Fabrication of circular microfluidic channels by combining mechanical micromilling and soft lithography

Abstract

The fabrication of microfluidic channels with complex three-dimensional (3D) geometries presents a major challenge to the field of microfluidics, because conventional lithography methods are mainly limited to rectangular cross-sections. In this paper, we demonstrate the use of mechanical micromachining to fabricate microfluidic channels with complex cross-sectional geometries. Micro-scale milling tools are first used to fabricate semi-circular patterns on planar metallic surfaces to create a master mold. The micromilled pattern is then transferred to polydimethylsiloxane (PDMS) through a two-step reverse molding process. Using these semi-circular PDMS channels, circular cross-sectioned microchannels are created by aligning and adhering two channels face-to-face. Straight and serpentine-shaped microchannels were fabricated, and the channel geometry and precision of the metallic master and PDMS molds were assessed through scanning electron microscopy and non-contact profilometry. Channel functionality was tested by perfusion of liquid through the channels. This work demonstrates that micromachining enabled soft lithography is capable of fabricating non-rectangular cross-section channels for microfluidic applications. We believe that this approach will be important for many fields from biomimetics and vascular engineering to microfabrication and microreactor technologies.

Non-photolithographic plastic-mold-based fabrication of cylindrical and multi-tiered poly(dimethylsiloxane) microchannels for biomimetic lab-on-a-chip applications

“…For example, Zhao et al 45 proposed a machining/reverse molding method to fabricate microuidic channels with non-rectangular cross sections on poly(methylmethacrylate) (PMMA) by embossing with a metal mold. Wilson et al 46 also proposed a similar concept to create microchannels with circular cross sections using a metal mold. Although high-precision micro-milling produces durable metal molds and sophisticated machining technique ensures mold fabrication in high resolution, the fabrication process takes a long time and is generally costly, which makes it inconvenient particularly when the design needs to be revised frequently.…”

Production of uniform droplets using membrane, microchannel and microfluidic emulsification devices

“…To enclose the channels, the PDMS mould is sealed to a flat surface of a glass slide or PDMS block either covalently by plasma oxydation or noncovalently by applying pressure. Cylindrical channels in PDMS can be fabricated by stereolithography (Morimoto et al, 2009), aligning and adhering two semi-circular PDMS channels face-to-face (Wilson et al, 2011), embedding a microfiber in PDMS mould before curing (Takeuchi et al, 2005) or introducing pressured air stream inside rectangular PDMS channels filled with liquid PDMS (Abdelgawad et al, 2011). PDMS is inherently hydrophobic, but can be rendered hydrophilic by oxidation of the PDMS surface (Hillborg et al, 2004), coating with inorganic materials such as silica and titania via sol-gel chemistry (Abate et al, 2008), through layer-by-layer deposition of polyelectrolytes (Bauer et al, 2010), ultraviolet graft polymerization of acrylic acid (Li et al, 2007), etc.…”

Silicones for Microfluidic Systems

“…Solid-object printing uses solid-object printers to transform CAD designs directly into masters made of a thermoplastic material. Circular channels can be fabricated in PDMS by pattern molding using templates (wires [18], micromilled masters [19] or alginic acid [20]), or by reshaping the formed rectangular channels [21,22].…”