Liubov Bakhchova

Natural wrinkling of metal films on silicone substrates can appear by means of the metal sputtering process and can be described by the continuous elastic theory and non-linear wrinkling model. Here, we report the fabrication technology and behavior of thin freestanding Polydimethylsiloxane (PDMS) membranes equipped with thermo-electric meander-shaped elements. The Cr/Au wires were obtained on the silicone substrate by magnetron sputtering. We observe wrinkle formation and suppose furrows appear once PDMS returns to its initial state after the thermo-mechanical expansion during sputtering. Although the substrate thickness is usually a negligible parameter in the theory of wrinkle formation, we found that the self-assembled wrinkling architecture of the PDMS/Cr/Au varies due to the membrane thickness of 20 µm and 40 µm PDMS. We also demonstrate that the wrinkling of the meander wire affects its length, and it causes a 2.7 times higher resistance compared to a calculated value. Therefore, we investigate the influence of the PDMS mixing ratio on the thermo-electric meander-shaped elements. For the stiffer PDMS with a mixing ratio of 10:4, the resistance due to wrinkle amplitude alterations is 25% higher compared to the PDMS of ratio 10:1. Additionally, we observe and describe a thermo-mechanically induced motion behavior of the meander wires on completely freestanding PDMS membrane under applied current. These results can improve the understanding of wrinkle formation, which influences thermo-electric characteristics and may promote the integration of this technology in applications.

Zusammenfassung: Es ist von höchster wissenschaftlicher Relevanz, Biosensoren in Lab-on-Chip-Systeme zu integrieren. Die Integration der Sensoren in die Zellkultursysteme ermöglicht die direkte Messung der biologischen und physiologischen Parameter während des Zellwachstums. Es erfordert ein spezielles Design des mikrofluidischen Chips und eine Mikrostrukturierung der leitfähigen Materialien. In dieser Arbeit präsentieren wir zwei Ansätze für in-situ Messungen von physiologischen Parametern. Der erste ist eine Integration eines kommerziellen optischen Sensors für die Sauerstoffgehaltsdetektion und der zweite ist ein eigener, von uns entworfener und hergestellter transepithelialer Widerstandssensor (TEER) für Zellkonfluenzmessungen. Beide Sensoren wurden in einen flexiblen Mikrofluidik-Chip auf Basis von Polydimethylsiloxan (PDMS) integriert.

Proteins in biological fluids (blood, urine, cerebrospinal fluid) are important biomarkers of various pathological conditions. Protein biomarkers detection and quantification have been proven to be an indispensable diagnostic tool in clinical practice. There is a growing tendency towards using portable diagnostic biosensor devices for point-of-care (POC) analysis based on microfluidic technology as an alternative to conventional laboratory protein assays. In contrast to universally accepted analytical methods involving protein labeling, label-free approaches often allow the development of biosensors with minimal requirements for sample preparation by omitting expensive labelling reagents. The aim of the present work is to review the variety of physical label-free techniques of protein detection and characterization which are suitable for application in micro-fluidic structures and analyze the technological and material aspects of label-free biosensors that implement these methods. The most widely used optical and impedance spectroscopy techniques: absorption, fluorescence, surface plasmon resonance, Raman scattering, and interferometry, as well as new trends in photonics are reviewed. The challenges of materials selection, surfaces tailoring in microfluidic structures, and enhancement of the sensitivity and miniaturization of biosensor systems are discussed. The review provides an overview for current advances and future trends in microfluidics integrated technologies for label-free protein biomarkers detection and discusses existing challenges and a way towards novel solutions.

Microfluidic devices for culturing cells have been successfully utilized for biomedical applications, including drug screening. Several cell lines could be cultivated in microengineered environments with promising results, but gastric cell lines have not yet been widely used or studied. Therefore, this study focuses on establishing a polarized gastric epithelial monolayer on-a-chip and describes a general-purpose methodology applicable for bonding any porous material to PDMS through an adhesive sublayer. The fully transparent microfluidic chip consists of two microfluidic channels separated by a collagen-coated porous membrane and lined by human polarized gastric epithelial (NCI-N87) cells. We present considerations on how to ensure continuous and stable flow through the channels. The continuous flow rate was achieved using a pressure-driven pump. Media flow at a constant rate (0.5 μL/min) rapidly led the gastric epithelial cells to develop into a polarized monolayer. The barrier integrity was assessed by the FITC-dextran test. The generation of a monolayer was faster than in the static Boyden chamber. Moreover, fluorescence microscopy was used to monitor the apoptotic cell death of gastric epithelial monolayers on-a-chip in response to camptothecin, a therapeutic gastric cancer drug.

Zusammenfassung: Die Implementierung von Biosensoren in mikrofluidische Strukturen für Organ-on-a-Chip-Anwendungen ist eine vielversprechende Forschungsrichtung. Es kann Messungen der biologischen Reaktion in unmittelbarer Nähe von kultivierten In-vitro-Zellen ermöglichen. Ein zu messender Schlüsselparameter ist die Ionenkonzentration. Daher stellen wir in dieser Arbeit das Design, die Herstellung und die erste Testung eines Biosensors auf Basis eines organischen elektrochemischen Transistors (OECT) vor, der in einen Mikrofluidikkanal implementiert ist. Zur Herstellung der Elektroden und der aktiven Schicht für OECT wurden nur organische Polymere verwendet. In ersten Messungen konnte eine sehr gute Korrelation zwischen dem gemessenen und berechneten UI-Diagramm des Transistors gezeigt werden. Es wurden Messungenauigkeiten im Zusammenhang mit der Streuung von Materialeigenschaften und Fertigungstoleranzen analysiert und die Ungenauigkeit der Drainstrommessung ermittelt.

Organ-on-a-chip devices are gaining popularity in medical research due to the possibility of performing extremely complex living-body-resembling research in vitro. For this reason, there is a substantial drive in developing technologies capable of producing such structures in a simple and, at the same time, flexible manner. One of the primary challenges in producing organ-on-chip devices from a manufacturing standpoint is the prevalence of layer-by-layer bonding techniques, which result in limitations relating to the applicable materials and geometries and limited repeatability. In this work, we present an improved approach, using three dimensional (3D) laser lithography for the direct integration of a functional part—the membrane—into a closed-channel system. We show that it allows the freely choice of the geometry of the membrane and its integration into a complete organ-on-a-chip system. Considerations relating to sample preparation, the writing process, and the final preparation for operation are given. Overall, we consider that the broader application of 3D laser lithography in organ-on-a-chip fabrication is the next logical step in this field’s evolution.

Desulfurization of hydrocarbons is an important step in the processing of petroleum products, which requires an accurate and robust method for the sulfur-containing component evaluation. On the other hand, sulfur-containing heteroatomic hydrocarbon additives are harmful for people and the environment. Therefore, it is advantageous to conduct laboratory tests at low volumes to reduce doses of exposure of sulfur-containing vapors to the personnel. Microfluidics is an emerging platform that provides an advantage to operate with low volumes. The microfluidic dielectric spectroscopy approach is proposed in the current contribution as a platform for determination of the concentration of polar heteroatomic components in binary mixtures. The presence of heteroatomic components in petroleum products leads to a perceptible change in the dielectric properties of the blend. This paper shows the technological aspects for the microfluidic sensor chip design. It was successfully used to determine the concentration of thiophene (as a typical sulfur-containing hydrocarbon) in gasoline. We compare the commercially available solution with the developed microfluidic sensor. We demonstrate the developed microfluidic sensor chip that has a comparable sensitivity as a macroscopic commercial measurement cell but at the microscale. It is able to operate at 10³ times reduced volume of liquid analyte, providing stable control of the sulfur-containing additive concentration. The obtained results are intended to be applied for lab monitoring of sulfur-containing components in petroleum products.

Experimental studies were conducted on the effects of lead oxide on the microstructure and the ferroelectric properties of lead zirconate-titanate (PZT) films obtained by the method of radio frequency (RF) magnetron sputtering of a ceramic PZT target and PbO₂ powder with subsequent heat treatment. It is shown that the change in ferroelectric properties of polycrystalline PZT films is attributable to their heterophase structure with impurities of lead oxide. It is also shown that, even in the original stoichiometric PZT film, under certain conditions (temperature above 580 °C, duration greater than 70 min), impurities of lead oxide may be formed. The presence of a sublayer of lead oxide leads to a denser formation of crystallization centers of the perovskite phase, resulting in a reduction of the grain size as well as the emergence of a charge on the lower interface. The formation of the perovskite structure under high-temperature annealing is accompanied by the diffusion of lead into the surface of the film. Also shown is the effect of the lead ions segregation on the formation of the self-polarized state of thin PZT films.