A method for producing a PMMA-based microfluidic chip and a microfluidic chip produced by this method

Abstract

The invention relates to a method for producing a polymethyl methacrylate (PMMA)-based microfluidic chip and a microfluidic chip produced by this method. In the method of the invention, surface roughness and opacity issues caused by laser cutting on the PMMA surface during microchannel production are resolved through the use of pure acetone.

Description

[0001] DESCRIPTION

[0002] A METHOD FOR PRODUCING A PMMA-BASED MICROFLUIDIC CHIP AND A MICROFLUIDIC CHIP PRODUCED BY THIS METHOD

[0003] Technical Field of the Invention

[0004] The invention relates to a method for producing a polymethyl methacrylate (PMMA)-based microfluidic chip and a microfluidic chip produced by this method. In the method of the invention, surface roughness and opacity issues caused by laser cutting on the PMMA surface during microchannel production are resolved through the use of pure acetone.

[0005] State of the Art

[0006] With the rapid acceleration of technological and scientific advancements, interdisciplinary approaches have increasingly been employed to develop novel systems each year. One of these is microfluidic chip systems. Microfluidic systems, whose foundations were laid in the 1960s and which began to find applications following the development of gas chromatography at Stanford University in 1979 [1], essentially refer to the behavior and control of fluids in a very small volume and size, below millimetric dimensions, dominated by surface forces. Microfluidic chips are devices that enable the manipulation and control of liquids in very small volumes. Microfluidic systems enable the miniaturization of biological processes by reducing reagent volumes [2], shortening reaction times with high efficiency [3-4], minimizing external intervention [5], being applicable to different protocols with many different modifications [6], and integrating all experimental steps in a single device, enabling multiple processes to be performed in parallel [7], Moreover, microfluidic systems allow for the investigation of the physiology of even a single cell, thereby enabling the understanding of heterogeneity within population. As a result, much more information can be accessed in a more controlled and faster way than is possible with existing techniques [8].

[0007] In recent years, microfluidic technologies have emerged as a powerful technology for biomedical research and clinical applications. However, the need for clean room facilities and advanced microfabrication equipment continues to hinder innovation in microfluidics. While the advent of soft lithography has encouraged the proliferation of microfluidic technologies, the most common method, the polydimethylsiloxane (PDMS) replication mold, still requires a photomask and microfabricated mold, which limits the capacity for iterative design optimization and poses an entry barrier for research groups interested in exploring microfluidic tools [9]. Therefore, in an effort to make microfluidics research more accessible and cost-effective, thermoplastic materials such as polymethyl methacrylate (PMMA), cyclic olefin copolymer (COC) or polycarbonate (PC) are gaining interest as alternatives to conventional materials. These materials offer superior mechanical properties compared to PDMS and are easier to manufacture than conventional materials such as silicon (Si) or glass. They are produced using a variety of techniques, including microinjection molding, hot embossing, casting, reactive ion etching and mechanical (milling) or laser micromachining

[0010] , making them easy to standardize and use, and suitable for industrial production.

[0008] The PMMA-based microfluidics are widely used in various applications in biological and chemical fields. During the production process of the PMMA-based microfluidics, bonding the substrate to a cover plate is typically required to seal the microchannel. The bonding is also done in two ways: permanent or reversible, as in some application scenarios the reversible bonding is required to retrieve samples within the channel or to reuse the chip

[0011] , In the state of the art, carbon dioxide laser ablation is considered to be the most attractive and effective method for the production of a polymer-based microfluidic device due to its low cost and operational flexibility. However, exposure to the laser beam can lead to melting of the material, increased surface roughness, and degradation of optical properties

[0012] , This eliminates the advantages of PMMA. The potential risks associated with the use of solutions that are harmful to human health in PMMA surface treatment and bonding should be considered, especially the hazards of chemicals such as chloroform gas used in these processes

[0013] . Furthermore, PMMA bonding techniques have challenges such as limited bond strength and the inability to provide a completely airtight joint

[0014] , This increases the likelihood of unwanted leaks, especially in sensitive applications such as microfluidic chips

[0015] .

[0009] In the state of the art, the patent application CN109772483A relates to a microfluidic chip, in particular a PMMA microfluidic chip solvent bonding process. The document discloses that dichloromethane, acetone, isopropanol or any two organic solutions prepared according to a specific ratio or any of three organic solutions prepared according to a specific ratio can be used as solvent. It is stated that the solvent bonding method described in the referenced study was realized in a short time with low cost and high bond strength. Moreover, the chip’s substrate and cover layer are hardened at 50-70°C for 1-3 hours to relieve internal stress. However, there is no solution to the surface roughness and opacity issues of the channels. In addition, the document requires annealing, so the bonding process takes a long time in the mentioned method.

[0010] The limitations and inadequacies of the solutions in the state of the art, the high cost and long production time of PMMA-based microchips, the use of harmful chemicals in the PMMA surface treatment and bonding process, as well as the limited bonding strength and inability to provide a completely airtight joint, resulting in undesirable leakage of microchips, necessitated an improvement in the production method of PMMA-based microchips.

[0011] Brief Description and Objects of the Invention

[0012] The invention describes a method for producing a polymethyl methacrylate (PMMA)-based microfluidic chip and a microfluidic chip produced by this method. In the method of the invention, surface roughness and opacity issues caused by laser cutting on the PMMA surface during microchannel production are resolved through the use of pure acetone.

[0013] The object of the invention is to eliminate surface roughness and opacity problems on the PMMA surface caused by laser cutting during the production of the microfluidic chips. In this invention, the use of pure acetone facilitates a self-healing mechanism on the PMMA surface, effectively reduces the roughness generated by laser processing, and simultaneously enhances the optical properties of the material.

[0014] Another object of the invention is to enable the production of a microfluidic chip with strong bonding characteristics, at low cost and within a short period of time. By utilizing acetone, a bonding strength equivalent to the intrinsic tensile strength of PMMA is achieved. Furthermore, in the invention, the bonding process requires only the use of clips, which reduces production costs and simplifies the production by eliminating the need for additional equipment. Description of the Figures

[0015] Figure 1.

[0016] Effect of acetone concentration (50-100%) and thermal treatment time at 100°C (5-15 minutes) on bonding strength.

[0017] Figure 2.

[0018] Effects of surface treatment on open microfluidic channels. (A) Micrographs of open microfluidic channels treated with acetone at room temperature or at 50°C for 3 or 5 minutes, followed by thermal treatment at 100°C for 5, 10 or 15 minutes and (B) SEM images: after engraving with laser cutter, i) untreated channel, ii) channel treated only with heat at 100°C for 15 minutes, iii) channel treated only with acetone at 50°C for 3 minutes, iv) channel treated with acetone at 50°C for 3 minutes followed by thermal treatment at 100°C for 15 minutes.

[0019] Detailed Description of the Invention

[0020] The invention relates to a method for producing a polymethyl methacrylate (PMMA)-based microfluidic chip and a microfluidic chip produced by this method.

[0021] A method for producing a PMMA-based microfluidic chip of the invention comprises the following process steps:

[0022] i. covering both the front and back surfaces of a PMMA substrate with a protective tape to prevent potential damages caused by acetone,

[0023] ii. processing the designed channel patterns onto the tapes using a laser cutter, iii. removing the tapes with the channels and cleaning any adhesive residues from the tape with isopropanol,

[0024] iv. engraving the PMMA components with the desired channel designs using a laser cutter,

[0025] v. holding the engraved PMMA parts with pure acetone and then in an oven, vi. removing the permanent tapes after surface treatment and cleaning the surfaces with an isopropanol solution,

[0026] vii. assembling the PMMA parts in an overlapping manner and securing them with clamps to apply pressure at the bonding interface, viii. spreading pure acetone between the overlapping surfaces of the assembled PMMA parts and holding PMMA at 100°C, the glass transition temperature, ix. removing the clamps after the microchip has cooled.

[0027] In one embodiment of the invention, a method for producing a PMMA-based microfluidic chip of the invention comprises the following process steps:

[0028] i. covering both the front and back surfaces of a PMMA substrate with a protective tape to prevent potential damages caused by acetone,

[0029] ii. processing the designed channel patterns onto the tapes using a laser cutter, iii. removing the tapes with the channels and cleaning any adhesive residues from the tape with 1-10% isopropanol,

[0030] iv. engraving the PMMA components with the desired channel designs using a laser cutter,

[0031] v. holding the engraved PMMA parts with pure acetone at 25-56°C for 1-5 minutes and then in an oven at 80-120°C for 1-20 minutes,

[0032] vi. removing the permanent tapes after surface treatment and cleaning the surfaces with 10% isopropanol solution,

[0033] vii. assembling the PMMA parts in an overlapping manner and securing them with clamps to apply pressure at the bonding interface,

[0034] viii. spreading pure acetone between the overlapping surfaces of the assembled PMMA parts and holding PMMA at 100-120°C, the glass transition temperature, for 1-10 minutes,

[0035] ix. removing the clamps after the microchip has cooled.

[0036] In another embodiment of the invention, a method for producing a PMMA-based microfluidic chip of the invention comprises the following process steps:

[0037] i. covering both the front and back surfaces of a PMMA substrate with a protective tape to prevent potential damages caused by acetone,

[0038] ii. processing the designed channel patterns onto the tapes using a laser cutter, iii. removing the tapes with the channels and cleaning any adhesive residues from the tape with 10% isopropanol,

[0039] iv. engraving PMMA components with the desired channel designs (linear, branching, zigzag and circular channels) using a laser cutter, v. holding the engraved PMMA parts with pure acetone at 50°C for 3 minutes and then in an oven at 100°C for 15 minutes,

[0040] vi. removing the permanent tapes after surface treatment and cleaning the surfaces with 10% isopropanol solution,

[0041] vii. assembling the PMMA parts in an overlapping manner and securing them with clamps to apply pressure at the bonding interface,

[0042] viii. spreading pure acetone between the overlapping surfaces of the assembled PMMA parts and holding PMMA at 100°C, the glass transition temperature, for 5 minutes,

[0043] ix. removing the clamps after the microchip has cooled.

[0044] In the invention, to prevent potential damages caused by acetone, both the front and back surfaces of the PMMA substrate are covered with protective tape. Using a laser cutter, the designed channel patterns are engraved on the tapes, then the tapes with the channels are removed and the adhesive residues from the tape are cleaned with 1%-10% isopropanol. The PMMA components are then engraved with the desired channel designs using a laser cutter. Then, the engraved PMMA parts are held with acetone at 25-56°C for 1-5 minutes and subsequently in an oven at 80-120°C for 1-20 minutes. Notably, elevated temperatures enhance the effectiveness of acetone on PMMA surfaces. The unprotected PMMA surfaces exposed to acetone soften, thereby smoothing the surface roughness. After acetone treatment, when exposed to 100-120°C (glass transition temperature of PMMA), the material softened on the surface spreads homogeneously on the channel surface, which enhances surface refinement. Once the surface treatment is complete, the permanent tapes are removed, and the surfaces are rinsed with 1%-10% isopropanol solution. The PMMA parts are then assembled in an overlapping manner and secured with clamps to apply pressure at the bonding interface. By capillary action, pure acetone solution is spread over the bonding area. The assembled PMMA parts are then held at 100-120°C, glass transition temperature of PMMA, for 1-10 minutes. This process leverages acetone’s ability to dissolve PMMA surfaces, forming a strong bond under mild pressure and elevated temperatures. After cooling, the clips are removed, and the microfluidic chip production process is completed.

[0045] To evaluate the bonding strength of the bonded PMMA parts, a tensile test was conducted at a rate of 0.5 mm / min. The effect of processing conditions on bonding was investigated by applying acetone treatments at various concentrations (50-100%) and performing thermal treatment at 100°C for different durations (Figure 1). We observed that, for acetone concentrations up to 70%, increasing the thermal treatment time resulted in higher bonding strength. Beyond this concentration, the average bonding strength remained constant for different thermal treatment durations. Moreover, even at low acetone concentrations (below 70%), a thermal treatment duration of 15 minutes was sufficient to achieve high bonding strength (>30 MPa). Within this context, the invention enables the achievement of bonding strengths on the order of PMMA’s tensile strength (>30 MPa).

[0046] The engraved channels were immersed in acetone at room temperature (25°C) or near its boiling point (50°C) for 3-5 minutes, followed by thermal treatment at 100°C for 5-15 minutes. As shown in Figure 2A, acetone at room temperature had no effect on surface improvement. In contrast, treatment with acetone at 50°C for 3-5 minutes followed by thermal processing at 100°C for 15 minutes significantly improved surface roughness. However, prolonged exposure to acetone (>5 minutes) may damage the PMMA surface. Therefore, the optimal protocol was determined to be acetone treatment at 50°C for 3 minutes, followed by thermal processing at 100°C for 15 minutes for effective surface enhancement. This procedure eliminates surface roughness and enhances the optical clarity of the channels more effectively than without any treatment, with acetone treatment only or with thermal treatment only (Figure 2B). It was observed that acetone initiates the dissolution and smoothing of the PMMA, and when combined with thermal treatment, the PMMA softens, facilitating the filling of grooves and reducing the roughness caused by engraving. Conversely, when thermal treatment is applied alone, the porous structure was reduced compared to untreated PMMA, but no significant effect on surface roughness was observed.

[0047] Industrial Applicability of the Invention

[0048] The invention relates to a method for producing a polymethyl methacrylate (PMMA)-based microfluidic chip and a microfluidic chip produced by this method, and is industrially applicable. The invention is not limited to the above descriptions, and a person skilled in the art can easily come up with different embodiments of the invention. These should be considered within the scope of protection claimed in the appended claims. REFERENCES

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[0051] [3] Shen S., Tian C., Li T., Xu J., Chen S. W., Tu Q., Wang, J. et al., “Spiral microchannel with ordered micro-obstacles for continuous and highly-efficient particle separation” Lab on a Chip, 17:21 3578-3591, (2017).

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Claims

CLAIMS1. A method for producing a PMMA (polymethyl methacrylate)-based microfluidic chip, characterized in that it comprises the following process steps:i. covering both the front and back surfaces of a PMMA substrate with a protective tape to prevent potential damages caused by acetone, ii. processing the designed channel patterns onto the tapes using a laser cutter,iii. removing the tapes with the channels and cleaning any adhesive residues from the tape with isopropanol,iv. engraving the PMMA components with the desired channel designs using a laser cutter,v. holding the engraved PMMA parts with pure acetone and then in an oven,vi. removing the permanent tapes after surface treatment and cleaning the surfaces with an isopropanol solution,vii. assembling the PMMA parts in an overlapping manner and securing them with clips to apply pressure at the bonding interface,viii. spreading pure acetone between the overlapping surfaces of the assembled PMMA parts and holding PMMA at 100°C, the glass transition temperature,ix. removing the clips after the microchip has cooled.

2. A method according to claim 1 , characterized in that it comprises the following process steps:i. covering both the front and back surfaces of a PMMA substrate with a protective tape to prevent potential damages caused by acetone, ii. processing the designed channel patterns onto the tapes using a laser cutter,iii. removing the tapes with the channels and cleaning any adhesive residues from the tape with 1-10% isopropanol,iv. engraving the PMMA components with the desired channel designs using a laser cutter,v. holding the engraved PMMA parts with pure acetone at 25-56°C for 1-5 minutes and then in an oven at 80-120°C for 1-20 minutes,vi. removing the permanent tapes after surface treatment and cleaning the surfaces with 10% isopropanol solution,vii. assembling the PMMA parts in an overlapping manner and securing them with clamps to apply pressure at the bonding interface,viii. spreading pure acetone between the overlapping surfaces of the assembled PMMA parts and holding PMMA at 100-120°C, the glass transition temperature, for 1-10 minutes,ix. removing the clamps after the microchip has cooled.

3. A method according to claim 2, characterized in that it comprises the following process steps:i. covering both the front and back surfaces of a PMMA substrate with a protective tape to prevent potential damages caused by acetone, ii. processing the designed channel patterns onto the tapes using a laser cutter,iii. removing the tapes with the channels and cleaning any adhesive residues from the tape with 10% isopropanol,iv. engraving the PMMA components with the desired channel designs using a laser cutter,v. holding the engraved PMMA parts with pure acetone at 50°C for 3 minutes and then in an oven at 100°C for 15 minutes,vi. removing the permanent tapes after surface treatment and cleaning the surfaces with 10% isopropanol solution,vii. assembling the PMMA parts in an overlapping manner and securing them with clamps to apply pressure at the bonding interface,viii. spreading pure acetone between the overlapping surfaces of the assembled PMMA parts and holding PMMA at 100°C, the glass transition temperature, for 5 minutes,ix. removing the clamps after the microchip has cooled.

4. A microfluidic chip produced by the method according to any one of claims 1 -3.

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