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Review
. 2022 Mar 20;13(3):486.
doi: 10.3390/mi13030486.

Recent Advances in Thermoplastic Microfluidic Bonding

Kiran Giri  1 , Chia-Wen Tsao  1
Affiliations
Review

Recent Advances in Thermoplastic Microfluidic Bonding

Kiran Giri et al. Micromachines (Basel). .

Abstract

Microfluidics is a multidisciplinary technology with applications in various fields, such as biomedical, energy, chemicals and environment. Thermoplastic is one of the most prominent materials for polymer microfluidics. Properties such as good mechanical rigidity, organic solvent resistivity, acid/base resistivity, and low water absorbance make thermoplastics suitable for various microfluidic applications. However, bonding of thermoplastics has always been challenging because of a wide range of bonding methods and requirements. This review paper summarizes the current bonding processes being practiced for the fabrication of thermoplastic microfluidic devices, and provides a comparison between the different bonding strategies to assist researchers in finding appropriate bonding methods for microfluidic device assembly.

Keywords: microfluidic bonding; microfluidic chip fabrication; polymer microfabrication; thermoplastic bonding.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Development trends of PDMS and thermoplastic in microfluidics. * The publication numbers are analyzed by the Web of Science website and the data were collected until December 2021.
Figure 2
Figure 2
(A) Schematic of the thermal fusion bonding process. Reprinted with permission from ref. [30]. Copyright 2015 IOP Publishing Ltd. (B) Image of a spring-driven press device for hot embossing and thermal bonding of PMMA microfluidic chips. Reprinted with permission from ref. [31]. Copyright 2010 John Wiley and Sons. (C) Optical micrographs of PMMA microchannel in PMMA to Thermoplastic Elastomer (TPE) joint after bonding at (a) Under 5.23 MPa. (b) Under 2.61 MPa. (c) Under 0.78 MPa. (d) Under 0.52 MPa. pressure condition. Reprinted with permission from ref. [33]. Copyright 2016 Elsevier. (D) Bond strength results of the wedge test for different times of UV/ozone exposure [34].
Figure 3
Figure 3
(A) (a) Schematic diagram of UV-assisted liquid solvent bonding process. (b,c) Chemical reaction on PMMA substrates after solvent and UV treatment. Reprinted with permission from ref. [53]. Copyright 2020 American Chemical Society. (B) Bonding strength at different chemical composition of chloroform and ethanol [54]. (C) Different defects in solvent bonding and solutions. Reprinted with permission from ref. [55]. Copyright 2017 JoVE (D) Schematic of the cyclo-olefin polymer (COP)-based microfluidic device fabrication process by vapor solvent bonding [56].
Figure 4
Figure 4
(A) Chemical structure of PMMA; chemical reaction during and after H2O plasma treatment while bonding between PMMA/silicon substrates [79]. (B) Surface roughness of PMMA and silicon before and after H2O plasma treatment [79]. (C) Water contact angle measured after UV irradiation on the PMMA substrate over time. Reprinted with permission from ref. [84]. Copyright 2015 IOP Publishing Ltd.
Figure 5
Figure 5
(A) (a) Ultrasonic bonding complete setup. (b) Schematic diagram of ultrasonic bonding apparatus. Reprinted with permission from ref. [97]. Copyright 2014 IOP Publishing Ltd. (B) Self-balancing jig apparatus. Reprinted with permission from ref. [100]. Copyright 2015 Royal Society of Chemistry. (C) Ultrasonic bonding test bench. Reprinted with permission from ref. [101]. Copyright 2019 John Wiley and Sons. (D) Interfacial fusion at the two characteristic points Reprinted with permission from ref. [101]. Copyright 2019 John Wiley and Sons.
Figure 6
Figure 6
(A) Schematic of the adhesive bonding process Reprinted with permission from ref. [123]. Copyright 2016 IOP Publishing Ltd. (B) A comparison of the burst pressure for five different intermediate layers (adhesive tape, PDMS/tape, UV glue, APTES, sputtered SiO2) Reprinted with permission from ref. [124]. Copyright 2019 IOP Publishing Ltd. (C) (a) Schematic of the capillary-assisted adhesive delivery method (b–e) PMMA microfluidic devices bonded via capillarity-assisted adhesive delivery on PMMA (b) glass (c) silicon (d) and LiNbO3 (e) substrates [121]. (D) Schematic of the method for bonding PMMA and PDMS layers at room temperature using pressure-sensitive adhesive (PSA) [94].
Figure 7
Figure 7
Schematic diagram of bonding of chemically treated PDMS–thermoplastic substrates [147].
Figure 8
Figure 8
Summarization of direct and indirect bonding methods for thermoplastic microfluidics.
See this image and copyright information in PMC

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