Enhanced osteogenesis properties of titanium implant materials by highly uniform mesoporous thin films of hydroxyapatite and titania intermediate layer.

Titanium (Ti) has been widely used for medical and dental applications; however, bare Ti cannot be properly connected to a living bone, and hence some modifications are needed for this purpose. The present study describes the synthesis of mesoporous hydroxyapatite thin films (MHF) on titanium implant materials for speeding up and shortening the processes of osteointegration. The uniform MHF was coated on a Ti substrate following the insertion of intermediate titania (TiO2) film via the sol-gel dip-coating method. The intermediate titania layer improved the bonding strength between the MHF and Ti substrate. MHFs were synthesized using a precursor solution containing phosphoric acid, calcium nitrate tetrahydrate, and a nonionic surfactant (C12E10) as the phosphate source, calcium source, and structure-directing agent, respectively. The effect of calcination temperature on phase composition, morphology, microstructure, roughness, and wettability of the MHFs was investigated using XRD, FE-SEM, COM, AFM, and contact angle measurement. The XRD results revealed the crystalline hydroxyapatite phase, which was improved with an increase in the calcination temperature. Moreover, the FE-SEM images showed the crack-free MHFs, uniform thickness of the layer, and mesoporous surface morphology. In addition, it was found that the roughness and wettability of the samples change upon the alteration of calcination temperature. The biological studies demonstrated that MHFs support the adhesion and proliferation of the mesenchymal stem cells (MSCs) and guid them toward osteogenic differentiation. Therefore, the MHFs prepared in this study may be useful in a wide range of applications, particularly in bone regeneration medicine.

Preparation of ordered mesoporous alumina-doped titania films with high thermal stability and their application to high-speed passive-matrix electrochromic displays.

Ordered mesoporous alumina-doped titania thin films with anatase crystalline structure were prepared by using triblock copolymer Pluronic P123 as structure-directing agent. Uniform Al doping was realized by using aluminum isopropoxide as a dopant source which can be hydrolyzed together with titanium tetraisopropoxide. Aluminum doping into the titania framework can prevent rapid crystallization to the anatase phase, thereby drastically increasing thermal stability. With increasing Al content, the crystallization temperatures tend to increase gradually. Even when the Al content doped into the framework was increased to 15 mol %, a well-ordered mesoporous structure was obtained, and the mesostructural ordering was still maintained after calcination at 550 °C. During the calcination process, large uniaxial shrinkage occurred along the direction perpendicular to the substrate with retention of the horizontal mesoscale periodicity, whereby vertically oriented nanopillars were formed in the film. The resulting vertical porosity was successfully exploited to fabricate a high-speed and high-quality passive-matrix electrochromic display by using a leuco dye. The vertical nanospace in the films can effectively prevent drifting of the leuco dye.

Structural basis for the simultaneous recognition of NEMO and acceptor ubiquitin by the HOIP NZF1 domain.

Ubiquitination of NEMO by the linear ubiquitin chain assembly complex (LUBAC) is essential for activating the canonical NF-κB signaling pathway. While the NZF1 domain of the HOIP subunit of LUBAC recognizes the NEMO substrate, it is unclear how it cooperates with the catalytic domains in the ubiquitination process. Here, we report a crystal structure of NEMO in complex with HOIP NZF1 and linear diubiquitin chains, in which the two proteins bind to distinct sites on NEMO. Moreover, the NZF1 domain simultaneously interacts with NEMO and Ile44 surface of a proximal ubiquitin from a linear diubiquitin chain, where the C-term tail of the ubiquitin is in the proximity of the NEMO ubiquitination site (Lys285). We further propose a model for the linear ubiquitination of NEMO by HOIP. In the model, NZF1 binds the monoubiquitinated NEMO and recruits the catalytic domains to the ubiquitination site, thereby ensuring site-specific ubiquitination of NEMO.

Synthesis of continuous mesoporous Ga-doped titania films with anatase crystallized framework.

Here we report synthesis of ordered mesoporous titania films with various amounts of Ga content. The influence of Ga contents on mesostructural ordering, surface morphology, thermal stability, and anatase crystallinity is carefully investigated, by using grazing incidence small angle X-ray scattering (GISAXS), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), and Raman spectroscopy. The presence of highly dispersed Ga contents in the titania frameworks can promote the thermal stability of mesoporous titania structures, resulting that the anatase crystallization successfully proceeds without collapse of mesostructures.

Meso-macroporous crack-free nanohydroxyapatite coatings templated by C12 E10 diblock copolymer on Ti6Al4V implant materials toward human osteoblast-like cells.

Meso-macroporous nanohydroxyapatite coatings (MHACs) were synthesized on Ti6Al4V implant materials calcined at different temperatures using a nonionic diblock copolymer template (C12 E10 ) by sol-gel and dip-coating methods. To improve the bonding strength between the substrate and coating, a TiO2 intermediate layer was applied on the surface of the substrates. The physicochemical and structural properties of MHAC samples were fully studied by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, scanning probe microscopy, field-emission scanning electron microscopy (FESEM), Brunauer-Emmett-Teller method, and contact angle measurements. Based on the data obtained, the hydroxyapatite phase with a flower-like morphology was formed on the Ti6Al4V substrates in all of the samples. According to confocal optical microscopy and FESEM images, there was no macrocrack and microcrack on the MHACs, whereas they were accompanied by macroporosities and mesoporosities on top of the coatings. By increasing the calcination temperature from 500°C to 650°C, the crystallite sizes increased, while the surface roughness value and hydrophilicity decreased. A reduction in specific surface area and an increase in the pore diameters occurred as the calcination temperature increased. In addition, the assessment of protein adsorption behavior over the samples revealed that the adsorption amounts significantly increased as the substrates were coated with HAP; however, the affinity of surface for protein adsorption was strictly dependent on the surface topography and hydrophilicity. in vitro cellular assay disclosed a great cytocompatibility in terms of adhesion and proliferation in MHAC samples as compared with that in TiO2 -coated and bare substrates. Regarding the physicochemical properties and biological studies, MHAC calcined at 650°C was deemed optimal for bone tissue engineering.

Catechin-conjugated mesoporous hydroxyapatite nanoparticle: A novel nano-antioxidant with enhanced osteogenic property.

Hydroxyapatite is the main component of mineral phase of bone which is widely employed for coating metal implants and scaffold materials in synthetic bone grafts owing to its osteoinductive property. In order to improve the bioactivity of hydroxyapatite, mesoporous hydroxyapatite nanoparticles (MHAP) were synthesized and chemically functionalized with 3-aminopropyltriethoxysilane. The amine-functionalized nanoparticles were conjugated with a natural antioxidant, catechin (Cat), through a stable amide linkage. The true structure of the bioconstruct was confirmed by calculating condensed Fukui indices. The functionalized-hydroxyapatite nanoparticles (Cat@MHAP) showed an outstanding antioxidant activity, having reactivity toward hydroxyl and superoxide radicals larger than that of free catechin. To explore the bone cell responses to this material, multilayer nanoparticle films were prepared by MHAP and Cat@MHAP on a glass substrate. Afterward, the short- and long-term responses of cultured mesenchymal stem cells (MSCs), osteosarcoma cells (Saos-2), and doxorubicin-resistant cells (RSaos-2/Dox) on the surface of the prepared films were investigated. Both the MSCs and bone tumor cells selectively adhered onto Cat@MHAP surface as compared with glass and MHAP at initial culture time. Moreover, it was found that Cat@MHAP decreases the proliferation of Saos-2 and RSaos-2/Dox cells in a time-dependent manner, while it supports the growth of MSCs, indicating the ability of Cat@MHAP to distinguish tumor cells from normal ones. Further, Cat@MHAP promotes the osteogenic differentiation in both the MSCs and tumor cells, accompanied by the attenuation of intracellular ROS. From these results, Cat@MHAP is a novel "nano-antioxidant," which could be considered as a promising biomaterial in treating bone defects, particularly after surgery in osteosarcoma patients.

Methotrexate-F127 conjugated mesoporous zinc hydroxyapatite as an efficient drug delivery system for overcoming chemotherapy resistance in osteosarcoma cells.

The resistance of cancer cells to chemotherapeutic agents and the poor selectivity of drugs toward tumor cells are regarded as the main impediments in successful cancer therapy. Currently, the design and fabrication of stimulus-responsive drug delivery systems with high specificity toward cancer cells are gaining increasing attention and they show a promising potential for clinical applications. In this study, mesoporous zinc-substituted hydroxyapatite has been synthesized and served as a drug delivery vehicle owing to its biocompatibility and high drug loading capacity. The mesoporous nanoparticles were decorated with F127 and subsequently conjugated with methotrexate (MTX) through a stable amide linkage. Since folate receptors are overexpressed on many tumor cell surfaces, MTX on the nanocarrier system plays a dual role as a targeting molecule and a chemotherapeutic drug. The evaluation of the drug release profile revealed that MTX was cleaved from the nanoparticles by a certain type of enzyme under low pH conditions that are meant to simulate the intracellular conditions in the lysosome. Cell viability studies on primary osteosarcoma cells (Saos-2) and MTX-resistance cell lines (RSaos-2/MTX) revealed that the drug-loaded nanoparticles possess high antitumor efficacy on both of the cell lines relative to free MTX. It was also found that the inhibition of P-glycoproteins by F127 and the release of Zn2+ ions from the nanoparticles in an acidic environment effectively potentiate the antitumor efficacy of the drug-loaded nanoparticles, leading to caspase-mediated cell death. Based on these data, MTX-F127@ZnHAP nanoparticles are pH-responsive nanocarriers with precise controlled drug release and targeting effect. Therefore, they are considered to be promising candidates capable of overcoming resistance in osteosarcoma cells.

Synthesis of highly ordered mesoporous alumina thin films and their framework crystallization to γ-alumina phase.

Here we report the preparation of highly ordered mesoporous alumina films existing both as P6(3)/mmc and Fm-3m mesostructures by using triblock copolymer Pluronic P123 as the structure-directing agent. 2D grazing-incidence small-angle X-ray scattering (GI-SAXS) completely proves the existence of two different mesopore structures (i.e., [001]-oriented P6(3)/mmc and [111]-oriented Fm-3m symmetries). After calcination at 1000 °C, the amorphous alumina framework is successfully converted to γ-alumina crystals. During the crystallization process, large uniaxial shrinkage occurs along the direction perpendicular to the substrate with the retention of horizontal mesoscale periodicity, thereby resulting in formation of partially vertical mesoporosity in the film. Through detailed electron microscopic study, we discuss the formation mechanism for the vertical mesoporosity upon calcination. The obtained mesoporous γ-alumina film shows high thermal stability up to 1000 °C, which is highly useful in wide research areas such as catalyst supports and separators.