Characterization of chitosan films and effects on fibroblast cell attachment and proliferation

Chitosan has been researched for implant and wound healing applications. However, there are inconsistencies in reports on the tissue and fibroblast responses to chitosan materials. These inconsistencies may be due to variations in chitosan material characteristics. The aim of this study was to correlate fibroblast responses with known chitosan material characteristics. To achieve this aim, chitosan was characterized for degree of deacetylation (DDA), molecular weight (MW), residual protein and ash contents, and then solution cast into films and characterized for hydrophilicity by water contact angle. The films were seeded with normal human dermal fibroblasts and the number of attached cells was evaluated for after 30 min. Cell proliferation was evaluated over 5 days. This study found no relationship between DDA, contact angle, cell attachment, and or proliferation. General trends were observed for increasing proliferation with increasing residual ash content and decreasing residual protein. These data indicate that chitosan characteristics other than DDA may be important to their biological performance.     

Bioassisted capture and release of nanoparticles on nanolithographed ZnO films

Using an artificial peptide library, we have identified a peptide that has strict selective affinity for ZnO surfaces. The binding affinity of the peptide on the ZnO surface can be controlled simply through changes in phosphate concentration at constant pH and temperature. In this study, we functionalized inorganic nanoparticles by orderly conjugating ZnO-binding peptides (ZnOBPs) on the surface of cadmium selenide (CdSe) nanoparticles and performed spontaneous and reversible nanopatterning of ZnOBP-displayed nanoparticles on lithographed ZnO films. Conjugation of ZnOBPs on CdSe nanoparticles caused spontaneous adsorption of the nanoparticles on a ZnO film, and fluorescence and cathodoluminescence images clearly showed specific adsorption of nanoparticles on the ZnO films lithographed on nano-?and micrometer scales. The selectively bound nanoparticles on ZnO films were completely released by changing the phosphate concentration in solution; such release did not require heat or mechanical applications. Repeated capture and release of nanoparticles were achieved on the micrometer scale. Our results show the potential of material-binding peptides for nanopatterning and dynamic microarrays.     

Deformation behavior of nanostructured ZnO films on glass

Nanostructured ZnO films on glass substrate were studied by nanoindentation, scanning electron and atomic force microscopy. The films were obtained by a straightforward mechanoactivated oxidation method. The morphology of the obtained films was grained with a grain size in the range 50-100 nm and the thickness was approximately 2 μm. A detailed deformation behavior of ZnO films, critical parameters and indentation induced plastic deformation mechanisms were determined in correlation to bulk ZnO, Si single crystal and commercial ZnO films. In comparison to a single crystal ZnO, nanostructured films exhibit increased hardness (9 GPa); however, the Young's modulus is decreased (120 GPa). A directly detectable evidence of brittleness, “pop-in” and “pile-up” phenomena in ZnO films was not observed. The ZnO/glass interface is stable and exhibits high adhesion, no signs of delamination or presence of brittleness cracks were detected (even at load P_max > 2 N). The role of grain boundaries on the properties of deformation behavior of ZnO nanostructured films has been discussed.     

Physical properties and molecular behavior of chitosan films

Chitosan films, varying in molecular weight and degree of deacetylation, were prepared by a casting technique using acetic acid as a dissolving vehicle. The physicochemical properties of the films were characterized. Both molecular weight and degree of deacetylation affected the film properties. Powder X-ray diffraction patterns and differential scanning calorimetry thermograms of all chitosan films indicated their amorphous state to partially crystalline state with thermal degradation temperature lower than 280-300°C. The increase in molecular weight of chitosan would increase the tensile strength and elongation as well as moisture absorption of the films, whereas the increase in degree of deacetylation of chitosan would either increase or decrease the tensile strength of the films depending on its molecular weight. Moreover, the higher the degree of deacetylation of chitosan the more brittle and the less moisture absorption the films became. All chitosan films were soluble in HCl-KCl buffer (pH 1.2), normal saline, and distilled water. They swelled in phosphate buffer (pH 7.4), and cross-linking between chitosan and phosphate anions might occur. Finally, transmission infrared and ¹³C-NMR spectra supported that chitosan films prepared by using acetic acid as a dissolving were chitosonium acetate films.     

Synthesis of ZnO nanoparticles and their ink-jetting behavior

Zinc oxide (ZnO) nanoparticles were synthesized by ultrasonically-assisted solution process without using any surfactants. The as-synthesized spherical ZnO nanoparticles with diameter of 20 +/- 5 nm possessed crystalline nature with wurtzite hexagonal phase and showed a blue-shifted near band-edge ultra-violet absorption at -340 nm due to quantum confinement effect of ZnO nanoparticles. The as-synthesized ZnO nanoparticles were further formulated as an ink for ink-jet printing application. Jetting and writing of various line patterns on Si and ITO substrates were demonstrated using the as-formulated ZnO ink. UV-treated substrates showed an improvement in the fixation of ink on substrate due to decreased contact angle with controlled surface wettability.     

Interfacial effects on the optical behavior of Ge:ITO and Ge:ZnO nanocomposite films

Nanophase semiconductors are of interest for their unique, size-tunable solar spectral absorption characteristics as well as their potential to contribute to the improved energy conversion efficiency of photovoltaics (PV). Embedding these nanoparticles within electrically active transparent conductive oxides (TCO) can also provide an opportunity for enhanced, long-range carrier transport. However, differences in the atomic and electronic structure, dielectric behavior, and chemistry between the matrix and semiconductor phases highlight the influence of interfacial effects on the optical absorption properties of the composite. In this work, nanocomposites of Ge:indium tin oxide (Ge:ITO) and Ge:ZnO were fabricated with sequential RF-magnetron sputtering and annealed at temperatures from 310 to 550?°C to investigate the impact of matrix identity on this interface and its contribution to nanostructure-mediated optical absorption. Transmission electron microscopy showed a decrease in Ge nanocrystal size relative to the initial semiconductor domain size in both matrices that was correlated with an increase in absorption onset energy after annealing. The effect was particularly pronounced in Ge:ITO composites in which Raman spectroscopy indicated the presence of germanium oxide at the semiconductor-ITO interface. These results support the primary contribution of carrier confinement in the Ge nanophase to the shifts in absorption onset energies observed.     

Development of novel guava puree films containing chitosan nanoparticles

One of the overall goals of industries is to use packages that do not cause environmental problems at disposal time, but that have the same properties as the conventional ones. The goal of this study is to synthesize edible films based on hydroxypropyl methylcellulose (HPMC) with guava puree and chitosan (CS) nanoparticles. This was divided into two stages, the first is the synthesis of chitosan nanoparticles and the second is the production of the films. For the nanoparticles, average size and zeta potential measurements were performed. The characterizations of mechanical and thermal properties, solubility and water vapor permeability tests were conducted in the films. It was observed that when the nanoparticles were added to HPMC and guava puree films, they improved their mechanical and thermal properties, as well as decreased the films solubility and permeability. The potential application of the films prepared would be in edible films with flavor and odor to extend the shelf life of products.     

Structural and nonlinear optical behavior of Ag-doped ZnO films

We present the structural and nonlinear optical behavior of Ag-doped ZnO (AZO) films prepared by magnetron sputtering. The structural of AZO films are systematically investigated by X-ray diffraction (XRD) and scanning electronic microscopy (SEM), respectively. The results show that AZO films can still retain a wurtzite structure, although the c-axis as preferred orientation is decreased by Ag doping. As the amounts of the Ag dopant were increased, the crystallinity as well as the absorptivity and optical band gap were increased. Moreover, the nonlinear optical characterized of the AZO films was studied using Z-scan technique. These samples show self-defocusing nonlinearity and good nonlinear absorption behavior which increases with increasing Ag volume fraction. AZO is a potential nanocomposite material for the development of nonlinear optical devices with a relatively small limiting threshold.     

Annealing effects on the photocatalytic activity of ZnO nanoparticles

This paper describes the development of ZnO nanoparticles by a chemical method, to test them in the photocatalysis of the degradation of textile dyes, using Rhodamine B (RhB) as a probe reaction. The samples were submitted to different heat treatments in order to observe the annealing effects on the photocatalytical properties, surface decontamination and the consequent particle change, in terms of crystallinity. The as-prepared samples (ZOA) correspond to a metastable phase (oxy or hydroxy zinc acetate) and post annealing leads to ZnO crystallization. In spite of the XRD patterns showing only the ZnO phase for heat treatment at 100 degrees C, FTIR data show that carboxylate groups remains attached to the ZnO surface up to 300 degrees C. Up to 300 degrees C the presence of these carboxylate groups, provided by the synthesis method, showed to be more relevant to photoactivity than the specific surface area. At higher temperatures, crystallinity becomes the dominant factor and an increasing of crystallinity favors the photoactivity.     

Surface nanomechanical behavior of ZrN and ZrCN films deposited on NiTi shape memory alloy by magnetron sputtering

Surface nanomechanical behavior under nanoindentation of ZrN and ZrCN film on NiTi substrate was studied. The surface hardness and modulus of the films increase initially with larger nanoindentation depths and then reach their maximum values. Afterwards, they diminish gradually and finally reaching plateau values which are the composite modulus and composite hardness derived from the ZrN/ZrCN film and NiTi substrate. They are higher than those of electropolished NiTi SMA due to the properties of ZrN and ZrCN. In comparison, the surface nanomechanical properties of electropolished NiTi exhibit a different change with depths.     

Optical and photoluminescence studies of gold nanoparticles embedded ZnO thin films

Gold nanoparticles (AuNPs) embedded ZnO thin films were prepared by sandwiching a thin thermally evaporated Au film between two sputtered ZnO films. The films were characterized by high resolution transmission electron microscopy (HRTEM), glancing angle X-ray diffraction (GXRD), optical absorption and photoluminescence (PL) measurements. GXRD data exhibited peaks which were attributed to the reflections from various ZnO and Au planes. Size dependence of the plasmon absorption was studied by forming nanoparticles with various sizes. Optical absorption spectra showed strong absorption due to localized surface plasmons at about 608, 638 and 676 nm for films having average AuNPs sizes of 27, 40 and 67 nm respectively. AuNPs embedded ZnO film showed a strong reduction in the intensity of photoluminescence, which was prominent in the case of pure ZnO film. The rise in temperature at a single nanoparticle site was calculated to be 22 K for a particle size of 80 nm.     

Doping induced structural and compositional changes in ZnO spray pyrolysed films and the effects on optical and electrical properties

Highly transparent, conductive ZnO films have been deposited by spray pyrolysis of a zinc acetate based solution. Quality films are yielded as our process is analogous to an aerosol assisted chemical vapour deposition rather than a droplet deposition spray pyrolysis technique. The properties of the films are governed by the additives to the base precursor solution. When aluminium acetylacetonate is added to the precursor solution, ZnO:Al films are grown with free charge carrier concentrations of more than 10²⁰ cm⁻³. The carrier density and mobility are measured by both Hall probe and near infrared spectroscopy. Film growth and grain size, morphology and orientation are altered using an increased percentage of ZnCl₂ in the precursor, which results in a 10 fold increase in charge carrier mobility. An investigation is presented correlating the composition of the precursor solution with the chemical, structural, electrical and optical properties of the grown films.     

Pulsed laser deposited ZnO films and their humidity sensing behavior

The present paper describes an opto-electronic humidity sensor based on thin film of zinc oxide prepared by pulsed laser deposition method. Being optical in nature it gives electromagnetic disturbance-free monitoring. The sensing element is a right-angled isosceles prism with its base coated with ZnO thin film. Films have been characterized by XRD, SEM, and optical transmission. Film grown with substrate at room temperature is amorphous whereas that grown at elevated temperature is single crystalline with grain size 38.52 nm. Film deposited at room temperature is sensitive to humidity over a wide range i.e. 5–90RH% while that deposited at elevated temperature is found to be insensitive to humidity. The sensor shows better sensitivity for higher range of humidity. The response and recovery time of the sensor element have also been evaluated. This sensor configuration can be used for on-line applications and in-situ monitoring.     

Influence of thickness on nanomechanical behavior of Black Diamond™ low dielectric thin films for interconnect and packaging applications

In the present study, we have investigated the thickness dependence of mechanical properties of the Black Diamond? (SiOC:H, BD, Low-k) films, which are of great interest in current Cu/low-k Back End of the Line (BEOL) interconnect/packaging technologies. For this investigation the BD thin films of six different thicknesses 100, 300, 500, 700, 1,000 and 1,200 nm were deposited on the 8″ Si wafer by using plasma enhanced chemical vapor deposition (PECVD) technique. Nanoindentation and nanoscratch tests of the BD films were performed by using the Nano Indenter^® XP (MTS Corp. USA). In nanoindentation testing of the BD films, significant differences in the elastic modulus of the BD films were observed. In nanoscratch testing, it is found that the critical load (Lc) and scratch width increases as the thickness of the film increases. Cross-sectional analysis of residual nanoindentation impressions was carried out using atomic force microscopy (AFM) to study the deformation behavior. The nanoindentation and nanoscratch responses of the BD thin films of six different thicknesses are different and they are expected mainly due to the molecular reorganization in thin/ultra thin films.     

Mapping the nanomechanical properties of graphene suspended on silica nanoparticles

Using nanoparticles to impart extrinsic rippling in graphene is a relatively new method to induce strain and to tailor the properties of graphene. Here, we study the structure and elastic properties of graphene grown by chemical vapour deposition and transferred onto a continuous layer of SiO₂ nanoparticles with diameters of around 25 nm, prepared by Langmuir–Blodgett technique on Si substrate. We show that the transferred graphene follows only roughly the morphology induced by nanoparticles. The graphene membrane parts bridging the nanoparticles are suspended and their adhesion to the atomic force microscope tip is larger compared to that of supported graphene parts. These suspended graphene regions can be deformed with forces of the order of 10 nN. The elastic modulus of graphene was determined from indentation measurements performed on suspended membrane regions with diameters in the 100 nm range.     

Controlled fabrication of gold nanoparticles biomediated by glucose oxidase immobilized on chitosan layer-by-layer films

The control of size and shape of metallic nanoparticles is a fundamental goal in nanochemistry, and crucial for applications exploiting nanoscale properties of materials. We present here an approach to the synthesis of gold nanoparticles mediated by glucose oxidase (GOD) immobilized on solid substrates using the Layer-by-Layer (LbL) technique. The LbL films contained four alternated layers of chitosan and poly(styrene sulfonate) (PSS), with GOD in the uppermost bilayer adsorbed on a fifth chitosan layer: (chitosan/PSS)₄/(chitosan/GOD). The films were inserted into a solution containing gold salt and glucose, at various pHs. Optimum conditions were achieved at pH 9, producing gold nanoparticles of ca. 30 nm according to transmission electron microscopy. A comparative study with the enzyme in solution demonstrated that the synthesis of gold nanoparticles is more efficient using immobilized GOD.     

Micromorphology and nanomechanical characteristics of sputtered aluminum thin films

Micromorphology and nanoindentation properties of sputtered aluminum thin films are presented. The field emission scanning electron microscope, atomic force microscopy (AFM) and nanoindentation results are presented for films prepared at a substrate temperature ranging between 44.5 °C and 100 °C. A multifractal approach on the microstructure is presented to comprehend the micromorphology of the films. The roughness decreases, whereas fractal dimension increases as the temperature increases. The hardness and Young's modulus do not exhibit any predictable trend. Hardness and Young's modulus exhibit a linear relationship.     

Deformation behavior during nanoindentation of epitaxial ZnO thin films on sapphire substrate

Nanoindentation studies were carried out on epitaxial ZnO thin films on (0001) sapphire substrates grown by radio frequency magnetron sputtering. A single discontinuity (‘pop-in’) in the load–displacement curve was observed at a specific depth (13−16 nm) irrespective of the film thickness. The physical mechanism responsible for the ‘pop-in’ event in these epitaxial films may be due to the nucleation, propagation and interaction behavior of the glissile threading dislocations during mechanical deformation. Indentation well below the critical depth was found to be plastic deformation behavior (residual impression of 4 nm).     

The effects of oxygen-catalysed and heat treatment on the precipitation synthesised ZnO nanoparticles

Nanocrystalline ZnO particles prepared by precipitation method from Zn and I₂ reaction with oxygen as catalyst were investigated. The addition of diethanolamine (DEA) as capping agent and fast pyrolysis treatment at 550, 700 and 850?°C were also characterised and elaborated. Compact and small spherical particles were observed for ZnO synthesised with O₂ catalysed whilst, uneven surface, fewer dense packing particles and macropore structures were observed for ZnO prepared without excess of O₂. It was shown that diffusion of O₂ has improved the structural and photoluminescence behaviour of the prepared ZnO nanoparticles. ZnO synthesised with O₂-catalysed exhibited better crystalline and leaned towards a pure state as shown by shifting of PL peak to higher energy of pure ZnO while, sample prepared without excess of O₂ exhibits poor crystalline and decreasing of the energy band gap with respect to increment of calcination temperatures. Single violet emission was observed in all samples synthesised with excess of O₂ whereby the highest intensity was obtained by calcining at 850?°C with photon energy at 2.95 eV. In contrast to sample with excess of O₂, ZnO calcined without excess of O₂ at 850?°C displays violet and green emission with energy at 2.93 eV and 2.35 eV, respectively.