Dielectric oxides are traditionally used to fabricate resistive surface humidity-sensing devices, as well as capacitive sandwich-structured sensors. In the present work, relative humidity (RH) sensors were fabricated by employing vertically aligned TiO(2) nanotubes array (TNA) film produced using electro-chemical anodization of Ti foil followed by a nitrogen-doping process, simultaneously showing resistive and capacitive humidity-sensing properties in the range of 11.3-93.6%. For the sample formed at optimized experimental conditions, the capacitance (C(S)) and resistance (R(S)) of the as-fabricated RH sensors made from nitrogen-doped TiO(2) nanotubes film could be simultaneously obtained. Both the resistive and capacitive sensitivity (K(R) and K(C)) of the as-fabricated TiO(2) nanotube RH sensors show distinct dependence on the frequency of alternating current (AC) voltage signal and RH. At higher water coverage, water-water interaction will result in lowering of the water dissociation barrier, leading to an increase of conductance. With the increase of RH, the polarization of as-adsorbed water molecules will also occur, causing a sharp increase of capacitance. For an explanation of the frequency response of both C(S) and R(S), ionic transport, as well as the polarization effect, should be comprehensively considered. The changes of capacitance and resistance at different temperatures are plausibly caused by thermal expansion and surface state modification by adsorption and desorption of oxygen and water.
To develop an optimized local delivery system of simvastatin (SV) with improved osseointegration of titanium (Ti) implants, SV-loaded poly(ethylene glycol)-poly(epsilon-caprolactone) (PECL) micelles (80 nm in diameter) were loaded in titania nanotube (TNT) arrays (80-100 nm in diameter and 400 nm in length) that were fabricated by anodizing Ti sheets. An in vitro release experiment was performed and revealed that TNTs and micelles can jointly provide a sustained release of SV, and that TNTs alone might function in drug release. The effect of the Ti surface with TNTs or TNTs-micelles on osteoblast-like MG-63 cells was determined by analyzing cell morphology, cytoskeletal arrangement, early adhesion, proliferation, alkaline phosphatase activity, and intracellular and extracellular osteocalcin content. The results indicate that the Ti surface with SV-loaded TNTs-micelles not only has better able to promote early adhesion, spreading and early differentiation of osteoblasts than the Ti surface with TNTs alone but it is able to promote calcification of osteoblasts. Therefore, a Ti surface with TNTs or TNTs-micelles is expected to promote contact osteogenesis of the Ti implant, thus contributing to early osseointegration of the implant, whereas the osteogenic effect of the Ti surface with TNTs-micelles is expected to be stronger. This local delivery system can bridge the gap between basic research and applied science for a wide range of titanium-based orthopedic implants in diverse bone-loss diseases, including osteoporosis.
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