearer.

[0089] Winding wire structure: The wire can adopt a spiral winding structure to make it stretchable, so that it can adapt to the deformation of the foot during dynamic activities without affecting signal transmission, ensuring stable data during monitoring.

[0090] Preparation method:

[0091] Carbon nanotube fiber conductor production:

[0092] First, combine the carbon nanotube fibers with an elastomer (such as silicone rubber PDMS) to prepare a stretchable wire. The specific operation is to mix the PDMS prepolymer and the curing agent in a ratio of 10:1, apply it on the carbon nanotube fibers, and then cure it at 60°C for 30 minutes. The coating of the PDMS layer not only improves the mechanical strength of the wire, but also increases its comfort with the skin. If higher conductivity is required, the carbon nanotube fibers can be bundled into bundles and then coated in an elastomer to form a multi-channel wire to improve the stability of signal transmission.

[0093] Liquid metal microfluidic wire fabrication:

[0094] A microchannel is made on a flexible substrate (such as PDMS). A microchannel with a diameter of 100-200 microns is engraved on the PDMS substrate using laser etching technology, and the shape is designed according to the connection requirements of the probe and the signal processing device.

[0095] Gallium-indium alloy liquid metal is injected into these microchannels to form conductive paths. The liquid metal has good fluidity in the microchannels and can adapt to stretching and bending.

[0096] Finally, the microfluidic channels were encapsulated with another layer of PDMS to prevent the liquid metal from leaking while maintaining the flexibility of the wires.

[0097] 2.2 Outer coating material

[0098] In order to improve the comfort and durability of the wire on the skin, it is necessary to cover the outer layer of the wire:

[0099] 2.2.1 Material selection:

[0100] Medical silicone: Medical-grade silicone materials (such as MED-4735 provided by Nusil, USA) have good biocompatibility, softness and waterproof properties. They can be used to cover the outer layer of the wire to enhance the durability of the wire and prevent skin irritation.

[0101] 2.2.2 Processing method:

[0102] Coating process: Coat a layer of medical silicone on the prepared flexible wire. The medical silicone is evenly coated on the wire with a thickness of about 50-100 microns to ensure the flexibility of the wire. It is then cured at room temperature to form a protective layer. This silicone layer has antibacterial properties and can prevent the skin from infection or irritation during long-term contact.

[0103] Connector treatment: Connectors should be reserved at both ends of the wire for connection with the probe and signal processing device. When coating the outer layer of silicone, both ends of the wire should be sealed in advance to ensure that the electrical connection part will not be affected by the external environment.

[0104] 2.3 Performance optimization and testing

[0105] After the wire is fabricated, it needs to be tested for flexibility, conductivity, and biocompatibility. The wire's tensile properties can be evaluated using a standard tensile testing machine to ensure that the wire remains conductive within the maximum stretch range.

[0106] To test biocompatibility, the wires can be attached to human skin and worn for 24 hours to assess their comfort and potential irritation to the skin.

[0107] Part III: Assembly and preparation methods

[0108] In order to ensure that the flexible probe and wire have good mechanical flexibility, biocompatibility and stable signal transmission performance in practical applications, the entire assembly and preparation process will use the following key technologies: printed electronics technology, spraying / self-assembly technology and packaging technology. The following is a detailed process flow for each step.

[0109] 1. Printed electronics technology

[0110] Printed electronics technology is used to make conductive circuits on a flexible substrate (PDMS) to ensure that the circuit board has good conductivity and stretchability.

[0111] Materials and Equipment:

[0112] Silver nanowires (AgNWs): Silver nanowire dispersion from Sigma-Aldrich, USA, was used as the conductive material.

[0113] Flexible substrate (PDMS): As the substrate of flexible circuit boards, PDMS has good flexibility and biocompatibility, ensuring that the circuit remains stable in dynamic environments.

[0114] Printing equipment: Use screen printing machine or inkjet printing equipment for precision printing of conductive materials.

[0115] Process steps:

[0116] Substrate preparation: First, the PDMS substrate was mixed in a ratio of 10:1 (PDMS prepolymer and curing agent), poured into a mold, spin-coated to the desired thickness (100-200 μm), and then cured in an oven at 60 °C for 1 hour to form a flexible substrate.

[0117] Surface treatment: Use oxygen plasma or UV / Ozone to activate the PDMS surface to enhance the adhesion between the subsequent conductive material and the substrate.

[0118] Circuit printing: Silver nanowire ink is printed onto the PDMS substrate according to the designed circuit pattern by screen printing or inkjet printing technology. The ink thickness is controlled at 5-10 microns to ensure the accuracy and stability of the conductive path.

[0119] Curing treatment: The printed silver nanowire circuit needs to be cured again in a 60°C oven for 30 minutes to enhance its adhesion and form a stable conductive network.

[0120] 2. Spraying or self-assembly technology

[0121] Spray coating or self-assembly technology is used to deposit conductive materials on the substrate to enhance the sensitivity and reliability of the conductive path, ensuring that the signal probe can stably receive and transmit biological signals.

[0122] Materials and Equipment:

[0123] Silver nanowires (AgNWs) and carbon nanotubes (CNTs): materials provided by Sigma-Aldrich and Carbon Solutions, Inc., USA, respectively.

[0124] Spraying equipment: Use a gas sprayer to evenly deposit the conductive material onto the PDMS substrate.

[0125] Process steps:

[0126] Spraying conductive material: Spray the silver nanowire or carbon nanotube solution evenly on the treated PDMS substrate to form a uniform conductive network layer. By adjusting the distance between the nozzle and the substrate of the spraying equipment, ensure that the thickness of the deposited layer is moderate, usually 10-20 microns.

[0127] Self-assembly: Silver nanowires or carbon nanotubes are formed into micrometer- or nanometer-scale conductive paths through a self-assembly reactor. This conductive path can significantly enhance the conductivity of the circuit and improve the sensitivity of the signal.

[0128] 3. Packaging process

[0129] The packaging process is crucial, as it not only provides protection for the probe and wires, but also ensures the stability and signal transmission performance of the flexible probe during bending and stretching. In particular, it is necessary to ensure a good interface bonding between the PDMS substrate and the Ecoflex packaging material.

[0130] Materials and Equipment:

[0131] Ecoflex (Smooth-On): As the main packaging material, Ecoflex is flexible and biocompatible, suitable for packaging signal probes and circuits.

[0132] Oxygen plasma treatment equipment: used to treat the surface of the PDMS substrate to ensure the adhesion between PDMS and Ecoflex.

[0133] Encapsulation mold: used for precise molding of Ecoflex encapsulation layer.

[0134] Process steps:

[0135] Surface activation treatment: On the PDMS substrate with printed conductive circuits, oxygen plasma treatment or UV / Ozone treatment is used to generate hydrophilic functional groups on the surface to enhance the bonding strength between PDMS and the subsequent Ecoflex encapsulation layer.

[0136] Encapsulate signal probe: Install LED and photodetector (PD) to the predetermined position on the PDMS substrate and encapsulate with Ecoflex material. The thickness of Ecoflex should be properly controlled to ensure that the probe encapsulation in the protective layer does not affect the signal transmission and the reception of optical signals. The recommended thickness is 100-200 microns.

[0137] Package wire part: Use liquid metal (such as gallium indium alloy, EGaIn) as the wire material, combined with a flexible substrate and Ecoflex package. The Ecoflex package of the wire part needs to reserve enough stretching space to adapt to the bending and stretching of the device under dynamic conditions.

[0138] Packaging protection layer design: An Ecoflex protective layer is added to the outside of the probe and circuit packaging layer, and ventilation holes are reserved in key areas (such as the skin contact surface) to improve the comfort and breathability of the device.

[0139] Curing treatment: Place the encapsulated probe in an oven at 80°C for 30 minutes to ensure that the Ecoflex encapsulation layer is fully formed and firmly bonded to the PDMS substrate.

[0140] 4. Mechanical interlocking design

[0141] In order to further enhance the bonding force between the PDMS substrate and the Ecoflex package, a mechanical interlocking structure can be added during the packaging process.

[0142] Mechanical interlock design steps:

[0143] Tiny holes or grooves are etched on the PDMS substrate, and the size and distribution of the holes are precisely controlled by laser etching technology. These microstructures allow Ecoflex to penetrate into the surface of the PDMS substrate during curing, forming a mechanical interlocking structure, further improving the adhesion between the two.

[0144] After Ecoflex is injected, it is ensured that it fully fills these micropores or grooves to form a solid mechanical joint, thus ensuring that the two will not separate when the device is stretched and bent.

[0145] 5. Fixing and accessory design

[0146] Finally, to ensure that the device can be firmly attached to the user's ankle or foot, a suitable fixation method needs to be designed.

[0147] Material selection:

[0148] 3M medical double-sided adhesive tape: As a replaceable fixing layer, it ensures the stable wearing of the device and is easy to remove and replace.

[0149] Elastic silicone strap: For extra fixation when long-term wear is required, adjustable tightness.

[0150] Fixed process:

[0151] A removable medical double-sided adhesive layer is designed on the outside of the Ecoflex packaging layer to fix the device on the skin surface.

[0152] To prevent the device from sliding or falling off while being worn, an elastic silicone strap can be added to ensure that the device remains stable during dynamic walking.

[0153] Magnetic adsorption wearing structure: In addition to the flexible fitting design, the connection between the probe and the wire can also be designed as a magnetic adsorption structure to facilitate the quick installation and removal of the probe, while realizing signal collection and monitoring of different parts of the foot, increasing the flexibility of wearing.

[0154] Adhesive probe: The probe can be designed to be adhesive and directly attached to the skin of the foot with disposable medical tape, allowing for burden-free wearing. It is suitable for short-term monitoring or non-continuous dynamic monitoring scenarios and reduces wearing discomfort.

[0155] Foot-covered integrated wearing structure: The probe, wire and data recording module are integrated into a foot cover or sock, which is easy to wear and adjust while ensuring stable data transmission. It is suitable for applications that require long-term wearing and continuous monitoring.

[0156] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A wearable flexible PPG device assembly method for foot microcirculation monitoring, characterized in that: The PPG device comprises a flexible substrate, a probe, and a wire, wherein the probe is fixed to the flexible substrate, the wire is used to transmit data of the probe, the probe comprises an LED and a photodetector, and the assembly method comprises the following steps: Mixing the raw materials of the flexible substrate, pouring them into a mold and curing them to obtain the flexible substrate; Performing activation treatment on the surface of the flexible substrate to obtain an activated flexible substrate; On the activated flexible substrate, a conductive circuit is designed for electrical connection between the LED and the photodetector, and the conductive circuit is used for connection of the internal circuit of the probe; Performing hydrophilic surface treatment on a flexible substrate having a conductive circuit to obtain a hydrophilic flexible substrate; Installing LEDs, photodetectors, and wires at predetermined positions on a hydrophilic flexible substrate, and encapsulating them with encapsulation materials to obtain a circuit encapsulation layer; A packaging protection layer is added outside the circuit packaging layer, and a vent hole is reserved on the skin contact surface to obtain a packaged probe; The encapsulated probe is cured to ensure that the encapsulation layer is fully formed and firmly bonded to the hydrophilic flexible substrate.

2. A wearable flexible PPG device assembly method for foot microcirculation monitoring according to claim 1, characterized in that: The flexible substrate raw material is a PDMS substrate or a PU substrate.

3. The method for assembling a wearable flexible PPG device for foot microcirculation monitoring according to claim 1, characterized in that: The conductive circuit preparation method is: AgNW ink is coated on a flexible substrate using a spraying or printing technique, and silver nanowires are deposited in an interlaced manner by a mask method according to a circuit pattern designed on the substrate material to form a conductive circuit.

4. A wearable flexible PPG device assembly method for foot microcirculation monitoring according to claim 1, characterized in that: The conductive circuit preparation method comprises: engraving microchannels on a flexible substrate, and injecting liquid gallium-indium alloy into the channels to form a conductive circuit.

5. The method for assembling a wearable flexible PPG device for foot microcirculation monitoring according to claim 1, characterized in that: The conductor is a carbon nanotube fiber conductor, and the preparation method is: PDMS prepolymer and curing agent are mixed in a ratio of 10:1, coated on carbon nanotube fibers, and then cured at 60° C. for 30 minutes to obtain the carbon nanotube fiber conductor.

6. A wearable flexible PPG device assembly method for foot microcirculation monitoring according to claim 1, characterized in that: The wire is a liquid metal microfluidic wire, and the preparation method is: using laser etching technology to carve microchannels with a diameter of 100-200 microns on PDMS, injecting gallium-indium alloy liquid metal into these microchannels to form a conductive path, and encapsulating the microchannels with another layer of PDMS to obtain the liquid metal microfluidic wire.

7. A wearable flexible PPG device assembly method for foot microcirculation monitoring according to claim 1, characterized in that: The wire also includes a protective layer, which is made of medical silica gel.

8. The method for assembling a wearable flexible PPG device for foot microcirculation monitoring according to claim 1, characterized in that: The activation treatment is to use oxygen plasma or UV / Ozone to activate the surface of the flexible substrate.

9. The method for assembling a wearable flexible PPG device for foot microcirculation monitoring according to claim 1, characterized in that: The assembly method also includes a mechanical interlocking design step: Tiny holes or grooves are etched on the flexible substrate, and the size and distribution of the holes are precisely controlled by laser etching technology, so that the packaging material can penetrate into the surface of the flexible substrate during curing to form a mechanical interlocking structure.

10. A wearable flexible PPG device obtained by the assembly method described in any one of claims 1 to 9.

Images