Formation of a polymer surface with a gradient of pore size using a microfluidic chip.

Here we demonstrate the generation of polymer monolithic surfaces possessing a gradient of pore and polymer globule sizes from ~0.1 to ~0.5 µm defined by the composition of two polymerization mixtures injected into a microfluidic chip. To generate the gradient, we used a PDMS microfluidic chip with a cascade micromixer with a subsequent reaction chamber for the formation of a continuous gradient film. The micromixer has zigzag channels of 400 × 680 µm(2) cross section and six cascades. The chip was used with a reversible bonding connection, realized by curing agent coating. After polymerization in the microfluidic chip the reversible bond was opened, resulting in a 450 µm thick polymer film possessing the pore size gradient. The gradient formation in the microfluidic reaction chamber was studied using microscopic laser-induced fluorescence (µLIF) and different model fluids. Formation of linear gradients was shown using the fluids of the same density by both diffusive mixing at flow rates of 0.001 mL/min and in a convective mixing regime at flow rates of 20 mL/min. By using different density fluids, formation of a two-dimensional wedge-like gradient controlled by the density difference and orientation of the microfluidic chip was observed.

Influence of the Available Surface Area and Cell Elasticity on Bacterial Adhesion Forces on Highly Ordered Silicon Nanopillars.

Initial bacterial adhesion to solid surfaces is influenced by a multitude of different factors, e.g., roughness and stiffness, topography on the micro- and nanolevel, as well as chemical composition and wettability. Understanding the specific influences and possible interactive effects of all of these factors individually could lead to guidance on bacterial adhesion and prevention of unfavorable consequences like medically relevant biofilm formation. On this way, the aim of the present study was to identify the specific influence of the available surface area on the adhesion of clinically relevant bacterial strains with different membrane properties: Gram-positive Staphylococcus aureus and Gram-negative Aggregatibacter actinomycetemcomitans. As model surfaces, silicon nanopillar specimens with different spacings were fabricated using electron beam lithography and cryo-based reactive ion etching techniques. Characterization by scanning electron microscopy and contact angle measurement revealed almost defect-free highly ordered nanotopographies only varying in the available surface area. Bacterial adhesion forces to these specimens were quantified by means of single-cell force spectroscopy exploiting an atomic force microscope connected to a microfluidic setup (FluidFM). The nanotopographical features reduced bacterial adhesion strength by reducing the available surface area. In addition, the strain-specific interaction in detail depended on the bacterial cell's elasticity and deformability as well. Analyzed by confocal laser scanning microscopy, the obtained results on bacterial adhesion forces could be linked to the subsequent biofilm formation on the different topographies. By combining two cutting-edge technologies, it could be demonstrated that the overall bacterial adhesion strength is influenced by both the simple physical interaction with the underlying nanotopography and its available surface area as well as the deformability of the cell.

Enhancing the soft-tissue integration of dental implant abutments-in vitro study to reveal an optimized microgroove surface design to maximize spreading and alignment of human gingival fibroblasts.

Within this work, we demonstrate the influences of different microgrooved surface topographies on the alignment and spreading of human gingival fibroblast (HGF) cells and present the optimal parameters for an improved soft-tissue integration design for dental implant abutments for the first time. Microgrooves with lateral widths from 2.5 to 75 µm were fabricated by UV-lithography and wet etching on bulk Ti6Al4V ELI material. The microstructured surfaces were compared to polished and ground surfaces as current state of the art. The resulting microtopographies were analyzed using vertical scanning interferometry and scanning electron microscopy. Samples loaded with HGF cells were incubated for 8 and 72 hr and cell orientation, spreading, resulting area, and relative gene expression were analyzed. The effect of contact guidance occurred on all microstructured surfaces yet there is a clear preferable range for the lateral widths of the microgrooves between approx. 11.5 and 13.9 µm and depths between 1.6 and 2.4 µm for an abutment surface design, where cell orientation and spreading maximizes. For structures larger than 30 µm, cell orientation, spreading and even gene expression of intercellular adhesion molecule-1 and yes-associated protein decrease.

Integration of digital microfluidics with whispering-gallery mode sensors for label-free detection of biomolecules.

We present a multi-sensor chip comprising an array of whispering-gallery mode (WGM) micro-goblet lasers integrated into a digital microfluidic (DMF) system. In contrast to earlier demonstrations, the lasers are fabricated from dye-doped poly-methyl methacrylate (PMMA) at low cost using spin-coating, mask-based optical lithography, wet chemical etching, and thermal reflow techniques. Pumping and read-out of the devices is accomplished via simple free-space optics, thereby allowing large-scale sensor arrays to be addressed. We demonstrate the viability of the system by bulk refractive index-sensing and by measuring the specific binding of streptavidin to a biotinylated sensor surface. This is the first time that optical cavities are used for label-free detection of biomolecules in a DMF system. This approach can be extended to a versatile detector platform that targets a wide range of clinically relevant biomolecules.

Time-resolved NMR metabolomics of plant cells based on a microfluidic chip.

The plant secondary metabolism generates numerous compounds harbouring pharmaceutical activity. In plants, these compounds are typically formed by different and specialised cell types that have to interact constituting a metabolic process chain. This interactivity impedes biotechnological production of secondary compounds, because cell differentiation is suppressed under the conditions of a batch bio-fermenter. We present a novel strategy to address this limitation using a biomimetic approach, where we simulate the situation in a real tissue by a microfluidic chamber system, where plant cells can be integrated into a process flow. We show that walled cells of the plant model tobacco BY-2 can be successfully cultivated in this system and that physiological parameters (such as cell viability, mitotic index and division synchrony) can be preserved over several days. The microfluidic design allows to resolve dynamic changes of specific metabolites over different stages of culture development. These results serve as proof-of-principle that a microfluidic organisation of cultivated plant cells can mimic the metabolic flows in a real plant tissue.

Fabrication of polymeric microfluidic devices with tunable wetting behavior for biomedical applications.

We demonstrate the fabrication of microchannels with specific fluidic behavior due to micro- and/or nanostructures on the surfaces. With a combination of hot embossing and microthermoforming it is possible to produce microchannels with specific surface properties. These surface properties are highly dependent on the micro- and nanostructures embossed into the material. Different structure sizes and geometries where examined by contact angle measurements. Here the dependency of diameter and pitch of the structures on the contact angle is examined as well as the material impact. These results enable the fabrication of highly specific surfaces tunable to an application.