In-situ transfer vat photopolymerization for transparent microfluidic device fabrication

Yang Xu,Fangjie Qi,Lu Wang,Songwei Li,Noah Malmstadt,Huachao Mao,Jingwen Gong,Yong Chen,Yizhen Zhu

doi:10.1038/s41467-022-28579-z

Yang Xu, Fangjie Qi + Show 7 more

Open Access

https://doi.org/10.1038/s41467-022-28579-z

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Abstract

While vat photopolymerization has many advantages over soft lithography in fabricating microfluidic devices, including efficiency and shape complexity, it has difficulty achieving well-controlled micrometer-sized (smaller than 100 μm) channels in the layer building direction. The considerable light penetration depth of transparent resin leads to over-curing that inevitably cures the residual resin inside flow channels, causing clogs. In this paper, a 3D printing process — in-situ transfer vat photopolymerization is reported to solve this critical over-curing issue in fabricating microfluidic devices. We demonstrate microchannels with high Z-resolution (within 10 μm level) and high accuracy (within 2 μm level) using a general method with no requirements on liquid resins such as reduced transparency nor leads to a reduced fabrication speed. Compared with all other vat photopolymerization-based techniques specialized for microfluidic channel fabrication, our universal approach is compatible with commonly used 405 nm light sources and commercial photocurable resins. The process has been verified by multifunctional devices, including 3D serpentine microfluidic channels, microfluidic valves, and particle sorting devices. This work solves a critical barrier in 3D printing microfluidic channels using the high-speed vat photopolymerization process and broadens the material options. It also significantly advances vat photopolymerization’s use in applications requiring small gaps with high accuracy in the Z-direction.

Highlights

While vat photopolymerization has many advantages over soft lithography in fabricating microfluidic devices, including efficiency and shape complexity, it has difficulty achieving well-controlled micrometer-sized channels in the layer building direction
Despite the advantages over material extrusion and material jetting in fabricating microfluidic chips, current Vat photopolymerization (VPP) technologies face a severe limitation in the Z-axis resolution that is critical for microfluidic devices
This paper presents a VPP process called In-situ Transfer VPP (IsT-VPP) to reliably produce microfluidic channels of 10 μm height without additional requirements on liquid resins such as reduced transparency (Fig. 1a)

Summary

Introduction

While vat photopolymerization has many advantages over soft lithography in fabricating microfluidic devices, including efficiency and shape complexity, it has difficulty achieving well-controlled micrometer-sized (smaller than 100 μm) channels in the layer building direction. A 3D printing process — in-situ transfer vat photopolymerization is reported to solve this critical over-curing issue in fabricating microfluidic devices. This work solves a critical barrier in 3D printing microfluidic channels using the high-speed vat photopolymerization process and broadens the material options It significantly advances vat photopolymerization’s use in applications requiring small gaps with high accuracy in the Z-direction. The second type is to decrease the light penetration depth of the used liquid resin by adding photosensitizing additives for the visible blue light source (405 nm)[35,36], or shifting the light source from visible blue light to ultraviolet (UV) light (≤385 nm)[37,38], or further adding UV absorbing dyes[8,39–41] These two kinds of methods will either result in channels >100 μm or render the printed structures colored, bringing difficulty to observe the fluidic flow when using a microscope[41]. The last type is to combine conventional manufacturing methods such as micro-molding for bulk device fabrication and nanoscale

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