An acceleration of differentiation, at the expense of proliferation, is observed after exposure of various biological models to low frequency and low amplitude electric and electromagnetic fields. Following these results showing significant modifications, we try to identify the biological mechanism involved at the cell level through microarray screening. For this study, we use epidermis cultures harvested from human abdominoplasty. Two platinum electrodes are used to apply the electric signal. The gene expressions of 38,500 well-characterized human genes are analyzed using Affymetrix® microarray U133 Plus 2.0 chips. The protocol is repeated on three different patients. After three periods of exposure, a total of 24 chips have been processed. After the application of ELF electric fields, the microarray analysis confirms a modification of the gene expression of epidermis cells. Particularly, four up-regulated genes (DKK1, TXNRD1, ATF3, and MME) and one down-regulated gene (MACF1) are involved in the regulation of proliferation and differentiation. Expression of these five genes was also confirmed by real-time rtPCR in all samples used for microarray analysis. These results corroborate an acceleration of cell differentiation at the expense of cell proliferation.

In minimally invasive surgery and endoscopy, the rise of soft robotics, using materials of similar softness as biological soft tissues, opens many new opportunities. Soft actuated catheters could become an alternative to current steerable catheters, by minimizing the risk of damage to surrounding tissues while enhancing the possibilities to navigate in confined space and to reach remote locations. Fluidic actuators present the advantage to be safe, since they do not require rigid parts nor voltage, to be lightweight, and to allow the reduction of the number of parts needed for a given movement. This work presents the design, development and characterization of a soft fluidic bending actuator for a steerable catheter. Methods A silicone prototype of 5 mm diameter has been designed. It has one degree of freedom in bending and achieves a radius of curvature below 10 mm. A numerical model has been developed and compared to the experimental results. Results Despite an overestimation of the bending, the numerical model properly captures the behaviour of the actuator. This allowed to identify and validate the key design parameters of the actuator, namely the ratio between the pressure channel surface and the actuator cross-section surface. Based on the results, an optimized design has been developed and numerically implemented. The miniaturization and the potential to carry devices with non-negligible bending stiffness have also been discussed. Conclusion In this work, a proof of concept of a soft fluidic actuator for a steerable catheter has been designed, developed and characterized. It showed promising results concerning the feasibility of a miniaturized actuator with two degrees of freedom.

Recent experiments on the magnetic properties of frozen ferroAuids indicate clear deviations from canonical spin glass behavior. To elucidate these differences we present simulations based on a localmean-field theory approach. This theoretical scheme was previously found to be quite successful for traditional spin glass and random field systems. In a parallel fashion we study frustration effects associated with a magnetic dipole-dipole interaction for a random spatial arrangement of Heisenberg spins in a quenched ferro6uid. Some of the experimental features can be reproduced if the spins are assumed to be inhomogeneously distributed in space.Glassy behavior in magnetic systems has received considerable attention over the past two decades. Frustration associated with Ruderman-Kit tel-Kasuya-Yosida interactions among impurity spins in nonmagnetic hosts leads to metalIic spin-glass behavior, in which the magnetization at a given temperature T and field H depends on the order in which T and H are cycled. Diluted antiferromagnets display a similar degree of history sensitivity with the new possibility of history-dependent long-range order. Recent studies' of frozen ferrofluids have added another member to the class of frustrated systems. Here the frustration arises from dipole-dipole interactions between ferromagnetic microcrystals which are randomly situated in space. In this paper we study this quenched ferrofluid using a mean-field simulation technique which has been widely applied to other glassy systems. Of particular interest is the behavior of the field-cooled (FC) and zero-field-cooled (ZFC) magnetizations, which are found experimentally to be di6'erent from their spin-glass analogs.Our physical picture of irreversibility derives from the evolution with H and T of metastable states on the freeenergy surface. ' Here the free energy F is assumed to be a function of N variables associated with the average magnetization m, of N spins in the system. The selfconsistent equations for the N-dimensional minima are derived from the simplest (local) mean-field theory, although more sophisticated functionals have been tried with less success. The system is prepared in a given state, say at high temperatures and the temperature is then lowered in the presence (FC) or absence (ZFC) of a field. Upon warming or changing H a given minimum may disappear and the system will then fall irreversibily into a nearby state. An iterative solution of the mean-field equation BE/Bm; =0, captures the physics of this irreversible behavior. For the spin-glass and random-field (or diluted antiferromagnet) systems this procedure has been found to yield results for the various history-dependent magnetizations which are remarkably similar to those measured experimentally. Recent attentionhas focused on the quenched ferrofiuid because (a) it provides an opportunity for studying frustration associated with dipole-dipole interactions at experimentally accessible temperatures and (b) provides a system in which there is random anisotropy along with ...

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