Cubic hollowed-out structure obtained through precursor solution photocuring 3D printing and application of cubic hollowed-out structure

Abstract

The invention belongs to the technical field of health and medical treatment, and relates to a cubic hollowed-out structure obtained through precursor solution photocuring 3D printing and application of the cubic hollowed-out structure, the cubic hollowed-out structure is in a regular hexahedron shape, the edge length ranges from 600 micrometers to 800 micrometers, the hollowed-out degree ranges from 25% to 35%, the Poisson ratio ranges from 0.425 to 0.525, through circular air holes are formed in the cubic hollowed-out structure, and the hole diameter of the circular air holes ranges from 200 micrometers to 400 micrometers; the cubic hollow structure comprises the following components: sodium alginate SA, acrylamide AM and methyl acrylate ACMO; the cubic hollow structure increases the flexibility and air permeability of the material, and is more sensitive to micro deformation such as pulse beat; the internal combination ensures that the mechanical property of the material is not affected, after multiple times of cycle work, the stability of signal output is still kept, no obvious peak attenuation or initial resistance offset exists, the long-term monitoring capability and reliability of the sensor are effectively improved, and the reliability of the sensor is improved. The problem that a traditional strain sensor depends on nanofiller to improve the sensitivity, so that the anti-fatigue performance is poor is solved.

Description

Technical Field

[0001] The present invention belongs to the field of health and medical technology, and relates to a cubic hollow structure printed by photocuring 3D printing using a precursor liquid and an application thereof. Background Art

[0002] Wearable Skin Monitoring Devices refer to electronic devices that are directly attached to or in close contact with the surface of human skin and are used to continuously and in real time monitor physiological parameters and health status. Such devices are usually designed to be very light, soft and biocompatible to ensure comfortable wearing and reduce the impact on daily activities. With the rapid development of the health and medical field, wearable skin monitoring devices have received a lot of attention due to their powerful interaction with the human body and long-term monitoring capabilities. Wearable skin monitoring devices have been widely used in many fields such as health care, sports and fitness, and environmental exposure assessment.

[0003] Strain sensors are used in the field of medical monitoring to detect and quantify small deformations or stress changes in objects (such as human tissue, medical devices, etc.). These sensors can convert mechanical deformation into electrical signals, thereby achieving accurate measurement of various physiological parameters. In medical applications, strain sensors are usually designed to be very sensitive and have good biocompatibility to ensure that they can safely contact the human body and provide reliable data. The core of the strain sensor is based on the phenomenon that the resistance, capacitance or other physical properties of a material change as its shape changes.

[0004] However, strain sensing components, which are key parts of signal response in skin wearable monitoring devices, still face challenges. The nanofiller composite functional materials commonly used in strain sensing components have weak fatigue resistance, while filler-free elastomer strain sensing components have poor sensing performance due to their simple shape. The positive high Poisson's ratio hydrogel prepared by surface exposure 3D printing process can make up for the performance defects caused by simple morphology, while avoiding the signal fluctuation problem caused by the tunnel effect of fillers. Therefore, we proposed a design method for photocuring printing gel precursor system.

[0005] Therefore, a structure, device or method is needed to solve the above technical problems by making up for the performance defects caused by the simple morphology while avoiding the tunnel effect of the filler. Summary of the invention

[0006] The technical solution adopted by the present invention to solve the technical problem is: a cubic hollow structure using precursor liquid photocuring 3D printing, the cubic hollow structure is in the shape of a regular hexahedron, the edge length of the cubic hollow structure is 600-800 microns, the hollowness is 25-35%, the Poisson's ratio is 0.425-0.525, and the cubic hollow structure is provided with penetrating circular pores, and the aperture of the circular pores is 200-400 microns; the components of the cubic hollow structure include: sodium alginate SA, acrylamide AM, and methyl acrylate ACMO; the cubic hollow structure has a cubic hollow geometric shape with positive high Poisson's ratio characteristics, which enhances the sensor's response ability to strain changes and solves the problem that strain sensors in traditional flexible electronic devices mostly rely on nanofillers to improve sensitivity, which may lead to poor fatigue resistance; and the combination of sodium alginate SA, acrylamide AM and methyl acrylate ACMO in a specific ratio not only improves the mechanical properties of the material, but also reduces transparency, reduces the diffusion of oligomers during printing, and realizes more accurate three-dimensional structure construction.

[0007] Preferably, the cubic hollow structure is prepared by photocuring 3D printing using a gel precursor; in the gel precursor, the weight ratio of sodium alginate SA to acrylamide AM is 3.5-4.5:1; the concentration of sodium alginate SA is 0.8-1.2wt%, and the viscosity of the gel precursor is not less than 198mPa·s; the viscosity is to inhibit the diffusion of methyl acrylate ACMO molecules, and the gel precursor has suitable rheological properties, which can not only ensure that the diffusion of oligomers is effectively inhibited during the printing process, but also can smoothly level when the printing platform moves.

[0008] More preferably, the viscosity of the gel precursor solution includes a viscosity value at a shear rate of 0.01 to 0.11 / s.

[0009] The present invention also discloses an application of a cubic hollow structure printed by precursor liquid photocuring 3D printing, the application adopts the above-mentioned cubic hollow structure, and the application uses the cubic hollow structure to form a sensor for disease monitoring, daily health management, and sports monitoring; the sensor composed of the cubic hollow structure can clearly sense the pulse signal, and due to the effect of pre-strain, the feedback of the pulse beat is more obvious, and the detected signal peak is higher and clearer; the sensor composed of the cubic hollow structure can also be used for daily heart rate monitoring, and promptly issue an alarm in critical situations. In sports health monitoring, it can track heart rate changes in real time and provide exercise intensity reference for athletes; the sensor composed of the cubic hollow structure can also be used to monitor the movement status of various parts of the human body, joint activities, muscle movements, etc., to provide data support for sports rehabilitation, sports training effect evaluation, human-computer interaction and other fields.

[0010] Preferably, the disease monitoring and daily health management include pulse monitoring and heart rate monitoring; and the exercise monitoring includes finger bending exercise monitoring.

[0011] More preferably, the sensor includes: a rubber bracelet, a sensor electrode, and a cubic hollow structure. The rubber bracelet is provided with a groove, the cubic hollow structure is embedded in the groove, and the sensor electrodes are arranged on both sides of the wristband of the rubber bracelet; the rubber bracelet serves as the packaging shell of the sensor, and the material of the bracelet has good flexibility, wear resistance and biocompatibility, and can adapt to the wearing needs of different parts of the human body, while providing effective protection for the sensor inside the bracelet; the hollow part of the bracelet is filled with transparent resin, and the selection of the resin focuses on its optical transparency, chemical stability and bonding performance with the rubber bracelet and the sensor; the filling resin can not only provide structural support for the bracelet to keep it in a certain shape and strength, but also protect the internal sensor from external physical impact and chemical erosion to a certain extent.

[0012] More preferably, the cubic hollow structure is firmly fixed in the groove and is flush with the surface of the rubber bracelet; the cubic hollow structure fits tightly with the bottom and sides of the groove; the cubic hollow structure is embedded in the bracelet groove to ensure that the hydrogel piece is accurately positioned and fits tightly with the bottom and sides of the groove without gaps or offsets, so as to ensure that the sensor can accurately transmit stress when subjected to strain and is not affected by poor installation.

[0013] More preferably, the sensor electrode is made using a silver paste printing process, and the electrode thickness of the sensor electrode is 8 to 12 microns; one end of the sensor electrode is directly connected to the filling resin, and the other end is a floating end; a certain electrode thickness can ensure good conductivity without having too much impact on the flexibility of the sensor; one end of the sensor electrode is directly connected to the filling resin to ensure good electrical contact, and the other end is a floating end, which can adapt to the deformation of the hydrogel during the strain process, avoiding electrode damage or signal transmission interruption due to excessive constraint.

[0014] More preferably, the sensor electrode surface is coated with a thin and uniform silicone waterproof film with a thickness of 80 to 300 microns. The silicone waterproof film completely covers the sensor surface without holes or bubbles. The material selection of the silicone waterproof film focuses on waterproof performance, flexibility and biocompatibility. The silicone waterproof film can effectively prevent external moisture from invading the sensor and affecting its performance, and will not excessively increase the thickness and hardness of the sensor, thereby ensuring the durability and long-term stability of the sensor.

[0015] More preferably, the groove depth is 0.7-1.1 mm, and the length and width of the groove are 0.9-1.1 cm×0.9-1.1 cm. The groove within this size range can accurately install the sensor, ensuring that the sensor is firmly fixed in the groove and flush with the surface of the bracelet, without affecting the wearing comfort and the normal operation of the sensor.

[0016] The beneficial effects of the present invention are:

[0017] 1. The cubic hollow geometric sensor of the present invention has a sensor structure that increases the flexibility and air permeability of the material and is more sensitive to tiny deformations such as pulse beating; the cubic hollow structure is well integrated internally to ensure that the mechanical properties of the material are not affected, and can stably respond to finger bending movements at different angles; after multiple cycles of operation, the signal output stability is still maintained, with no obvious peak attenuation or initial resistance shift, which effectively improves the long-term monitoring capability and reliability of the sensor and solves the problem of poor anti-fatigue performance caused by traditional strain sensors relying on nanofillers to improve sensitivity.

[0018] 2. The cubic hollow structure of the present invention adopts sodium alginate SA, acrylamide AM and methyl acrylate ACMO to prepare a light-curing printing gel precursor by mixing them in a weight ratio; this ratio enhances the mechanical properties of the material, reduces transparency, limits the penetration depth of ultraviolet light, and ensures that each layer can be fully cured without affecting the printing quality of the next layer; SA provides biocompatibility and viscosity, AM enhances elastic modulus and toughness, and ACMO reduces oligomer diffusion, thereby achieving more precise three-dimensional structure construction, solving the problem of weak fatigue resistance of nano-filler composite materials, and avoiding the performance limitations brought about by simple modeling of unfilled elastomers. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a flow chart of the preparation of a photocurable printing gel precursor for a cubic hollow structure using precursor liquid photocuring 3D printing and its application;

[0020] Figure 2 is a flow chart of a method for light-curing 3D printing using a precursor liquid system of the present invention;

[0021] Figure 3 It is a manufacturing flow chart of the sensor of the present invention;

[0022] Figure 4 It is a flow chart of the method for pulse monitoring using a cubic hollow structure of the present invention;

[0023] Figure 5 This is a partial enlarged view of the sensor prepared by the cubic hollow structure of the present invention;

[0024] Figure 6This is a diagram of a sensor prepared by a cubic hollow structure of the present invention;

[0025] Figure 7 is a schematic diagram of the pulse monitoring result of the present invention;

[0026] Figure 8 It is a schematic diagram of the finger bending test results of the present invention. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the relevant technologies in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] refer to Figures 1 to 8 As shown, the cubic hollow structure of this embodiment uses a specific ratio of sodium alginate SA, acrylamide AM and methyl acrylate ACMO in light-curing 3D printing, which not only improves the mechanical properties of the material, but also reduces transparency, reduces the diffusion of oligomers during printing, and achieves more accurate three-dimensional structure construction; at the same time, a special design is made for the sensor structure, using a cubic hollow geometric shape with a positive high Poisson's ratio characteristic, which enhances the sensor's ability to respond to strain changes and solves the problem that strain sensors in traditional flexible electronic devices rely on nanofillers to improve sensitivity, which may lead to poor fatigue resistance, and the problem that filler-free elastomers have good flexibility but are limited in complex modeling and sensing performance. The specific plan is:

[0029] The light-curing printing gel precursor of the cubic hollow structure includes: sodium alginate SA and acrylamide AM are mixed in a weight ratio of 4:1, and methyl acrylate ACMO is added as a third component to prepare a precursor.

[0030] The concentration of sodium alginate SA is 1 wt % and it is dissolved in deionized water and ultrasonically treated for 30 minutes to ensure complete dissolution. The viscosity of the precursor solution is not less than 100 mPa·s at a shear rate of 0.01-0.11 / s to inhibit the diffusion of methyl acrylate ACMO molecules.

[0031] The preparation process of the precursor solution includes the following steps:

[0032] Step 1: dissolve sodium alginate SA in deionized water to form a uniform solution, the concentration of which is precisely controlled to be 1 wt%, and then stir at room temperature for 30 minutes and then perform ultrasonic treatment for 30 minutes;

[0033] Step 2: Add acrylamide AM to the above solution so that the mass ratio of acrylamide AM to sodium alginate SA is strictly 1:4, and continue stirring for at least 60 minutes;

[0034] Step 3: Add methyl acrylate (ACMO) and gradually adjust the total solvent amount until a predetermined viscosity value is obtained, ensuring that the final viscosity is 198 mPa·s;

[0035] Step 4: Use ultraviolet light source to measure transparency and ensure that the transmittance at a wavelength of 405nm does not exceed 0.00536%;

[0036] Step 5: Add a high-efficiency photoinitiator Irgacure 2959 to the solution to a final concentration of 0.5 wt % to promote the polymerization reaction.

[0037] A method for photocuring 3D printing of a cubic hollow structure includes photocuring printing gel precursor liquid, and further includes the following steps:

[0038] Step 1: Use a digital light processing (DLP) device, adopt an ultraviolet light source with a wavelength of 405 nanometers and a power setting of 3 milliwatts per square centimeter;

[0039] Step 2: Set the slice thickness to 100 microns and the exposure time to 2 seconds to ensure that each layer is fully cured;

[0040] Step 3: Move the printing platform up and down repeatedly to make the solution level itself and ensure that the molding layer is evenly spread. The shear rate range is 0.01-0.11 / s;

[0041] Step 4: Print a hydrogel piece with a cubic hollow structure, where each unit has a side length of 700 microns, a hollowing degree of 29.4%, and a Poisson's ratio of 0.475;

[0042] Step 5. A circular pore with a diameter of 300 microns is provided in the center of each unit to improve air permeability.

[0043] In the cubic hollow structure: each unit has a side length of 700 microns, a hollowness of 29.4%, and a Poisson's ratio of 0.475; a circular pore with a diameter of 300 microns is set in the center of each unit to improve air permeability; there is no obvious boundary inside the cubic hollow structure, and the layers are well bonded to ensure that the mechanical properties of the material are not affected;

[0044] After printing, the cubic hollow structure was immersed in 0.1 M CaCl solution for 20 minutes, then washed with deionized water and dried naturally.

[0045] A sensor prepared by a cubic hollow structure, comprising a cubic hollow structure, wherein the cubic hollow structure is encapsulated in a hollow rubber bracelet, and the bracelet is provided with a square groove of 1 cm×1 cm and a depth of about 0.9 mm for installing the sensor;

[0046] The sensor electrodes are printed with silver paste with a thickness of 10 microns and fixed to both sides of the wristband by conductive silver glue, with one end directly connected to the resin and the other end floating; ensure that the sensor surface is coated with a thin and uniform layer of silicone waterproof film to enhance durability.

[0047] The sensor production process includes the following steps:

[0048] Step 1: Insert the cube hollow structure into the groove of the bracelet;

[0049] Step 2: Fill with transparent resin to fix the sensor electrodes on both sides of the wristband, with one end directly connected to the resin and the other end floating;

[0050] Step 3: Apply pre-strain to the sensor to make the pulse feedback more obvious, thereby achieving clear heart rate monitoring;

[0051] Step 4. Tests show that the sensor can work normally in the range of 0-40 degrees Celsius and the relative humidity can reach 95% without affecting the performance.

[0052] A method for pulse monitoring using a sensor prepared with a cubic hollow structure, comprising a cubic hollow structure and a sensor, further comprising the following steps:

[0053] Step 1: Apply pre-strain to the sensor to enhance the pulse feedback signal;

[0054] Step 2: Achieve clear heart rate monitoring and stably respond to finger bending movements at different angles;

[0055] Step 3: After fatigue testing, it is proved that the structure has the potential to work in multiple cycles, the signal output is stable, and there is no obvious peak attenuation or initial resistance shift.

[0056] Example

[0057] 1. Material preparation

[0058] Sodium alginate SA: High-purity sodium alginate powder is selected to provide biocompatibility and viscosity. It has a wide source and high biosafety, and is one of the ideal basic materials for preparing hydrogels.

[0059] Acrylamide AM: As an organic compound, it is a white, odorless solid that is easily soluble in water and a variety of organic solvents. Its chemical formula is CH2=CHC(O), NH2. AM is used in combination with SA to form a hydrogel. It can introduce hydrophilic centers into lipophilic polymers, thereby improving the overall water solubility. At the same time, it plays an important role in enhancing the elastic modulus and toughness, so that the final prepared hydrogel has better mechanical properties.

[0060] Methyl acrylate ACMO: As the key third component in the present invention, its main function is to reduce the diffusion of oligomers; there is a special solvation effect between ACMO and SA, which has an important influence on the performance of the entire precursor liquid system and can effectively improve some key performance indicators in the printing process.

[0061] Deionized water: Deionized water that has been specially treated to remove impurity ions in the water is used to dissolve SA to ensure that the solution is pure and free of impurities, and to avoid the interference of impurity ions on the chemical reaction and physical properties of the precursor solution system.

[0062] Photoinitiator Irgacure2959: A highly efficient photoinitiator, with a final concentration of 0.5wt% in the final precursor solution. Its function is to absorb ultraviolet light energy of a specific wavelength during the photocuring printing process to produce active substances such as free radicals, thereby initiating polymerization of monomers in the precursor solution, prompting the liquid precursor solution to quickly transform into a solid gel structure, ensuring a smooth printing process and a stable structure.

[0063] 2. Precursor Preparation Steps

[0064] Step 1: Accurately weigh a certain amount of sodium alginate SA, dissolve it in an appropriate amount of deionized water to form a uniform solution, and strictly control the SA concentration to be 1wt%; use a magnetic stirrer to continuously stir for 30 minutes at room temperature to fully disperse SA in water; then transfer the solution to an ultrasonic cleaner for ultrasonic treatment for 30 minutes, and the ultrasonic frequency and power are set according to the actual equipment parameters. The cavitation effect generated by ultrasound further promotes the dissolution of SA to ensure that SA is completely dissolved, thereby obtaining solution A;

[0065] Step 2: According to the mass ratio of acrylamide AM to sodium alginate SA of 1:4, accurately weigh AM and add it to solution A; continue to stir with a magnetic stirrer for at least 60 minutes at a moderate stirring speed to ensure that AM and SA in solution A are fully mixed and the intermolecular interaction is sufficient to obtain solution B;

[0066] Step 3: Slowly add methyl acrylate ACMO to solution B, and gradually adjust the overall solvent amount; during the addition of ACMO, use a rotational viscometer or other viscosity measuring equipment to monitor the viscosity of the solution, set different shear rates during measurement, and focus on the viscosity change when the shear rate is 0.01-0.11 / s; continue to adjust until the solution is within this shear rate range and the viscosity reaches 198mPa·s. At this time, the solution has suitable rheological properties, which can not only ensure that the diffusion of oligomers is effectively suppressed during the printing process, but also can smoothly level when the printing platform moves, and obtain a precursor solution;

[0067] Step 4: Use ultraviolet light source equipment such as ultraviolet-visible spectrophotometer to measure the transparency of the precursor solution; during measurement, put the precursor solution into a quartz cuvette, set the measurement wavelength range, and focus on the transmittance at a wavelength of 405nm; by adjusting the solution composition or preparation process, ensure that the transmittance at a wavelength of 405nm does not exceed 0.00536% to meet the printing accuracy requirements and reduce the problem of print-through caused by deep hydrogel curing;

[0068] Step 5: Add high-efficiency photoinitiator Irgacure2959 to the precursor solution, use an analytical balance to accurately weigh an appropriate amount of photoinitiator to make its final concentration 0.5wt%; after adding, use a magnetic stirrer to slowly stir evenly to avoid introducing bubbles, and complete the preparation of the photocuring printing gel precursor solution. At this time, the precursor solution has the basic conditions for photocuring 3D printing.

[0069] 3. Light-curing 3D printing process

[0070] Equipment preparation

[0071] A digital light processing (DLP) device is used, which has a high-precision optical system and a stable mechanical structure; it is equipped with a UV light source with a wavelength of 405 nanometers. The luminous intensity and stability of the UV light source are strictly calibrated, and the power is set to 3 milliwatts / square centimeter to ensure that the light source can provide sufficient and stable energy to accurately trigger the photocuring reaction, so that the monomers in the precursor liquid are polymerized and cured according to the preset pattern and structure.

[0072] Print parameter settings

[0073] The slice layer thickness is set to 100 microns. This parameter is determined based on comprehensive consideration of printing accuracy and efficiency. A thinner slice layer thickness can improve the printing resolution, so that the final printed hydrogel structure has finer details, but it will also increase the printing time. After many tests and comparisons, a slice layer thickness of 100 microns can complete the printing task within a reasonable time while ensuring printing accuracy, and is suitable for the preparation of the hydrogel structure in the present invention.

[0074] The exposure time was determined to be 2 seconds, which was an optimized result obtained through a large number of experimental tests on precursor solutions of different thicknesses and compositions. Under this exposure time, ultraviolet light can penetrate the precursor solution layer, allowing the monomer to fully absorb light energy and undergo polymerization, ensuring that each layer of precursor solution can be uniformly and fully cured to form a stable gel structure. At the same time, changes in material properties caused by excessive exposure, such as increased brittleness caused by excessive cross-linking, are avoided.

[0075] Print Operation

[0076] Slowly pour the prepared precursor solution into the printing tank of the DLP device, taking care to avoid introducing bubbles and ensure that the surface of the solution is flat; start the printing program, and the printing platform begins to move up and down repeatedly under program control, and the moving speed and stroke are set according to the equipment parameters and printing requirements; during the movement of the platform, the solution self-levels under the action of surface tension to ensure that the molding layer is evenly spread, and the shear rate range is maintained at 0.01-0.11 / s. This shear rate range matches the viscosity characteristics of the precursor solution, which is conducive to the solution forming a uniform and stable thin layer on the printing platform; during the printing process, the ultraviolet light source exposes and cures the precursor solution layer by layer according to the preset pattern and parameters; the digital micromirror device (DMD) in the DLP device accurately controls the irradiation area and intensity of the ultraviolet light, so that each layer of the precursor solution is cured layer by layer according to the designed three-dimensional structure, and gradually forms a hydrogel with a specific structure; during the printing process, the printing status is monitored in real time to ensure that the printing process proceeds smoothly. If problems such as uneven leveling of the solution and incomplete curing are found, the parameters are adjusted or processed in time.

[0077] 4. Preparation and optimization of cubic hollow structure hydrogel

[0078] Structural design and printing

[0079] According to the pre-designed structural parameters, a cubic hollow structure model was designed using professional 3D modeling software. The side length of each unit in the model is 700 microns. This side length was determined through a large number of simulation calculations and actual printing tests. Under the premise of ensuring structural stability, the hydrogel piece has good flexibility and strain response performance. The side length of 700 microns will not be too small to make the structure too fragile and difficult to withstand the stress during printing and use, nor will it be too large to reduce the strain response sensitivity and affect the sensor performance.

[0080] The hollowing degree is designed to be 29.4%, which is determined on the basis of weighing the structural strength and deformation space. Through precise structural design and simulation analysis, the hollowing degree of 29.4% can provide enough space to accommodate deformation while maintaining the overall strength of the structure, so that the hydrogel can effectively transmit stress when it is strained, resulting in obvious changes in resistance and capacitance, thereby enhancing the sensor's ability to respond to strain changes.

[0081] The Poisson's ratio is 0.475. This high positive Poisson's ratio is one of the key advantages of the structural design of the present invention. When subjected to external pressure or stretching, the high positive Poisson's ratio structure will produce unique deformation behavior, making the internal microstructure of the hydrogel part change more significantly during the strain process, thereby causing a greater change in resistance and capacitance, greatly improving the sensitivity and response performance of the sensor.

[0082] A through circular pore with a diameter of 300 microns is set at the center of each unit. The design and size of the pore are determined after comprehensive consideration of air permeability and structural integrity. The existence of the pore significantly improves the air permeability of the hydrogel piece, which is beneficial for gas exchange with the external environment in practical applications, especially in wearable device application scenarios, and improves the user's comfort. At the same time, under the premise of ensuring air permeability, the 300-micron diameter will not excessively weaken the structural strength, ensuring that the hydrogel piece can maintain stable mechanical properties during use.

[0083] The designed model is imported into the DLP device, and printing is performed according to the printing parameters and operation steps in Example 2, and finally a hydrogel piece with a cubic hollow structure is obtained.

[0084] Post-processing optimization

[0085] After printing, the cubic hollow structure hydrogel was immersed in 0.1 M CaCl solution for 20 minutes. During the immersion process, the calcium ions (Ca 2+) undergoes ionic crosslinking reaction with the carboxyl groups in sodium alginate to form stronger chemical bonds, further enhancing the mechanical properties of the hydrogel and improving the stability and durability of the structure; the immersion time is strictly controlled at 20 minutes, which is determined by microstructural analysis and mechanical property testing of the hydrogel pieces at different immersion times; if the immersion time is too short, the crosslinking reaction is insufficient and the optimal mechanical property improvement effect cannot be achieved; if the immersion time is too long, cracks will appear in the covalently crosslinked grid, which may be due to the internal stress imbalance caused by excessive crosslinking, thereby seriously affecting the material properties; after the immersion is completed, the hydrogel piece is quickly washed with a large amount of deionized water to remove the residual CaCl solution on the surface, and then the hydrogel piece is placed in a well-ventilated environment to dry naturally, ready for subsequent packaging and testing; during the drying process, the hydrogel piece is prevented from being squeezed or contaminated by external force to ensure its structural integrity and stable performance.

[0086] 5. Fabrication and packaging of sensors

[0087] Sensor assembly

[0088] A commercial rubber bracelet is selected as the packaging shell of the sensor. The material of the bracelet has good flexibility, wear resistance and biocompatibility, which can adapt to the wearing needs of different parts of the human body, and at the same time provide effective protection for the sensor inside the bracelet; the hollow part of the bracelet is filled with transparent resin, and the selection of resin focuses on its optical transparency, chemical stability and bonding performance with the rubber bracelet and sensor; the filling resin can not only provide structural support for the bracelet to maintain a certain shape and strength, but also protect the internal sensor from external physical impact and chemical erosion to a certain extent;

[0089] A 1cm×1cm square groove is reserved at the sensor installation position in the middle of the bracelet. The depth of the groove is about 0.9mm. This size is precisely designed according to the size and shape of the cubic hollow structure hydrogel sensor so that the sensor can be accurately installed and ensure that the sensor is firmly fixed in the groove and flush with the surface of the bracelet without affecting the wearing comfort and the normal operation of the sensor.

[0090] Carefully embed the prepared cubic hollow structure hydrogel into the groove of the bracelet. Use appropriate tools to assist in the embedding process to ensure that the hydrogel is positioned accurately and fits tightly with the bottom and sides of the groove without gaps or offsets, so as to ensure that the sensor can accurately transmit stress when subjected to strain and is not affected by poor installation.

[0091] Electrode fixation and waterproofing

[0092] The sensor electrodes are made using a silver paste printing process. The silver paste is made of a material with high conductivity and good adhesion. The electrode thickness is 10 microns, which can ensure good conductivity without affecting the flexibility of the sensor. During the printing process, high-precision screen printing equipment is used to ensure that the electrode pattern is clear and the lines are uniform. The contact area and position between the electrode and the hydrogel meet the design requirements to achieve the best electrical signal transmission effect.

[0093] The printed electrodes are fixed to both sides of the wristband through conductive silver glue. The conductive silver glue has excellent conductivity and bonding properties, and can form a stable electrical connection between the electrode and the wristband; one end is directly connected to the filled resin to ensure good electrical contact, and the other end is designed as a floating end. The design of the floating end can adapt to the deformation of the hydrogel during the strain process, avoiding electrode damage or signal transmission interruption due to excessive constraint;

[0094] A thin and uniform layer of silicone waterproof film is coated on the surface of the sensor. The material selection of the silicone waterproof film focuses on its waterproof performance, flexibility and biocompatibility. Precision spraying equipment or dipping process is used during the coating process to control the thickness of the film within an appropriate range, generally between tens of microns and hundreds of microns, which can effectively prevent external moisture from invading the interior of the sensor and affecting its performance, and will not excessively increase the thickness and hardness of the sensor, thereby ensuring the durability and long-term stability of the sensor. The coating of the waterproof film must ensure that the sensor surface is completely covered without holes or bubbles, especially the connection between the electrode and the hydrogel component must be strengthened to prevent moisture from penetrating from these weak parts.

[0095] 6. Sensor performance test

[0096] Pulse monitoring test

[0097] Apply pre-strain to the packaged sensor. The pre-strain is applied by a specially designed fixture or stretching device. According to different application scenarios and sensor characteristics, the pre-strain size is optimized through multiple tests and is generally adjusted within a certain range to enhance the pulse feedback signal. Wear the sensor on the wrist of the experimenter. When wearing it, ensure that the sensor is in close contact with the skin without looseness or slippage. Use an appropriate bandage or fixing device to assist in fixing. The sensor starts working and monitors the pulse signal in real time. Use high-precision data acquisition equipment to record the changes in the electrical signal output by the sensor.

[0098] The experimental results show that the sensor can clearly sense the pulse signal of the experimenter. Due to the effect of pre-strain, the feedback of the pulse beat is more obvious, and the detected signal peak is higher and clearer. This is because the pre-strain puts the hydrogel sensor in an initial deformation state. When the pulse beat causes a slight deformation of the skin, the sensor can more sensitively capture this change and convert it into an electrical signal change. However, due to the existence of pre-strain, the sensor's ability to feedback smaller signals is reduced. It can only detect the main peak of arterial pulsation caused by left ventricular ejection, but cannot sense the peak formed by blood rebound caused by aortic valve closure. Despite this, the sensor still has important application value in the field of commercial wearable health devices. It can be used for daily heart rate monitoring and timely alarm in critical situations. For example, in sports health monitoring, it can track heart rate changes in real time and provide exercise intensity reference for athletes. In the daily health management of the elderly or patients with chronic diseases, it can be used as a convenient heart rate monitoring tool to detect abnormal heart rate changes in time and remind them to seek medical attention.

[0099] Finger flexion movement monitoring test

[0100] The experimenters bend the fingers of the hands wearing the sensors at different angles. The finger bending angle range is set according to the actual application requirements, generally covering the common bending angles in daily activities. The sensor records the signal changes during the movement in real time, and uses the data acquisition system to collect the electrical signals output by the sensor at a higher sampling frequency to ensure that the rapid signal changes during the finger bending process can be accurately captured.

[0101] The test results show that the sensor can successfully monitor the continuous movement of the finger and can respond to signals of corresponding amplitudes for different bending angles. The signal change pattern is closely related to the finger bending angle and the movement amplitude. As the finger bending angle increases, the amplitude of the electrical signal output by the sensor increases accordingly. This is because the bending of the finger causes the internal structure of the sensor to deform, resulting in changes in resistance and capacitance, which are then reflected in the electrical signal. This shows that the sensor has good application potential in the field of motion monitoring and can be used to monitor the movement status of various parts of the human body, such as joint movement, muscle movement, etc., to provide data support for sports rehabilitation, sports training effect evaluation, human-computer interaction and other fields. For example, in rehabilitation treatment, doctors can use sensors to monitor the patient's joint movement and develop personalized rehabilitation training plans. In virtual reality (VR) or augmented reality (AR) devices, sensors can be used as key components for gesture recognition to achieve more natural and accurate human-computer interaction operations.

[0102] Fatigue testing

[0103] The sensor was installed on a special fatigue test device that can accurately control the applied strain and the number of cycles. A 10% compressive strain was applied to the specimen. This strain was determined based on the strain range that the sensor may withstand in actual applications and is representative. A 200-cycle signal response output test was performed. During the test, high-precision data acquisition equipment and analysis software were used to record key parameters of the sensor in each cycle, such as the signal peak value and initial resistance value, in real time, and observe the signal change trend.

[0104] During the test, it was observed that although there were small fluctuations between the adjacent signal peaks, the signal output was stable overall, and there was no obvious peak attenuation and initial resistance shift. This shows that the cubic hollow structure has excellent stability and can withstand the pressure of multiple cycles. Its stability comes from the reasonable design of the structure. The positive high Poisson's ratio structure can maintain good mechanical properties during cyclic strain and is not prone to fatigue cracks or structural damage. At the same time, the characteristics of the hydrogel material itself and the optimization measures in the post-processing process (such as CaCl immersion cross-linking) also help to improve the stability of the structure. This stability ensures the reliability of the sensor during long-term use and can be effectively applied to scenarios that require long-term continuous monitoring, such as long-term physiological parameter monitoring in the health and medical field, and long-term operating status monitoring of industrial equipment. For example, in hospitals, it can be used for long-term ECG monitoring and respiratory monitoring of patients, providing doctors with continuous and accurate disease observation data. On industrial automation production lines, it can be used to monitor parameters such as vibration and deformation of key components of equipment, timely discover potential faults, and ensure the safety and stability of the production process.

[0105] It can be seen that the design method of the photocurable printing gel precursor system is to prepare the photocurable printing gel precursor by mixing sodium alginate SA, acrylamide AM and methyl acrylate ACMO in a weight ratio of 4:1; this ratio enhances the mechanical properties of the material, reduces transparency, limits the penetration depth of ultraviolet light, and ensures that each layer can be fully cured without affecting the printing quality of the next layer; SA provides biocompatibility and viscosity, AM enhances elastic modulus and toughness, and ACMO reduces oligomer diffusion, achieving more precise three-dimensional structure construction, solving the problem of weak fatigue resistance of nanofiller composite materials, and avoiding the performance limitations brought about by simple modeling of unfilled elastomers.

[0106] In addition, the design method of the photocurable printing gel precursor system designs a cubic hollow geometric sensor, each unit of which has a side length of 700 microns, a hollowness of 29.4%, a Poisson's ratio of 0.475, and a through circular pore with a diameter of 300 microns in the center; this structure increases the flexibility and air permeability of the material, and is more sensitive to small deformations such as pulse beating; the cubic hollow structure is well combined internally to ensure that the mechanical properties of the material are not affected, and can stably respond to finger bending movements at different angles; after multiple cycles of operation, the stability of the signal output is still maintained, without obvious peak attenuation or initial resistance shift, which effectively improves the long-term monitoring capability and reliability of the sensor, and solves the problem that traditional strain sensors rely on nanofillers to improve sensitivity and result in poor fatigue resistance, and solves the problem that strain sensors in traditional flexible electronic devices mostly rely on nanofillers to improve sensitivity, but this may lead to poor fatigue resistance, and the problem that unfilled elastomers have good flexibility but are limited in complex modeling and sensing performance.

[0107] In summary, the cubic hollow structure of the present invention increases the flexibility and air permeability of the material, and is more sensitive to tiny deformations such as pulse beating; the cubic hollow structure is well bonded internally, ensuring that the mechanical properties of the material are not affected, and can stably respond to finger bending movements at different angles; after multiple cycles of operation, the stability of the signal output is still maintained, with no obvious peak attenuation or initial resistance shift, which effectively improves the long-term monitoring capability and reliability of the sensor, and solves the problem of poor anti-fatigue performance caused by traditional strain sensors relying on nanofillers to improve sensitivity.

[0108] It should be emphasized that the above are only preferred embodiments of the present invention and do not limit the present invention in any form. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A cubic hollow structure printed by photocuring 3D printing using a precursor liquid, characterized in that: The cubic hollow structure is in the shape of a regular hexahedron, with an edge length of 600 to 800 microns, a hollowness of 25 to 35%, a Poisson's ratio of 0.425 to 0.525, and a through circular pore having an aperture of 200 to 400 microns. The components of the cubic hollow structure include sodium alginate SA, acrylamide AM, and methyl acrylate ACMO.

2. The cubic hollow structure printed by photocuring 3D printing using a precursor liquid according to claim 1, characterized in that: The cubic hollow structure is prepared by photocuring 3D printing using a gel precursor; in the gel precursor, the weight ratio of sodium alginate SA to acrylamide AM is 3.5-4.5:1; the concentration of the sodium alginate SA is 0.8-1.2wt%, and the viscosity of the gel precursor is not less than 198mPa·s.

3. The cubic hollow structure printed by photocuring 3D printing using a precursor liquid according to claim 2, characterized in that: The viscosity of the gel precursor solution includes the viscosity value when the shear rate is 0.01 to 0.11 / s.

4. An application of a cubic hollow structure printed by photocuring 3D printing using a precursor liquid, characterized in that: The application adopts the cubic hollow structure described in any one of claims 1 to 3, and the application forms the cubic hollow structure into a sensor for disease monitoring, daily health management, and exercise monitoring.

5. The application of a cubic hollow structure printed by photocuring 3D printing using a precursor liquid according to claim 4, characterized in that: The disease monitoring and daily health management include pulse monitoring and heart rate monitoring; the exercise monitoring includes finger bending exercise monitoring.

6. The use of a cubic hollow structure printed by photocuring 3D printing using a precursor liquid according to claim 4, characterized in that: The sensor comprises: a rubber bracelet, sensor electrodes, and a cubic hollow structure. The rubber bracelet is provided with a groove, the cubic hollow structure is embedded in the groove, and the sensor electrodes are arranged on both sides of the wristband of the rubber bracelet.

7. The use of a cubic hollow structure printed by photocuring 3D printing using a precursor liquid according to claim 6, characterized in that: The cubic hollow structure is fixed in the groove and is flush with the surface of the rubber bracelet; the cubic hollow structure is tightly fitted with the bottom and side surfaces of the groove.

8. The use of a cubic hollow structure printed by photocuring 3D printing using a precursor liquid according to claim 6, characterized in that: The sensor electrode is made by silver paste printing process, and the electrode thickness of the sensor electrode is 8-12 microns; one end of the sensor electrode is directly connected to the filling resin, and the other end is a floating end.

9. The use of a cubic hollow structure printed by photocuring 3D printing using a precursor liquid according to claim 6, characterized in that: The sensor electrode surface is coated with a silicone waterproof film, the thickness of the silicone waterproof film is 80 to 300 microns, and the silicone waterproof film completely covers the sensor surface without holes or bubbles.

10. The cubic hollow structure using precursor liquid photocuring 3D printing and its application according to claim 6, characterized in that: The depth of the groove is 0.7-1.1 mm, and the length and width of the groove are 0.9-1.1 cm×0.9-1.1 cm.

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