Sonochemical synthesis of hydroxyapatite from H3PO4 solution with Ca(OH)2

Ultrasound was irradiated to an aqueous suspension containing phosphoric acid (H3PO4) and calcium hydroxide (Ca(OH)2) to investigate the sonochemical effect on preparation of hydroxyapatite (Ca10(PO4)6(OH)2, HAp). HAp monophase could be synthesized from the suspension sonicated for 60 min. The reaction for HAp was promoted more effectively than that of the heating method conducted at the same conditions as those for the sonicating method. The equilibrium pH of the suspensions sonicated over 60 min was maintained neutral, suggesting that the synthesis reaction was almost completed. The ultrasonic irradiation played an important role to progress the heterogeneous reaction and the preparation of very fine HAp powder.     

Fabrication of hydroxyapatite and TiO2 nanorods on microarc-oxidized titanium surface using hydrothermal treatment

AC-type microarc oxidation (MAO) and hydrothermal treatment techniques were used to enhance the bioactivity of commercially pure titanium (CP-Ti). The porous TiO₂ layer fabricated by the MAO treatment had a dominant anatase structure and contained Ca and P ions. The MAO-treated specimens were treated hydrothermally to form HAp crystallites on the titanium oxide layer in an alkaline aqueous solution (OH-solution) or phosphorous-containing alkaline solution (POH-solution). A small number of micro-sized hydroxyapatite (HAp) crystallites and a thin layer composed of nano-sized HAps were formed on the Ti-MAO-OH group treated hydrothermally in an OH-solution, whereas a large number of micro-sized HAp crystallites and dense anatase TiO₂ nanorods were formed on the Ti-MAO-POH group treated hydrothermally in a POH-solution. The layer of bone-like apatite that formed on the surface of the POH-treated sample after soaking in a modified simulated body fluid was thicker than that on the OH-treated samples.     

Enhanced mechanical strength of hydroxyapatite nanorods reinforced with polyethylene

Hydroxyapatite (HAp) nanostructures may be an advanced candidate in biomedical applications for an apatite substitute of bone and teeth than other form of HAp. In contrast, well-defined size and shape control in synthesizing HAp nanostructures is always difficult. In this study, hydroxyapatite nanorods (HAp NRs) were prepared by simple hydrothermal method with controlling the reaction time without using any surfactant or templating agents. The nanostructure clearly depicts the growth stages of the HAp NRs by increasing the reaction time. The synthesized HAp has the rod like morphology with uniform size distribution with the aspect ratio of about 8–10. Transmission electron microscopic (TEM) and high resolution TEM (HRTEM) images show that the growth direction of the HAp is parallel to the (001) plane. The interplanar distances measured in segments (fringes) of the HRTEM micrograph were ~0.35 nm, corresponding to the interplanar spacing of the (002) plane of the hexagonal HAp. X-ray diffraction (XRD) measurements indicate that the improved crystallinity of the HAp by increasing the reaction time. The mechanical studies reveal that the improved tensile strength and the abrasion resistance are observed for the HAp nanorods reinforcing with high molecular weight polyethylene (HMWPE).     

Water-dispersible hydroxyapatite nanorods synthesized by a facile method

A simple and effective method, using calcium nitrate and triammonium phosphate as starting materials, for the preparation of water-dispersible hydroxyapatite nanorods (HAp) was reported. The process primarily involves the preparation of HAp with the addition of sodium citrate (NaC) and the exchange of absorbed ions (NaC) with sodium hexame taphosphate (NaP). The end products were investigated using various means in order to confirm the particles’ crystal phase and morphology and to understand how to improve their stability. The results demonstrate that the resulting HAp at 90 °C is rod-like with length of 300-400 nm and width of 40-60 nm. The zeta potential values of pure HAp, HAp-NaC, HAp-NaC/NaP are from −15.20, −30.89 to −44.84 mV. The settling time test shows the HAp-NaC/NaP could keep stable above 7 months without any creaming or visible sedimentation. The amount of NaC and the reaction temperature play significant roles in the whole process due to the formation of Ca containing precipitates.     

Synthesis and hyperthermia property of hydroxyapatite-ferrite hybrid particles by ultrasonic spray pyrolysis

Biocompatible hybrid particles composed of hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HAp) and ferrite (γ-Fe₂O₃ and Fe₃O₄) were synthesized using a two-step procedure. First, the ferrite particles were synthesized by co-precipitation. Second, the suspension, which was composed of ferrite particles by a co-precipitation method, Ca(NO₃)₂, and H₃PO₄ aqueous solution with surfactant, was nebulized into mist ultrasonically. Then the mist was pyrolyzed at 1000 °C to synthesize HAp-ferrite hybrid particles. The molar ratio of Fe ion and HAp was (Fe²⁺ and Fe³⁺)/HAp=6. The synthesized hybrid particle was round and dimpled, and the average diameter of a secondary particle was 740 nm. The cross section of the synthesized hybrid particles revealed two phases: HAp and ferrite. The ferrite was coated with HAp. The synthesized hybrid particles show a saturation magnetization of 11.8 emu/g. The net saturation magnetization of the ferrite component was calculated as 32.5 emu/g. The temperature increase in the AC-magnetic field (370 kHz, 1.77 kA/m) was 9 °C with 3.4 g (the ferrite component was 1.0 g). These results show that synthesized hybrid particles are biocompatible and might be useful for magnetic transport and hyperthermia studies.     

Spectroscopic studies of hydroxyapatite in PVP/PVA polymeric matrix as biomaterial

This system is focusing on characterization and spectroscopic studies of PVA and PVP blend and the blend filled with various mass fractions (2.5, 5 and 10%) of HAp because it has great potential for applications in the medical purposes. The films have been prepared by solution casting technique. The characteristic properties of the films were examined by FT-IR, X-ray, SEM, TGA and DSC techniques from room temperature to 500 °C. XRD scans reveal the semicrystalline nature of the prepared films and demonstrated that complexation between the blend and the HAp were occur. SEM and thermal studies confirmed these results. Three main weight loss regions were observed in TGA thermograms that reveal reduction in the thermal stability of the prepared samples as HAp content increases. Three main transition peaks were observed in DSC with a single T_g which indicates a good miscibility of the films. The ratio Ca:P is 1.65:1 which confirm the formation of hydroxyapatite. So, the present work can be used in various bio-applications.     

Electrophoretic deposition of PVA coated hydroxyapatite on 316L stainless steel

Polyvinyl alcohol (PVA) coated hydroxyapatite was deposited onto a 316L stainless steel substrate by electrophoretic deposition. Deposition was carried out in a methanol suspension at pH 5.5 using a graphite rod as an anode. Parameters such as PVA concentration, deposition voltage and time were optimized to achieve a homogeneous, crack-free adhesive coating. Techniques such as X-ray diffraction and Fourier transform infrared spectroscopy were used to study the phase composition of the coated materials and the stability of hydroxyapatite in the presence of PVA.     

Hydroxyapatite Nano Sol Prepared via A Mechanochemical Route

Well-dispersed sol with crystalline hydroxyapatite (HAp) was obtained directly by milling a mixture comprising Ca(OH)₂, an aqueous solution of H₃PO₄ and a dispersant, an ammonium salt of polyacrylic acid. The average crystallite size of HAp was below 20 nm. Ca/P molar ratio of the product was 1.51 ± 0.04, i.e. Ca deficient from stoichiometric HAp. Minimum apparent viscosity was attained at a dispersant concentration 0.92wt% of sol. An as-milled sol was diluted by a factor 10–2.61 solid wt% to give a Newtonian fluid of 2 mPa s. From the diluted sol, we obtained a few m thick dense film of HAp by dip coating on the slide glass precoated by chitosan.     

Preparation and Mechanical and Tribological Properties of High-Density Polyethylene/Hydroxyapatite Nanocomposites

High-density polyethylene (HDPE) nanocomposites reinforced with hydroxyapatite nanorods (nHA) were fabricated by means of extrusion and injection molding. The thermal, mechanical, and dry sliding wear properties of HDPE-based nanocomposites filled with nHA loadings up to 20 wt% were investigated. The results of mechanical property characterization showed that nHA additions improved the hardness, elastic modulus, and yield strength of HDPE at the expense of its tensile ductility and impact strength. Thermogravimetric analysis and heat deflection temperature measurements revealed that nHA fillers are very effective to enhance the thermal stability of HDPE. The wear behavior of HDPE/nHA nanocomposites was studied using a pin-on-disk tribometer. nHA fillers of a large aspect ratio improved the wear resistance of HDPE substantially because of their load-bearing effect and the formation of a continuous transfer film on the steel counterface.     

Real-time SAXS and ultraviolet-visible spectral studies on size and shape evolution of gold nanoparticles in aqueous solution

Gold nanoparticles were synthesized with seed mediated wet growth method. A coexistent system with gold nanorods and nanospheres was prepared. In-situ real-time small angle X-ray scattering (SAXS) and ultraviolet-visible (UV-vis) absorption were used to monitor the growth process of Au nanoparticles in the aqueous solution. Combining SAXS measurement and UV-vis spectra, the contribution of gold nanorods was separated from that of gold nanospheres. The growth behavior of the gold nanorods and the gold nanospheres was studied. The size and shape evolution of both gold nanoparticles as well as their volume fractions were obtained. After adding the seed-solution into the growth solution to form a particle suspension, within the first 18 min, a mutual competitive growth occurred between the gold nanorods and nanospheres. And their average particle sizes always increased with growth time. 18-min later, the evolution of size and shape of gold nanoparticles was almost stopped. The results demonstrate that the aspect ratio of gold nanorods in the particle suspension follows an exponential decay change after the initial 5-min growth. The evolution process of size and shape of gold nanoparticles in the particle suspension has been discussed.