Microfluidic contact lens and tear collection and analysis method

Abstract

The invention discloses a microfluidic contact lens and a tear collection and analysis method, and belongs to the technical field of biomedical detection. The micro-fluidic contact lens comprises an outer layer and an inner layer, a micro-channel and a plurality of micro-cavities are arranged on the side, facing the inner layer, of the outer layer, inlets of the micro-cavities are sequentially connected to the side wall of the micro-channel, and the inlets of the micro-cavities form first capillary rupture valves through divergence angle design; a second capillary rupture valve is arranged on the micro-channel between every two adjacent micro-cavities, and a third capillary rupture valve is arranged on the micro-channel between each micro-cavity and the exhaust port of the micro-cavity; the inner layer is a smooth bent film; a paper microfluid sensor, a colorimetric sensor and a temperature-sensitive cholesteric liquid crystal (TSLC) sensor which are used for detecting tear indexes are arranged in the microcavity. The contact lens has good accuracy and stability in the aspects of measuring the secretion amount, the pH value and the temperature of tear, and particularly keeps relatively high reliability in comparison experiments under different illumination conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of biomedical detection, and particularly relates to a microfluidic contact lens and a method for collecting and analyzing tear fluid. Background Art

[0002] Emerging microfluidics-based biosensor technologies have been applied to devices, including smart patches and wristbands, capable of collecting and analyzing trace amounts of body fluids and providing non-invasive and flexible self-testing solutions for users. These biosensors are capable of detecting biomarkers in human biological fluids such as sweat, saliva, urine, and tears. Among them, tear fluid exhibits unique diagnostic potential due to its stable secretion rate and ease of collection at any time of the day, positioning it as a valuable medium for biomarker analysis.

[0003] Smart contact lenses that directly contact the eye represent a promising advancement in wearable biosensors. Compared with devices such as smart patches and wristbands, contact lenses directly collect continuous real-time tear fluid from the ocular surface, providing an uninterrupted data stream of biomarkers, facilitating point-of-care testing and continuous analysis. In addition, human tear fluid is a complex mixture of proteins, lipids, salts, and enzymes, and there are biomarkers such as glucose, sodium, potassium, and chloride ions, providing important diagnostic potential for various diseases, including dry eye disease, glaucoma, diabetes, and even cancer. This functionality allows for early screening and rapid diagnosis to meet the growing demand for efficient health monitoring tools. Moreover, the commercial maturity and high market acceptance of contact lenses make them particularly suitable for large-scale applications. Therefore, microfluidics-based smart contact lenses can serve as an effective medium for tear fluid collection and analysis, meeting the stringent requirements of rapid diagnosis and early intervention.

[0004] Traditional tear fluid collection methods rely on tools such as Schirmer's strip dry eye test strips, ophthalmic sponges, and microcapillaries. However, these methods have obvious limitations, including low efficiency in collecting, storing, and extracting small amounts of tear fluid, especially when precise and continuous monitoring is required. In addition, a key challenge in this field is the separation between tear fluid collection and analysis, and traditional methods involve different and time-consuming steps. This fragmentation not only reduces diagnostic efficiency but also hinders the possibility of point-of-care diagnosis. Moreover, the ocular surface environment is very sensitive to any external stimuli, and most diagnostic tests are overly invasive and require professional operation. Therefore, patients can only go to the corresponding medical institutions for testing. Therefore, using soft contact lenses for tear fluid sampling is a promising method, especially suitable for situations where high wearer comfort and non-invasive sampling are required. A new method worth exploring is to integrate contact lenses with a microfluidic system to achieve automatic tear fluid collection, storage, and analysis without any additional elution steps.

[0005] So far, several prototypes of contact lenses have been proposed for disease diagnosis. Colorimetric sensor-based smart contact lenses mostly rely on microfluidic technology to achieve visual detection of biomarkers in tears. Such systems usually construct microchannels in the lens to passively guide tears into the detection area when the wearer blinks, and then identify indicators such as glucose and lactate through colorimetric reactions. To improve the efficiency and accuracy of sampling, some designs introduce multi-inlet structures or curved channels in the lens to enhance the collection stability of tears and prevent backflow. In addition, some solutions combine paper-based materials to utilize their natural capillary action to enhance liquid flow and colorimetric detection performance. There are also studies that construct radial microchannels on the lens by laser etching to passively distribute tears to multiple sensing areas, improving the comprehensiveness of analysis. In addition to bioanalysis functions, smart contact lenses are also used for intraocular pressure monitoring, reflecting corneal curvature changes through the movement of the staining solution in the channel to achieve continuous perception of intraocular pressure. Some systems further combine a micro-pump structure for blink-triggered drug release, showing their potential for expansion in ophthalmic treatment.

[0006] Despite the rapid development, existing smart contact lens systems still have obvious limitations. First of all, most designs still remain in the stage of passive sampling and single-point analysis, lacking the ability to actively control tear flow and failing to achieve systematic microfluidic manipulation like smart patches. Especially in the design of micro-pumps, valves, and liquid guiding structures, there is still a lack of optimization research for the curved environment of the eye. The current microfluidic structures are mostly constructed based on planar platforms, and their flow characteristics are significantly different from their behavior in a closed curved surface environment, restricting their efficient migration and application in contact lenses.

[0007] In addition, most smart contact lenses only integrate a single type of biosensor to detect a single indicator in tears. This single-function design has limited reliability and accuracy in clinical diagnosis. In contrast, integrating multiple biosensing modules to achieve multi-parameter collaborative analysis has been considered a key direction to improve the accuracy of early disease diagnosis. Therefore, how to integrate multiple sensing elements in the limited lens space and optimize their microfluidic channels and signal reading strategies remains an important challenge in the current development of smart contact lenses. Summary of the Invention

[0008] To overcome the deficiencies of the prior art, the present invention provides a microfluidic contact lens and a tear collection and analysis method. The microfluidic contact lens of the present invention integrates multiple biosensors in a microchannel, can simultaneously detect various biomarkers, automatically collects tears, and with the help of a capillary rupture valve, directs the tears to a designated micro-reaction chamber, providing more accurate sampling capabilities.

[0009] The present invention first provides a microfluidic contact lens, which comprises an outer layer and an inner layer. The outer layer and the inner layer are attached to each other. Wherein, a microchannel and a plurality of microcavities are provided on the side of the outer layer facing the inner layer. Each microcavity has a microcavity inlet and an exhaust port. Among them, the inlets of the respective microcavities are sequentially connected to the side wall of the microchannel. The inlets of the respective microcavities form a first capillary break valve through a divergence angle design. A second capillary break valve is provided on the microchannel between adjacent two microcavities. A third capillary break valve is provided on the microchannel between each microcavity and its exhaust port; the bursting pressure of the first capillary break valve is less than the bursting pressure of the second capillary break valve, and the bursting pressure of the second capillary break valve is less than the bursting pressure of the third capillary break valve; the inlet of the last microcavity is connected to the end of the microchannel;

[0010] The inner layer is a smooth curved film; a tear inlet penetrating the inner layer is provided at a position corresponding to the inlet of the microchannel on the inner layer; at least one of the microcavities is provided with a biosensor for detecting tear indexes.

[0011] According to a preferred embodiment of the present invention, the number of the microcavities is not less than four. Among the four microcavities, a paper microfluidic sensor for detecting tear secretion amount is provided in the first microcavity and the second microcavity located upstream of the microchannel, a colorimetric sensor for detecting tear pH is provided in the third microcavity, and a thermosensitive cholesteric liquid crystal (TSLC) sensor for detecting tear temperature is provided in the fourth microcavity.

[0012] According to a preferred embodiment of the present invention, the paper microfluidic sensor is composed of methyl red and cellulose filter paper. The methyl red powder is coated on one side of the filter paper and faces the inner layer of the contact lens. According to the characteristic that the color of the filter paper changes when it is wetted by tears, it is detected whether tears enter the corresponding microcavity. According to the time when tears enter the two microcavities provided with the paper microfluidic sensors, the tear secretion amount is judged.

[0013] The colorimetric sensor is formed by coating a pH reagent on the filter paper. The color of the pH reagent changes when it contacts solutions with different pH values.

[0014] The thermosensitive cholesteric liquid crystal sensor uses the characteristic that the color or optical property of the liquid crystal changes with temperature for visual temperature measurement. Specifically, the pitch of the thermosensitive cholesteric liquid crystal changes with temperature, thereby causing a change in the wavelength of the reflected light, realizing a reversible change in color or optical property, and can be used for visual temperature measurement.

[0015] According to a preferred embodiment of the present invention, the microfluidic contact lens further comprises a fifth microcavity connected to the end of the microchannel. No sensor is provided in the fifth microcavity. The fifth microcavity leaves extra space to avoid excessive tears from overflowing.

[0016] According to a preferred embodiment of the present invention, the materials of the outer layer and the inner layer are both PDMS, and the bending geometries of the outer layer and the inner layer match the shape of the eye surface.

[0017] According to a preferred embodiment of the present invention, the cross-section of the microchannel is a square with a side length of 400 μm, the microcavity is a circular microcavity with a diameter of 1.5 mm and a depth of 400 μm, and the diameter of the exhaust port is 400 μm; the first capillary rupture valve is a gradually expanding transition section between the circular microcavity and the microchannel, the divergence angle of the first capillary rupture valve is 25°, and the width and height of the divergent part are both 400 μm; the divergence angle of the second capillary rupture valve is 90°, and the width and height of the divergent part are both 400 μm, and the divergence angle of the third capillary rupture valve is 120°, the width of the divergent part is 200 μm, and the height is 400 μm.

[0018] According to a preferred embodiment of the present invention, the distances from each microcavity to the center of the outer layer are equal, and each microcavity is evenly arranged in the circumferential direction of the outer layer.

[0019] According to a preferred embodiment of the present invention, the exhaust port is communicated with the surface of the outer layer away from the inner layer, and is used to release gas so that tears can smoothly enter the microchannel.

[0020] According to a preferred embodiment of the present invention, the inner layer and the outer layer are crosslinked together by plasma surface treatment.

[0021] The present invention also provides a method for collecting and analyzing tears based on the microfluidic contact lens, which includes the following steps:

[0022] The user wears the microfluidic contact lens, and the tears secreted by the user enter the microchannel through the tear inlet provided on the inner layer;

[0023] The tears flow along the microchannel. Since the bursting pressure of the second capillary rupture valve provided on the microchannel is greater than that of the first capillary rupture valve, the tears will first break through the first capillary rupture valve at the entrance of the first microcavity and enter the first microcavity, and the tears fill the first microcavity to make the paper microfluidic sensor inside change color;

[0024] Since the bursting pressure of the second capillary rupture valve is less than that of the third capillary rupture valve, after the tears fill the first microcavity, it will break through the second capillary rupture valve located between the first microcavity and the second microcavity, and then break through the first capillary rupture valve at the entrance of the second microcavity and enter the second microcavity, making the paper microfluidic sensor inside the second microcavity change color; the secretion volume of tears can be obtained according to the time difference of color change between the first microcavity and the second microcavity;

[0025] Under the regulation of the capillary break valve, the tear fluid then sequentially enters the third chamber and the fourth chamber. The colorimetric sensor in the third chamber changes color according to the pH of the tear fluid; the thermosensitive cholesteric liquid crystal sensor in the fourth chamber generates color or optical property changes according to the temperature of the tear fluid; by collecting the image data of the microfluidic contact lens, the pH data and temperature data of the tear fluid can be obtained.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention first uses capillary break valves (CBVs) to control the microfluidics in the contact lens environment. The tear fluid is sequentially guided to the reaction chambers and interacts with the embedded biosensors, enabling the simultaneous and immediate diagnosis of three key indicators of dry eye disease: tear fluid secretion volume, tear fluid temperature, and tear fluid pH. Generally, the width of the microchannels in contact lenses ranges from dozens of micrometers to hundreds of micrometers. At this microscopic scale, surface tension and capillary force play a more important role than gravity. When the eyelids blink, a layer of tear fluid covers the surface of the contact lens and enters the microchannels under the drive of capillary force. When the liquid flows through these narrow channels, capillary action pushes it forward, causing the tear fluid to move within the microfluidic channels. Guiding the tear fluid to flow through these microchannels is crucial for guiding the liquid to specific sensing areas. By simply geometrically modifying the microchannels, the capillary break valve can effectively control the flow rate and flow direction of the fluid. Due to the guiding effect of the capillary break valve, the liquid in each reaction chamber is not contaminated by other reaction chambers.

[0028] The microfluidic contact lens provided by the present invention can immediately diagnose biological indicators including tear fluid volume, tear fluid pH value, and tear fluid temperature. Through the precise design of the microfluidic channels and microcavity layout, the synchronous operation of each sensor is achieved. The CBVs effectively control the liquid flow, ensuring the independence of each microcavity. Compared with previous research on multifunctional contact lenses, our research innovatively integrates biosensors and CBVs of different detection methods more effectively into wearable technology, improving accuracy and usability. Experimental results show that the contact lens has good accuracy and stability in measuring tear fluid secretion, pH value, and temperature, especially maintaining high reliability in comparative experiments under different lighting conditions. The contact lens has great potential in the diagnosis of dry eye syndrome and other eye health monitoring fields, providing an important reference for the development of future intelligent wearable devices. Description of the Drawings

[0029] Figure 1Schematic diagram of the preparation process of the microfluidic contact lens. (a) Plastic inner mold. (b) Inject PDMS into the outer mold. (c) Insert the inner mold into the PDMS and heat. (d) Cure and separate from the mold. (e) Two-layer contact lens. (f) Fabrication of the paper microfluidic sensor, colorimetric sensor, and TSLC sensor. (g) Apply a small amount of PDMS liquid in the microchamber to adhere the biosensor. (h) Heat to ensure the secure installation of the biosensor. (i) Plasma-bonded contact lens. (j) Optical images of the front (left) and back (right) of the contact lens. (k) Cross-sectional image of the contact lens after encapsulation with the PDMS layer.

[0030] Figure 2 Schematic diagram of the detection process of the microfluidic contact lens. (a) Schematic diagram of the experimental process of the microfluidic contact lens. (b) Schematic diagram of the biosensor embedded in the contact lens. (c) Place the smartphone and the silicone surface on the custom mold at a fixed angle and position. (d) Screenshot interface of the RGB color reading, with the viewfinder function above and the color display box and RGB value below. (e) Schematic diagram and optical image of the artificial tear in the microchannel. i) Preparation stage. ii) The artificial tear enters from the inlet and fills the first microchamber with the paper microfluidic sensor. iii) Design the first two microchambers to detect whether the tear secretion reaches the normal level (3 μl / 5 min). iv) The tear enters the third microchamber equipped with the colorimetric sensor for measuring pH. v) The fourth microchamber is equipped with thermotropic cholesteric liquid crystal for detecting temperature.

[0031] Figure 3 Schematic diagram of a specific microfluidic contact lens in the embodiment. (a) Three-dimensional rendered image of the contact lens, which includes two PDMS layers and four biosensors. (b) Structure of the microfluidic channel network of the contact lens. (c) Top view of the contact lens after encapsulating the PDMS layer and the biosensor. (d) Optical images under different mechanical forces: stretching, compression, and torsion.

[0032] Figure 4 Schematic diagram of the design of the capillary bursting valve in the embodiment.

[0033] Figure 5 On-site sampling of the microfluidic contact lens under different ambient lights. Detailed implementation mode

[0034] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0035] Example 1

[0036] As Figure 1 shown, the microfluidic contact lens of the present invention includes an outer layer and an inner layer. Among them, a microchannel and a plurality of microcavities are provided on the side of the outer layer facing the inner layer. Each microcavity has a microcavity inlet and an exhaust port. Among them, the inlets of the respective microcavities are sequentially connected to the side wall of the microchannel. The inlets of the respective microcavities form a first capillary break valve through a divergence angle design. A second capillary break valve is provided on the microchannel between adjacent two microcavities. A third capillary break valve is provided on the microfluidic channel between each microcavity and its exhaust port; the bursting pressure of the first capillary break valve is less than the bursting pressure of the second capillary break valve, and the bursting pressure of the second capillary break valve is less than the bursting pressure of the third capillary break valve; the inlet of the last microcavity is connected to the end of the microchannel; at least one of the microcavities is provided with a biosensor for detecting tear indexes. The inner layer is a smooth curved film; a tear inlet penetrating the inner layer is provided at a position corresponding to the microchannel inlet on the inner layer; the outer layer and the inner layer are mutually adhered.

[0037] In a specific embodiment of the present invention, the number of the microcavities is five. Among the five microcavities, a paper microfluidic sensor for detecting tear secretion amount is provided in the first microcavity and the second microcavity located upstream of the microfluidic channel. A colorimetric sensor for detecting tear pH is provided in the third microcavity. A thermosensitive cholesteric liquid crystal (TSLC) sensor for detecting tear temperature is provided in the fourth microcavity. The fifth microcavity is connected to the end of the microchannel, and no sensor is provided in the fifth microcavity. The fifth microcavity leaves extra space to avoid excessive tear overflow.

[0038] Among them, the paper microfluidic sensor is composed of methyl red and cellulose filter paper. The methyl red powder is coated on one side of the filter paper and faces the inner layer of the contact lens. According to the characteristic that the color of the filter paper changes when it is wetted by tears, it is detected whether tears enter the corresponding microcavity. According to the time when tears enter the two microcavities provided with the paper microfluidic sensor, the tear secretion rate is judged; the colorimetric sensor is formed by coating a pH reagent on the filter paper. The color of the pH reagent changes when it contacts solutions with different pH values; the thermosensitive cholesteric liquid crystal sensor uses the characteristic that the color or optical property of the liquid crystal changes with temperature for visual temperature measurement.

[0039] The distances from each microcavity to the center of the outer layer are equal, and each microcavity is evenly arranged in the circumferential direction of the outer layer. The exhaust port is communicated with the surface of the outer layer away from the inner layer for releasing gas so that tears can smoothly enter the microchannel.

[0040] Example 2 Preparation Example

[0041] Refer to Figure 1, embodiments of the present invention provide a manufacturing process for the aforementioned microfluidic contact lens. The manufacturing process of the microfluidic contact lens is divided into three parts: contact lens manufacturing, biosensor manufacturing, and encapsulation. To avoid adverse effects on wearing comfort and protect the sensing element and tear fluid from contamination, a two-layer manufacturing method is selected. The outer layer is microfabricated into a thin film layer with microchannels and microchambers, and the inner layer is a smooth curved thin film. Exploratory research on the microfluidic contact lens is carried out using polydimethylsiloxane (PDMS). Since PDMS has characteristics such as optical transparency, flexibility, biocompatibility, and stability in water, it is a good choice for encapsulating microchannels and microcavities and collecting tear fluid.

[0042] Resin mold of the microfluidic contact lens ( Figure 1 a) is produced by stereolithography 3D printing (HP 3D Printer, California, US). The outer mold and the inner mold determine the shape and thickness of the microfluidic contact lens. These molds are made of plastic and designed with micron-level precision to ensure the perfect formation of the microfluidic contact lens. In a specific embodiment of the present invention, PDMS (DC 184, Dow Corning, Michigan, US) is prepared by mixing sylgard 184 silicone elastomer base with sylgard 184 silicone elastomer curing agent at a mass ratio of 10:1. After sufficient stirring, the PDMS is placed in a vacuum dryer to degas and remove air bubbles. Figure 1 b illustrates injection molding for manufacturing a double-layer contact lens. A certain volume of PDMS is injected into a precisely manufactured outer mold. Once the PDMS is poured into the mold, it undergoes a curing process ( Figure 1 c). The PDMS is heated in an electrothermal constant temperature drying oven (DHG-9053A, Keelrein, China) at 60 °C for 2 hours to solidify the liquid PDMS into a lens shape ( Figure 1 e). After curing, the mold is carefully opened ( Figure 1 d).

[0043] Figure 1f shows the manufacturing process of the biosensor. The paper microfluidic sensor consists of methyl red and cellulose filter paper (NEWSTAR, China). The methyl red powder was coated on one side of the filter paper, facing the inner layer of the contact lens, so that the filter paper remained white when not wetted by tears. The colorimetric sensor for detecting tear pH was made by coating the pH reagent (SANAISI, China) on the filter paper and then drying it in an oven at 30 °C for 5 minutes. The pH reagent on the filter paper undergoes a structural change when in contact with an acidic or alkaline solution, resulting in a color change due to the change in light absorption characteristics. The method for making the thermosensitive cholesteric liquid crystal (TSLC) is based on the research of Moreddu et al. The TSLC sensor was obtained by melting cholesteryl oleate, cholesteryl benzoate, and cholesteryl nonanoate in a mass ratio of 0.35:0.10:0.55. The chiral liquid crystals (CLCs) with a helical structure can induce selective reflection of light through temperature changes. Finally, a micro-biosensor with a diameter of 1.5 mm and a thickness of 0.2 mm was fabricated using punching to match the size of the microchamber.

[0044] The sampling method has an impact on tear components. Therefore, it is necessary to further encapsulate the exfoliated contact lens film to ensure its integrity and reliability. These encapsulated microchannels and microchambers are ideal places for integrating biosensors. A thin layer of uncured PDMS was brushed on the first to fourth microchambers, and the prepared biosensor was placed into them ( Figure 1 g), and reheated in an oven at 60 °C for 30 minutes ( Figure 1 h). The microfluidic layer and the cover layer were crosslinked together by plasma surface treatment (HC-z600s, HC, Guangdong, China) for treating the surface of the cured PDMS to improve surface adhesion ( Figure 1 i). Figure 1 j-k show the two layers of PDMS after demolding, consisting of the microchannel layer and the sealing layer. The biosensor was installed in the microchamber of the microchannel layer.

[0045] Example 3 Simulated Tear Detection

[0046] This contact lens does not utilize any rigid components and connections to avoid damaging the cornea. Figure 2a illustrates the experimental setup for evaluating the device performance. A personal computer controls a piezoelectric diaphragm micropump (PS15I&GS15I, CurieJet, Taiwan, China) through a microcontroller (STM32F103ZET6, STMicroelectronics, Shenzhen, China) to deliver a uniform volume of tear fluid (1 μL / min). Teflon tubes (inner diameter 0.3 ± 0.10 mm, outer diameter 0.6 ± 0.10 mm) are connected to both sides of the micropump. One end of the Teflon tube serves as the liquid inlet and is immersed in a beaker filled with artificial tear fluid. The other end of the Teflon tube serves as the liquid outlet. A 1-mm hole is drilled in a plastic eyeball simulating a human eyeball, and it is mounted on the surface of a silicone mold. The Teflon tube passes through them, so that the artificial tear fluid is delivered to the tear inlet of the contact lens. Before the experiment, the artificial tear fluid is sent into the Teflon tube until the air inside is completely removed to prevent air bubbles from entering the contact lens. Figure 2 b shows two paper microfluidic sensors, a colorimetric sensor, and a TSLC sensor embedded in the microchamber, which are used to detect the tear secretion volume, tear pH value, and tear temperature, respectively. Figure 2 c shows the setup where a smartphone (used to take pictures to obtain the results of tear fluid analysis) and the sample are placed on the experimental platform at a fixed spacing and angle. Use the existing color picker app on the smartphone to take pictures, place the cavity containing the liquid crystal and colorimetric paper in the scanning area, and save the RGB values ( Figure 2 d). Figure 2 e(i-v) shows the working sequence of the biosensor after the artificial tear fluid enters through the inlet.

[0047] In a specific embodiment, the microfluidic contact lens is designed to accommodate approximately 7.5 μl of tear fluid, aiming to evaluate tear secretion and other related parameters. The test time is set to 10 minutes to match the standard range of tear secretion rate. According to the average Schirmer test value of unstimulated tear secretion (“basal secretion”), the tear secretion rate is estimated to be 0.6 - 1.1 μl / min (or 3 - 5.5 μl / 5 min) when normal, which is used as a reference value for subsequent judgment of whether the tear secretion volume is normal.. In the first 5 minutes before the test, the tear fluid gradually fills the first and second microchambers of the contact lens, with a total capacity of 3 μl. Once the tear fluid fills the chamber, the embedded methyl red test paper will change color to help people visually judge whether the tear secretion reaches the standard level. In the next 5-minute test, the tear fluid continues to flow into the third and fourth microchambers, which are used to measure the temperature and pH of the tear fluid respectively. The fifth chamber leaves extra space to avoid excessive tear overflow.

[0048] Example 4 Preparation Example

[0049] In a specific embodiment, as Figure 3As shown in a, the contact lens includes two layers of polydimethylsiloxane (PDMS). The outer layer has microchannels, the inner layer is for encapsulation, and four biosensors. The microfluidic channel network structure is as Figure 3 shown in b. The first layer is designed as a microfluidic channel network, which includes microfluidic channels with a square cross-section (diameter 400 μm), 5 circular microchambers (thickness 400 μm, diameter 1.5 mm), and multiple capillary break valves with different shapes. The thickness of the microfluidic layer is 600 μm. The network connects five independent microchambers through microchannels. Each chamber has an outlet hole with a diameter of 400 μm for releasing gas, enabling tears to smoothly enter the microchannels. The second layer serves as an encapsulation layer (thickness 200 μm), and its inlet hole (diameter 800 μm) allows tears to enter the microfluidic system. The total thickness is approximately 800 μm. Figure 3 c shows the effect of the microfluidic contact lens worn on a plastic eye. Good mechanical properties ensure that the cornea is not scratched during the wearing process. Figure 3 d shows the deformation of the microfluidic contact lens under different mechanical forces. The contact lens maintains good elastic deformation under stretching, bending, and torsion without damage.

[0050] Example 5 Design of capillary burst valve

[0051] Since it is difficult to collect and circulate small-volume fluids and cross-contamination between different microchambers needs to be prevented, capillary break valves (CBVs) and micro-outlet holes are designed to guide the flow of fluids in the microchannels ( Figure 4 a). CBVs can regulate microfluids by simply introducing simple geometric or surface chemical changes to the microchannels. In the microchannels, the gas-liquid interface of the liquid is affected by the capillary force, which is jointly determined by the surface tension of the liquid and the channel geometry. When the driving force is not sufficient to overcome the capillary force, the liquid will stay at the valve orifice. When the driving force exceeds the capillary force, the valve ruptures and the liquid enters the channel behind the valve. Therefore, an important index of valve performance is how much pressure it can withstand before rupture. The Yang-Laplace equation provides the calculation formula for the burst pressure (BP):

[0052]

[0053] where σ is the surface tension of the liquid; θ A is the channel contact angle; is the minimum value [θ A +β; 180°); β is the channel divergence angle; b is the width of the divergence section; h is the height of the divergence part. When the fluid encounters two independent CBVs with different BPs, the fluid will first pass through the CBV with the lower BP under sufficient pressure. In this way, by positioning two CBVs with different BP values near the intersection of the two channels, the flow direction can be controlled.

[0054] Table 1 Calculation of the bursting pressures of CBV1, CBV2, and CBV3.

[0055]

[0056] For simplicity of description, the first capillary bursting valve, the second capillary bursting valve, and the third capillary bursting valve are denoted as CBV1, CBV2, and CBV3, respectively. As Figure 4 shown in Fig. 10b, the β values of CBV1, CBV2, and CBV3 are 25°, 90°, and 120°, respectively. From this, the θ values of CBV1, CBV2, and CBV3 can be further calculated I * to be 132°, 180°, and 180°, respectively. The θ value of the sample A is 107°. σ is 72.8 dynes / cm. The b values of CBV1 and CBV2 are 400 μm, and the b value of CBV3 is 200 μm. h is 400 μm. Table 1 gives the BP values of the three CBVs and the values in their calculation formulas. Therefore, the BPs of CBV1, CBV2, and CBV3 are 350.0 Pa, 470.4 Pa, and 834.4 Pa, respectively. Figure 4 Figs. 17c and 17d show the sequence of fluid movement. In the microchannel, the fluid flows towards the bifurcation, where it encounters two CBVs. The liquid first passes through CBV1 with a lower BP, while the liquid in the other branch stays at CBV2. CBV2 does not rupture until the downstream microchamber of CBV1 is filled. Once this happens, the fluid passes through CBV2 smoothly. At CBV3, the driving force is less than the capillary force, thus stopping the fluid movement. This can prevent the liquid from passing through CBV3 and avoid any potential leakage that may contaminate the ocular surface. Preliminary experiments on tear fluid flow were conducted in vitro to simulate the tear fluid environment. The stained artificial tear fluid can capture the flow process. The contact lens was placed on a flat surface. Figure 4 Fig. 19e shows the sequence and time of the stained artificial tear fluid filling the microchannel and the five microchambers.

[0057] To demonstrate the feasibility of the three types of biosensors working simultaneously in one detection, artificial tear fluids of different colors were fed into the microfluidics in sequence to ensure no unnecessary mixing. Since the channel size is several hundred micrometers and the Reynolds number of the fluid is low at a flow rate of 1 μl / min, the fluid behaves as laminar flow. Previous experiments have shown that mixing occurs only through molecular diffusion. Figure 4f is artificial tears dyed in different colors and sequentially introduced into the microchannel. Within 10 minutes, diffusion occurred only within 100 μm at the junction of the red and black dyed artificial tears, which is only less than 6.7% of the total volume of the microchamber. 4.5 μl of red dye was injected into the microchannel from the contact lens inlet. After it filled the first two microchambers, 3 μl of black dye was injected from the same position. The already filled chambers were not contaminated by the subsequently entering dye, providing the feasibility of simultaneously diagnosing multiple biological indicators. Figure 4 g shows that the contact angle of the microchannel after plasma treatment is 95.4°. After more than 12 hours, the contact angle recovered to about 107° and remained relatively stable for a long time.

[0058] Example 6 Temperature Detection Results and Colorimetric Readings

[0059] In the experiment, both colorimetry and temperature-sensitive CLCs detect the corresponding information (i.e., concentration and temperature) through color changes, but their principles are different. Colorimetry is a method of determining the concentration or composition of a substance by measuring the color change at a specific wavelength. It is based on the principle of light absorption, that is, the chemical substances in the solution absorb light at a specific wavelength, reducing the amount of transmitted or reflected light. By measuring the degree of light absorption, the concentration of the substance can be inferred. On the contrary, temperature-sensitive cholesteric liquid crystals are a type of liquid crystal material composed of molecules with a helical structure. Due to the change in the molecular arrangement, their color changes with the change in temperature, which affects their optical properties, resulting in a color change.

[0060] The experiment was carried out under three common light sources: indoor fluorescent lamp environment, dim indoor lights-off environment, and bright indoor lights-off environment. Figure 5 a shows the transition of the liquid crystal from red to blue with the tear temperature ranging from 30 °C to 36 °C under three different lighting conditions. Figure 5c-e shows that the RGB percentage trends of all three environments display almost the same pattern. The normal ocular surface temperature range is 32.8 - 35.4 °C. At a lower temperature of 30 °C, the red content is 12.94% - 24.71%. As the temperature increases, the red level gradually decreases. When the temperature reaches 32.75 °C within the healthy standard range, the red level drops to 2.35% - 12.16% and then tends to stabilize. Within the temperature range of 30 °C - 32.75 °C, the green and blue levels gradually increase. The green level rises from 6.67% to 25.88%, with a peak of 19.22% - 27.45%; the blue level rises from 3.92% to 24.31%, with a peak of 16.08% - 25.88%, and then continues to rise. Temperatures exceeding 35.5 °C are considered unhealthy for the ocular surface. At this temperature, the red level ranges from 5.49% to 12.16%, and there is no significant difference from the data within the normal temperature range. Therefore, for temperatures above 35.5 °C, it is necessary to refer to the other two sets of data. At 35.5 °C, the green level is 3.14% to 15.29%, and then the data tends to stabilize. At 34.25 °C, the blue level reaches a peak of 19.61% - 35.29%, and at 35.5 °C, the blue level is 13.33% - 23.53%, and then also reaches a stable state.

[0061] The red and green levels are the highest in the dim indoor environment and the lowest in the indoor fluorescent light environment. This is due to the influence of the light received by the camera sensor. The brighter the environment, the more light is reflected by the object, and the more light the camera sensor can capture, making the object in the photo appear whiter. The opposite is true in a dim environment. Due to Rayleigh scattering enhancing the blue tone of the object, the blue level is the highest in the outdoor sunlight environment. The standard deviation of the RGB values is the largest and the fluctuation is the greatest in the bright indoor environment. This is because the bright indoor environment is more susceptible to changes in external lighting conditions, unlike the more stable lighting in the indoor fluorescent light and dim environments. However, the overall trend remains unchanged. Therefore, when using CL for detection, it is necessary to first determine the corresponding environment and adjust the exposure, white balance, etc. to make the color readings more accurate.

[0062] The pH value range of a healthy ocular surface is between 6.5 and 7.6. Figure 5 b shows the transition of the pH test paper from yellow to green within the pH range of 6.0 to 9.0 under three different lighting conditions. In the dim and light-off indoor environment, the colorimetry tends to be more yellowish, while in the light-on indoor environment, the colorimetry tends to be more greenish, mainly due to the influence of different lighting conditions on color perception. The indoor fluorescent light environment usually provides more uniform white or cool-toned light, which enhances the appearance of green. Figure 5f-h are the corresponding RGB levels in the colorimetric experiment. The red level shows a gradually decreasing trend. When the pH is 6.0, the red content ranges from 51% to 58%, and when the pH is 9.0, the red content decreases from 30% to 40%. The levels of green and blue do not show significant overall changes. Under outdoor sunlight conditions, the blue level is 20% higher than the other two sets of data, also due to the Rayleigh scattering effect.

[0063] Overall, the detection methods based on colorimetric sensors and TSLC sensors can distinguish healthy and non-healthy eyes in daily environments, but to some extent, the environment may slightly affect the measurement accuracy.

[0064] The embodiments of the present invention have been described above. The above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A microfluidic contact lens, characterized in that, It includes an outer layer and an inner layer, and the outer layer and the inner layer are attached to each other. Among them, a microchannel and a plurality of microcavities are provided on the side of the outer layer facing the inner layer. Each microcavity has a microcavity inlet and an exhaust port. Among them, the inlets of the microcavities are sequentially connected to the side wall of the microchannel, and the inlets of each microcavity form a first capillary rupture valve through a divergence angle design. A second capillary rupture valve is provided on the microchannel between adjacent two microcavities, and a third capillary rupture valve is provided on the microfluidic channel between each microcavity and its exhaust port; the bursting pressure of the first capillary rupture valve is less than that of the second capillary rupture valve, and the bursting pressure of the second capillary rupture valve is less than that of the third capillary rupture valve; the inlet of the last microcavity is connected to the end of the microchannel; The inner layer is a smooth curved film; a tear inlet penetrating the inner layer is provided at a position corresponding to the microchannel inlet on the inner layer; at least one of the microcavities is provided with a biosensor for detecting tear indicators.

2. The microfluidic contact lens according to claim 1, characterized in that, The number of the microcavities is not less than four. Among the four microcavities, a paper microfluidic sensor for detecting tear secretion volume is arranged in the first microcavity and the second microcavity located upstream of the microfluidic channel, a colorimetric sensor for detecting tear pH is arranged in the third microcavity, and a temperature-sensitive cholesteric liquid crystal (TSLC) sensor for detecting tear temperature is arranged in the fourth microcavity.

3. The microfluidic contact lens according to claim 2, wherein, The paper microfluidic sensor is composed of methyl red and cellulose filter paper. The methyl red powder is coated on one side of the filter paper and faces the inner layer of the contact lens. According to the characteristic that the color of the filter paper changes when it is wetted by tears, it is detected whether tears enter the corresponding microcavity, and the tear secretion volume is judged according to the time when tears enter the two microcavities provided with the paper microfluidic sensor. The colorimetric sensor is formed by coating a pH reagent on the filter paper, and the color of the pH reagent changes when it contacts solutions with different pH values. The temperature-sensitive cholesteric liquid crystal sensor uses the characteristic that the color or optical property of the liquid crystal changes with temperature for visual temperature measurement.

4. The microfluidic contact lens according to claim 2, characterized in that, It also includes a fifth microcavity connected to the end of the microchannel. No sensor is arranged in the fifth microcavity, and the fifth microcavity leaves extra space to avoid excessive tears from overflowing.

5. The microfluidic contact lens according to claim 1, wherein The materials of the outer layer and the inner layer are both polydimethylsiloxane (PDMS), and the curved geometries of the outer layer and the inner layer match the shape of the eyeball surface.

6. The microfluidic contact lens according to claim 1, wherein The cross-section of the microchannel is a square with a side length of 400μm, the microcavity is a circular microcavity with a diameter of 1.5mm and a depth of 400μm, and the diameter of the exhaust port is 400μm; the first capillary rupture valve is a gradually expanding transition section between the circular microcavity and the microchannel, the divergence angle of the first capillary rupture valve is 25°, and the width and height of the divergent part are both 400μm; the divergence angle of the second capillary rupture valve is 90°, and the width and height of the divergent part are both 400μm, and the divergence angle of the third capillary rupture valve is 120°, the width of the divergent part is 200μm, and the height is 400μm.

7. The microfluidic contact lens according to claim 1, characterized in that, The distances from each microcavity to the center of the outer layer are equal, and each microcavity is evenly arranged in the circumferential direction of the outer layer.

8. The microfluidic contact lens according to claim 1, wherein The exhaust port is communicated with the surface of the outer layer far from the inner layer for releasing gas to enable tears to smoothly enter the microchannel.

9. The microfluidic contact lens according to claim 1, wherein The inner layer and the outer layer are crosslinked together by plasma surface treatment.

10. A method for collecting and analyzing tears of the microfluidic contact lens according to any one of claims 2-4, characterized in that, It includes the following steps: The user wears the microfluidic contact lens, and the tear fluid secreted by the user enters the microchannel through the tear fluid inlet provided on the inner layer; The tear fluid flows along the microchannel. Since the bursting pressure of the second capillary rupture valve provided on the microchannel is greater than that of the first capillary rupture valve, the tear fluid will first break through the first capillary rupture valve at the entrance of the first microcavity and enter the first microcavity. The tear fluid fills the first microcavity and causes the paper microfluidic sensor therein to change color; Since the bursting pressure of the second capillary rupture valve is less than that of the third capillary rupture valve, after the tear fluid fills the first microcavity, it will break through the second capillary rupture valve located between the first microcavity and the second microcavity, and then break through the first capillary rupture valve at the entrance of the second microcavity and enter the second microcavity, causing the paper microfluidic sensor therein to change color; The tear fluid secretion volume can be obtained according to the time difference of color change between the first microcavity and the second microcavity; Under the regulation of the capillary rupture valve, the tear fluid then sequentially enters the third chamber and the fourth chamber. The colorimetric sensor in the third chamber changes color according to the pH of the tear fluid; The thermosensitive cholesteric liquid crystal sensor in the fourth chamber generates color or optical property changes according to the tear fluid temperature; By collecting the image data of the microfluidic contact lens, the pH data and temperature data of the tear fluid can be obtained.

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