Broadband Enhancement of Anti-reflectivity for a High Angle of Incidence Using Nanocone Geometry.

The broadband antireflective (AR) effect for wide incident angles has a significant effect on the photoconversion efficiency of photovoltaics and visibility of large-format display panels. The fabrication of surface nanostructures has continued to attract research interest as an effective way to provide such optical performance. However, the effects of different nanostructure geometries are not fully understood, especially for wide-angle AR effects. In this work, we conduct a systematic analysis of the effect of periodic nanostructures such as nanocones (NCs) and inverted nanocones (INCs) on anti-reflectivity at high angles of incidence (AOIs) in terms of light scattering, guided-mode resonance (GMR), and internal reflections. NCs provide good coupling of light scattering and GMR because of their protruding geometry; hence, reduced reflectance can be obtained in the short wavelength region. Further, NCs exhibit relatively weaker GMR intensities and internal reflections, resulting in low reflectance in the long wavelength region. Therefore, NCs offer a superior broadband AR effect for high AOIs compared with INCs. Based on this analysis, we demonstrate an extremely low average reflectance (5.4%) compared to that of the bare substrate (34.7%) for the entire visible range at an AOI of 75° by fabricating NCs on both sides of the substrate.

Quantitative Correlation of Nanotopography with Cell Spreading via Focal Adhesions Using Adipose-Derived Stem Cells.

Nanotopography mimicking extracellular environments reportedly impact cell morphological changes; however, elucidating this relationship has been challenging. To control cellular responses using nanostructures, in this study, the quantitative relationship between nanotopography and cell spreading mediated by focal adhesions (FAs) is demonstrated using adipose-derived stem cells (ASCs). The spreading of ASCs and area of FAs are analyzed for the distribution of filamentous actin and vinculin, respectively, using fluorescent images. FAs require a specific area for adhesion (herein defined as effective contact area [ECA]) to maintain cell attachment on nanopillar arrays. An ECA is the area of FAs supported by nanopillars, multiplying the area fraction (AF) of their top surface. Regarding the spreading of cells, the mean area of ASCs linearly decreases as the mean area of FAs increases. Because the area of FAs is inversely correlated to the AF of the nanopillar arrays, the spreading of cells can be quantitatively correlated with nanotopography. The results provide a conceptual framework for controlling cell behaviors to design artificial substrates for tissue-engineering applications.

In vitro characterization of osteoblast cells on polyelectrolyte multilayers containing detonation nanodiamonds.

Nanoparticle-enhanced coatings of bone implants are a promising method to facilitate sustainable wound healing, leading to an increase in patient well-being. This article describes the in vitro characterization of osteoblast cells interacting with polyelectrolyte multilayers, which contain detonation nanodiamonds (NDs), as a novel class of carbon-based coating material, which presents a unique combination of photoluminescence and drug-binding properties. The cationic polyelectrolyte, namely polydiallyldimethylammonium chloride (PDDA), has been used to immobilize NDs on silica glass. The height of ND-PDDA multilayers varies from a minimum of 10 nm for one bilayer to a maximum of 90 nm for five bilayers of NDs and PDDA. Human fetal osteoblasts (hFOBs) cultured on ND-PDDA multilayers show a large number of focal adhesions, which were studied via quantitative fluorescence imaging analysis. The influence of the surface roughness on the filopodia formation was assessed via scanning electron microscopy and atomic force microscopy. The nano-rough surface of five bilayers constrained the filopodia formation. The hFOBs grown on NDs tend to show not only a similar cell morphology compared to cells cultured on extracellular matrix protein-coated silica glass substrates, but also increased cell viability by about 40%. The high biocompatibility of the ND-PDDA multilayers, indicated via high cell proliferation and sound cell adhesion, shows their potential for biomedical applications such as drug-eluting coatings and biomaterials in general.

Stem cell behaviors on periodic arrays of nanopillars analyzed by high-resolution scanning electron microscope images.

The biocompatible polyurethane acrylate (PUA) nanopillars were fabricated by soft lithography using three different sizes of nanobeads (350, 500, and 1000 nm), and the human adipose-derived stem cells (hASCs) were cultured on the nanopillars. The hASCs and their various behaviors, such as cytoplasmic projections, migration, and morphology, were observed by high resolution images using a scanning electron microscope (SEM). With the accurate analysis by SEM for the controlled sizes of nanopillars, the deflections are observed at pillars fabricated with 350- and 500-nm nanobeads. These high-resolution images could offer crucial information to elucidate the complicated correlations between nanopillars and the cells, such as morphology and cytoplasmic projections.