Stop flow lithography in perfluoropolyether (PFPE) microfluidic channels

Abstract

5Stop Flow Lithography (SFL) is a microfluidic-based particle synthesis method for creating anisotropic multifunctional particles with applications that range from MEMs to biomedical engineering. Polydimethylsiloxane (PDMS) has been typically used to construct SFL devices as the material enables rapid prototyping of channels with complex geometries, optical transparency, and oxygen permeability. However, PDMS is not compatible with most organic solvents which limit the current range of materials 10 that can be synthesized with SFL. Here, we demonstrate that a fluorinated elastomer, called perfluoropolyether (PFPE), can be an alternative oxygen permeable elastomer for SFL microfluidic flow channels. We fabricate PFPE microfluidic devices with soft lithography and synthesize anisotropic multifunctional particles in the devices via the SFL process -this is the first demonstration of SFL with oxygen lubrication layers in a non-PDMS channel. We benchmark the SFL performance of the PFPE 15 devices by comparing them to PDMS devices. We synthesized particles in both PFPE and PDMS devices under the same SFL conditions and found the difference of particle dimensions was less than a micron. PFPE devices can greatly expand the range of precursor materials that can be processed in SFL because the fluorinated devices are chemically resistant to most organic solvents, an inaccessible class of reagents in PDMS-based devices due to swelling.

High‐Throughput Fabrication and Modular Assembly of 3D Heterogeneous Microscale Tissues

“…Furthermore, flow lithography can be divided into continuous flow lithography (CFL) and stop flow lithography (SFL) . CFL fabricated microstructures are under a continuous flow of the monomer, which limits its resolution.…”

“…CFL fabricated microstructures are under a continuous flow of the monomer, which limits its resolution. In contrast, the SFL microstructure fabrication process was performed in a stationary solution, which greatly improved the resolution . In addition, once structure fabrication process was complete, a much greater flow rate could be applied to flush away the structures.…”

“…Furthermore, flow lithography can be divided into continuous flow lithography (CFL) and stop flow lithography (SFL). [45][46][47][48][49] CFL fabricated microstructures are under a continuous flow of the monomer, which limits its resolution. In contrast, the SFL microstructure fabrication process was performed in a stationary solution, which greatly improved the resolution.…”

Flow lithography in ultraviolet-curable polydimethylsiloxane microfluidic chips

“…UV-curable PDMS as a material of microfluidic chips for flow lithography Before fabricating microfluidic chips for SFL, we first verified whether oxygen was permeable to UV-cured PDMS as reported previously. 20 When we photopolymerized the PEGDA prepolymer solution through two glass slides either with or without UV-cured PDMS ( Fig. 1(a)), the synthesized cylinders in contact with UV-cured PDMS became mobile immediately after UV exposure for 100 ms (top panels in Fig.…”

“…19 Materials that enable microfluidic devices to perform FL must satisfy two major requirements. 20 First, the materials that are in contact with the photopatternable polymers and photoinitiators ought to be permeable to oxygen, which is the most critical criterion. The oxygen molecules that permeate through the materials serve as great radical scavengers, which consequently generates thin boundary layers of photocrosslinking inhibition (a few micrometers in depth) at the contact surfaces between the materials and the photopatternable polymers.…”