Fabrication of a Three-Dimensional Microfluidic System from Poly(methyl methacrylate) (PMMA) Using an Intermiscibility Vacuum Bonding Technique

Abstract

In this study, the fabrication of microfluidic chips through the bonding of poly (methyl methacrylate) (PMMA) boards featuring designed patterns to create a three-dimensional sandwich structure with embedded microchannels was explored. A key focus was optimization of the interface quality of bonded PMMA pairs by adjusting the solvent, such as such as acetone, alcohol, and their mixture. Annealing was conducted below 50 °C to leverage the advantages of low-temperature bonding. Because of the differences in the chemical reactivity of PMMA toward acetone, alcohol, and their combinations, the resulting defect densities at the bonding interfaces differed significantly under low-temperature annealing conditions. To achieve the optimal sealing integrity, bonding pressures of 30 N, 40 N, and 50 N were evaluated. The interface was analyzed through microstructural examination via optical microscopy and stress measurements were determined using digital photoelasticity, while the bonding strength was assessed through tensile testing.

Keywords: PMMA bonding; digital photoelasticity analysis; intermiscibility bonding technique; microfluidic chip fabrication; solvent miscibility.

Figure 1

Transesterification chemical formula.

Figure 2

Schematic representation of chemical activation bonding in PMMA/PMMA. This diagram illustrates the step-by-step process of bonding PMMA to PMMA, highlighting the chemical radicals involved in the bonding mechanism, specifically COOR, OH⁻, and R⁺. Ref. [25] Prior to applying solvents for bonding, the bonding surfaces were mirror polished with 1 µm alumina powder to eliminate any scratches. Then, all PMMA specimens were cleaned with D.I. water.

Figure 3

Tensile test program model.

Figure 4

Illustration of microchannel conditions in PMMA Specimens under a bonding pressure of 30 N in various solvents. Optical microscopy (OM) 50× images demonstrating the effect of each bonding solvent: (a) alcohol, (b) acetone, and (c) an alcohol–acetone mixture. These images highlight the presence of bubbles at the PMMA bonding interfaces. Notably, compared with the individual solvents, the alcohol–acetone mixture resulted in a markedly reduced number of bubbles. (scalebar = 1 mm).

Figure 5

Microchannel status of PMMA specimens under a bonding pressure of 40 N in diverse solvents. Optical microscopy (OM) 50× images showing the impacts of each solvent: (a) alcohol, (b) acetone, and (c) a mixture of alcohol and acetone. Minor cracks are observable around the microchannels compared to the results obtained with a bonding pressure of 30 N (scalebar = 1 mm).

Figure 6

Microchannel conditions in PMMA specimens at a bonding pressure of 50 N in various solvents. Optical microscopy (OM) 50× images displaying the effects of (a) alcohol, (b) acetone, and (c) an alcohol–acetone mixture. Compared to the images obtained at a pressure of 30 N, these figures show an increase in the number of minor cracks and more severe damage around the microchannels (scalebar = 1 mm).

Figure 7

Tensile testing of bonded PMMA pairs and the results of measurements at a bonding pressure of 30 N. The graph shows three distinct curves corresponding to the solvents used: blue for alcohol, orange for acetone, and gray for the mixed solvent. Notably, the gray curve indicates enhanced ductility and superior rupture strength in comparison to those for the other solvents.

Figure 8

Tensile testing of bonded PMMA pairs and the results of measurements at a bonding pressure of 40 N. The graph displays three distinct curves for the solvents used: blue for alcohol, orange for acetone, and gray for the mixed solvent. Compared to the results obtained at a bonding pressure of 30 N, each curve here demonstrates not only an increase in rupture strength for all solvents but also a more pronounced deformation. Notably, the separation between the three curves is more substantial, indicating a clearer distinction in the performance of the sample in each solvent under increased bonding pressure.

Figure 9

Tensile testing of bonded PMMA pairs and the results of measurements at a bonding pressure of 50 N. This graph features three distinct curves representing the solvents used: blue for alcohol, orange for acetone, and gray for the mixed solvent. Relative to the results obtained at a bonding pressure of 40 N, each curve indicates an increased rupture strength for all solvents. Notably, the gray curve exhibits the highest rupture strength, while the blue curve, corresponding to alcohol, shows the lowest rupture strength, potentially because of the higher bubble density.