Microfluidic chip, preparation method thereof and microfluidic driving method

Abstract

The application discloses a micro-fluidic chip, comprising: a substrate made of a photo-induced deformation cross-linking liquid crystal polymer material, comprising a first surface, a groove is opened on the first surface, and a notch is arranged on the top of the groove; a film made of a photo-induced deformation linear liquid crystal polymer material, attached to the first surface and covering the notch, the groove and the film covering the notch surround to form a micro-channel, the micro-channel is used for transporting micro-fluid; wherein when a part of the micro-channel is irradiated by light, the micro-channel forms an irradiation area channel and a non-irradiation area channel, the groove and the film of the irradiation area channel are deformed, so that the cross-sectional area of the irradiation area channel is larger than that of the non-irradiation area channel, thereby driving the micro-fluid in the irradiation area channel to flow to the non-irradiation area channel. By using the deformation of the groove and the film together, the deformation amount of the micro-channel is increased, and the driving force on the micro-fluid is significantly improved. The application also discloses a micro-fluidic chip preparation method and a micro-fluid driving method.

Description

Technical Field

[0001] This invention relates to the field of microfluidics, and in particular to a microfluidic chip and its fabrication method, as well as a microfluidic driving method. Background Technology

[0002] The importance of microfluidic manipulation technology in fields such as chemistry, biology, and medicine is increasingly prominent, with its applications expanding from multicellular organisms to single-cell and even single-molecule level analysis and detection. Currently reported microfluidic manipulation technologies can be broadly classified into several categories based on their driving mechanisms: pressure-driven, centrifugal-driven, magnetic-driven, electric-driven, optical-driven, and capillary-driven (self-driven). Among these, optical-driven microfluidics, or photofluidics, can directly convert light energy into the kinetic energy of liquids and realize multimodal liquid manipulation on a chip. This allows for the replacement of traditional complex microfluidic manipulation units (such as pumps, mixers, and separators) with simple light sources, providing a promising solution to the key challenges of miniaturization and integration in microfluidic systems. The core device—the all-optically controlled microfluidic chip (AOMC)—utilizes light as the sole energy source, enabling liquid manipulation processes including transport, mixing, fusion, and separation on a single chip, potentially realizing the miniaturization and integration of microfluidic manipulation technology. Photodeformable liquid crystal polymers (LCPs) can achieve large and reversible macroscopic deformations through changes in liquid crystal orientation under remote, targeted, and precise light irradiation. Through special structural design and novel driving mechanisms, this deformation can be used for precise manipulation of micro-volume liquids. Among them, photodeformable linear liquid crystal polymers (LLCPs) possess both good processability and photodeformation properties, making them excellent candidate materials for constructing optically oriented liquid crystal polymers (AOMCs). In recent years, scientists have constructed a series of optofluidic devices based on this material and proposed novel fluid manipulation mechanisms, realizing functions such as transport, fusion, mixing, separation, and high-throughput manipulation of micro-volume liquids. This represents a significant breakthrough in the field of ultra-micro-volume liquid manipulation technology.

[0003] All-optical microfluidics relies on the Laplace pressure difference induced by photo-induced deformation of liquid crystal polymers to drive the liquid. The magnitude of the driving force is directly related to the deformation of the material in the channel. As the liquid volume decreases further, the surface effect intensifies, leading to increased fluid resistance, which poses a severe challenge to the performance of all-optical microfluidic chips. All-optical chips are constructed using a composite of linear liquid crystal polymer films and PMMA (polymethyl methacrylate) substrates, but the deformation is insufficient to generate a sufficient driving force to propel the flow of small-volume microfluidics.

[0004] The microtube actuator proposed by Lv et al. (Jiu-an Lv, Yuyun Liu, Jia Wei, Erqiang Chen, Lang Qin and Yanlei Yu*, Photocontrol of Fluid Slugs in Liquid Crystal Polymer Microactuators, Nature, 537(7619)(2016), 179-184.) has a faster liquid driving speed than fully optically controlled microfluidic chips and a larger deformation than microchips composed of linear liquid crystal polymer films and PMMA substrates, enabling a transport volume of 1-2 microliters. However, the fabrication of this microtube actuator is relatively complex, and when the droplet volume is reduced to nanoliters or even picoliters, the liquid surface effect is further significantly enhanced, and the fluid resistance increases sharply, making it impossible for the microtube actuator to achieve fluid transport at even ultra-micro volume levels. Summary of the Invention

[0005] To address the aforementioned technical problems, embodiments of the present invention disclose a microfluidic chip, comprising:

[0006] The substrate is made of a photodeformation cross-linked liquid crystal polymer material and includes a first surface, on which a groove is formed and a slot is provided at the top of the groove.

[0007] The thin film, made of photodeformable linear liquid crystal polymer material, is attached to the first surface and covers the groove. The groove and the thin film covering the groove surround each other to form a microchannel, which is used to transport microfluidics.

[0008] When a portion of the microchannel is illuminated, it forms an illuminated area channel and a non-illuminated area channel. The grooves and films in the illuminated area channel deform, making the cross-sectional area of ​​the illuminated area channel larger than that of the non-illuminated area channel, thereby driving the microfluidic fluid in the illuminated area channel to flow into the non-illuminated area channel.

[0009] By adopting the above technical solution, the deformation of the microchannel under light can be increased by utilizing the combined deformation of the groove and the thin film, thereby increasing the Laplace pressure difference caused by the deformation, significantly improving the driving force of the microfluidic, enhancing the transport capacity of the microchannel, and further expanding the application range of microfluidic chips.

[0010] Optionally, the channel wall of the microchannel is formed by the groove and the thin film, and the orientation of the liquid crystal molecules in each channel wall is perpendicular to the channel wall.

[0011] Optionally, when the microchannel does not deform, the cross-section of the microchannel is rectangular along the depth direction of the microchannel.

[0012] Optionally, the substrate has a thickness of 40-70 μm, the microchannel has a depth of 30-50 μm, and the film has a thickness of 20-30 μm.

[0013] Optionally, along the depth direction, the maximum deformation of the substrate or the thin film is d, where d satisfies:

[0014]

[0015] Where P is the photoinduced stress of the substrate or thin film, h is the thickness of the channel wall in the depth direction, a is the width of the microchannel, and E is the elastic modulus of the substrate or thin film.

[0016] Optionally, the photodeformable crosslinked liquid crystal polymer material is prepared from a monomer mixture via a crosslinking reaction. The monomer mixture includes a photoresponsive liquid crystal monomer, a crosslinking agent monomer, and a flexible liquid crystal monomer. The photoresponsive liquid crystal monomer has the structure shown in Formula I, the crosslinking agent monomer has the structure shown in Formula II, and the flexible liquid crystal monomer has the structure shown in Formula III.

[0017]

[0018] Optionally, in the monomer mixture, the mass percentage of the photoresponsive liquid crystal monomer is 60-75%, the mass percentage of the crosslinking agent monomer is 10-30%, and the mass percentage of the flexible liquid crystal monomer is 5-20%.

[0019] According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for fabricating the above-mentioned microfluidic chip, comprising the following steps: preparing a substrate with grooves: filling a monomer mixture into a liquid crystal cell for a crosslinking reaction to form a substrate with grooves, wherein the liquid crystal cell includes a convex template and a planar template disposed opposite to each other, the convex template including a first plate and a second protrusion protruding from the first plate to the planar template, the liquid crystal cell further including a spacer disposed between the first plate and the planar template, the spacer causing a gap between the second protrusion and the planar template, the convex template, the planar template and the spacer together forming a chamber for filling the monomer mixture;

[0020] Fabrication of a microfluidic chip with microchannels: A thin film is attached to a substrate, and the film and substrate are heated to obtain a microfluidic chip with microchannels.

[0021] Using the above technical solution, microfluidic chips with microchannels can be easily fabricated. By utilizing the combined deformation of the groove and the thin film, the deformation of the microchannel under light illumination is increased, thereby enhancing the Laplace pressure difference caused by deformation, which significantly improves the driving force of the microfluidic fluid and strengthens the transport capacity of the microchannel.

[0022] Optionally, the step of preparing a substrate with grooves may further include a step of preparing a liquid crystal alignment layer. In the step of preparing the liquid crystal alignment layer, a polyimide precursor solution is spin-coated onto the convex template and the planar template, and then the convex template and the planar template are heated to form the liquid crystal alignment layer. The liquid crystal alignment layer is used to control the orientation of the liquid crystal molecules of the substrate.

[0023] Optionally, in the step of preparing the substrate with grooves, the crosslinking polymerization reaction is carried out under light irradiation, and after the crosslinking reaction, the liquid crystal molecules have an orientation perpendicular to the surface of the convex template.

[0024] Optionally, the spacing is 10-20 μm.

[0025] According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for driving microfluidics in the above-mentioned microfluidic chip, comprising the following steps:

[0026] When a light source is used to illuminate a microfluidic chip containing microfluidics, the cross-sectional area of ​​the microchannel in the illuminated area will increase compared to the unilluminated area, thereby driving the microfluidic fluid to move towards the unilluminated area.

[0027] By adopting the above technical solution, the deformation of the microchannel under light can be increased by utilizing the combined deformation of the groove and the film, thereby increasing the Laplace pressure difference caused by the deformation, which significantly enhances the driving force of the microfluidic fluid and strengthens the transport capacity of the microchannel. Attached Figure Description

[0028] Figure 1 A schematic diagram of a microfluidic chip structure according to an embodiment of the present invention is shown;

[0029] Figure 2(a) shows a cross-sectional schematic diagram of a microchannel in an embodiment of the present invention when no deformation occurs;

[0030] Figure 2(b) shows a cross-sectional schematic diagram of a microchannel of an embodiment of the present invention under 470nm light illumination when it deforms.

[0031] Figure 3(a) shows a schematic diagram of the structure of a liquid crystal cell according to an embodiment of the present invention. Figure 1 ;

[0032] Figure 3(b) shows a schematic diagram of the structure of a liquid crystal cell according to an embodiment of the present invention;

[0033] Figure 4 This diagram illustrates the thermal bonding process between a thin film and a substrate according to an embodiment of the present invention.

[0034] Figure 5 A photograph of a groove according to an embodiment of the present invention is shown;

[0035] Figure 6 A photograph of the microfluidic chip of Embodiment 1 of the present invention is shown;

[0036] Figure 7 The image shows a photograph illustrating the process of using the microfluidic chip of Example 1 to drive silicone oil according to the present invention.

[0037] 1. Substrate, 11. First surface, 12. Groove, 2. Thin film, 3. Microchannel, 4. Liquid crystal cell, 41. Protruding template, 411. First flat plate, 412. Second protrusion, 42. Planar template, 43. Spacer, 44. Liquid crystal alignment layer. Detailed Implementation

[0038] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Although the description of the present invention will be presented in conjunction with preferred embodiments, this does not mean that the features of the invention are limited to this embodiment. On the contrary, the purpose of describing the invention in conjunction with embodiments is to cover other options or modifications that may be derived based on the claims of the present invention. To provide a deep understanding of the invention, many specific details will be included in the following description. The invention may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of the invention, some specific details will be omitted in the description. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0039] It should be noted that in this specification, similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0040] The terms “first”, “second”, etc., are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0041] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0042] refer to Figure 1The first aspect of this invention discloses a microfluidic chip, comprising a substrate 1 and a thin film 2. The substrate 1 is made of photodeformable cross-linked liquid crystal polymer (CLCP) and includes a first surface 11. A groove 12 is formed on the first surface 11, and a slot is formed at the top of the groove 12; that is, the substrate 1 has a structure recessed relative to its first surface 11. The thin film 2 is made of photodeformable linear liquid crystal polymer (LLCP) and is attached to the first surface 11, covering the slot. The groove 12 and the thin film 2 covering the slot surround and form a microchannel 3 for transporting microfluidics; that is, the groove 12 and the thin film 2 together constitute the channel wall of the microchannel 3, and the microfluidic fluid flows in the space formed by the groove 12 and the thin film 2. In other words, this invention provides a cross-linked linear liquid crystal polymer composite fully photo-controlled microfluidic chip.

[0043] When a portion of microchannel 3 is irradiated with light, microchannel 3 has irradiated and non-irradiated channels. That is, when a portion of a microchannel is irradiated with light, that portion becomes the irradiated channel, and the portion not irradiated by light becomes the non-irradiated channel. Since both substrate 1 and thin film 2 are photodeformable polymer materials, the grooves in the irradiated channels and the thin film deform under light irradiation. Specifically, the irradiated channels expand under light excitation, resulting in a cross-sectional area larger than that of the non-irradiated channels, which drives the microfluidic fluid in the irradiated channels to flow into the non-irradiated channels. For example, when one side of a microchannel is irradiated with light, that side expands, and its cross-sectional area becomes larger than that of the other side, causing the microfluidic fluid to flow towards the side with the smaller cross-sectional area. As shown in Figure 2(a), when there is no light irradiation, the microchannel 3 is in an undeformed state. As shown in Figure 2(b), when irradiated with 470nm visible light, the microchannel 3 expands outward and the channel wall deforms outward (only the deformation along the depth direction of the microchannel is shown in the figure). Compared with the undeformed state, the cross-sectional area of ​​the microchannel is significantly larger.

[0044] Existing fully optically controlled microfluidic chips are constructed using a composite of a linear liquid crystal polymer film and a PMMA substrate. Under illumination, only the linear liquid crystal polymer film deforms. When the volume of the microfluidic fluid in the microchip decreases to the microliter or picoliter level, the deformation of the linear liquid crystal polymer film is insufficient to generate enough driving force to propel the flow of the microfluidic fluid. The microfluidic chip of this invention uses a photodeformable cross-linked liquid crystal polymer material as the substrate. This means that the driving force is no longer solely derived from the linear liquid crystal polymer film, but rather from the deformation of both the substrate and the film, collectively forming the driving force source. This increases the Laplace pressure difference, thereby enhancing the driving force of the microfluidic fluid. The microchannels are entirely surrounded by photodeformable material, allowing deformation of the channel walls in all directions, significantly increasing the deformation and thus greatly improving the driving force. The microchannels possess strong transport capabilities, improving analysis and detection efficiency and expanding the range of samples that can be used. Furthermore, compared to microtube actuators, the microfluidic chip of this invention can achieve the driving of various types of liquids at the nanoliter level, and is easier to fabricate, making it more promising for applications. Meanwhile, using photodeformable cross-linked liquid crystal polymer material as a substrate can ensure the mechanical properties of the substrate while deforming, and increase the deformation while ensuring the stability of the microchip structure. The photodeformable linear liquid crystal polymer material, as a thin film, can be tightly bonded to the substrate after heating, which is conducive to processing. Together, they can ensure the reliability of the microfluidic chip.

[0045] In embodiments of the present invention, the number and shape of the microchannels can be adjusted according to actual needs, for example, as follows: Figure 1 As shown, the microchannels can work together to form a trident shape.

[0046] In an embodiment of the present invention, as shown in FIG2(a), the channel wall of the microchannel 3 is formed by grooves 12 and thin film 2. The orientation of liquid crystal molecules in each channel wall is perpendicular to the channel wall, that is, the liquid crystal molecules around the microchannel have a vertical orientation, perpendicular to the channel surface. By utilizing the synergistic deformation of liquid crystal molecules in all directions, a large deformation is generated under illumination, increasing the deformation value of the microchannel. In particular, along the depth direction of the microchannel, the deformation of liquid crystal molecules on the upper and lower channel walls is greater, generating a larger Laplace pressure difference, which significantly improves the liquid driving capability.

[0047] In an embodiment of the present invention, as shown in FIG2(a), when the microchannel 3 is not deformed, the cross-section of the microchannel 3 is rectangular along the depth direction of the microchannel 3. That is, when not exposed to light, the groove is a rectangular groove, and the microchannel formed together with the film has a rectangular cross-section, which facilitates the processing and formation of the microchannel.

[0048] Furthermore, in an embodiment of the present invention, the substrate thickness is 40-70 μm, the microchannel depth is 30-50 μm, and the film thickness is 20-30 μm. That is, the substrate has an overall thickness of 40-70 μm, and the recessed grooves on the substrate have a depth of 30-50 μm, so that the microchannel also has a depth of 30-50 μm. In this case, as shown in FIG2(a), the substrate constituting the top wall of the microchannel 3 in FIG2(a) has a thickness of 10-20 μm. By controlling the thickness, the microchannel structure has both good mechanical properties and deformation, ensuring sufficient liquid driving force and sufficient reliability.

[0049] Furthermore, in an embodiment of the present invention, the film has a length and width of 40mm × 30mm, the substrate has a length and width of 40mm × 30mm, the microchannel has a width of 50μm, and the microchannel has a height of 35μm. This is more conducive to the overall microchip having good mechanical properties, while ensuring the microchannel's ability to control the liquid.

[0050] In an embodiment of the present invention, the maximum deformation of the substrate or thin film along the depth direction of the microchannel is d, and d satisfies:

[0051]

[0052] Where P is the photoinduced stress of the substrate or thin film, h is the thickness of the channel wall in the depth direction, a is the width of the microchannel, and E is the elastic modulus of the substrate or thin film. As shown in Figure 2(b), along the depth direction of the microchannel 3, the maximum deformation of the substrate 1 is d1, the maximum deformation of the thin film 2 is d2, and the channel depth increases from a in Figure 2(a) to a' in Figure 2(b).

[0053] Furthermore, based on the theoretical model of the relationship between material deformation and fluid drive, namely Formula 2, it is estimated that the microfluidic chip of the present invention can increase the driving force of the liquid by 1.5-2 times.

[0054]

[0055] Where F is the Laplace pressure difference, i.e. the fluid driving force in the chip, a is the microchannel depth, d is the deformation of the thin film or substrate, γ is the fluid surface tension, and θ is the contact angle between the fluid and the thin film or substrate.

[0056] Furthermore, when the thickness and microchannel width are constant, the deformation and the material's expansion rate... It is estimated that the expansion rate of CLCP substrates can reach 0.15%-0.5%.

[0057] Specifically, when the microfluidic is hydrophilic, the inner wall of the chip is coated with a hydrophilic coating; when the microfluidic is hydrophobic, the inner wall of the chip is coated with a hydrophobic coating or not coated with a hydrophobic coating. The hydrophilic or hydrophobic coating can be applied using commercially available materials (such as polyvinyl alcohol, polyacrylamide, silica sol-gel, etc.).

[0058] Specifically, the microfluidic is a mixture of silicone oil, n-hexane, petroleum ether, ethyl acetate, acetone, methanol, ethanol, water, isopropanol, pentane, octane, cyclohexanone, diethyl ether, propylene oxide, methyl butyl ketone, methyl isobutyl ketone, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, acetonitrile, pyridine, gas-liquid fluid, emulsion, liquid-solid fluid, gasoline, biochemical liquid, aqueous solution, and mixtures thereof. Preferably, the microfluidic is any one of silicone oil, n-hexane, ethyl acetate, acetone, methanol, ethanol, water, isopropanol, gas-liquid fluid, emulsion, liquid-solid fluid, gasoline, and biochemical liquid. It can not only manipulate various non-polar and polar liquids, but also complex fluids, reducing the volume of the driving liquid by two orders of magnitude, achieving highly efficient driving of various types of liquids at the nanoscale.

[0059] Specifically, when illuminating a microfluidic chip for microfluidic control, the light source is 470nm visible light, and the light source can be any one of a single point light source, a line light source, or an array-type integrated light source.

[0060] In an embodiment of the present invention, the photodeformable cross-linked liquid crystal polymer material is prepared from a monomer mixture via a cross-linking reaction. The monomer mixture includes a photoresponsive liquid crystal monomer, a cross-linking agent monomer, and a flexible liquid crystal monomer. The photoresponsive liquid crystal monomer has the structure shown in Formula I, the cross-linking agent monomer has the structure shown in Formula II, and the flexible liquid crystal monomer has the structure shown in Formula III.

[0061]

[0062] Among them, the photoresponsive liquid crystal monomer is A11AB6, which is used to generate photo-induced stress; the crosslinking agent monomer is DA11AB long-spacer crosslinking agent, which is used to construct a crosslinking network; and the flexible liquid crystal monomer is A11BZ6, which is used to reduce the elastic modulus of the material.

[0063] Preferably, the proportions of A11AB6, DA11AB6, and A11BZ6 in the monomer mixture are adjusted to 60-75%, 10-30%, and 5-20%, respectively. That is, the mass percentage of the photoresponsive liquid crystal monomer is 60-75%, the mass percentage of the crosslinking agent monomer is 10-30%, and the mass percentage of the flexible liquid crystal monomer is 5-20%, which better balances the elastic modulus and photoinduced stress of the substrate.

[0064] Furthermore, the photodeformable linear liquid crystal polymer material was synthesized using the cyclooctene derivative monomer C11AB6 via ring-opening metathesis polymerization. The photodeformable linear liquid crystal polymer material is a side-chain linear azobenzene liquid crystal polymer material PC11AB6. C11AB6 has the structure shown in Formula IV. PC11AB6 has the structure shown in Formula V.

[0065]

[0066] The second aspect of the present invention discloses a method for fabricating the microfluidic chip according to the above embodiments, comprising the following steps:

[0067] Preparation of a grooved substrate 1: A monomer mixture is filled into a liquid crystal cell for a crosslinking reaction to form a grooved substrate 1. The groove structure of substrate 1 is as follows: Figure 5 As shown.

[0068] Fabrication of microfluidic chips with microchannels: such as Figure 4 As shown, the thin film 2 is attached to the substrate 1, and the thin film 2 and the substrate 1 are heated by a hot stage to obtain a microfluidic chip with microchannels.

[0069] As shown in Figures 3(a) and 3(b), the liquid crystal cell 4 includes a convex template 41 and a planar template 42 disposed opposite to each other. The convex template 41 includes a first plate 411 and a second protrusion 412 protruding from the first plate 411 toward the planar template 42. The liquid crystal cell also includes spacers 43 disposed between the first plate 411 and the planar template 42, with the spacers 43 creating a gap L between the second protrusion 412 and the planar template 42. The convex template 41, the planar template 42, and the spacers 43 together form a chamber for filling the monomer mixture. That is, two spacers 43 are sandwiched between the convex template 41 and the planar template 42, and the second protrusion 412 is located between the two spacers 43. Therefore, the liquid crystal cell can be used to process a substrate with grooves, the shape of which corresponds to the shape of the second protrusion. The height of the second protrusion relative to the first plate is the depth of the microchannel, for example, 30-50 μm. The height of the spacers determines the overall thickness of the substrate, for example, the height of the spacers is 40-70 μm. Furthermore, the height difference between the spacer and the second protrusion determines the spacing between the second protrusion and the planar template. Specifically, the spacing L is 10-20 μm, which makes the thickness of one channel wall in the depth direction of the microchannel 10-20 μm.

[0070] Specifically, the convex template is a silicon wafer convex template, which uses wet etching technology to directly process microstructures on the surface of the silicon wafer as the convex template; the planar template is a glass substrate, for example, with a size of 30mm×40mm; and the spacer is a commercial PET film.

[0071] Furthermore, before the step of preparing the substrate with grooves, a step of preparing a liquid crystal alignment layer is included. In the step of preparing the liquid crystal alignment layer, a polyimide precursor solution (PI precursor solution) is spin-coated onto a convex template and a planar template. Subsequently, the convex template and the planar template are heated to form a liquid crystal alignment layer. The liquid crystal alignment layer is used to control the orientation of the liquid crystal molecules on the substrate. In a specific embodiment of the present invention, a 30mm × 40mm glass substrate is ultrasonically cleaned in ethanol. A PI precursor solution is spin-coated onto the glass substrate and the silicon wafer convex template. Subsequently, the glass substrate / silicon wafer convex template is placed on a hot stage, heated to evaporate the solvent, and then heated for thermal imidization. Specifically, the liquid crystal alignment layer causes the liquid crystal molecules near the convex template to align vertically along the surface. After polymerization and crosslinking, the orientation of the liquid crystal molecules is fixed. As shown in Figure 3(a), the liquid crystal cell 4 also has a liquid crystal alignment layer 44. Through the anchoring effect of the liquid crystal alignment layer and the confinement effect of the spacers, the orientation of the liquid crystal molecules and the thickness of the upper and lower surfaces of the chip microchannel are simultaneously controlled.

[0072] Furthermore, in the step of preparing the substrate with grooves, the monomer mixture is uniformly mixed with a photoinitiator and filled into a liquid crystal cell for photopolymerization crosslinking. Specifically, the photoinitiator is Irgacure 784, which has the structure shown in Formula VI:

[0073]

[0074] Furthermore, the monomer mixture is thoroughly mixed with 0.5-5% molar proportion of the photoinitiator Irgacure 784.

[0075] Specifically, the liquid crystal cell is placed on a hot stage, and the mixture of monomers and photoinitiator is heated to above the isotropic temperature under dark conditions, then poured into the liquid crystal cell under capillary force. The temperature is then slowly lowered below the clearing point temperature of the monomer mixture. A 530nm laser source is turned on, and the light intensity is adjusted to initiate polymerization. After polymerization, the liquid crystal cell is opened to obtain a cross-linked liquid crystal polymer substrate. The liquid crystal alignment layer causes the liquid crystal molecules near the convex template to align perpendicularly along the surface; the orientation of the liquid crystal molecules is fixed after photopolymerization and cross-linking.

[0076] A third aspect of the present invention discloses a method for driving microfluidics in a microfluidic chip according to the above embodiments, comprising the following steps:

[0077] When a light source is used to illuminate a microfluidic chip containing microfluidics, the cross-sectional area of ​​the microchannel in the illuminated area will increase compared to the unilluminated area, thereby driving the microfluidic fluid to move towards the unilluminated area.

[0078] The following description will be based on more specific embodiments. The embodiment is a microfluidic chip composed of a substrate and a thin film.

[0079] The preparation method is as follows:

[0080] 1. Preparation of convex and planar templates coated with liquid crystal alignment layers: Microstructures were directly fabricated on the silicon wafer surface using wet etching technology to serve as convex templates. A glass substrate was used as a planar template. A 30mm × 40mm glass substrate was ultrasonically cleaned in ethanol for 30 minutes. A PI precursor solution was spin-coated onto the glass substrate and the silicon wafer convex template (spin-coating parameters: 400 rpm, 20 s; 3000 rpm, 30 s). Subsequently, the glass substrate and the silicon wafer convex template were placed on a hot stage and heated at 80°C for 1 hour to evaporate the solvent, followed by thermal imidization at 200°C for 2 hours.

[0081] 2. Fabrication of a liquid crystal cell based on the template method: Referring to Figure 3(a), the liquid crystal cell, from top to bottom, consists of a silicon wafer convex template, a PI liquid crystal alignment layer, spacers, a liquid crystal vertical alignment layer, and a glass substrate. Spacers with a thickness of 50 μm coated with UV adhesive are placed on both edges of the silicon wafer convex template coated with the PI alignment layer, and then the glass substrate is placed on top. UV light is used to cure the UV adhesive. The height difference between the spacers and the second protrusion on the convex template is 15 μm, that is, the distance between the second protrusion and the glass substrate is 15 μm, and the groove depth is 35 μm.

[0082] 3. Preparation of a substrate with grooves: The monomer mixture was uniformly mixed with 2% molar proportion of photoinitiator Irgacure 784. The liquid crystal cell was placed on a hot stage, and the mixture was heated to above the isotropic temperature under dark conditions, then poured into the liquid crystal cell under capillary action. Subsequently, the temperature was slowly reduced to 4°C below the clearing point temperature of the monomer mixture at a rate of 0.2°C / min. A 530nm laser source was turned on, and the light intensity was adjusted to 3mW / cm². 2 The reaction polymerization was carried out for 3 hours. After polymerization, the liquid crystal cell was opened to obtain a substrate with grooves. The liquid crystal alignment layer caused the liquid crystal molecules near the convex template to align vertically along the surface, and the orientation of the liquid crystal molecules was fixed after photopolymerization crosslinking. The monomer mixture included A11AB6, DA11AB, and A11BZ6, and the feeding ratio of A11AB6, DA11AB, and A11BZ6 was 7:2:1.

[0083] 4. Fabrication of microfluidic chips with microchannels: A thin film is attached to a substrate, and both the film and the substrate are heated to obtain a microfluidic chip with microchannels, such as... Figure 6 As shown in the figure. The heating temperature is 80℃.

[0084] Under the same channel size conditions, the liquid transport rate of the microfluidic chip in this embodiment is 1.5-2 times that of the LLCP-PMMA composite AOMC, showing a significant performance improvement. With a microchannel size of 50 μm, the microfluidic chip in Example 1 can still effectively drive 3.5 nL of n-octane at a speed of 1.28 mm / s, which is the fastest reported speed for optically controlled liquid transport at this liquid volume. According to the theoretical model of the relationship between material deformation and fluid drive in AOMC, as the channel size decreases, the fluid drive force decreases accordingly, leading to increased difficulty in transporting high-viscosity liquids. However, at this scale, as... Figure 7 As shown, the microfluidic chip in Example 1 can still drive high-viscosity silicone oil (with... Figure 7 (marked by the red dashed box in the image), the transport volume is 2.5 nL and the transport rate is 0.01 mm / s. This performance is comparable to the silicone oil transport rate of an LLCP-PMMA composite chip with a channel size of 200 μm.

[0085] While the present invention has been illustrated and described with reference to certain preferred embodiments, those skilled in the art should understand that the above description is a further detailed explanation of the invention in conjunction with specific embodiments, and should not be construed as limiting the specific implementation of the invention to these descriptions. Various changes in form and detail can be made by those skilled in the art, including several simple deductions or substitutions, without departing from the spirit and scope of the invention.

Claims

1. A microfluidic chip, characterized in that, include: The substrate is made of a photodeformation cross-linked liquid crystal polymer material and includes a first surface, on which a groove is formed and a slot is provided at the top of the groove. A thin film, made of photodeformable linear liquid crystal polymer material, is attached to the first surface and covers the groove. The groove and the thin film covering the groove surround each other to form a microchannel, which is used to transport microfluidics. When a portion of the microchannel is irradiated by light, the microchannel forms an irradiated area channel and a non-irradiated area channel. The groove and the film in the irradiated area channel deform, making the cross-sectional area of ​​the irradiated area channel larger than the cross-sectional area of ​​the non-irradiated area channel, thereby driving the microfluidic fluid in the irradiated area channel to flow into the non-irradiated area channel. The photodeformable cross-linked liquid crystal polymer material is prepared by a cross-linking reaction of a monomer mixture. The monomer mixture includes a photoresponsive liquid crystal monomer, a cross-linking agent monomer, and a flexible liquid crystal monomer. The photoresponsive liquid crystal monomer has the structure shown in Formula I, the cross-linking agent monomer has the structure shown in Formula II, and the flexible liquid crystal monomer has the structure shown in Formula III. I II III。 2. The microfluidic chip as described in claim 1, characterized in that, The channel wall of the microchannel is formed by the groove and the thin film, and the orientation of the liquid crystal molecules in each channel wall is perpendicular to the channel wall.

3. The microfluidic chip as described in claim 2, characterized in that, When the microchannel is not deformed, its cross-section is rectangular along the depth direction of the microchannel.

4. The microfluidic chip as described in claim 3, characterized in that, The substrate has a thickness of 40-70 μm, the microchannel has a depth of 30-50 μm, and the film has a thickness of 20-30 μm.

5. The microfluidic chip as described in claim 4, characterized in that, Along the depth direction, the maximum deformation of the substrate or the thin film is d, and d satisfies: Formula 1 Where P is the photoinduced stress of the substrate or thin film, h is the thickness of the channel wall in the depth direction, a is the width of the microchannel, and E is the elastic modulus of the substrate or thin film.

6. The microfluidic chip as described in claim 1, characterized in that, In the monomer mixture, the mass percentage of the photoresponsive liquid crystal monomer is 60-75%, the mass percentage of the crosslinking agent monomer is 10-30%, and the mass percentage of the flexible liquid crystal monomer is 5-20%.

7. A method for fabricating a microfluidic chip as described in any one of claims 1-6, characterized in that, Includes the following steps: Preparation of a substrate with grooves: A monomer mixture is filled into a liquid crystal cell for a crosslinking reaction to form a substrate with grooves. The liquid crystal cell includes a convex template and a planar template disposed opposite to each other. The convex template includes a first plate and a second protrusion protruding from the first plate toward the planar template. The liquid crystal cell also includes a spacer disposed between the first plate and the planar template. The spacer creates a gap between the second protrusion and the planar template. The convex template, the planar template, and the spacer together form a chamber for filling the monomer mixture. Fabrication of a microfluidic chip with microchannels: A thin film is attached to a substrate, and the film and substrate are heated to obtain a microfluidic chip with microchannels.

8. The method for fabricating a microfluidic chip as described in claim 7, characterized in that, The step of preparing a substrate with grooves is preceded by a step of preparing a liquid crystal alignment layer. In the step of preparing the liquid crystal alignment layer, a polyimide precursor solution is spin-coated onto the convex template and the planar template. Then, the convex template and the planar template are heated to form the liquid crystal alignment layer. The liquid crystal alignment layer is used to control the orientation of the liquid crystal molecules of the substrate.

9. The method for fabricating a microfluidic chip as described in claim 8, characterized in that, In the step of preparing the substrate with grooves, the crosslinking polymerization reaction is carried out under light irradiation, and after the crosslinking reaction, the liquid crystal molecules have an orientation perpendicular to the surface of the convex template.

10. The method for fabricating a microfluidic chip as described in claim 7, characterized in that, The spacing is 10-20 μm.

11. A method for driving microfluidics in a microfluidic chip as described in any one of claims 1-6, characterized in that, Includes the following steps: When a light source is used to illuminate a microfluidic chip containing microfluidics, the cross-sectional area of ​​the microchannel in the illuminated area will increase compared to the unilluminated area, thereby driving the microfluidic fluid to move towards the unilluminated area.

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