Epicardial, off-pump, beating-heart ablation with acoustic energy is safe and cures 80% of patients with permanent atrial fibrillation associated with long-standing structural heart disease.

Implantable electrical conductor wires and coils of MP35N and drawn MP35N tube filled with a silver core (DFT) were tested in rotary bending to evaluate fatigue characteristics and failure mechanisms. Detailed stress analysis enabled evaluation of helical coil fatigue in bending with respect to theoretical stress. The relations between the maximum cyclic stress (S) and the cycles to failure (N) were obtained by introducing cyclic stresses on over 600 samples. Microscopic evaluation using scanning electron microscopy was performed to identify failure mechanisms. The results show that the stress analysis presented is a viable means for assessing the stress state in a composite coil structure in rotary loop testing, comparable S-N fatigue data sets for MP35N and DFT conductors are not consistently significantly different, S-N relationships for coils and wires of the MP35N and DFT appear to lie on the same curves, and failures of all sample types initiate on the outside surface of the wire. Differences in crack propagation and final fracture are shown as a function of sample type and cyclic stress.

Dynamics in poly(dimethylsi1oxane) (PDMS) melts from Tg + 75 to T, + 175 K have been measured by the fluorescence anisotropy decay of a probe chromophore. The reorientational dynamics of the probe chromophore, 5-(dimethylamino)-1-naphthalenesulfonamide (dansylamide), attached to a trifunctional silane, are characterized in a small molecule solvent, cyclohexanol, and compared to its reorientation in the polymer system. In cyclohexanol, the orientational dynamics obey the Debye-Stokes-Einstein equation with a thermal activation energy equal to that of the cyclohexanol viscosity. In contrast, the rate of reorientation of the probe dispersed in PDMS polymer melts does not reflect the bulk properties of the samples. The local dynamics are exponentially activated, with activation energies that are higher than that of the viscosity of the bulk material. This result is different than conclusions of analogous studies made on carbon-based polymers. Two possible explanations are given based on the unique characteristics of the silicon-oxygen bonds in PDMS.

End-linked polydimethylsiloxane networks have been synthesized with 5-dimethylaminonaphthalene-1 -sulfonamide (dansyl) chromophores covalently bound to trifunctional silane cross-linkers. The solvatochromic behaviour of the dansyl-tagged cross-linkers, dissolved in solvents and bound in swollen networks, has been investigated. The spectral shifts in one-component solvents are characteristic of the dansyl probe and are explained in terms of dielectric solvent relaxation and solvophobic effects. In binary solvent mixtures, analogous to the swollen network, preferential solvation of the probe by the more polar solvent is observed and explained using a model for dielectric enrichment. Solvent partitioning in swollen networks is stronger than in the binary solutions and is attributed to a combination of dipoledipole interactions and configurational restriction effects. Owing to large spectral shifts measured from networks swollen with small amounts of alcohols, this material may find application as a transducing element in a fibre-optic alcohol sensor.

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