The Fabrication and Bonding of Thermoplastic Microfluidics: A Review

Abstract

Various fields within biomedical engineering have been afforded rapid scientific advancement through the incorporation of microfluidics. As literature surrounding biological systems become more comprehensive and many microfluidic platforms show potential for commercialization, the development of representative fluidic systems has become more intricate. This has brought increased scrutiny of the material properties of microfluidic substrates. Thermoplastics have been highlighted as a promising material, given their material adaptability and commercial compatibility. This review provides a comprehensive discussion surrounding recent developments pertaining to thermoplastic microfluidic device fabrication. Existing and emerging approaches related to both microchannel fabrication and device assembly are highlighted, with consideration toward how specific approaches induce physical and/or chemical properties that are optimally suited for relevant real-world applications.

Keywords: bonding strategies; fabrication strategies; microfluidics; thermoplastics.

Figure 1

(a) Fabrication process of PC/TPE-hybrid microchannels via hot embossing method. Reproduced with permission [31] 2022, MDPI. (b) (i–iii) Incorporation of ultrasonic vibration in hot embossing process to form PC microchannels (iv–vi) ultrasonic welding of PC layers. Reproduced with permission [33], 2022, Springer. (c) Injection mold design for fabrication of PMMA microfluidic devices. (i) Injection molding parts, (ii) Mold assembly, (iii) Cooling system, (iv) Final product. Reproduced with permission [45] 2022, Springer. (d) SEM images of nanocones made of COC through injection molding techniques. Reproduced with permission [48] 2022, ACS. (e) Silicon mold with photoresist patterns and plexiglass frame. The setup was used to cast PDMS master molds for hot embossing COC and creating microchannels. Reproduced with permission [26] 2022, Elsevier.

Figure 2

(a) (i) SEM image of PMMA microchannel’s cross-section fabricated by CO₂ laser ablation (ii) Optical image of PMMA microchannel’s cross-sectional fabricated by micro-milling technique. Reproduced with permission [70] 2022, Springer. (b) Optical images of PMMA and POM microchannels’ cross-sections fabricated by laser ablation. Reproduced with permission [72] 2022, Springer. (c) Fabrication of PEG layers containing microchannels or microwells features and bonding to flat PET or PEG layers through UV polymerization technique. Reproduced with permission [97] 2022, Royal Society of Chemistry.

Figure 3

(a) Fabrication process of laser cut PMMA microchannels (pneumatic channels in gray and a fluidic channel in blue) sandwiching a TPE film. The device was bonded via UV assisted thermal fusion bonding. Reproduced with permission [30] 2022, MDPI. (b) Solvent bonding of PC microfluidic channels. FOTS molecules are entangled with the polymer chains and hydrolysed. Reproduced with permission [25] 2022, Elsevier. (c) Retention grooves embedded in microfluidic design to promote the solving bonding process in a PMMA-based microfluidic device. Reproduced with permission [66] 2022, Elsevier. (d) Chemical bonding of thermoplastic layers via iCVD polymerization of poly(glycidyl methacrylate) (PGMA) and poly(4-aminostyrene) (PAS). (i–iv) The induced chemical groups on the surface at each step. Reproduced with permission [115] 2022, ACS publications.

Figure 4

(a) Ultrasonic welding apparatus. In the microchannel design, the laser ablated grooves and bulges can create strong bonding and secure the melted polymer during the ultrasonic welding. Reproduced with permission [130] 2022, Elsevier. (b) Bonding PMMA layers through UV-curable PAA adhesive layer. Reproduced with permission [94] 2022, Elsevier. (c) Thermal bonding of PMMA layers using an optically clear adhesive (OCA) film. Reproduced with permission [63] 2022, Springer.