Use of SU8 as a stable and biocompatible adhesion layer for gold bioelectrodes.

Gold is the most widely used electrode material for bioelectronic applications due to its high electrical conductivity, good chemical stability and proven biocompatibility. However, it adheres only weakly to widely used substrate materials such as glass and silicon oxide, typically requiring the use of a thin layer of chromium between the substrate and the metal to achieve adequate adhesion. Unfortunately, this approach can reduce biocompatibility relative to pure gold films due to the risk of the underlying layer of chromium becoming exposed. Here we report on an alternative adhesion layer for gold and other metals formed from a thin layer of the negative-tone photoresist SU-8, which we find to be significantly less cytotoxic than chromium, being broadly comparable to bare glass in terms of its biocompatibility. Various treatment protocols for SU-8 were investigated, with a view to attaining high transparency and good mechanical and biochemical stability. Thermal annealing to induce partial cross-linking of the SU-8 film prior to gold deposition, with further annealing after deposition to complete cross-linking, was found to yield the best electrode properties. The optimized glass/SU8-Au electrodes were highly transparent, resilient to delamination, stable in biological culture medium, and exhibited similar biocompatibility to glass

Multiwell capillarity-based microfluidic device for the study of 3D tumour tissue-2D endothelium interactions and drug screening in co-culture model

The tumour microenvironment is very complex, and essential in tumour development and drug resistance. The endothelium is critical in the tumour microenvironment: it provides nutrients and oxygen to the tumour and is essential for systemic drug delivery. Therefore, we report a simple, user-friendly microfluidic device for co-culture of a 3D breast tumour model and a 2D endothelium model for cross-talk and drug delivery studies. First, we demonstrated the endothelium was functional, whereas the tumour model exhibited in vivo features, e.g., oxygen gradients and preferential proliferation of cells with better access to nutrients and oxygen. Next, we observed the endothelium structure lost its integrity in the co-culture. Following this, we evaluated two drug formulations of TRAIL (TNF-related apoptosis inducing ligand): soluble and anchored to a LUV (large unilamellar vesicle). Both diffused through the endothelium, LUV-TRAIL being more efficient in killing tumour cells, showing no effect on the integrity of endothelium. Overall, we have developed a simple capillary force-based microfluidic device for 2D and 3D cell co-cultures. Our device allows high-throughput approaches, patterning different cell types and generating gradients without specialised equipment. We anticipate this microfluidic device will facilitate drug screening in a relevant microenvironment thanks to its simple, effective and user-friendly operation

Three-Dimensional Anisotropic Metamaterials as Triaxial Optical Inclinometers

Split-ring resonators (SRRs) present an attractive avenue for the development of micro/nano scale inclinometers for applications like medical microbots, military hardware, and nanosatellite systems. However, the 180 degrees isotropy of their two-dimensional structure presents a major hurdle. In this paper, we present the design of a three-dimensional (3D) anisotropic SRR functioning as a microscale inclinometer enabling it to remotely sense rotations from 0 degrees to 360 degrees along all three axes (X, Y, and Z), by employing the geometric property of a 3D structure. The completely polymeric composition of the cubic structure renders it transparent to the Terahertz (THz) light, providing a transmission response of the tilted SRRs patterned on its surface that is free of any distortion, coupling, and does not converge to a single point for two different angular positions. Fabrication, simulation, and measurement data have been presented to demonstrate the superior performance of the 3D micro devices