Claudia Gärtner

Polymer microfabrication methods for microfluidic analytical applications

A growing number of microsystem technology (MST) applications, particularly in the field of microfluidics with its applications in the life sciences, have a need for novel fabrication methods which account for substrates other than silicon or glass. We present in this paper an overview of existing polymer microfabrication technologies for microfluidic applications, namely replication methods such as hot embossing, injection molding and casting, and the technologies necessary to fabricate the molding masters. In addition, techniques such as laser ablation and layering techniques are examined. Methods for bonding and dicing of polymer materials, which are necessary for complete systems, are evaluated.

Polymer based micro-reactors.

In this paper, we describe the fabrication technologies necessary for the production of polymer-based micro-fluidic devices. These technologies include hot embossing as a micro-structuring method as well as so-called back-end processes to complete the micro-devices. Applications such as capillary electrophoresis, micro-mixers and nanowell plates are presented.

Microfluidic toolbox: tools and standardization solutions for microfluidic devices for life sciences applications

After more than a decade of activities in the field of microfluidics, an increasing need for standardized modules and off-the-shelf components can be observed. In particular the compatibility with existing laboratory equipment o procedures greatly helps the acceptance of miniaturized systems, as in practice, miniaturized systems are very likely to be used in parallel with existing equipment and are not totally replacing this. In this paper we present the basic concept of a microfluidic toolbox with interchangeable components where the external dimensions are adopted from existing standards. Furthermore the fluidic interfaces were selected for compatibility to established systems.

Methods and instruments for continuous-flow PCR on a chip

PCR is the most commonly used method to identify DNA segments. Several methods have been used to miniaturize PCR and perform it in a microfluidic chip. A unique approach is the continuous-flow PCR, where the conventional thermocycling is replaced by pumping the sample through a channel which meanders over stationary temperature zones, allowing fast temperature changes in the sample due to the low thermal mass as well as a continuous production of PCR products. In this paper we present a system comprising a polymer microfluidic chip, a thermocycler unit and the protocols necessary to perform fast continuous-flow PCR including experimental results in comparison with a conventional PCR system.

Microfluidics and the Life Sciences

The field of microfluidics, often also referred to as “Lab-on-a-Chip” has made significant progress in the last 15 years and is an essential tool in the development of new products and protocols in the life sciences. This article provides a broad overview on the developments on the academic as well as the commercial side. Fabrication technologies for polymer-based devices are presented and a strategy for the development of complex integrated devices is discussed, together with an example on the use of these devices in pathogen detection.

Portable CE system with contactless conductivity detection in an injection molded polymer chip for on-site food analysis

We present a compact portable chip-based capillary electrophoresis system that employs capacitively coupled contactless conductivity detection (C4D) operating at 4 MHz as an alternative detection method compared to the commonly used optical detection employing laser-induced fluorescence. The disposable chip for this system is fabricated out of PMMA using injection molding; the electrodes are screen-printed or thin-film electrodes. The system allows the measurement of small ions like Li, Na, K typically present in foodstuff like milk and mineral water as well as acids in wine.

Hybrid microfluidic systems: combining a polymer microfluidic toolbox with biosensors

In this paper we present polymer based microfluidic chips which contain functional elements (electrodes, biosensors) made out of a different material (metals, silicon, organic semiconductors). These hybrid microfluidic devices allow the integration of additional functionality other than the simple manipulation of liquids in the chip and have been developed as a reaction to the increasing requirement for functional integration in microfluidics.

A lab-on-a-chip system for the development of complex assays using modular microfluidic components

For complex biological or diagnostic assays, the development of an integrated microfluidic device can be difficult and error-prone. For this reason, a modular approach, using individual microfluidic functional modules for the different process steps, can be advantageous. However often the interconnection of the modules proves to be tedious and the peripheral instrumentation to drive the various modules is cumbersome and of large size. For this reason, we have developed an integrated instrument platform which has generic functionalities such as valves and pumps, heating zones for continuous-flow PCR, moveable magnets for bead-based assays and an optical detection unit build into the instrument. The instrument holds a titerplate-sized carrier in which up to four microscopy-slide sized microfluidic modules can be clipped in. This allows for developing and optimizing individual assay steps without the need to modify the instrument or generate a completely new microfluidic cartridge. As a proof-of-concept, the automated sample processing of liquor or blood culture in microfluidic structures for detection of currently occuring Neisseria meningitidis strains was carried out. This assay involves the extraction of bacterial DNA, the fluorescent labeling, amplification using PCR as well as the hybridization of the DNA molecules in three-dimensional capture sites spotted into a microchannel. To define the assay sensitivity, chip modules were tested with bacteria spiked samples of different origins and results were controlled by conventional techniques. For liquor or blood culture, the presence of 200 bacteria was detected within 1 hour.

An integrative microfluidically supported in vitro model of an endothelial barrier combined with cortical spheroids simulates effects of neuroinflammation in neocortex development

The development of therapeutic substances to treat diseases of the central nervous system is hampered by the tightness and selectivity of the blood-brain barrier. Moreover, testing of potential drugs is time-consuming and cost-intensive. Here, we established a new microfluidically supported, biochip-based model of the brain endothelial barrier in combination with brain cortical spheroids suitable to detect effects of neuroinflammation upon disruption of the endothelial layer in response to inflammatory signals. Unilateral perfusion of the endothelial cell layer with a cytokine mix comprising tumor necrosis factor, IL-1β, IFNγ, and lipopolysaccharide resulted in a loss of endothelial von Willebrand factor and VE-cadherin expression accompanied with an increased leakage of the endothelial layer and diminished endothelial cell viability. In addition, cytokine treatment caused a loss of neocortex differentiation markers Tbr1, Tbr2, and Pax6 in the cortical spheroids concomitant with reduced cell viability and spheroid integrity. From these observations, we conclude that our endothelial barrier/cortex model is suitable to specifically reflect cytokine-induced effects on barrier integrity and to uncover damage and impairment of cortical tissue development and viability. With all its limitations, the model represents a novel tool to study cross-communication between the brain endothelial barrier and underlying cortical tissue that can be utilized for toxicity and drug screening studies focusing on inflammation and neocortex formation.

A sample-in result-out lab-on-a-chip device: from prototype to mass fabrication

In this paper we demonstrate the development of an integrated lab-on-a-chip system for the point-of-care diagnostics of Coeliac disease. A two-step approach is used, using two different microfluidic chips with identical footprint and functional landscape, one for the analysis of the genetic predisposition using human leukocyte antigen typing, the second for a serology assay. Emphasis has been put on using a seamless technology path from prototyping to final device manufacture in order to allow an upscaling of production volumes without a chance in production technology. Therefore, injection molding has been extensively used, however using standard formats allowing the use of family tools in order to reduce the cost of manufacturing.