Biodegradable polymeric coatings on cochlear implant surfaces and their influence on spiral ganglion cell survival.

To improve the electrode-nerve interface of cochlear implants (CI), the role of poly(L-lactide) (PLLA) and poly(4-hydroxybutyrate) (P(4HB)) as potential coating matrices for CI was assessed both in vitro and in vivo in terms of degradation behavior and effects on spiral ganglion neurons, the main target of the electrical stimulation with a CI. Growth rates of fibroblasts on the polymers were investigated and a direct-contact test with freshly isolated spiral ganglion cells (SGC) was performed. In addition, the effects of the polymer degradation inside the inner ear were evaluated in vivo. The polymer degradation was assessed by use of scanning electron microscopy in combination with an energy-dispersive X-ray analysis. In vitro, no influence of the polymers was detected on fibroblasts' viability and on SGC survival rate. In vivo, SGC density was decreased only 6 months after implantation in the basal and middle turns of the cochlea in comparison to normal-hearing animals but not between implanted groups (coated or uncoated). The analysis of the electrode models showed that in vivo P(4HB) is characterized by a gradual degradation completed after 6 months; whereas, the PLLA coatings burst along their longitudinal axis but showed only little degradation within the same time frame. In conclusion, both polymers seem to justify further evaluation as possible coating for CI electrodes. Of the two options, due to its excellent coating adhesion/stability and optimal degradation behavior, P(4HB) may prove to be the more promising biodegradable polymer for designing a drug delivery system from the surface of CI electrodes.

Core-hole screening as a probe for a metal-to-nonmetal transition in lead clusters.

Metal clusters serve as model systems to study basic problems of electronic correlation. Vacuum ultraviolet light from the free-electron laser FLASH ionizes 5d electrons from mass-separated negatively charged clusters, thus transiently leading to core-ionized neutral systems. Shielding of the core hole affects the electron binding energy. From the strong deviation from expectations of the metallic droplet and jellium models we conclude on reduced electronic shielding once the cluster size falls below about 20 atoms. This suggests a metal-to-nonmetal transition, in agreement with previous local density approximation calculations.

Perpendicular spin orientation in ultrasmall Fe islands on W(110).

We have studied the magnetism of Ag-coated Fe islands on W(110) by nuclear resonant scattering of synchrotron radiation at the 14.4 keV resonance of (57)Fe. Separated islands with an average diameter of 2.0 nm and monolayer thickness are formed at a Fe coverage of theta = 0.57 bulk monolayers. Time spectra of the nuclear decay were measured in the temperature range from 4.5 to 300 K. We find strong evidence for perpendicular spin orientation, which most likely results from the interplay of shape anisotropy and elastic strain in the islands.

Analysis of the metallic phase of two-dimensional holes in SiGe in terms of temperature dependent screening

We find that temperature dependent screening can quantitatively explain the metallic behavior of the resistivity on the metallic side of the so-called metal-insulator transition in p-SiGe. Interference and interaction effects exhibit the usual insulating behavior which is expected to overpower the metallic background at sufficiently low temperatures. We find empirically that the concept of a Fermi liquid describes our system with its large interaction parameter r(s) approximately 8.