Microfluidic chip driven by acoustically excited droplet-shaped microbubbles and its fabrication process

Abstract

This invention relates to a microfluidic chip driven by acoustically excited droplet-shaped microbubbles and its fabrication process. A droplet-shaped microbubble array is obtained through microfluidic chip structure design. Under acoustic excitation, the microbubbles oscillate, generating asymmetric acoustic-flow vortices, which in turn directionally drive the microfluidic fluid within the microchannels. The flow rate can be linearly controlled by adjusting the driving voltage, offering advantages such as non-contact, pollution-free, and highly efficient directional driving. The fabrication process is based on MEMS technology, employing nitrogen plasma bonding and soft lithography, resulting in low cost and suitability for mass production. This invention solves the problem of the lack of directionality in traditional symmetrical acoustic-flow vortices and can be widely applied in fields such as biomedicine, drug delivery, and chemical analysis.

Description

Technical Field

[0001] This invention belongs to the field of microfluidic drive technology, specifically relating to a microfluidic chip and its fabrication process that uses acoustic wave excitation to cause droplet-shaped microbubbles to oscillate, and the oscillating microbubbles to drive microfluidics. Background Technology

[0002] Microfluidics offers advantages such as low sample consumption, high integration, and fast reaction speed, making it promising for applications in the biomedical field, including drug delivery and cell analysis. Among these, acoustic fluid dynamics, driven by acoustic vortices generated by excitating microbubbles with sound waves, offers advantages such as non-contact and pollution-free operation.

[0003] In microbubble-based acoustic fluid control systems, the morphology control of microbubbles is crucial for driving microfluidics. However, in existing technologies, acoustically excited microbubbles often employ symmetrical structures such as spherical or hemispherical shapes, resulting in acoustic flows that are typically symmetrical vortices. This type of flow field has a weak directional gradient, making it difficult to achieve directional driving of microfluidics and greatly limiting the application of acoustically excited microbubbles for microfluidic actuation. Summary of the Invention

[0004] This invention proposes a microfluidic chip driven by acoustically excited droplet-shaped microbubbles and its fabrication process. By designing an array of droplet-shaped microgrooves at the bottom of the microchannel, when liquid is injected into the microchannel, surface tension causes the droplet-shaped microbubbles to self-close and form at the microgrooves. Subsequently, acoustic waves excite the microbubbles to oscillate, generating asymmetric acoustic vortices. The asymmetry of the acoustic flow is used to achieve directional driving of the microfluidic stream.

[0005] The present invention provides a technical solution to solve the aforementioned technical problem:

[0006] A microfluidic chip driven by acoustically excited droplet-shaped microbubbles includes a glass substrate (1), a groove layer (2), a flow channel layer (3), an inlet pipe (4), an outlet pipe (5), and a piezoelectric transducer (6).

[0007] The groove layer (2) is fabricated on the glass substrate (1) by soft photolithography, and an array of droplet-shaped grooves (9) is designed in the groove layer (2). The radius of the large end of the droplet-shaped groove (9) is 50-100μm, the angle of the small end is 30-90°, and the groove depth is 100-150μm;

[0008] The flow channel layer (3) is fixed to the upper surface of the groove layer (2) by a bonding process. The flow channel layer (3) is designed with a microchannel (10) structure to restrict the liquid flow area.

[0009] The inlet pipe (4) and outlet pipe (5) are respectively connected to the two ends of the microchannel (10) of the flow channel layer (3), wherein the inlet pipe (4) is used to inject liquid and the outlet pipe (5) is used to discharge liquid;

[0010] The piezoelectric transducer (6) is fixed on the upper surface of the glass substrate (1). The piezoelectric transducer (6) is used to generate sound waves of a specific frequency and amplitude, so that the microbubble (11) oscillates under the excitation of the sound waves, thereby generating an asymmetric acoustic vortex (12) near the microbubble (11) to drive the microfluid in the microchannel in a directional manner.

[0011] The microbubble (11) is subjected to the surface tension of the liquid. When the liquid flows through the droplet-shaped groove (9), it spontaneously seals part of the gas in the groove to form a microbubble (11). Under the restriction of the droplet-shaped groove (9), it is in the shape of a droplet. The large end radius of curvature of the droplet-shaped microbubble (11) is 50-100μm, the small end radius of curvature is 10-20μm, and the long axis length is 170-240μm.

[0012] The usage method of the microfluidic chip driven by acoustically excited droplet-shaped microbubbles is as follows:

[0013] Liquid is injected through the inlet pipe (4). When the liquid flows through the droplet-shaped groove (9) of the groove layer (2), microbubbles (11) are spontaneously formed under the action of liquid surface tension and confined to the droplet-shaped groove.

[0014] The piezoelectric transducer (6) is connected to the driver and a sinusoidal voltage with the same resonant frequency as the microbubble (11) is input. The amplitude of the driving voltage is adjusted, and the piezoelectric transducer (6) vibrates to generate sound waves. The microbubble (11) oscillates under the excitation of the resonant sound waves, and then generates asymmetric acoustic vortices (12) in its vicinity.

[0015] The fluid in the microchannel is subjected to acoustic vortex (12), which realizes directional driving from the large end to the small end of the droplet-shaped microbubble (11);

[0016] The speed of driving the microfluidic can be controlled by adjusting the driving voltage, and the driving speed is linearly related to the driving voltage.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The droplet-shaped microbubbles of the microfluidic chip described in this invention generate asymmetric acoustic vortices under acoustic excitation, breaking through the limitations of traditional symmetric acoustic vortices and realizing directional and efficient driving of microfluids.

[0019] (2) The microfluidic chip of the present invention can precisely and dynamically control the flow rate of the directional microfluidic by adjusting the driving voltage;

[0020] (3) The microfluidic chip of the present invention avoids mechanical damage to biological samples through non-contact driving and can be widely used in biomedicine, chemical analysis and other fields.

[0021] (4) The microfluidic chip of the present invention is based on MEMS technology, which can realize mass production, low cost and high reliability. Attached Figure Description

[0022] Figure 1 : A schematic diagram of the structure of the microfluidic chip driven by acoustically excited droplet-shaped microbubbles proposed in this invention;

[0023] Figure 2 A front view of a microfluidic chip driven by acoustically excited droplet-shaped microbubbles;

[0024] Figure 3 Schematic cross-section of a microfluidic chip driven by acoustically excited droplet-shaped microbubbles Figure 1 (The cross-section is a horizontal plane passing through the chip flow channel);

[0025] Figure 4 Schematic cross-section of a microfluidic chip driven by acoustically excited droplet-shaped microbubbles Figure 2 ;

[0026] Figure 5 : A magnified view of a local cross-section of the microchannel and microbubble in a microfluidic chip driven by acoustically excited droplet-shaped microbubbles;

[0027] Figure 6 Schematic diagram of microbubbles in a microfluidic chip driven by acoustically excited droplet-shaped microbubbles;

[0028] Figure 7 : A schematic diagram of the acoustic vortex and its directional driving of microfluidics;

[0029] Figure 8 Flowchart of the manufacturing process for the grooved layer;

[0030] Figure 9 Flowchart of the fabrication process for the flow channel layer;

[0031] In the figure: 1 Glass substrate, 2 Groove layer, 3 Flow channel layer, 4 Liquid inlet pipe, 5 Liquid outlet pipe, 6 Piezoelectric transducer, 7 Liquid inlet, 8 Liquid outlet, 9 Droplet-shaped groove, 10 Microchannel, 11 Droplet-shaped microbubble, 12 Acoustic vortex, 13 SU-8 negative photoresist GM1070, 14 Groove layer mask, 15 Flow channel layer mask, 16 Flow channel layer mold. Detailed Implementation

[0032] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings. The content mentioned in the embodiments is only used to explain the present invention and is not intended to limit the scope of the present invention.

[0033] The fabrication process of the microfluidic chip driven by the ultrasonic excitation of droplet-shaped microbubbles includes: the fabrication process of the groove layer (2), the fabrication process of the channel layer (3), and the bonding assembly process of the groove layer (2) and the channel layer (3).

[0034] See Figure 8 The process flow diagram of the groove layer fabrication of the microfluidic chip driven by acoustically excited droplet-shaped microbubbles of the present invention.

[0035] The manufacturing process of the groove layer (2) is as follows:

[0036] a. Spin-coat a layer of SU-8 negative photoresist GM 1070 (13) with a thickness of 150 μm on a glass substrate (1); first bake it on a constant temperature baking stage at 65°C for 30 min, then bake it on a constant temperature baking stage at 95°C for 120 min, and finally cool it naturally to room temperature to obtain the cured SU-8 photoresist.

[0037] b. Place the groove layer mask (14) on the surface of the cured SU-8 photoresist and expose it using an exposure machine with a light intensity of 10mW / cm². 2 The exposure time was 3.5 min; then, it was baked on a constant temperature baking stage at 65℃ for 15 min, and on a constant temperature baking stage at 95℃ for 40 min. Finally, it was naturally cooled to room temperature to obtain the exposed SU-8 photoresist.

[0038] c. Rinse the exposed SU-8 photoresist with developer, the unexposed parts are washed away, and then wash with deionized water to leave the patterned SU-8 photoresist structure; then bake on a constant temperature baking stage at 130℃ for 120 minutes, and finally cool naturally to room temperature to obtain the groove layer (2).

[0039] See Figure 9 The fabrication process diagram of the flow channel layer of the microfluidic chip driven by acoustically excited droplet-shaped microbubbles of the present invention.

[0040] The specific manufacturing process of the flow channel layer (3) is as follows:

[0041] a. Spin-coat a layer of SU-8 negative photoresist GM 1070 (13) with a thickness of 150 μm on a glass substrate (1); first bake it at a constant temperature baking station of 65℃ for 30 min, then bake it at a constant temperature baking station of 95℃ for 120 min, and then cool it naturally to room temperature to obtain the cured SU-8 photoresist.

[0042] b. Place the flow channel layer mask (15) on the surface of the cured SU-8 photoresist and expose it using an exposure machine with a light intensity of 10mW / cm². 2 The exposure time was 3.5 min; then, it was baked on a constant temperature baking stage at 65℃ for 15 min, then baked on a constant temperature baking stage at 95℃ for 40 min, and finally cooled naturally to room temperature to obtain the exposed SU-8 photoresist.

[0043] c. Rinse the exposed SU-8 photoresist with developer, and wash away the unexposed parts. Then wash with deionized water to leave the patterned SU-8 photoresist structure. Then bake at 130℃ for 120 minutes and then cool naturally to room temperature to obtain the flow channel layer mold (16).

[0044] d. Polydimethylsiloxane and curing agent are thoroughly mixed at a mass ratio of 10:1 and the air bubbles are removed in a vacuum chamber. Then, the mixture is poured into the flow channel layer mold (16). After curing, the polydimethylsiloxane is peeled off from the mold to obtain the flow channel layer (3). Then, a biopsy piercing tool is used to drill holes with a diameter of 1000 μm at both ends of the microchannel.

[0045] The bonding and assembly process of the microfluidic chip involves nitrogen plasma surface treatment of the flow channel layer (3). The parameters of the nitrogen plasma treatment are set as follows: gas pressure 50 Pa, power 70 W, and treatment time 50 s. After that, the groove layer (2) and the flow channel layer (3) are tightly bonded together. The -NH2 functional group on the surface of the flow channel layer (3) forms a covalent bond -HN-HO- with the epoxy group on the surface of the groove layer (2), so that the groove layer (2) and the flow channel layer (3) are firmly connected.

[0046] Finally, the piezoelectric transducer (6) is glued to the glass substrate (1) with epoxy adhesive, and the liquid inlet pipe (4) and liquid outlet pipe (5) are connected to the liquid inlet (7) and liquid outlet (8) respectively to complete the fabrication of the microfluidic chip.

[0047] The working principle of the acoustically excited droplet-shaped microbubble-driven microfluidic chip provided in this embodiment of the invention is as follows:

[0048] The piezoelectric transducer generates sound waves under the excitation of a sinusoidal signal. The frequency and amplitude of the sound waves can be adjusted by the frequency of the input sinusoidal signal and the driving voltage, respectively. The droplet-shaped microbubble oscillates under the excitation of the sound waves at its resonant frequency and generates asymmetric acoustic vortices (12) in its vicinity. The acoustic vortices (12) exert a directional driving effect on the fluid in the microchannel.

[0049] The acoustically excited droplet-shaped microbubbles of the present invention can adjust the flow rate of the driving microfluidic by controlling the driving voltage during the process of directional driving microfluidic flow.

[0050] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any structures or modifications made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A microfluidic chip driven by acoustically excited droplet-shaped microbubbles, characterized in that: It includes a glass substrate (1), a groove layer (2), a flow channel layer (3), an inlet pipe (4), an outlet pipe (5), and a piezoelectric transducer (6); The groove layer (2) is fabricated on the glass substrate (1) by soft photolithography, and a droplet-shaped groove (9) array is designed in the groove layer (2); the large end of the droplet-shaped groove (9) has a radius of 50-100μm, the small end has a sharp angle of 30-90°, and the groove depth is 100-150μm. The flow channel layer (3) is fixed to the upper surface of the groove layer (2) by a bonding process. The flow channel layer (3) is designed with a microchannel (10) structure to restrict the liquid flow area. The inlet pipe (4) and outlet pipe (5) are respectively connected to the two ends of the microchannel (10) of the flow channel layer (3), wherein the inlet pipe (4) is used to inject liquid and the outlet pipe (5) is used to discharge liquid; The piezoelectric transducer (6) is fixed on the upper surface of the glass substrate (1). The piezoelectric transducer (6) is used to generate sound waves, causing the microbubble (11) to oscillate under the excitation of the sound waves, thereby generating an asymmetric acoustic vortex (12) near the microbubble (11) to directionally drive the microfluid in the microchannel.

2. The method of using the acoustically excited droplet-shaped microbubble-driven microfluidic chip as described in claim 1, characterized in that: Liquid is injected through the inlet pipe (4). When the liquid flows through the droplet-shaped groove (9) of the groove layer (2), microbubbles (11) are spontaneously formed under the action of liquid surface tension and confined to the droplet-shaped groove. The piezoelectric transducer (6) is connected to the driver and a sinusoidal voltage with the same resonant frequency as the microbubble (11) is input. The amplitude of the driving voltage is adjusted, and the piezoelectric transducer (6) vibrates to generate sound waves. The microbubble (11) oscillates under the excitation of the resonant sound waves, and then generates an asymmetric acoustic vortex (12) in its vicinity. The fluid in the microchannel is subjected to acoustic vortex (12), which realizes directional driving from the large end to the small end of the droplet-shaped microbubble (11); The speed of the microfluidic drive is controlled by adjusting the driving voltage, and the driving speed is linearly related to the driving voltage.

Images