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Review
. 2022 Sep 10;13(9):1503.
doi: 10.3390/mi13091503.

Bonding Strategies for Thermoplastics Applicable for Bioanalysis and Diagnostics

Kieu The Loan Trinh  1 , Duc Anh Thai  2 , Nae Yoon Lee  2
Affiliations
Review

Bonding Strategies for Thermoplastics Applicable for Bioanalysis and Diagnostics

Kieu The Loan Trinh et al. Micromachines (Basel). .

Abstract

Microfluidics is a multidisciplinary science that includes physics, chemistry, engineering, and biotechnology. Such microscale systems are receiving growing interest in applications such as analysis, diagnostics, and biomedical research. Thermoplastic polymers have emerged as one of the most attractive materials for microfluidic device fabrication owing to advantages such as being optically transparent, biocompatible, cost-effective, and mass producible. However, thermoplastic bonding is a key challenge for sealing microfluidic devices. Given the wide range of bonding methods, the appropriate bonding approach should be carefully selected depending on the thermoplastic material and functional requirements. In this review, we aim to provide a comprehensive overview of thermoplastic fabricating and bonding approaches, presenting their advantages and disadvantages, to assist in finding suitable microfluidic device bonding methods. In addition, we highlight current applications of thermoplastic microfluidics to analyses and diagnostics and introduce future perspectives on thermoplastic bonding strategies.

Keywords: microfabrication; microfluidic device; microfluidic technology; thermoplastic bonding; thermoplastic polymers.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 2
Figure 2
(a) Schematics showing the representative procedures for thermal bonding for fabricating thermoplastic devices. (b) Photographs of PET, ABS, and PC substrates bonded under the optimal heating conditions at 107, 152, and 202 °C using the thermal bonding method, respectively, the squares indicated by black dotted lines show the parts cut out using the picosecond laser to measure bonding strength. Adapted with permission from Ref. [51]. Copyright 2018, Elsevier. (c) PMMA microfluidic device with integrated metal microelectrodes bonded at 85 °C using a plasma-assisted thermal bonding method: (i) photograph of the chip with copper IDMAs, (ii) connection wire at the edge of the cover plate without cracks, (iii) copper IDMAs in the microchannel. Adapted with permission from Ref. [52]. Copyright 2009, Elsevier.
Figure 4
Figure 4
(a) Schematics showing the representative procedures for adhesive bonding using a dry adhesive film for fabricating thermoplastic microdevices. (b) Schematic illustration of the overall procedure for bonding PMMA device using PAA assisted by UV, the photograph of a clog-free PMMA microdevice including a serpentine microchannel with various channel dimensions. Adapted with permission from Ref. [77]. Copyright 2021, Elsevier. (c) Schematics showing the procedures of PMMA microdevice fabrication using an adhesive tape and press machine for bonding microdevice. Adapted with permission from Ref. [80]. Copyright 2020, Royal Society of Chemistry.
Figure 1
Figure 1
Summary of representative bonding methods (thermal bonding, solvent bonding, and adhesive bonding) and the applications of thermoplastic microfluidics in nucleic acid diagnosis and cell-based analysis.
Figure 3
Figure 3
(a) Schematics showing the procedures for solvent bonding for fabricating thermoplastic devices. (b) The overall procedure for bonding two PMMA substrates via ethanol treatment followed by UV irradiation, a chemical reaction is anticipated to take place on the surfaces of two PMMAs substrates after ethanol and UV treatment. Adapted with permission from Ref. [61]. Copyright 2013, Elsevier. (c) The overall procedure for bonding two PMMA substrates at room temperature by acetic acid under pressure. The photographs show bonded PMMA microdevice and cross-section of the microchannels after the bonding, chemical bonds are anticipated to form between two PMMA substrates after acetic acid and pressure treatment. Adapted with permission from Ref. [33]. Copyright 2019, Elsevier.
Figure 5
Figure 5
(a) Schematics showing PMMA bonding process using CuS/rGO-PEG nanocomposite and the photothermal effect. (b) Photographs of the PMMA device. (c) The synthesis process of the CuS/rGO-PEG nanocomposite [99].
Figure 6
Figure 6
(a) Schemes illustrating a sol-gel coated polycarbonate (PC) microdevice for DNA purification and amplification, results of capturing of DNA using sol-gel coating layers used for DNA purification: (i) a photo of the purification microdevice, (ii,iii) schematic showing DNA elution using PCR reagent inside the microchannel with and without BSA treated, respectively, (iv) results of the PCR performed from the on-chip purification. Adapted with permission from Ref. [106]. Copyright 2014, Elsevier. (b) Results showing successful culture of SMCs and HUVECs inside a bonded PMMA microdevice using poly(acrylic acid) as an adhesion agent, schemes illustrating a layered co-culture model of SMCs and HUVECs using a poly(methyl methacrylate) (PMMA) microdevice. Adapted with permission from Ref. [77]. Copyright 2021, Elsevier. (c) Schematic representation of the MSC spheroids formed inside a closed-microchannel fabricated using the CS–pDA hydrogel complex, optical image showing MSC spheroids formed after five days of cell culture inside the microchannel, reproduced from [76]. (d) Schemes illustrating the PMMA platform for the drug-response testing system. Adapted with permission from Ref. [112]. Copyright 2020, Royal Society of Chemistry.
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