Photolithography and plasma processing of polymeric lab on chip for wetting and fouling control and cell patterning

• Lithographic processes for strippable photoresists directly on polymeric substrates.
• Plasma nanotexturing to etch, roughen, and chemically modify polymeric substrates and microfluidics.
• Fabrication of microchannel surfaces with patterns ranging from superhydrophilic to superhydrophobic.
• Enhanced cell attachment on nanotextured hydrophilic surfaces.
• On-off cell patterning by highly selective cell adhesion on the hydrophilic versus the superhydrophobic areas.

We propose a planar technology for fabrication and surface modification of disposable, polymeric, microfluidic devices, and show applications in cell patterning. By planar technology we mean lithography directly on a polymeric plate followed by plasma etching of the plate. In this context, we developed lithographic processes directly on the polymeric substrate, employing easily strippable photoresists, for which stripping is performed without attacking the polymeric substrate. We then applied oxygen plasma etching to transfer the pattern and chemically modify the polymeric substrates, followed by optional fluorocarbon plasma deposition through stencil masks, producing microfluidic channels with desired geometrical and wetting characteristics. We tested various organic photoresists such as AZ 15nXT, AZ 9260, maP-1275, a silicon containing resist Ormocomp® on an organic strippable underlayer (LOR®), as well as metal masks in order achieve high resolution (1–4 μm), plasma etch resistance, and stripability for photoresists with thickness of ∼5–20 μm (for details see Supporting information). We selected the Ormocomp® stack as the best candidate to define microfluidics with plasma etching onto PMMA, PEEK and COP substrates containing hydrophilic and superhydrophobic areas. We demonstrate significantly increased cell attachment on the plasma treated PMMA areas compared to untreated ones, and highly selective cell attachment (on–off) onto hydrophilic versus the superhydrophobic areas using a particular cell line. Such control of cell attachment and growth on plasma nanotextured surfaces can be applied to creation of microdevices aiming to cell patterning, cell isolation, as well as cell arrays.

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