Efficient laser fabrication method of high aspect ratio microfluidic channel and microfluidic device

Abstract

The application provides a high-efficiency laser preparation method of a high-depth-width-ratio microfluid channel, which utilizes a ps laser and a multi-time focusing scanning method to prepare a high-depth-width-ratio channel on a resin material. After laser scanning ablation of the material each time, the channel depth is measured again and the focusing is downward, so that the laser beam is still focused near the surface of the material in the next scanning instead of being defocused, thereby ensuring that the channel cross section is U-shaped after each laser ablation. The laser scanning process is repeated for multiple times, so that a micro channel with a larger channel depth and a depth-width ratio is prepared under the premise of ensuring a low channel width. The application can efficiently prepare a high-depth-width-ratio micro channel with a U-shaped cross section. Compared with other laser-ablated V-shaped channels, the U-shaped channel is more conducive to improving the working efficiency of microfluid devices such as micro mixers and microfluid channel heat sinks, and is also helpful to reducing the channel length and the volume of a working unit, and is conducive to the miniaturization and low energy consumption of microfluid chips and devices.

Description

Technical Field

[0001] This invention relates to the field of manufacturing processes for microfluidic chips and devices, specifically to an efficient laser fabrication method and microfluidic equipment for high aspect ratio microfluidic channels. Background Technology

[0002] Microfluidic chips have been widely used in fields such as biology, medicine, and chemical analysis. They represent a technology for precisely manipulating fluids at the micrometer and millimeter scale. They possess the ability to integrate fundamental functions related to biology, chemistry, physics, and medicine onto a very small chip, hence the name "lab-on-a-chip." Microfluidic chips not only feature miniaturization, automation, speed, and convenience, but also reduce resource and energy consumption, aligning with today's low-carbon and environmentally friendly themes.

[0003] For microfluidic devices such as micromixers and microfluidic heat sinks, the aspect ratio of microchannels has a significant impact on their performance. Increasing the aspect ratio increases the specific surface area (surface area to volume) of the channel, leading to enhanced mass and heat transfer capabilities. Replacing traditional microchannels with widths of hundreds of micrometers with several to dozens of narrow-width, high-aspect-ratio channels significantly improves the mixing efficiency of micromixers and the heat transfer efficiency of microfluidic heat sinks. This is because reducing the channel width limits the diffusion range of the fluid within the channel. For micromixers, the smaller width increases the probability of collisions between different liquid molecules. For microfluidic heat sinks, the smaller width increases the temperature gradient, increasing the heat flux density during heat transfer. Simultaneously, the high aspect ratio of the channel increases the contact area for liquid mixing and the heat transfer area. Furthermore, utilizing narrow-width, high-aspect-ratio channels to improve the efficiency of microfluidic chips and devices allows for a reduction in channel length, thereby reducing the micropump power required for the chip and device, and shrinking the size and energy consumption of related working units.

[0004] Polymethyl methacrylate (PMMA) resin materials have become the preferred material for most microfluidic chip manufacturing due to their low cost and ease of processing. The fabrication of microfluidic chips mainly involves the formation of microchannels. Using lasers to ablate microchannels on resin materials such as PMMA offers advantages such as rapid prototyping, no pollution, and low cost. Currently, relevant laser-based microchannel fabrication technologies mainly include CO2 laser ablation and femtosecond (FS) laser ablation. However, CO2 laser ablation produces channels with a larger width and a lower aspect ratio; FFS laser ablation produces high aspect ratio channels with a V-shaped cross-section. For the same width and depth dimensions, the V-shaped channel has the smallest cross-sectional area compared to other shapes, which reduces the efficiency of microfluidic devices such as micromixers and microchannel heat sinks. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and to provide an efficient laser fabrication method and microfluidic device for high aspect ratio microfluidic channels.

[0006] The technical solution adopted in this invention is as follows: a highly efficient laser fabrication method for high aspect ratio microfluidic channels. It involves the fabrication of high aspect ratio channels on colored resin materials using near-infrared ps lasers; including the following steps: Using a multi-focus scanning method, the laser ablation is repeated and then refocused downwards. While maintaining a low channel width, a high aspect ratio microfluidic channel is created through multiple laser ablations, and the channel cross-section is U-shaped.

[0007] Preferably, the coloring resin material is black PMMA.

[0008] Preferably, after each laser ablation, the channel depth is remeasured, and the average depth of the channel is taken as the downward focusing depth for the next laser scan. The focus position is then reset within the channel so that the focus is located near the bottom of the channel.

[0009] Preferably, the near-infrared ps laser with a peak power density range of 1×10⁻⁶ is used. 9 W / cm 2 ~1×10 12 W / cm 2 Further preferred is 1×10. 10 W / cm 2 ~1×10 11 W / cm 2 .

[0010] Preferably, the near-infrared ps laser used has a single-scan energy density range of 0.5 J / mm². 2 ~50 J / mm 2 Further preferably 5 J / mm 2 ~20 J / mm 2 .

[0011] Preferably, the near-infrared ps laser pulse width used is less than 100 ps. More preferably, it is 10 ps or less.

[0012] Preferably, the laser system used has a focusing accuracy of 10μm or higher in the height direction.

[0013] A microfluidic device, the fabrication process of which includes the high aspect ratio microfluidic channel high-efficiency laser fabrication method as described above.

[0014] PS laser refers to a picosecond laser, whose pulse duration is on the picosecond scale. This invention utilizes a near-infrared PS laser to fabricate microchannels on a colored PMMA surface. A multi-focus scanning method is employed to increase the channel depth while maintaining a small microchannel width, resulting in channels with a high aspect ratio. Compared to existing technologies, this invention offers the following advantages: (1) This invention utilizes infrared ps laser and multiple focusing scanning method to prepare high aspect ratio channels on colored PMMA, which takes into account both processing efficiency and production cost.

[0015] (2) The channel cross-sectional shape after each scan is U-shaped. Compared with the V-shaped channel, the U-shaped channel has a larger channel volume and cross-sectional area under the same maximum depth-to-width ratio, which is beneficial to improving the working efficiency of microfluidic devices such as micro mixers and microchannel heat sinks. At the same time, it helps to reduce the channel length and the volume of the working unit, which is beneficial to the miniaturization and low energy consumption of microfluidic chips and devices.

[0016] (3) Compared with existing methods for preparing microchannels by laser ablation of resin materials such as PMMA, this invention can achieve greater channel depth and aspect ratio while ensuring low channel width. Currently, channels with a width of less than 100 μm prepared by this method can achieve an aspect ratio of more than 5; channels with a width of less than 200 μm can achieve an aspect ratio of more than 8. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0018] Figure 1 This is a schematic diagram of the device used in this invention; Figure 2 These are microscope images of the channel cross-section after multiple laser scanning ablation processes performed in accordance with Example 1; Figure 3 These are microscope images of the channel cross-section after multiple scans and ablation by other researchers using ultraviolet fs lasers; Figure 4 These are microscope images of the channel cross-section after multiple laser scanning ablation processes performed in accordance with Example 2; Figure 5 This is a photograph of the channel path on the surface of the micromixer prepared according to the method of Example 2; Figure 6These are photographs of the mixing experiment results of the micromixer prepared according to the method in Example 2; Figure 7 These are microscope images of the liquid mixing inside the microchannels of the micromixer prepared according to Example 2; Among them, 1-near-infrared PS laser source, 2-two-dimensional moving platform, 3-colored PMMA board, 4-first galvanometer, 5-second galvanometer, 6-laser processing head, 7-field mirror, 8-channel depth measuring device, and 9-computer. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0020] A highly efficient laser fabrication method for high aspect ratio microfluidic channels, comprising the following steps: Step 1, as follows Figure 1 As shown, the colored PMMA sheet 3 is fixed on the electrically controlled two-dimensional moving platform 2; the two-dimensional moving platform 2 is controlled to move along the two vertical directions of X and Y, which drives the colored PMMA sheet 3 on the platform to move. The computer 9 controls the movement of the laser processing head 6 and the field lens 7 in the Z direction, so that the laser beam is focused on the surface of the PMMA sheet 3.

[0021] Step 2: Set the laser parameters using computer 9, and scan the PMMA surface with the laser beam by controlling the rotation of galvanometer 4 and galvanometer 5 to complete the first laser scanning ablation.

[0022] Step 3: Use the depth measuring device 8 to measure the depth of the channel in the first laser scan, and take the average of the depths at multiple different channel positions as the ablation depth of the channel in this laser scan.

[0023] Step 4: The computer 9 controls the movement of the laser processing head 6 and the field lens 7 in the Z direction, and refocuses downwards according to the current ablation depth, so that the laser focus moves to near the bottom of the channel, and then performs a second laser scanning ablation.

[0024] Step 5: Repeat the above steps, using multiple laser scanning ablation processes until the desired high aspect ratio channel is fabricated.

[0025] The working principle of this invention is as follows: By using colored PMMA to increase the absorption rate of near-infrared lasers, microfluidic channels can be efficiently fabricated on material surfaces. With proper design of laser parameters, the desired microchannel width can be achieved. A focused scanning method is used for multiple laser ablation scans. After each scan, the channel depth is remeasured and the focus is adjusted downwards, ensuring the laser beam remains focused near the material surface during the next scan, avoiding defocusing and preventing wasted laser energy. This ensures a U-shaped channel cross-section. Because the ps laser pulse width is short, the heat-affected zone is small, and material removal mainly occurs at the bottom of the channel, the impact on channel width is minimal. This allows for the fabrication of high aspect ratio microchannels while maintaining a low channel width.

[0026] Example 1 This embodiment uses, as follows: Figure 1 The processing apparatus shown uses a YAG laser as the laser source 1, with a wavelength of 1064nm, a pulse width of 10ps, and a focused spot diameter of 20μm. A black PMMA sheet 3 with dimensions of 60mm×60mm×2mm is fixed on an electrically controlled two-dimensional moving platform 2.

[0027] The laser pulse frequency used was 1000kHz, the laser power was 0.5W, the scanning speed was 2mm / s, and the scanning was performed 4 times using a multi-focus scanning method.

[0028] The resulting cross-sectional photographs of the channel are as follows: Figure 2 As shown, the channel cross-section is U-shaped, with a channel width of 80 μm and a channel depth of 464 μm, resulting in an aspect ratio of 5.8. In contrast, a cross-sectional image of the channel after 24 hours of scanning with a UV fs laser on a transparent PMMA surface is shown below. Figure 3 As shown, the channel cross-section is V-shaped, with a channel width of 167 μm and a channel depth of 539 μm, resulting in an aspect ratio of only 3.2. This demonstrates that the method used in this invention is superior to existing methods in both processing efficiency and channel shape.

[0029] Example 2 The processing equipment and material specifications used in this embodiment are the same as those in Embodiment 1.

[0030] In this embodiment, the laser pulse frequency is 1000kHz, the laser power is 0.9W, the scanning speed is 3mm / s, and the multiple focusing scanning method is used to scan 7 times.

[0031] The resulting cross-sectional photographs of the channel are as follows: Figure 4 As shown, the channel cross-section is U-shaped, with a channel width of 156μm and a channel depth of 1312μm, resulting in a depth-to-width ratio of 8.4.

[0032] A micromixer with multiple serpentine structures was fabricated using the above process. The surface channel paths of the micromixer are as follows: Figure 5As shown, a and b are the input ports of the two liquids to be mixed, and c is the output port of the mixed liquid.

[0033] This micromixer was used to conduct experiments mixing two liquids, such as... Figure 6 As shown, liquids containing yellow and blue pigments enter through ports a and b on the back of the micro mixer, respectively. After mixing, they become green liquids and exit through port c on the back, indicating that the micro mixer is effective.

[0034] The instantaneous mixing of two liquids inside the micromixer channel is as follows: Figure 7 As shown in (I), the mixed situation after entering the first serpentine bend is as follows: Figure 7 As shown in (II). Figure 7 The results show that the two liquids exhibit a high degree of mixing upon contact, indicating that the micro-mixer has good performance.

[0035] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A highly efficient laser fabrication method for high aspect ratio microfluidic channels, characterized in that: It involves the fabrication of high aspect ratio channels on colored resin materials using near-infrared ps lasers; including the following steps: Using a multi-focus scanning method, after each laser ablation, the focus is refocused downwards. While maintaining a low channel width, a high aspect ratio microfluidic channel is created through multiple laser ablations, and the channel cross-section is U-shaped. After each laser ablation, the channel depth is remeasured, and the average channel depth is taken as the downward focusing depth for the next laser scan. The focus position is then reset within the channel so that the focus is located near the bottom of the channel.

2. The efficient laser fabrication method for high aspect ratio microfluidic channels according to claim 1, characterized in that: The coloring resin material is black PMMA.

3. The efficient laser fabrication method for high aspect ratio microfluidic channels according to claim 1, characterized in that: The near-infrared ps laser used has a peak power density range of 1×10⁻⁶. 9 W / cm 2 ~1×10 12 W / cm 2 .

4. The efficient laser fabrication method for high aspect ratio microfluidic channels according to claim 1, characterized in that: The near-infrared ps laser used has a single-scan energy density range of 0.5 J / mm². 2 ~50 J / mm 2 .

5. The efficient laser fabrication method for high aspect ratio microfluidic channels according to claim 1, characterized in that: The near-infrared ps laser pulse width used is less than 100 ps.

6. The efficient laser fabrication method for high aspect ratio microfluidic channels according to claim 1, characterized in that: The laser system used has a focusing accuracy of 10μm or higher in the height direction.

7. A microfluidic device, the fabrication process of which includes the efficient laser fabrication method for high aspect ratio microfluidic channels as described in any one of claims 1-6.

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