Wrinkled Thermo-Electric Meander-Shaped Element on a Thin Freestanding PDMS Membrane.

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.

Label-Free Physical Techniques and Methodologies for Proteins Detection in Microfluidic Biosensor Structures.

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.

From 3D Back to 2D Monolayer Stomach Organoids-on-a-Chip.

2D monolayer gastric organoids (2DMGOs)-on-a-chip have consistent structures and can live for more than a year in culture. This state-of-the-art cell physiological system in a microfluidic device provides a way to investigate biomedically relevant, stimuli-dependent cellular responses in a variety of differentiated 2DMGOs.

On-a-Chip-Based Sensitive Detection of Drug-Induced Apoptosis in Polarized Gastric Epithelial Cells.

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.

Femtosecond Laser-Based Integration of Nano-Membranes into Organ-on-a-Chip Systems.

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.

Microstructure and Properties of PZT Films with Different PbO Content-Ionic Mechanism of Built-In Fields Formation.

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.