Sorachon Yoriya

Highly-ordered TiO2 nanotube arrays up to 220 µm in length: use in water photoelectrolysis and dye-sensitized solar cells

The fabrication of highly-ordered TiO2 nanotube arrays up to 134 µm in length by anodization of Ti foil has recently been reported (Paulose et al 2006 J. Phys. Chem. B 110 16179). This work reports an extension of the fabrication technique to achieve TiO2 nanotube arrays up to 220 µm in length, with a length-to-outer diameter aspect ratio of ≈1400, as well as their initial application in dye-sensitized solar cells and hydrogen production by water photoelectrolysis. The highly-ordered TiO2 nanotube arrays are fabricated by potentiostatic anodization of Ti foil in fluoride ion containing baths in combination with non-aqueous organic polar electrolytes including N-methylformamide, dimethyl sulfoxide, formamide, or ethylene glycol. Depending upon the anodization voltage, the inner pore diameters of the resulting nanotube arrays range from 20 to 150 nm. As confirmed by glancing angle x-ray diffraction and HRTEM studies, the as-prepared nanotubes are amorphous but crystallize with annealing at elevated temperatures.

Long-Term Small Molecule and Protein Elution from TiO2 Nanotubes

In this study, TiO(2) nanotubes of various dimensions were used to elute albumin, a large protein molecule, as well as sirolimus and paclitaxel, common small molecule drugs. The nanotubes controlled small molecule diffusion for weeks and large molecule diffusion for a month. Drug eluted from the nanotubes was bioactive and decreased cell proliferation in vitro. Elution kinetics was most profoundly affected by tube height. This study demonstrates that TiO(2) nanotubes may be a promising candidate for a drug-eluting implant coating.

High-Efficiency Förster Resonance Energy Transfer in Solid-State Dye Sensitized Solar Cells

Solid-state dye-sensitized solar cells (SS-DSCs) offer the potential to make low cost solar power a reality, however their photoconversion efficiency must first be increased. The dyes used are commonly narrow band with high absorption coefficients, while conventional photovoltaic operation requires proper band edge alignment significantly limiting the dyes and charge transporting materials that can be used in combination. We demonstrate a significant enhancement in the light harvesting and photocurrent generation of SS-DSCs due to Förster resonance energy transfer (FRET). TiO(2) nanotube array films are sensitized with red/near IR absorbing SQ-1 acceptor dye, subsequently intercalated with Spiro-OMeTAD blended with a visible light absorbing DCM-pyran donor dye. The calculated Förster radius is 6.1 nm. The donor molecules contribute a FRET-based maximum IPCE of 25% with a corresponding excitation transfer efficiency of approximately 67.5%.

Self-Assembled TiO2 Nanotube Arrays by Anodization of Titanium in Diethylene Glycol: Approach to Extended Pore Widening

We report on the formation of titanium dioxide nanotube arrays having the largest known pore size, approximately 350 nm diameter. The nanotube arrays are synthesized by Ti foil anodization in a diethylene glycol electrolyte containing low (0.5-2%) concentrations of hydrofluoric acid. The large pore size nanotube arrays are achieved with extended anodization durations of approximately 120 h, with the anodization duration showing a more significant effect on pore diameter than the anodization voltage. It appears that the combined effects of hydrofluoric acid content and anodization duration determine the lateral etching rate of the nanotubes, leading to the larger pore size nanotubes.

Hemocompatibility of titania nanotube arrays

Hemocompatibility is a key consideration for the long-term success of blood contacting biomaterials; hence, there is a critical need to understand the physiological response elicited from blood/nano-biomaterial interactions. In this study, we have investigated the adsorption of key blood serum proteins, in vitro adhesion and activation of platelets, and clotting kinetics of whole blood on titania nanotube arrays. Previous studies have demonstrated improved mesenchymal stem cell functionality, osteoblast phenotypic behavior, localized drug delivery, and the production of endothelial cell ECM on titania nanotube arrays. Furthermore, these titania nanotube arrays have elicited minimal levels of monocyte activation and cytokine secretion, thus exhibiting a very low degree of immunogenicity. Titania nanotube arrays were fabricated using anodization technique and the surface morphology was examined through scanning electron microscopy (SEM). The crystalline phases were identified using glancing angled X-ray diffraction (GAXRD). Nanoindentation and scratch tests were used to characterize the mechanical properties of titania nanotube arrays. The adsorption of key blood proteins (albumin, fibrinogen, and immunoglobulin-g) was evaluated using a micro-BCA assay and X-ray photoelectron spectroscopy (XPS). The adhesion and activation of platelets was investigated using live-cell staining, MTT assay, and SEM. Whole blood clotting kinetics was evaluated by measuring the free hemoglobin concentration, and SEM was used to visualize the clot formation. Our results indicate increased blood serum protein adsorption, platelet adhesion and activation, and whole blood clotting kinetics on titania nanotube arrays.

Synthesis of ordered arrays of discrete, partially crystalline titania nanotubes by Ti anodization using diethylene glycol electrolytes

We report the fabrication of self-organized titania nanotube arrays comprised of separated, discrete nanotubes by Ti anodization in fluoride ion containing diethylene glycol (DEG) electrolytes. We describe the effect of the fluoride bearing species used in the anodization electrolyte on the tube morphology, degree of tube-to-tube separation, and crystallization. The arrayed nanotubes achieved from DEG electrolytes containing either HF or NH4F are fully separated with open pores.

Dermal fibroblast and epidermal keratinocyte functionality on titania nanotube arrays

Transcutaneous implants that penetrate through the depth of the skin are used in numerous clinical applications, including prosthetics and dental implants. Favorable interactions between the implant surface and the respective skin layers are critical for the long-term success of transcutaneous implantable devices, hence, it is essential to understand the physiologic response elicited by skin-biomaterial interactions. Recent studies have shown that material surfaces that provide topographic cues at the nanoscale level may provide one possible solution to enhanced biomaterial integration, thus preventing biomaterial rejection. In this study titania nanotube arrays were fabricated using a simple anodization technique as potential interfaces for transcutaneous implantable devices. The in vitro functionality of human dermal fibroblasts and epidermal keratinocytes were evaluated on these nanotube arrays (diameter 70-90 nm, length 1-1.5 μm). Cellular functionality in terms of adhesion, proliferation, orientation, viability, cytoskeletal organization, differentiation and morphology were investigated for up to 4 days in culture using fluorescence microscope imaging, a cell viability assay, indirect immunofluorescence and scanning electron microscopy. The results reported in this study indicate increased dermal fibroblast and decreased epidermal keratinocyte adhesion, proliferation and differentiation on titania nanotube arrays.

Self-assembled anodic TiO2 nanotube arrays: electrolyte properties and their effect on resulting morphologies

Self-assembled TiO2 nanotube arrays fabricated by electrochemical anodization of titanium are of great interest having been successfully used in many applications including gas sensing, water photoelectrolysis, drug delivery and photovoltaics. Nanotube array synthesis techniques have been studied and developed through several electrolyte systems, however, the key parameters controlling self-organization of the nanotubes have remained unclear. Herein we examine nanotube array morphological growth parameters as dependent upon electrolyte conductivity and titanium concentration. Electrolyte properties establish a regime wherein the TiO2 nanotube arrays self-assemble. Nanotube morphological parameters, including pore diameter, wall thickness and tube-to-tube spacing, are all found to increase with electrolyte conductivity. Using diethylene glycol (DEG) based electrolytes as a model, we detail how manipulation of electrolyte conductivity enables control of nanotube array morphological features.

Titania nanoporous/tubular structures via electrochemical anodization of titanium: effect of electrolyte conductivity and anodization voltage on structural order and porosity

The formation mechanisms of self-organized anodic titania nanotube arrays have been widely studied with an aim towards enabling precise control of nanotube array morphology and properties, thereby allowing control of fabrication parameters for optimal performance of the resulting films in their given application. Building upon recent work [S. Yoriya and C. A. Grimes, J. Mater. Chem., 2011, 21, 102–108], we elucidate the self-ordering and porosity of nanoporous and nanotubular anodic titania films as a function of anodization conditions.