This work introduces a contact line pinning based microfluidic platform for the generation of interstitial and intramural flows within a three dimensional (3D) microenvironment for cellular behaviour studies. A contact line pinning method was used to confine natively derived biomatrix, collagen, in microfluidic channels without walls. By patterning collagen in designated wall-less channels, we demonstrated and validated the intramural flows through a microfluidic channel bounded by a monolayer of endothelial cells (mimic of a vascular vessel), as well as slow interstitial flows within a cell laden collagen matrix using the same microfluidic platform. The contact line pinning method ensured the generation of an engineered endothelial tube with straight walls, and spatially uniform interstitial fluid flows through the cell embedded 3D collagen matrix. Using this device, we demonstrated that the breast tumour cells’ (MDA-MB-231 cell line) morphology and motility were modulated by the interstitial flows, and the motility of a sub-population of the cells was enhanced by the presence of the flow. The presented microfluidic platform provides a basic framework for studies of cellular behaviour including cell transmigration, growth, and adhesion under well controlled interstitial and intramural flows, and within a physiologically realistic 3D co-culture setting.
In this work, we present a novel printing technique that enables the usage of PDMS and ceramic powder mixed PDMS composites (we refer as “PDMS-ceramic composites” in this context), as a substrate for printing of copper conduction layers. This technique is based on microtransfer molding (μTM) and lift-off for pattern formation [4]. Another key feature is the usage of microtextured PDMS and PDMS-ceramic composites before any copper film deposition. Our microtextured surface is composed of pyramid shaped wells (100 μm depth and 150 μm sides on PDMS surface). The poor adhesion between PDMS and copper is overcome by oxygen plasma application and titanium deposition before copper layer.In order to demonstrate the convenience of this technique in RF applications, copper conduction lines (5 mm wide, different lengths) were printed on microtextured PDMS substrates. These transmission lines successfully maintained a low resistance during large strain. The printed lines have the DC resistance of 0.5 Ω and conductivity of 1.3e6 S/m, and the transmission analysis of these lines show good results especially in the MHz range when compared to copper tape measurements.Apart from the conduction lines, the substrates can have ranging dielectric constants from 3 (no powder) to 23 (50% D270 powder, provided by TransTech) by volume mixing rule. Dielectric constant is important for RF applications, especially antenna designs. Therefore, provided with a range of dielectric constants, these composite substrates are a great promise in RF field for pliable antenna fabrication [5]. For experiment purposes, some of the transmission lines are printed on these composite substrates as well as pure PDMS.In this study, apart from the fabrication of transmission lines, this novel technique will be applied in a GPS antenna design for demonstration purposes. This antenna design is a single-fed circularly-polarized stacked antenna for tri-band GPS (L1, L2 and L5) applications [6]. For the fabrication of the antenna, polymer-ceramic materials of ε1=16 and ε2=30 will be utilized as the substrates [6].
IntroductionMany mobile structures (aircrafts, ships and automobiles) require conformal antennas for high data rate connectivity, which brings the need for material compatibility and for structurally reinforced antennas. The latter requirement is particularly challenging for small platforms since a large antenna is needed at these frequencies. For small unmanned air vehicles (UAVs) spanning a few feet, it is inevitable that the antennas be part of the structure. As the antennas become part of the structural airframe, there is a need for materials that concurrently serve the electrical and structural requirements. Among available materials, fibreglass, although suitable for load bearing applications, is not attractive for antennas due to its higher losses [1]. Suitable materials are polymerbased mixtures [2, 3] because of their inherent low-loss properties, and mixing ease with ceramic and/or magnetic powders [4].Not surprisingly, polymers are rapidly becoming important among materials for microwave and electronic applications. For example, polymerceramic composites were proposed as substrate materials for a scanning antenna [5]. Epoxy mixed with ceramic powders has been reported to make embedded capacity films [6]. Polymers are also targeted for packaging, for integration with radio frequency front-end circuits and for 3D electronics (multilayered packaged electronics). For example, liquid crystal polymers (LCP) have also been proposed for System on Package (SoP) applications, displaying attractive properties like low loss, low water absorption, and low cost [7]. However, LCPs are associated with low and very limited choices for dielectric constants. In contrast, polymerceramic composites [2] offer much greater range of dielectric values from ε r =3 to ε r =20 or higher. Of importance about the polymer-ceramic composites are that a) polymers can be doped to make them functional and control their dielectric properties; b) they are "soft" and pliable (unlike crystalline materials); c) thin polymer layers can be printed and then stacked to form packaged 3D electronics and d) they can be reinforced with carbon-based nanotubes to render them structurally capable for UAV embedded antennas and smart skins.In spite of their attractive electrical properties, printing on polymers is a major issue, and has been the topic of recent papers [8,9]. For RF applications, a challenge is that of retaining high conductivity of the printed metallic pattern when the polymer surface is bent or deformed. This is due to poor metal adhesion, and to surface expansion (surface area increase) after bending causing detachment of the metal particles forming the printed area. In this paper we propose (for the first time to our knowledge) novel techniques for printing on ceramic-reinforced elastic polymer composite substrates targeting truly conformal microwave applications suitable for a wide range of operating frequencies, i.e. 100MHz -
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