Organ-on-Chips (OOCs) are micro-fabricated devices which are used to culture cells in order to mimic functional units of human organs. The devices are designed to simulate the physiological environment of tissues in vivo. Cells in some types of OOCs can be stimulated in situ by electrical and/or mechanical actuators. These actuations can mimic physiological conditions in real tissue and may include fluid or air flow, or cyclic stretch and strain as they occur in the lung and heart. These conditions similarly affect cultured cells and may influence their ability to respond appropriately to physiological or pathological stimuli. To date, most focus has been on devices specifically designed to culture just one functional unit of a specific organ: lung alveoli, kidney nephrons or blood vessels, for example. In contrast, the modular Cytostretch membrane platform described here allows OOCs to be customized to different OOC applications. The platform utilizes silicon-based micro-fabrication techniques that allow low-cost, high-volume manufacturing. We describe the platform concept and its modules developed to date. Membrane variants include membranes with (i) through-membrane pores that allow biological signaling molecules to pass between two different tissue compartments; (ii) a stretchable micro-electrode array for electrical monitoring and stimulation; (iii) micro-patterning to promote cell alignment; and (iv) strain gauges to measure changes in substrate stress. This paper presents the fabrication and the proof of functionality for each module of the Cytostretch membrane. The assessment of each additional module demonstrate that a wide range of OOCs can be achieved.
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Microelectrode arrays (MEAs) are widely used in biological application to locally stimulate and record the electrical activity of living cells. Here, a novel fabrication process for a carbon nanotube (CNT)-based MEA integrated on the backside of a free standing stretchable membrane is reported. The new process flow overcomes the manually intensive procedures used in the previous works. The microfabricated upside-down CNT MEA consists of microelectrodes with an area of 110 μm2 covered with cobalt-grown CNTs. The surface area enhancement and the foamlike morphology of the CNTs allow an increase of the charge injection per unit area at the electrode–electrolyte interface, resulting in a significantly lower electrochemical impedance of the electrodes. In particular, at 1 kHz, the fabricated CNT-MEA electrodes show a reduction of the overall impedance up to 96% in comparison with benchmark TiN electrodes. The obtained results confirm the effectiveness of the proposed surface texturing through CNT integration. Moreover, the quality and the morphology as well as the biocompatibility of the fabricated CNT-based electrodes were assessed. The obtained results demonstrate that significant improvement can be achieved by integrating structured nanoporous material on MEAs.@en

Wnt signaling has been implicated in regulating bone formation by controlling osteoblast proliferation and function. Although stabilization of ß-catenin by Wnt has been shown to increase alkaline phosphatase expression and osteoblast differentiation, the precise role of Wnt signaling during the process of osteoblast differentiation is largely unknown. In this study, we used microarray technology to investigate expression regulation of Wnt signaling components during in vitro osteoblast differentiation. Expression was analyzed during bone morphogenetic protein 2 (BMP2)-induced osteoblast differentiation of murine C2C12 and MC3T3 cells and data were compared with expression in BMP2-treated NIH3T3 fibroblasts. During osteoblast differentiation, particularly strong expression regulation of the Wnt antagonists Sfrp2 (secreted frizzled related protein 2) and Wif1 (Wnt inhibitory factor 1) was observed in the late phase of differentiation. In situ expression analysis in murine tail vertebrae supported Wif1 expression during late phase bone cell differentiation, since Wif1 was found to be expressed in vivo in trabecular, but not in cortical bone. We further analyzed the effects of continuous activation of Wnt signaling by lithium chloride and observed that osteoblast differentiation was reduced, as measured by expression of osteoblast marker genes encoding alkaline phosphatase, osteocalcin, and osterix, as well as by the amount of calcium release. Taken together, our data indicate that endogenous expression of Wnt antagonists by osteoblasts provides a negative Wnt feedback loop which is essential in controlling osteoblast maturation. Keywords: Microarray; Osteoblast; Wnt antagonists; BMP; C2C12 cells@en