High Crystalline Hydroxyapatite Research Articles

Nano-hydroxyapatite filled EPDM nanocomposite: towards green elastomeric thermal insulating coating with superior mechanical, thermal, and ablation properties

ABSTRACT Heat-shielding composite materials containing asbestos has been used for thermal insulation of aerospace rocket motors. However, asbestos has carcinogenic effects on both human and environment. This study was directed to the development of novel elastomeric nanocomposite thermal-shielding coating (asbestos-free); the developed elastomeric nanocomposite was based on hydroxyapatite (HA) nanoparticles (NPs) in an ethylene propylene diene monomer (EPDM) matrix. HA is a bio-ceramic material with 18.5 wt % phosphorus; HA can act as nano phosphorus-based fire extinguisher. HA NPs were synthesized by continuous hydrothermal technique; high crystalline HA nanoplates of 350 nm length, and 100 nm width were successfully developed. HA NPs were integrated into EPDM matrix; uniform dispersion of HA particles was verified via EDAX analysis. The impact of HA NPs on EPDM tensile strength, elongation-at-break, hardness, density, thermogravimetric analysis (TGA), thermal conductivity test, and ablation test was assessed to asbestos fibers. HA/EPDM secured superior mechanical properties compared with Asbestos/EPDM; HA NPs secured an increase the tensile strength, elongation at break by 16.2% and 105.3% respectively. HA with surface hydroxyl groups could be integrated into EPDM matrix via chemical bonding. HA offered novel thermal shielding properties; HA secured a decrease in thermal conductivity coefficient by −21.1%; and the best ablation resistance was increased by + 31.5%. Residual weight was increased by 13%, compared with asbestos fibers.

Synthesis, Characterization, In Vitro Cytological Responses, and In Vivo Bone Regeneration Effects of Low-Crystalline Nanocarbonated Hydroxyapatite.

Hydroxyapatite (HA) has been commonly used as an alternative bone substitute. But it has drawbacks, such as poor degradation and limited osteogenesis. Low-crystalline carbonated hydroxyapatite (L-CHA), which has greater biodegradability than HA, is suggested as one of the main components of bone minerals, but the exact mechanism behind the roles of carbonate substituted in biological behaviors of low-crystalline HA is still a mystery. In this study, L-CHAs with different carbonate contents were prepared, and the effects of the content on the physicochemical properties, in vitro cytological responses, and in vivo bone defects repair effects of L-CHAs were investigated. The results demonstrated that CO32- had successfully entered the lattice structure of L-CHAs with a maximum content of 9.2 wt %. Both low-crystalline undoped HA (L-HA) and L-CHAs were nanocrystalline (20-30 nm) with significantly higher specific surface areas, protein adsorption capacities, and biodegradability compared to high-crystalline HA (H-HA) with submicron crystalline size (200-400 nm). Besides, the amounts of the adsorbed protein and released Ca2+ ions increased in a carbonate-content-dependent manner. Compared to L-HA and H-HA, L-CHAs promoted the adhesion and proliferation of bone marrow mesenchymal stem cells and significantly upregulated the levels of alkaline phosphatase (ALP) activity and the expression of osteogenesis-related genes. In addition, L-CHA-9 not only showed a faster biodegradation rate but also effectively promoted bone regeneration when implanted in the critical-sized bone defects of rabbit femora. This study provided evidence for the development of L-CHA as a promising biodegradable and bioactive material with great osteoconductivity and osteogenic capability with respect to conventional HA.

High crystalline hydroxyapatite coating by eclipse type pulsed-laser deposition for low annealing temperature

The eclipse type pulsed-laser deposition (PLD) scheme as a droplet-eliminated method with irradiation on a β-tricalcium phosphate (β-TCP) slab target was employed to achieve high density without holes, high purity, and high crystallinity hydroxyapatite (HAp) coating on a zirconia substrate with a low annealing temperature under an H2O vapor pressure. An obstacle ball was set between the target and the substrate so that ablated droplets would collide with the ball and be eliminated, while other ablated atoms went around the ball and were deposited on the substrate. A flat, transparent, and high-density coating layer was deposited on the substrate in an H2O vapor atmosphere at 0.1 Torr for different substrate surface temperatures from 20 °C to 650 °C. The phase of the coating layers was significantly changed from amorphous calcium phosphate to crystalline HAp when the temperature was set to over 360 °C, as determined from Raman microscopy measurements. Raman spectroscopy also showed that the HAp crystal size became larger as the temperature was increased to over 360 °C. It was concluded that the eclipse type PLD method with irradiation on a β-TCP target would improve the quality of HAp coatings and allow effective lowering of the annealing temperature.

Early Bone Healing on Hydroxyapatite-Coated and Chemically-Modified Hydrophilic Implant Surfaces in an Ovine Model.

Implant topography affects early peri-implant bone healing by changing the osteoconduction rate in the surrounding biological environment. Implant surfaces have been designed to promote faster and stronger bone formation for rapid and stable prosthesis loading. Early peri-implant bone healing has been observed with a sandblasted, acid-etched implant that was chemically modified to be hydrophilic (cmSLA). The present study investigates whether early peri-implant bone healing extends to a rough surface implant with a high crystalline hydroxyapatite surface (TSV MP-1 HA). Three implants were randomly placed in porous trabecular bone within both medial femoral condyles of 10 sheep. Early peri-implant bone stability was measured at 3- and 6-weeks healing time following implant insertion. Results indicated a similar implant stability quotient between the implants at insertion and over time. The significant increase over time of reverse torque values with respect to insertion torque (p < 0.001) did not differ between the implants. However, the bone-to-implant contact of TSV MP-1 HA was significantly higher than that of cmSLA implants at 6 weeks (p < 0.01). These data validate previous findings of a hydrophilic implant surface and extend the observation of early osseointegration to a rough surface implant in porous trabecular bone.

In situ synthesis of three dimensional graphene-hydroxyapatite nano powders via hydrothermal process

Abstract In this study, in situ formation of three dimensional graphene-hydroxyapatite using graphene oxide, calcium nitrate tetra hydrate, and diammonium hydrogen phosphate solutions in a chemical synthesis system was investigated. First, the solutions were mixed and calcium phosphate was precipitated on graphene oxide sheets followed by performing a hydrothermal method at 180 °C, 2.2 MPa, pH = 11, and 6 h. The latter process resulted in the formation of three dimensional graphene while it was coated on hydroxyapatite nanorods. The synthesized powders were characterized in two steps for calcium phosphate-graphene oxide powders before hydrothermal process and three dimensional graphene-hydroxyapatite powders after hydrothermal process with Fourier-Transform Infrared spectroscopy (FT-IR), Field Emission Scanning Electron Microscope (FESEM), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Energy Dispersive Spectroscopy (EDS), and Raman spectroscopy. The results of XRD and FTIR analysis showed that in the first step, di-calcium phosphate dehydrates were formed on graphene oxide sheets and converted to hydroxyapatite after the hydrothermal process. Raman spectroscopy analysis and FTIR confirmed that graphene oxide has been reduced in the hydrothermal process. Also, microscopic images confirmed the three-dimensional structure of graphene after hydrothermal process. Finally, the results showed that the hydrothermal method leads to the formation of a high crystalline hydroxyapatite nanorods that cover the surface of the three dimensional graphene.

Bioactive glass nanoparticles with negative zeta potential

The purpose of this work was to produce and characterize SiO 2–CaO–P 2O 5 bioactive glass nanoparticles with negative zeta potential for possible use in biomedical applications. 63S bioactive glass was obtained using the sol–gel method. X-ray fluorescence (XRF) spectroscopy and dispersive X-ray analysis (EDX) confirmed the preparation of the 63S bioactive glass with 62.17% SiO 2, 28.47% CaO and 9.25% P 2O 5 (in molar percentage). The in vitro apatite forming ability of prepared bioactive glass was evaluated by Fourier transform infrared spectroscopy (FTIR) after immersion in simulated body fluid (SBF). The result showed that high crystalline hydroxyapatite can form on glass particles. By the gas adsorption (BET method), particle specific surface area and theoretical particle size were 223.6 ± 0.5 m 2/g and ∼24 nm, respectively. Laser dynamic light scattering (DLS) indicated particles were mostly agglomerated and had an average diameter between 100 and 500 nm. Finally, using laser Doppler electrophoresis (LDE) the zeta potential of bioactive glass nanoparticles suspended in physiological saline was determined. The zeta potential was negative for acidic, neutral and basic pH values and was −16.18 ± 1.8 mV at pH 7.4. In summary, the sol–gel derived nanoparticles revealed in vitro bioactivity in SBF and had a negative zeta potential in physiological saline solution. This negative surface charge is due to the amount and kind of the ions in glass structure and according to the literature, promotes cell attachment and facilitates osteogenesis. The nanometric particle size, bioactivity and negative zeta potential make this material a possible candidate for bone tissue engineering.

Bone Substitute Fabrication Based on Dissolution-Precipitation Reactions

Although block- or granular-type sintered hydroxyapatite are known to show excellent tissue responses and good osteoconductivity, apatite powder elicits inflammatory response. For the fabrication of hydroxyapatite block or granules, sintering is commonly employed. However, the inorganic component of bone and tooth is not high crystalline hydroxyapatite but low crystalline B-type carbonate apatite. Unfortunately, carbonate apatite powder cannot be sintered due to its instability at high temperature. Another method to fabricate apatite block and/or granule is through phase transformation based on dissolution-precipitation reactions using a precursor phase. This reaction basically is the same as a setting and hardening reaction of calcium sulfate or plaster. In this paper, apatite block fabrication methods by phase transformation based on dissolution-precipitation reactions will be discussed, with a focus on the similarity of the setting and hardening reaction of calcium sulfate.

Effect of gun current on the microstructure and crystallinity of plasma sprayed hydroxyapatite coatings

Hydroxyapatite (HA) is a bioactive material because its chemical structure is close to the natural bone. Its bioactive properties make it attractive material in biomedical applications. Gas tunnel type plasma spraying (GTPS) technique was employed in the present study to deposit HA coatings on SUS 304 stainless steel substrate. GTPS is composed of two plasma sources: gun which produces internal low power plasma (1.3–8 kW) and vortex which produces the main plasma with high power level (10–40 kW). Controlling the spraying parameters is the key role for spraying high crystalline HA coatings on the metallic implants. In this study, the arc gun current was changed while the vortex arc current was kept constant at 450 A during the spraying process of HA coatings. The objective of this study is to investigate the influence of gun current on the microstructure, phase crystallinity and hardness properties of HA coatings. The surface morphology and microstructure of as-sprayed coatings were examined by scanning electron microscope. The phase structure of HA coatings was investigated by X-ray diffraction analysis. HA coatings sprayed at high gun current (100 A) are dense, and have high hardness. The crystallinity of HA coatings was decreased with the increasing in the gun current. On the other hand, the hardness was slightly decreased and the coatings suffer from some porosity at gun currents 0, 30 and 50 A.

Preparation of a Bioactive Xenograft

The method which gives a low crystalline hydroxyl carbonated apatite forming ability to originally non-bioactive high crystalline hydroxyapatite surface was newly developed. The granules of trabecular bovine bone, which had a size range from 212 to 1000 μm, were defatted, deproteinized, and then heat-treated at 1000 oC for 3 hours to remove organics completely. They were treated with the mixed solution of calcium chloride and calcium hydroxide in Soxhlet’s apparatus at 100 oC for 3 days and then dried completely. Low crystalline hydroxyl carbonated apatite was observed to occur on the surface of high crystalline hydroxyapatite granules after soaking them into the simulated body fluid (SBF) for 1 week. This method is likely to have a potential to be used as a new process to give a bioactivity to originally non-bioactive materials.

Synthesis of hydroxyapatite via mechanochemical treatment

Hydroxyapatite powder was synthesized with calcium pyrophosphate (Ca 2P 2O 7) and calcium carbonate (CaCO 3) through solid-state reaction. The two powders were mixed in acetone and water, respectively, and the single phase of hydroxyapatite was observed to occur only in the powder milled in water, without the additional supply of water vapor during heat-treatment at 1100°C for 1 h. The results were explained in terms of the mechanochemical reaction that could supply enough amount of hydroxyl group to the starting powders to form a single phase of hydroxyapatite. Practical implication of the results is that the powder of high crystalline hydroxyapatite can be obtained by the simple milling in water and subsequent heat-treatment.