Design Optimization of Printed Multi-Layered Electroactive Actuators Used for Steerable Guidewire in Micro-Invasive Surgery.

To treat cardiovascular diseases (i.e., a major cause of mortality after cancers), endovascular-technique-based guidewire has been employed for intra-arterial navigation. To date, most commercially available guidewires (e.g., Terumo, Abbott, Cordis, etc.) are non-steerable, which is poorly suited to the human arterial system with numerous bifurcations and angulations. To reach a target artery, surgeons frequently opt for several tools (guidewires with different size integrated into angulated catheters) that might provoke arterial complications such as perforation or dissection. Steerable guidewires would, therefore, be of high interest to reduce surgical morbidity and mortality for patients as well as to simplify procedure for surgeons, thereby saving time and health costs. Regarding these reasons, our research involves the development of a smart steerable guidewire using electroactive polymer (EAP) capable of bending when subjected to an input voltage. The actuation performance of the developed device is assessed through the curvature behavior (i.e., the displacement and the angle of the bending) of a cantilever beam structure, consisting of single- or multi-stack EAP printed on a substrate. Compared to the single-stack architecture, the multi-stack gives rise to a significant increase in curvature, even when subjected to a moderate control voltage. As suggested by the design framework, the intrinsic physical properties (dielectric, electrical, and mechanical) of the EAP layer, together with the nature and thickness of all materials (EAP and substrate), do have strong effect on the bending response of the device. The analyses propose a comprehensive guideline to optimize the actuator performance based on an adequate selection of the relevant materials and geometric parameters. An analytical model together with a finite element model (FEM) are investigated to validate the experimental tests. Finally, the design guideline leads to an innovative structure (composed of a 10-stack active layer screen-printed on a thin substrate) capable of generating a large range of bending angle (up to 190°) under an acceptable input level of 550 V, which perfectly matches the standard of medical tools used for cardiovascular surgery.

Transparent and Mechanically Resistant Silver-Nanowire-Based Low-Emissivity Coatings.

This article reports on the fabrication and investigation of low-emissivity (low-E) coatings based on random networks of silver nanowires (AgNWs). The transparent layers based on AgNWs do exhibit low emissivity while being still transparent: an overall emissivity as low as 0.21 at 78% total transmittance was obtained. A simple physical model allows to rationalize the emissivity-transparency dependence and a good agreement with experimental data is observed. This model demonstrates the role played by AgNWs which partially reflect IR photons emitted by the substrate, exacerbating then the presence of AgNWs and lowering the total emissivity. The potential use of such layers in functional devices is hampered by the poor intrinsic surface adhesion of the AgNWs, which renders the coating fragile and prone to mechanical damaging. Two very efficient encapsulation processes based on the deposition of a conformal alumina thin film using the spatial atomic layer deposition technique and the solution processed layer deposition of a polysiloxane varnish have been developed to thwart this weakness. Both coatings combine sturdy mechanical resistance relying on a strong interfacial adhesion and excellent optical transmittance properties. The performances for the mechanically resistant low-E coatings achieve an overall emissivity as low as 0.34 at 74% total transparency. The set of optical properties and mechanical resistance of the reported AgNWs based low-E coatings combined with the ease of fabrication and the cost-effective production process make it an excellent candidate for a wide set of applications, including smart windows for energy-saving buildings.

Fast current-induced domain-wall motion controlled by the Rashba effect.

The propagation of magnetic domain walls induced by spin-polarized currents has launched new concepts for memory and logic devices. A wave of studies focusing on permalloy (NiFe) nanowires has found evidence for high domain-wall velocities (100 m s(-1); refs,), but has also exposed the drawbacks of this phenomenon for applications. Often the domain-wall displacements are not reproducible, their depinning from a thermally stable position is difficult and the domain-wall structural instability (Walker breakdown) limits the maximum velocity. Here, we show that the combined action of spin-transfer and spin-orbit torques offers a comprehensive solution to these problems. In an ultrathin Co nanowire, integrated in a trilayer with structural inversion asymmetry (SIA), the high spin-torque efficiency facilitates the depinning and leads to high mobility, while the SIA-mediated Rashba field controlling the domain-wall chirality stabilizes the Bloch domain-wall structure. Thus, the high-mobility regime is extended to higher current densities, allowing domain-wall velocities up to 400 m s(-1).