Synthesis, characterization, and cytocompatibility of yttria stabilized zirconia nanopowders for creating a window to the brain.

Transparent cranial window to the brain is highly desirable for brain therapies because such cranial implant would allow for continuous monitoring of brain disorders and long-term delivery of photodynamic therapy into the brain without repeated surgeries for opening skull. Nanostructured yttria-stabilized zirconia (YSZ) is a potential candidate for the window to the brain application because of its promising mechanical and optical properties. In this study, a new process using aerosol spray pyrolysis was established for synthesizing 6-7 nm YSZ nanopowders with precisely controlled compositions. YSZ nanopowders with 3 M ratios of yttria to zirconia, specifically 3, 6, and 8% yttria in zirconia (referred to as 3YSZ, 6YSZ, and 8YSZ, respectively) were synthesized and characterized. The size, structure, and composition of the produced YSZ nanoparticles are highly controllable and scalable. The in vitro cytocompatibility of the YSZ nanoparticles with bone marrow mesenchymal stem cells (BMSCs) was investigated using a direct exposure culture method for cranial implant applications. Nondoped ZrO2 and commercially available 8YSZ (named as C_8YSZ) served as controls for the in vitro cell studies. BMSCs exhibited normal morphology when cultured with the YSZs of 3 M ratios in the concentrations of 10 mM, 30 mM, and 60 mM, as well as ZrO2 and C_8YSZ controls. The BMSCs cultured with 3YSZ and 6YSZ showed no statistical differences in cell adhesion density when compared with the ZrO2 and C_8YSZ controls at respective concentrations of 10-60 mM. The possible release of YSZ nanoparticles from cranial window implants should be carefully considered and further studied.

Grain-to-Grain Compositional Variations and Phase Segregation in Copper-Zinc-Tin-Sulfide Films.

We have performed a rigorous investigation of the structure and composition of individual grains in copper-zinc-tin-sulfide (CZTS) films realized by sulfurization of a sputtered metal stack. Although on average close to the ideal CZTS stoichiometry, elemental analysis shows significant grain-to-grain variations in composition. High-resolution Raman spectroscopy indicates that this is accompanied by grain-to-grain structural variations as well. The intensity from the 337 cm(-1) Raman peak, generally assigned to the kesterite phase of CZTS, remains constant over a large area of the sample. On the other hand, signals from secondary phases at 376 cm(-1) (copper-tin-sulfide) and 351 cm(-1) (zinc-sulfide) show significant variation over the same area. These results confirm the great complexity inherent to this material system. Moreover, structural and compositional variations are recognized in the literature as a factor limiting the efficiency of CZTS photovoltaic devices. This study demonstrates how a seemingly homogeneous CZTS thin film can actually have considerable structural and compositional variations at the microscale, and highlights the need for routine microscale characterization in this material system.