J. Mikael Karlsson

Inertial microfluidics in parallel channels for high-throughput applications

Passive particle focusing based on inertial microfluidics was recently introduced as a high-throughput alternative to active focusing methods that require an external force-field to manipulate particles. In this study, we introduce inertial microfluidics in flows through straight, multiple parallel channels. The scalable, single inlet and two outlet, parallel channel system is enabled by a novel, high-density 3D PDMS microchannel manufacturing technology, mediated via a targeted inhibition of PDMS polymerization. Using single channels, we first demonstrate how randomly distributed particles can be focused into the centre position of the channel in flows through low aspect ratio channels and can be effectively fractionated. As a proof of principle, continuous focusing and filtration of 10 μm particles from a suspension mixture using 4- and 16-parallel-channel devices with a single inlet and two outlets are demonstrated. A filtration efficiency of 95-97% was achieved at throughputs several orders of magnitude higher than previously shown for flows through straight channels. The scalable and low-footprint focusing device requiring neither external force fields nor mechanical parts to operate is readily applicable for high-throughput focusing and filtration applications as a stand-alone device or integrated with lab-on-a-chip systems.

Active liquid degassing in microfluidic systems.

We present a method for efficient air bubble removal in microfluidic applications. Air bubbles are extracted from a liquid chamber into a vacuum chamber through a semipermeable membrane, consisting of PDMS coated with amorphous Teflon(®) AF 1600. Whereas air is efficiently extracted through the membrane, water loss is greatly reduced by the Teflon even at elevated temperatures. We present the water loss and permeability change with the amount of added Teflon AF to the membrane. Also, we demonstrate bubble-free, multiplex DNA amplification using PCR in a PDMS microfluidic device.

Fabrication and transfer of fragile 3D PDMS microstructures

We present a method for PDMS microfabrication of fragile membranes and 3D fluidic networks, using a surface modified water-dissolvable release material, poly(vinyl alcohol), as a tool for handling, ...

Low gas permeable and non-absorbent rubbery OSTE+ for pneumatic microvalves

In this paper we introduce a new polymer for use in microfluidic applications, based on the off-stoichiometric thiol-ene-epoxy (OSTE+) polymer system, but with rubbery properties. We characterize and benchmark the new polymer against PDMS. We demonstrate that Rubbery OSTE+: has more than 90% lower permeability to gases compared to PDMS, has little to no absorption of dissolved molecules, can be layer bonded in room temperature without the need for adhesives or plasma treatment, can be structured by standard micro-molding manufacturing, and shows similar performance as PDMS for pneumatic microvalves, albeit allowing handling of larger pressure.

Low-stress transfer bonding using floatation

A novel method for transferring thin, large-area polymer layers from a mould and its subsequent bonding to a destination substrate is presented here. Buoyancy is used for transfer via floatation to ...