Sample transport on microscale

Surface modification of PDMS

Polymer based autonomous capillary structures could be substantial brickstones of cheap, simple microfluidic systems managing sample transport in Lab-on-a-Chip applications. Our recent achievements in fabrication polymer based autonomous capillary systems are presented. The fluid conducting behaviour of originally hydrophobic polydimethylsiloxane (PDMS) capillary channels can be systematically controlled by surface assembling of embedded amphiphillic molecules.

In-situ modification of originally hydrophobic polymer surfaces by local plasma enhanced oxidation and its application in electrically controlled fluid capillary systems are demonstrated. A microfabricated coplanar dielectric barrier discharge (DBD) plasma source was developed, integrated and applied to modify in-situ the surface properties of polydimethylsiloxane (PDMS) capillary channels.

DBD microplasma in microfluidic channels

This work is intended to characterize the fluid conducting behaviour of microcapillary systems containing various 3D microstructures and surface modifying molecular layers. The microchannels are patterned by secondary structures mimicking the natural water-conducting tissue (xylem) of dry-habitat plants.

Mixing on microscale

Stochastic mixing in microfluidics

The present work is intended to describe the design aspects of microfluidic structures applicable to dilute and transport analyte solutions to the sensing areas of biosensors. The behaviours of different chaotic mixer structures were analyzed numerically and experimentally to determine their efficiency.

Particle Mixing by Chaotic Advection

The present work is intended to describe the functional aspects and working principles of special microfluidic structures applicable to dilute and transport real biologic sample (e.g. whole blood) to subsequent functional parts of the sample preparation system or the sensing areas of biosensors. According to the preliminary expectations the fluidic layouts consisted of different advanced chaotic mixer systems and fabricated in PDMS polymer. The performance of the fluidic structures was characterized by experimental methods and numerical modeling. The particle transport in the different mixer structures was visualized and the results were explained by simulation of the particle motion.

DBD microplasma in microfluidic channels

Ongoing: Concentration gradient generation for cell chemotaxis studies

Separation on microscale

Blood plasma separation based on Zweifach-Fung effect

When aiming a complete microfluidic analysis system for human blood tests the blood plasma separation should be preferably also integrated in the device. The sensitivity of the analysis is significantly affected by the sample quality, so in this work the efficiency of the Zweifach-Fung effect based microfluidic separation systems was characterized.

Series of different geometric singularities (extractions) were characterized regarding their
enhancement of blood plasma separation performance of cascade Zweifach-Fung bifurcations. Flow
fields and particle trajectories evolving in geometric perturbations were studied by Computational
Fluid Dynamics (CFD) simulation and the model was verified experimentally also. The development
of cell-depleted layer near the channel walls due to lift and shear forces were analyzed considering the
applied flow rates and number of singularities. An optimal flow rate was defined to avoid cell
recirculation in the extractions to be deteriorating purity of the proposed plasma. The effect of the
developing cell-depleted layer thickness on the plasma purity was studied to prove the improvement of
the separation technique due to the integrated inertial subsystems.

Particle trajectories in geometric singularities

Simulation and Experimental Validation of Particle Trapping in Microfluidic Magnetic Separation (MMS) System

Microfluidic magnetic particle trapping system was modelled, designed and manufactured to characterise and enhance the separation efficiency during sample preparation and analysis. Coupled multiphysics model of the evolving magnetic field, fluid dynamics and particle trajectories was implemented in COMSOL Multiphysics. The movement and entrapment of magnetic beads in the microfluidic magnetic separation (MMS) system were analysed and the spatial distribution of the trapped magnetic particles were compared to experimental results. For functional validation the microfluidic system was manufactured in polydimethylsiloxane (PDMS) by soft lithography technique, and special Fe-Ni patterns were deposited to locally amplify the magnetic field. The measured flow and particle motion characteristics were in good correlation with the simulations.