Harrick Plasma → Applications → Life Sciences → Microfluidics →
Polycarbonate (PC) is a widely used engineering thermoplastic in microfluidics and lab-on-a-chip systems, valued for its high optical transparency, exceptional impact strength and toughness, dimensional stability, and a high glass transition temperature (Tg ≈ 145–150 °C) that allows it to withstand thermal processing and sterilization. PC is readily manufactured by injection molding, hot embossing, and CNC machining, and is also the base material for commercial track-etched membranes (PCTE) used in filtration, cell-culture inserts, and organ-on-a-chip barriers.
Compared with PDMS, PC offers greater rigidity, lower absorption of small hydrophobic molecules, and compatibility with high-throughput, mass-manufacturable production of disposable devices. As with other thermoplastics, however, the native PC surface is hydrophobic (water contact angles typically ~75–90°), which impedes capillary filling, bonding, coating adhesion, and biological interactions.
Plasma surface treatment provides a fast, controllable, and solvent-free method to overcome these limitations by introducing oxygen-containing polar functional groups and raising surface energy.
Plasma Treatment of PC Surfaces
Exposure to air or oxygen plasma generates reactive species (ions, radicals, and excited molecules) that break surface polymer chains and graft oxygen-containing groups such as hydroxyl (–OH) and carboxyl (–COOH) onto the PC surface. The practical consequences are immediate:
- Increased surface energy and wettability (reduced water contact angle)
- Improved adhesion of coatings, biomolecules, and metallizations
- Enhanced bonding to PC, PDMS, glass, and membrane layers
- Reactive –OH/–COOH handles for downstream silane and covalent chemistries
Zilio et al. demonstrated that oxygen-plasma oxidation renders a broad range of microfluidic thermoplastics, including PC, COC, and PET, markedly more hydrophilic, and that the resulting surface groups serve as anchoring sites for stable hydrophilic copolymer coatings applicable across these materials (Zilio, Biomed. Microdevices, 2014). As with all plasma-treated polymers, treated PC surfaces undergo hydrophobic recovery (“aging”) over time, so bonding, coating, or functionalization steps should be performed promptly after treatment.
Microfluidic Applications
Plasma activation is a standard first step for sealing PC microchannels and assembling multilayer devices. By creating polar surface groups, plasma enables strong, uniform bonds, often at temperatures below the bulk Tg, preserving channel geometry while avoiding the deformation associated with high-temperature thermal fusion. For PC track-etched membranes, Teng et al. fabricated multi-stacked PC membranes by plasma-enhanced thermal bonding, treating both membrane surfaces in an oxygen plasma chamber (Harrick Plasma PDC-32G) for 90 s at 18 W RF power before lamination (Teng, Biomicrofluidics, 2015).
Heterogeneous and Membrane Bonding
PC is frequently integrated with PDMS, glass, or functional membranes, where plasma supplies the –OH functionality that is the gateway to aminosilane coupling and covalent bonding. Farnese et al. developed a detailed aminosilane-mediated procedure for bonding PCTE membranes to PDMS: surfaces were oxygen-plasma activated in a Harrick Plasma Expanded cleaner for 9 s at 30 W and 500 mTorr, mated, then held on a hotplate at 95 °C for 10 min to promote bonding. The study found that surface roughness, treatment sequence, and the use of APTES strongly govern final bond strength, with optimized joints withstanding water pressures well above 700 mbar (Farnese, Int. J. Adhes. Adhes., 2021).
Paoli et al. likewise evaluated direct plasma bonding and APTES functionalization for rapid manufacturing of multilayer COP/PC organ-on-a-chip devices, reporting that low-power O₂ plasma combined with APTES functionalization (e.g., ~2–10 min low-power O₂ plasma) produced good PC bonding, whereas plasma or UV-ozone alone gave generally poor results, underscoring that plasma dose and post-plasma chemistry must be tuned together (Paoli, Sensors, 2021).
Wettability Control and Fluid Handling
The native hydrophobicity of PC impedes channel filling and fluid control. Plasma treatment raises hydrophilicity, enabling improved capillary flow, reduced bubble entrapment, and more reproducible fluid handling. Where durable wettability is required, plasma-grafted –OH groups can anchor stable hydrophilic copolymer coatings, as demonstrated for PC and other thermoplastics by Zilio et al., extending the useful lifetime of the hydrophilic surface beyond that of plasma treatment alone (Zilio, Biomed. Microdevices, 2014).
Cell-Based Microfluidics
Surface wettability strongly influences protein adsorption and cell adhesion. Mild plasma treatment of PC and COP surfaces (final contact angles in the ~19–36° range) supports cell attachment and growth comparable to commercial culture-treated ware (Paoli, Sensors, 2021). In multilayer microphysiological systems, oxygen plasma is used both to bond PC-membrane barriers and to activate PDMS layers: Achyuta et al. built a neurovascular unit-on-a-chip using a Harrick Plasma asher (O₂ plasma, 300 mTorr, 30 W, 2 min) to bond the device layers (Achyuta, Lab Chip, 2013).
Surface Functionalization & Integrated Electrodes
Plasma-generated functional groups also serve as a foundation for metallization and biosensor fabrication on PC. Kong et al. used air plasma (5 min, 18 W) to prepare polycarbonate electrophoresis chips prior to electroless gold plating of integrated microelectrodes for amperometric detection (Kong, Electrophoresis, 2006). More broadly, the reactive surface produced by plasma allows selective patterning of wettability and chemistry, enabling spatially defined coatings, biofunctionalization, and electrode integration on PC microdevices.
Polycarbonate (PC) Microfluidic Articles
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Chen Q., He Z., Liu W., et al. “Engineering Cell-Compatible Paper Chips for Cell Culturing, Drug Screening, and Mass Spectrometric Sensing.” Advanced Healthcare Materials 4, 2291–2296 (2015). doi:10.1002/adhm.201500383
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Conclusion
Across the literature, PC microfluidic workflows share a consistent pattern: activate with air or oxygen plasma, then immediately proceed to bonding, coating, or silanization before hydrophobic recovery occurs. Reported recipes range from short, low-power exposures for rapid hydrophilization and bonding (e.g., 9–90 s at 18–30 W) to longer, low-power treatments (minutes) where a higher density of functional groups is needed for robust functionalization. Because outcomes depend on plasma dose (power, pressure, gas, and time) and on the chosen downstream chemistry, parameters should be optimized for each device geometry and instrument.