Preparation of electromechanically active silicone composites and some evaluations of their suitability for biomedical applications

Some films based on electromechanically active polymer composites have been prepared. Polydimethylsiloxane-α,ω-diols (PDMSs) having different molecular masses (Mv = 60 700 and Mv = 44 200) were used as matrix in which two different active fillers were incorporated: titanium dioxide in situ generated from its titanium isopropoxide precursor and silica particles functionalized with polar aminopropyl groups on surface. A reference sample based on simple crosslinked PDMS was also prepared. The composites processed as films were investigated to evaluate their ability to act as efficient electromechanical actuators for potential biomedical application. Thus, the surface morphology of interest for electrodes compliance was analysed by atomic force microscopy. Mechanical and dielectric characteristics were evaluated by tensile tests and dielectric spectroscopy, respectively. Electromechanical actuation responses were measured by interferometry. The biocompatibility of the obtained materials has been verified through tests in vitro and, for valuable films, in vivo. The experimental, clinical and anatomopathological evaluation of the in vivo tested samples did not reveal significant pathological modifications

Concurrent engineering in designing a system for sensing gas leaks in harsh space environment

Leak monitoring is an essential operation that must be taken into consideration while making the design of a spatial vehicle. In order to make these vehicles function correctly in space and to avoid disasters, one needs to integrate multiple sensors to determine the exact concentrations of fuels such as hydrogen, hydrazine, hydrocarbon or oxygen which are frequently used while launching a space vehicle. These concentrations are important, as hydrogen-oxygen mixtures can ignite with a very small amount of energy. Moreover, it is almost impossible for people to sense the presence of hydrogen, as this gas is odorless and colorless. In the propulsion industry, hydrogen leaks generated several disasters. In 1990 such an error affected the propulsion system while workers were on the launching platform. They were forced to abort all the current processes until the source of leakage could be identified. Another example is the APOLLO 13 mission that took place in 1970 when N.A.S.A aimed to land on the Moon. Two days after the launch there has been a malfunction of the electrical system which caused an explosion leading to the loss of oxygen in both tanks. The crew used a module called lifeboat on their way back to Earth where they completed the landing. The goal of this paper is the describe the concept of an intelligent system that will monitor the presence of oxygen, hydrogen gas in harsh space environments such as vacuum, temperature variations and also beta and gamma radiations. Therefore, some aspects such as the weight of the device or environmental conditions must be taken into consideration when doing concurrent engineering. Micro and nanotechnologies allow the presence of multiple sensors without increasing the size, the weight or the energy consumption. Also, they must resist harsh conditions from space

Micro Electromagnetic Actuator - Static Behavior

The article presents a comparative study regarding the design and experimental results for a miniature electromagnetic actuator with a modified design comparing with the classical type, including a mobile array of micro-magnets and a fixed coil in two configurations (planar spiral multi-layered and cylindrical). Previous work on design, modeling and simulation of this type of actuator indicated the optimum design and conducted to dimensions and material parameters. Different types of actuators were produced and experimentally tested, showing good results but also some drawbacks. Three of these design solutions are presented together with the static voltage-deflection and electrical impedances curves, experimentally derived. The results confirmed the feasibility of two actuating solution, showing good linearity and possibility to control the position at h accuracy and indicated improving directions

Well-defined silicone–titania composites with good performances in actuation and energy harvesting

Although silicones possess low dielectric constant, they are between the most used polymers in actuation due to their appropriate mechanical properties (low modulus and high elongation). These can be easily tuned by the preparation strategy: proper choice of the molecular mass and microstructure of the polymer matrix; adding or not of more or less active fillers; whether these are incorporated in the polymeric matrix (ex situ) or generated in situ; crosslinking mode (through the side or ending functional groups) or mechanism (condensation, radicalic or by hydrosilylation). A relatively low cost and easy scalable procedure was used in this article to prepare silicone composites based on high molecular weight polydiorganosiloxane copolymer and hydrophobized silica and titania nanoparticles. The matrix polymer was synthesized by bulk ring opening copolymerization of different substituted cyclosiloxanes and characterized by FTIR, 1H NMR and gel permeation chromatographic analysis. The composites prepared by the mechanical incorporation of the fillers were crosslinked by radicalic mechanism and investigated by dielectrical spectroscopy, mechanical tests, dynamo-mechanical analysis and dynamic vapor sorption. The actuation measurements revealed displacement values in the range 0.04–5.09 nm/V/mm, while energy harvesting measurements revealed impulse electrical voltage in the range 6–20 V for a dynamic force of 0.1–1 Kgf. The robustness of these composites supported by their thermal, mechanical and surface properties recommends them for use inclusively in harsh environmental conditions, when their behavior is not significantly affected