Ultra-low percolation threshold POSS-PCL/graphene electrically conductive polymer: Neural tissue engineering nanocomposites for neurosurgery.

An ultra-low percolation threshold electrically conductive polymer nanocomposite incorporating graphene into a polyhedral oligomeric silsesquioxane polycaprolactone (POSS-PCL/graphene) is described in this paper. Multilayer graphene flakes were homogeneously dispersed into POSS-PCL at 0.08, 0.4, 0.8, 1.6, and 4.0 wt% concentrations. The impedance spectroscopy of 0.08 wt% and higher concentration of graphene in POSS-PCL represented major improvement in conductivity over pristine POSS-PCL. The percolation threshold occurred at 0.08 wt% graphene concentration, and at 4.0 wt% the electrical conductivity exceeded 10-4 Scm-1. Furthermore, the chemical, morphological, and mechanical of the POSS-PCL/graphene with various graphene concentrations were investigated. Finally, neural cells cultured on all POSS-PCL/graphene constructs indicated higher metabolic activity and cell proliferation in comparison with pristine POSS-PCL. Herein, we demonstrate a method of developing a neural-compatible and electrically conductive polymer nanocomposite that could potentially function as a neural tissue engineered platform technology for neurological and neurosurgical applications.

Reflectometry-Ellipsometry Reveals Thickness, Growth Rate, and Phase Composition in Oxidation of Copper.

The oxidation of copper is a complicated process. Copper oxide develops two stable phases at room temperature and standard pressure (RTSP): cuprous oxide (Cu2O) and cupric oxide (CuO). Both phases have different optical and electrical characteristics that make them interesting for applications such as solar cells or resistive switching devices. For a given application, it is necessary to selectively control oxide thickness and cupric/cuprous oxide phase volume fraction. The thickness and composition of a copper oxide film growing on the surface of copper widely depend on the characteristics of as-deposited copper. In this Research Article, two samples, copper films prepared by two different deposition techniques, electron-beam evaporation and sputtering, were studied. As the core part of the study, the formation of the oxidized copper was analyzed routinely over a period of 253 days using spectroscopic polarized reflectometry-spectroscopic ellipsometry (RE). An effective medium approximation (EMA) model was used to fit the RE data. The RE measurements were complemented and validated by using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and X-ray diffraction (XRD). Our results show that the two samples oxidized under identical laboratory ambient conditions (RTSP, 87% average relative humidity) developed unique oxide films following an inverse-logarithmic growth rate with thickness and composition different from each other over time. Discussion is focused on the ability of RE to simultaneously extract thickness (i.e., growth rate) and composition of copper oxide films and on plausible physical mechanisms responsible for unique oxidation habits observed in the two copper samples. It appears that extended surface characteristics (i.e., surface roughness and grain boundaries) and preferential crystalline orientation of as-deposited polycrystalline copper films control the growth kinetics of the copper oxide film. Analysis based on a noncontact and nondestructive measurement, such as RE, to extract key material parameters is beneficial for conveniently understanding the oxidation process that would ultimately enable copper oxide-based devices at manufacturing scales.