Mechanical and photocatalytic properties of hydroxyapatite/titania nanocomposites prepared by combined high gravity and hydrothermal process

Hydroxyapatite/titania nanocomposites of different ratios have been successfully synthesized by combined high gravity and hydrothermal methods. SEM and TEM observations showed that small spheres of TiO₂, identified as anatase crystals of 10–15 nm, were deposited on HAp rod-like crystals. EDAX analysis confirmed the presence of Ca, P, Ti and O. X-ray diffraction patterns indicated the presence of hydroxyapatite and anatase phase. More number of anatase peaks appeared in the XRD patterns with higher colloidal concentration of TiO₂ in the HAp/TiO₂ compound. Mechanical stability of the HAp/TiO₂ nanocomposites was determined by reinforcing them with high molecular weight polyethylene (HMWPE) and the tensile strength of the samples was analyzed. Photocatalytic activity of the HAp/TiO₂ particles was examined by decomposition of methyl orange (MO). The results showed that photocatalytic properties of HAp/TiO₂ composites are more effective than that of individual HAp and TiO₂ which implied that the HAp improved the photocatalytic activity of well known photocatalyst TiO₂.     

Photoluminescence and doping mechanism of theranostic Eu3+/Fe3+ dual-doped hydroxyapatite nanoparticles

Theranostic nanoparticles currently have been regarded as an emerging concept of ‘personalized medicine’ with diagnostic and therapeutic dual-functions. Eu³⁺ doped hydroxyapatite (HAp) has been regarded as a promising fluorescent probe for in vivo imaging applications. Additionally, substitution of Ca²⁺ with Fe³⁺ in HAp crystal may endow the capability of producing heat upon exposure to a magnetic field. Here we report a preliminary study of doping mechanism and photoluminescence of Eu³⁺ and Fe³⁺ doped HAp nanoparticles (Eu/Fe:HAp). HAp with varied concentration of Eu³⁺ and Fe³⁺ doping are presented as Eu(10 mol%):HAp, Eu(7 mol%)-Fe(3 mol%):HAp, Eu(5 mol%)-Fe(5 mol%):HAp, Eu(3 mol%)-Fe(7 mol%):HAp, and Fe(10 mol%):HAp in the study. The results showed that the HAp particles, in nano-size with rod-like morphology, were successfully doped with Eu³⁺ and Fe³⁺, and the particles can be well suspended in cell culture medium. Photoluminescence analysis revealed that particles have prominent emissions at 536 nm, 590 nm, 615 nm, 650 nm and 695 nm upon excitation at a wavelength of 397 nm. Moreover, these Eu/Fe:HAp nanoparticles belonged to B-type carbonated HAp, which has been considered an effective biodegradable and biocompatible drug/gene carrier in biological applications.     

Hydroxyapatite nanorod-reinforced biodegradable poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid) composites for bone plate applications

Novel PLLA composite fibers containing hydroxyapatite (HAp) nanorods with or without surface lactic acid grafting were produced by extrusion for use as reinforcements in PLLA-based bone plates. Fibers containing 0–50% (w/w) HAp nanorods, aligned parallel to fiber axis, were extruded. Lactic acid surface grafting of HAp nanorods (lacHAp) improved the tensile properties of composites fibers better than the non-grafted ones (nHAp). Best tensile modulus values of 2.59, 2.49, and 4.12 GPa were obtained for loadings (w/w) with 30% lacHAp, 10% nHAp, and 50% amorphous HAp nanoparticles, respectively. Bone plates reinforced with parallel rows of these composite fibers were molded by melt pressing. The best compressive properties for plates were obtained with nHAp reinforcement (1.31 GPa Young’s Modulus, 110.3 MPa compressive strength). In vitro testing with osteoblasts showed good cellular attachment and spreading on composite fibers. In situ degradation tests revealed faster degradation rates with increasing HAp content. To our knowledge, this is the first study containing calcium phosphate–polymer nanocomposite fibers for reinforcement of a biodegradable bone plate or other such implants and this biomimetic design was concluded to have potential for production of polymer-based biodegradable bone plates even for load bearing applications.     

CHA/UHMWPE复合关节材料的生物摩擦学研究

采用热压成型工艺制备了超高分子量聚乙烯 (U HMWPE) /珊瑚羟基磷灰石 (CHA) 复合关节材料 , 利用人工髋关节模拟磨损试验系统 , 研究了该类复合材料与 CoCrMo 合金组合关节在小牛关节液润滑条件下的摩擦磨损性能。实验结果表明 , 添加 CHA 能有效提高 U HMWPE关节材料的表面硬度 , 降低其磨损率。当CHA添加量为 20 wt %时 , 可获得表面硬度与抗磨损性能的良好匹配。小牛关节液润滑条件下 , U HMWPE及其复合材料的磨损机理主要表现为研磨磨损和疲劳磨损 , 磨损颗粒尺寸随 CHA粉体添加量的增加而增大。      

Hydrothermal microemulsion synthesis of stoichiometric single crystal hydroxyapatite nanorods with mono-dispersion and narrow-size distribution

The stoichiometric single crystal hydroxyapatite (HAp) nanorods with mono-dispersion and narrow-size distribution in diameter were successfully synthesized via a hydrothermal microemulsion method, and the as-synthesized powders were characterized by XRD, FETEM, FTIR and ICP-AES. In the present work, a novel technique of w/o microemulsions of CTAB/n-pentanol/n-hexane/water under hydrothermal condition to synthesize single crystal HAp nanorods with diameter 25–40 nm and length 55–350 nm, was described. The homogeneity in size distribution and shape of the HAp nanorods was probably attributed to the w/o nano-reactors and the soft template of the surfactants, and the high crystallization of the products was attributed to the hydrothermal treatment. The sintering ability of the nanorods and the mechanical properties of the fabricated HAp bioceramics were also preliminarily investigated. The results showed that the fabricated HAp bioceramics possessed high mechanical properties.     

Synthesis and characterization of high purity hydroxyapatite nanorods by hydrothermal technique

High purity hydroxyapatite (HAp) nanorods were synthesized by hydrothermal technique using Ca(NO3)2 x 4H2O and (NH4)2HPO4 as starting materials in a hydrothermal reactor at 150-200 degrees C for 12-24 h with pH6 and pH9.5, respectively. The prepared HAp nanorods were characterized by XRD, FTIR, and TEM techniques. The XRD results confirmed the formation of pure phase of HAp at pH9.5. With increasing temperature and time, the crystallinity of the HAp was increased, showing the hexagonal structure of HAp with the lattice parameter a in a range of 1.144-1.148 nm and c of 0.723-0.724 nm. The crystalline sizes of the powders were found to be 44-85 nm as evaluated by the XRD line broadening technique. The chemical compositions of the HAp nanorods were characterized by FTIR spectroscopies. The peaks of the phosphate carbonate and hydroxyl vibration modes were observed in the FTIR spectra for all the samples. The morphology of the HAp was nanorods of diameter less than 100 nm, as revealed by TEM. Increasing the temperature and time resulted in the transition from polycrystalline to single crystalline phase of the HAp, as clearly confirmed by the analysis of TEM diffraction patterns.     

Synthesis of nanosize single-crystal hydroxyapatite via mechanochemical method

Single-crystal hydroxyapatite (HAp) nanorods and nanogranules have been synthesized successfully by a mechanochemical process using two distinct experimental procedures. The experimental outcomes are characterized by transmission electron microscopy (TEM), and powder X-ray diffraction (XRD) techniques. In this work, the feasibility of using polymeric milling media to prepare hydroxyapatite nanoparticles is described. The resulting hydroxyapatite powder exhibits an average size of about 20 to 23 nm. Final results indicate that the proposed synthesis strategy provides a facile pathway to obtain single-crystal HAp with high quality and suitable morphology.     

Doping transition of doped ZnO nanorods measured by Kelvin probe force microscopy

We have investigated the doping transition of one-dimensional (1-D) doped-ZnO nanorods with Kelvin probe force microscopy (KPFM). Vertically aligned (undoped, As-doped, and undoped/As-doped homo-junction) ZnO nanorods were grown on Si (111) substrates without any catalyst by vapor phase transport. Individual ZnO nanorods are removed from the substrates and transferred onto thin Au films grown on Si substrates. The morphology and surface potentials of the nanorods were measured simultaneously by the KPFM. For the homo-junction nanorods with ~ 250 nm in diameter, the KPFM image shows localization of the doping transition along the nanorods. The measured Kelvin signal (surface potential) across the junction induces the work function difference between the undoped and the As-doped region of ~ 85 meV. Also, the work function of As-doped nanorods is ~ 95 meV higher than that of intrinsically undoped nanorods grown in similar conditions. These consistent results indicate that the KPFM is reliable to determine the localization of the doping transition in 1-D structures.     

Microporous Hydroxyapatite Ceramic Composites as Tissue Engineering Scaffolds: An Experimental and Computational Study

Bone‐tissue engineering mandates the development of multi‐functional bioactive porous hydroxyapatite (HAp) scaffolds. Herein, microwave sintered HAp/ZnO and HAp/Ag composite scaffolds with ≈5–19% porosity are developed using 0–30 vol% graphite as a porogen. The mechanical properties of the porous scaffold are analyzed in detail, revealing that even being more porous, the reinforcement of ZnO (9% porosity, hardness of 2.8 GPa, and toughness of 3.5 MPa.m^1/2) has shown to have better hardness and fracture toughness when compared to Ag (5% porosity, hardness of 1.6 GPa, and toughness of 2.6 MPa.m^1/2). The flexural strength obtained experimentally are complemented with a finite‐element technique that adopts microstructural features in visualizing the effect of porosity on stress distribution. The antibacterial efficacy and cytocompatibility of these composites are validated by increased metabolic activity and conspicuous cell‐matrix interactions. The anticipation of the results reveal that HAp/ZnO (9% porosity) and HAp/Ag (5% porosity) composites can be used as a potential multi‐functional bone implant scaffolds.

     

Fracture behavior and biocompatibility evaluation of nylon-infiltrated porous hydroxyapatite

Hybrid hydroxyapatite/polymer composites were prepared by the infiltration of nylon into porous hydroxyapatite. Porous hydroxyapatite (HAp) bodies were prepared from a whisker-like powder with high aspect ratio by pressureless-sintering at various temperatures. Pore characteristics, such as the fraction of open porosity and the pore size distribution, were designed and evaluated by mercury porosimeter. Through the in situ polymerization of -caprolactam, infiltrated into the porous HAp body, a polymeric secondary phase network interpenetrated with the HAp phase was obtained. The obtained hybrid HAp/nylon composites were evaluated with respect to their fracture behavior, i.e., fracture energy, and in vitro bioactivity in simulated body fluid (SBF) in the present paper. These HAp/nylon hybrid composite have a K _IC of 1.65 MPam^1/2 and also a good bioactivity according to the results of SBF immersion tests.     

Surface modification of nanophase hydroxyapatite with chitosan

Nanophase hydroxyapatite (HAp) particles were aged in 0–2.5 wt.% chitosan acetate solutions for 30 days to evaluate the influence of chitosan on HAp surface chemistry. The HAp characterization results from Fourier transform infra-red spectroscopy (FTIR), thermal gravimetric analysis (TGA), Carbon–Hydrogen–Nitrogen (CHN) analysis, and BET N₂ adsorption revealed measurable changes in the HAp surface chemistry after aging in the chitosan acetate solutions. The TGA mass loss exhibited by HAp increased from 3.3–6.5 mass% as the chitosan acetate gel concentration increased from 0–2.5 mass%. The CHN analysis revealed an increase in C and H contents with increasing chitosan acetate concentration while the N concentration remained relatively constant (0.30–0.32 mass%). Chitosan interactions with HAp caused an increase in specific surface area from 85 m²/g up to 160 m²/g for HAp aged in 1.5 mass% chitosan acetate solution (HAp[1.5]). Chitosan exhibits strong adsorption interactions with HAp and enhances colloid stability for processing of chitosan/hydroxyapatite nanocomposites.     

Selective and controlled synthesis of multiform morphologies Y2O3:Eu3+ and luminescence properties

Uniform Y2O3 nanorods, nanosheets, nanotubes and nanoshperes were controllably synthesized via an urea-based homogeneous precipitation and hydrothermal synthesis through choosing appropriate yttrium sources, the water/ethanol ratio of mixed solvents and precipitators. The nanopheres and nanotubes were obtained through homogeneous precipitation method using soluble yttrium nitrate as the yttrium source. The nanosheets and nanorods were obtained via a facile hydrothermal synthetic method using yttrium chloride and yttrium acetate as the yttrium source. During these experiments Urea and NaOH were used as precipitators and added in correct order. We also studied the spectroscopic properties of Y2O3:Eu3+ phosphor. The Eu3+ ion mainly shows its characteristic red (611 nm, 5D0 --> 7F2) emissions in all kinds of morphologies Y2O3:Eu3+ phosphor, but emission intensity are different. It can be explain from the viewpoint of their different absorption properties closely related to their micro-morphologies.     

CTAB-assisted hydrothermal synthesis of single-crystalline copper-doped ZnO nanorods and investigation of their photoluminescence properties

A simple CTAB-assisted hydrothermal synthesis of undoped and copper-doped ZnO nanorods is reported. The phase and structural analysis carried out by X-ray diffraction, shows the formation of hexagonal wurtzite structure of ZnO. Morphology of the ZnO nanorods was investigated by electron microscopy techniques which showed the formation of well dispersed regular shape ZnO nanorods of 100 ± 10 nm in diameter and 900 ± 100 nm in length. However, size of the copper doped ZnO nanorod slightly increased with increasing copper concentration. Furthermore, the selected area electron diffraction pattern and high resolution transmission electron microscopy reveal that both the undoped and copper doped ZnO nanorods were single crystalline in nature and preferentially grew up along [0001] direction. Optical property was investigated by photoluminescence spectroscopy. The effects of copper doping on the photoluminescence property of ZnO nanorods were investigated.     

Doped polycrystalline TiO2 electrodes for the photo-assisted electrolysis of water

The optical-to-chemical photoelectrolytic conversion efficiency of polycrystalline TiO₂ anodes has been studied as a function of metal dopant. For anodes nominally doped to a level of $\text{100}$ ppm, an enhancement of the conversion efficiency over that for undoped anodes was observed upon doping with Al, V, Cu, Y, Ta, Nb, Mo, Ni, and Pd. Greatest enhancement was observed for the Y-doped anodes. Optical measurements indicate no significant shift in band gap due to the doping, and it is suggested that efficiency-enhancement may be achieved via a dopantinduced shifting of the flat-band potential.     

Novel chelate-setting calcium-phosphate cements fabricated with wet-synthesized hydroxyapatite powder

The hydroxyapatite (HAp) powder preparation process was optimized to fabricate inositol phosphate-HAp (IP6-HAp) cement with enhanced mechanical properties. Starting HAp powders were synthesized via a wet chemical process. The effect of the powder preparation process on the morphology, crystallinity, median particle size, and specific surface area (SSA) of the cement powders was examined, together with the mechanical properties of the resulting cement specimens. The smallest crystallite and median particle sizes, and the highest SSA were obtained from ball-milling of as-synthesized HAp powder under wet conditions and then freeze-drying. IP6-HAp cement fabricated with this powder had a maximum compressive strength of 23.1 ± 2.1 MPa. In vivo histological studies using rabbit models revealed that the IP6-HAp cements were directly in contact with newly formed and host bones. Thus, the present chelate-setting HAp cement is promising for application as a novel paste-like artificial bone.     

Influence of pentavalent dopant addition to polarization and bioactivity of hydroxyapatite

Influence of pentavalent tantalum doping in bulk hydroxyapatite (HAp) ceramics has been investigated for polarizability and bioactivity. Phase analysis from X-ray diffraction measurement indicates that increasing dopant concentration decreased the amount of HAp phase and increased β-TCP and/or α-TCP phases during sintering at 1250 °C in a muffle furnace. Results from thermally stimulated depolarization current (TSDC) measurements showed that doping hindered charge storage ability in HAp ceramics, and doped samples stored fewer charge compared to pure HAp. However, doping enhanced wettability of HAp samples, which was improved further due to polarization. In vitro human osteoblast cell–material interaction study revealed an increase in bioactivity due to dopant addition and polarization compared to pure HAp. This increase in bioactivity was attributed to the increase in wettability due to surface charge and dopant addition.     

Synthesis and characterization of HAp nanorods from a cationic surfactant template method

Hydroxyapatite (HAp) [Ca₁₀(PO₄)₆(OH)₂] nanorods were synthesized using a surfactant templating method, with cetyltrimethylammonium bromide (CTAB) micelles acting as template for HAp growth. The effects of the sintering temperature on the morphological and crystallographic characteristics and on chemical composition of the “as-prepared” structures are discussed. The experimental results show that low heat-treatment temperatures are preferred in order to obtain high quality nanorods, with diameters ranging between 20 and 50 nm. High heat-treatment temperatures enhance the thermal decomposition of HAp into other calcium phosphate compounds, and the sintering of particles into micrometer ball-like structures. The stability of aqueous suspensions of HAp nanorods is also discussed.     

The influence of the rotation frequency of a planetary ball mill on the limiting value of the specific surface area of the WC and Co nanopowders

An increase in the hardness and wear resistance of WC-Co alloys with a decrease in the grain diameter of WC and Co makes it relevant to search for methods for producing powders with a maximum specific surface area (SSA). SSA growth is limited even when milling powders of WC and Co in the most high-energy mills. Effect of increasing the rotation speed of a planetary ball mill on the limiting value of the SSA of obtained nano sized WC and Co powders is studied. According to the developed model, an increase in the rotational speed of the mill leads to an increase in the limiting value of SSA if the cause is particle hardening. If the cause is coalescence, an increase in frequency leads to a decrease in the limiting value of the SSA. It was determined that the limiting value of SSA of WC particles increases from 1.0⋅10⁸ m²/m³ to 2.2⋅10⁸ m²/m³ (Sauter average diameter decreases from 60 to 27 nm) with increase of mill rotation frequencies from 2.5 to 4.2 rps due to a decrease in the volume of “indestructible” particles. And the limiting value of SSA of WC particles decreases from 2.2⋅10⁸ m²/m³ to 1.1⋅10⁸ m²/m³ (Sauter average diameter increases from 26 to 55 nm) with increase of mill rotation frequencies from 5 to 6.7 rps due to the increase of the coalescence rate. The experiment showed that the limiting value of SSA for Co powder decreases from 1.0⋅10⁸ m²/m³ to 1.1⋅10⁶ m²/m³ with increasing of the rotational speed of the mill from 2.5 rps to 6.7 rps (Sauter average diameter increases from 60 to 5450 nm) due to the increase of the coalescence rate. Studies have shown that the growth of SSA of WC grains is limited by a certain value (11.5 nm).     

The transformation of single-crystal calcium phosphate ribbon-like fibres to hydroxyapatite spheres assembled from nanorods

Two precursors of ribbon-like anhydrous dicalcium phosphate (DCPA) and calcium phosphate fibres were successfully synthesized at 85?°C through a simple and mild pathway from Ca(NO(3))(2)·4H(2)O and (NH(4))(2)HPO(4) upon the hydrolysis of urea. Different molar concentrations of urea resulted in different precursors, including precursor I (DCPA phase) and precursor II (calcium phosphate with DCPA, octacalcium phosphate (OCP) and hydroxyapatite (HAp) phase). By immersing the two precursors in ammonium hydroxide solution (pH = 12), the transformation from precursors to hydroxyapatite could be achieved. X-ray diffraction (XRD) results combined with transmission electron microscopy (TEM) indicated that DCPA fibres (precursor I) were transformed to HAp nanorods in transformation I. In transformation II, dandelion-like spheres assembled by HAp nanorods were obtained from calcium phosphate (precursor II). The mechanisms of transformations I and II are also proposed and discussed based on the XRD and TEM results.     

Influence of Au Photodeposition and Doping in CdS Nanorods: Optical and Photocatalytic Study

Au-modified CdS nanorods (100–200 nm × 5–10 nm) are synthesized via two different techniques, namely photodeposition and doping. The prepared samples are characterized by x-ray powder diffraction, transmission electron microscopy (TEM), and UV–vis and fluorescence spectroscopy. X-ray diffraction study confirmed the hexagonal phase of bare and Au-CdS samples, whereas, 5 wt% Au³⁺ doping into CdS resulted in a slight distortion in the crystal structure toward higher degree side. TEM images revealed the fine distribution of Au nanodeposits of size in the range of 2.5–4.5 nm on to the CdS surface in the photodeposited sample. The optical spectrum shows a significant red-shift in absorption onset (485 nm → 515 nm) and band-edge emission (505 nm → 512 nm) of CdS nanorods with the replacement of certain Cd²⁺ ions with Au³⁺. The influence of Au photodeposition and doping in CdS nanorods was comparatively tested by photooxidation of RhB (50 ppm) dye aqueous solution under direct sunlight irradiation (35–40 mWcm^?2). Our results point out that 5 wt% Au³⁺ doping into CdS nanorods remarkably improved its activity and stability due to homogeneous dispersion of charge throughout the crystal, quick Fermi level equilibration, and an improvement in ionic bond formation.