Complex microstructured 3D surfaces using chitosan biopolymer

A technique for producing micrometer-scale structures over large, nonplanar chitosan surfaces is described. The technique makes use of the rheological characteristics (deformability) of the chitosan to create freestanding, three-dimensional scaffolds with controlled shapes, incorporating defined microtopography. The results of an investigation into the technical limits of molding different combinations of shapes and microtopographies are presented, highlighting the versatility of the technique when used irrespectively with inorganic or delicate organic moulds. The final, replicated scaffolds presented here are patterned with arrays of one-micrometertall microstructures over large areas. Structural integrity is characterized by the measurement of structural degradation. Human umbilical vein endothelial cells cultured on a tubular scaffold show that early cell growth is conditioned by the microtopography and indicate possible uses for the structures in biomedical applications. For those applications requiring improved chemical and mechanical resistance, the structures can be replicated in poly(dimethyl siloxane)

Nanoscale electrical conductivity of the purple membrane monolayer

Nanoscale electron transport through the purple membrane monolayer, a two-dimensional crystal lattice of the transmembrane protein bacteriorhodopsin, is studied by conductive atomic force microscopy. We demonstrate that the purple membrane exhibits nonresonant tunneling transport, with two characteristic tunneling regimes depending on the applied voltage (direct and Fowler-Nordheim). Our results show that the purple membrane can carry significant current density at the nanometer scale, several orders of magnitude larger than previously estimated by macroscale measurements

Directional alignment of MG63 cells on polymer surfaces containing point microstructures

MG63 cells cultured on regular arrays of point microstructures (posts and holes) are shown to preferentially align at certain angles to the pattern of the structures, at 08, 308, and 458 in particular. The effect is found to be more pronounced for post rather than hole structures(although no significant difference is found for the angles the cells make to the holes or posts) and is thought to be due to the fact that the cells use the posts as anchorage points to hold themselves to the surface. It is also shown that cells preferentially align with the structures depending on the dimensions of the structures and the distance between neighboring structures. This is important when designing structured surfaces for cell–surface interaction studies for materials to be used in, for example, drug delivery or tissue engineering.Postprint (published version

Development of an artificial nose integrating NEMS and biological olfactory receptors

Development of an artificial nose integrating NEMS and biological olfactory receptor

A stabilising control strategy for Cyber-Physical Power Systems

The cyber-physical nature of electric power systems has increased immensely over the last decades, with advanced communication infrastructure paving the way. It is now possible to design wide-area controllers, relying on remote monitor and control of devices, that can tackle power system stability problems more effectively than local controllers. However, their performance and security relies extensively on the communication infrastructure and can make power systems vulnerable to disturbances emerging on the cyber side of the system. In this paper, we investigate the effect of communication delays on the performance of wide-area damping controllers (WADC) designed to stabilise oscillatory modes in a Cyber-Physical Power System (CPPS). We propose a rule-based control strategy that combines wide-area and traditional local stabilising controllers to increase the performance and maintain the stable operation of CPPS. The proposed strategy is validated on a reduced CPPS equivalent model of Great-Britain (GB)

Analysis of geometrical effects on the behavior of transverse and longitudinal modes of amorphous silicon compounds

The peak frequency, width, and shape of the transverse-optical (TO) and longitudinal-optical (LO) infrared absorption modes of silicon oxides (SiO2, SiOx), silicon nitrides (Si3N4, SiNx), silicon oxynitrides (SiOxNy), and other silicon compounds have often been connected with stress, stoichiometry, defects, structural order, and other properties of the layers. However, certain geometrical effects strongly influence the spectral response of the material independent of its physical or structural properties. The influence of layer thickness, multilayer configuration, substrate effects, angles, and polarization on the behavior of TO and LO bands are presented and discussed. Some corrections are suggested to reduce experimental error and for the reliable measurement of stress, composition, disorder, and structure