HA Crystals Research Articles

Resorption Rate of Calcium Sulfate Bone Fillers Adjusted by Incorporation of Hydroxyapatie

Calcium sulfate/hydroxyapatie (CaSO4/HA) composite bone fillers were fabricated through molding method. Their structure and properties were characterized by infrared spectroscope, scanning electronic spectroscope, x-ray diffraction and degradation test. The results show that HA crystals were attached to the CaSO4 crystals and prevented the growing of sulfate crystals. So their size is shorter than that of CaSO4 crystals prepared from pure CaSO4 semihydrate, and some even had defect. The resorption rate of CaSO4 bone fillers was decreased when HA was incorporated.

Formation of Nano-Phase Hydroxyapatite Film on TiO<SUB>2</SUB> Nano-Network

Nano- and micro-phase HA film formed on TiO2 nano-network surface by simple electrochemical treatment. The range of lateral pore size of the network specimen was about 10-120 nm on Ti surface by anodized in 5 M NaOH solution at 0.3 A for 10 min. Nano-network TiO2 surface were formed by this anodization step which acted as templates and anchorage for growth of the HA during subsequent pulsed electrochemical deposition process at 85 degrees C. The phase and morphologies of deposits HA were influenced by the electrolyte concentration. The nano needle-like precipitates formed under low SBF concentration were identified to be HA crystals orientated parallel to the c-axis direction. Increasing electrolyte concentration, needle-like deposits transferred to the plate-like and micro plate like precipitates in the case of high SBF concentration.

The influence of chromium ions on the growth of the calcium hydroxyapatite crystal

Hydroxyapatite (Ca10(PO4)6(OH)2) is widely used as bio-ceramic materials and as adsorbents for separation of bio-molecules. These materials have also been used as adsorbents for heavy metals, supports and as catalysts in oxidation and dehydrogenation reactions. The catalytic performance of these materials depend on the lattice substitution of Ca sites in Hydroxyapatite structure by varied cations as Na, Mg, Sr and Mn, which result in changes in various structural pro perties as crystallinity and morphology. Pure calcium hydroxyapatite (S1) and Cr loaded hydroxyl apatite (S2, S3, S4 and S5) of different chromium concentrations have been prepared by wet precipitated method. An in-vitro examination is essential to investigate the mechanism of the deficient HA and tissue interface reaction by preparing SBF (Simulated Body Fluid) through the elemental and chemical analysis of Ca, P and Cr. FTIR used to analyze the samples after incubation in SBF for 24 day. PH of the samples also was measured at the first period of immersion time. At high loading of chromium ions, the formation of carbonate apatite decrease. The concentrations of the chromium in the Cr_HA crystal during the soaking in SBF are very safe dose for human.

Synthesis and Luminescence Properties of Tb<sup>3+</sup>-Doped Hydroxyapatites

In this paper, the terbium -doped nano-HA powders with strong fluorescence was prepared by hydrothermal synthesis and its crystal structure，morphology and fluorescent properties are characterized by XRD, TEM, XPS, ICP and PL spectroscopy. Results showed that with the doping concentration of Tb3+increasing, the aspect ratio of Tb3+-doped HA particles decreased, while the fluorescence intensity excited by ultraviolet ray at 272 nm is significantly enhanced. With pH values increased from 6.5 to 10.0, the aspect ratio of Tb3+-doped HA decreased greatly, and the morphology of nano-Tb:HA particles changes from rod particles to equiaxed particles and the actual doping content and the fluorescence intensity tends to increase correspondingly, which can be explained that under alkaline solution, Tb3+was more easier entering the HA crystal, and the Tb3+would substitute the Ca2+ in both hydroxyapatite Ca(Ⅰ) and Ca(Ⅱ) site, which may block the active growth sites of the seed crystals and resulted in the growth rate and the ratio of length to radius decreasing.

Effects of Aging and Temperature on the Oriental Growth of Hydroxyapatite

In order to find a simple way to prepare oriental HA, only by controlling the preparation conditions, a co-precipitation method was used to prepare an oriented HA. The influences of temperature and aging on its directional growth were investigated kinetically and thermodynamically. The chemical composition was characterized by X-Ray diffraction and Fourier transform infrared. The morphologies were observed by scanning electron microscopy (SEM). The oriented parameters of HA (c/a) were calculated by Scherrer equation. The results show that the temperature rise in the process of synthesis, aging or calcining inhibited the growth of HA crystal in the direction of c-axis. Aging for 24 h benefited the growth along c-axis, whereas aging for 36 h was in favor of the decreasing of the c/a value. The supernatant-replacement during aging exerted the same effect on the growth with the rising of temperature. The SEM analysis result shows that the morphology of the produced HA particles looked like a uniform needle shape and had a good dispersion.

Proposed model for growth preference of plate-like nanohydroxyapatite crystals on superhydrophilic vertically aligned carbon nanotubes by electrodeposition

For the first time, the mechanism of growth of plate-like n-HA electrodeposited on superhydrophilic vertically aligned multi-walled carbon nanotubes (VACNT) is presented and a model for the specific growth preference is discussed. Results show that the carboxyl (carboxylic acid)/carboxylate functional groups directly attached on VACNT tips after oxygen plasma treatment were essential for the acceleration of the OH− formation and the deposition of plate-like HA crystals. FEG-SEM, EDX and XRD showed that a homogeneous highly crystalline HA film, stoichiometric and with preferential growth in the (002) plane direction, was formed.

Formation of Hydroxyapatite Whiskers by Hydrothermal Homogeneous Precipitation Using Acetamide

Well‐crystallized, compositionally homogeneous HA whiskers with uniform morphology and high aspect ratio were successfully prepared by hydrothermal homogeneous precipitation from aqueous solution using acetamide (AA). The product had a mean length of 116 μm and an aspect ratio of 102. The nucleation and crystal growth of such whiskers were studied by quenching the solution from various temperatures. It was found that the nuclei could be formed at about 120°C, while stable and well‐grown whisker‐like precipitation only occurred above 140°C. The product had the same crystallographic characteristics as normal HA crystals. No other phase than HA was detected. Compared with widely used wet chemical routes, the slow hydrolysis of AA provided a stable and continuous growth environment with a low degree of supersaturation, facilitating rapid growth of long HA whiskers directly from a hydrothermal solution, free of any interference from other phases. The whiskers showed spiral growth, with preferential c‐axis orientation.

Microstructure and mechanical characteristics of hydroxyapatite coatings on Ti/TiN/Si substrates synthesized by pulsed laser deposition

We synthesized by pulsed laser deposition a bilayer of Ti/TiN on Si(100) wafers which was coated in a next step with hydroxyapatite (samples labelled HA-1). Some of the structures were further thermally treated in a water vapour jet (samples labelled HA-2). In SEM, the HA surface looked rough, with micronic droplets. TEM and SAED investigations revealed a compact organization of HA crystals in the case of the HA-1 sample, while two regions (one compact and one porous) were identified for the HA-2 sample, with triclinic HA crystals within the 500 nm range. In XTEM, at the Si/TiN border, a 2–3 nm SiO2 layer was visible, whereas at the TiN/Ti border there was a smooth transition from fcc (111) TiN to hcp (100) Ti. The HA crystals were elongated normal to the surface. According to Berkovich indentation qualitative analyses, the sample HA-1 was more homogeneous and harder but brittle. Scratch tests confirmed quantitatively that HA-1 was more resistant and adherent than HA-2 films. In the first case, the big droplets only were removed by the indenter, while the HA-2 films were delaminated on large areas as a result of wedge spallation failure.

Modulation of hydroxyapatite crystals formed from α-tricalcium phosphate by surfactant-free hydrothermal exchange

In the present work, an unusual precursor, α-tricalcium phosphate [Ca3(PO4)2, α-TCP] was used for the modulation of hydroxyapatite [Ca10(PO4)6(OH)2, HA] crystals. Micro-structure and morphology controllable HA crystals were successfully synthesized via direct hydrothermal treatment of α-TCP particles in the absence of any surfactants or additives, and were investigated by field emission scanning electron microscopy, field emission transmission electron microscopy, X-ray diffraction, X-ray fluorescence spectroscopy and Fourier transform infrared spectroscopy. Well developed HA crystals with different structures and morphologies (chrysanthemum-like HA microflowers, enamel-like HA microparticles, rectangle shaped HA microplates and HA microrods) could be obtained by adjusting the reaction temperature and the concentration of Ca2+ ions. The experimental results showed that different aggregation routes of HA nanorods which grow along the c-axis were the reason for the formation of various micro-structures and morphologies. The possible mechanism of the formation of HA crystal was based on the Cluster Growth Model. This study suggested that the hydrothermal phase transformation from α-TCP to HA could be a promising way for the delicate morphology control of HA crystals.

Bacterial Cellulose-Hydroxyapatite Nanocomposites for Bone Regeneration

The aim of this study was to develop and to evaluate the biological properties of bacterial cellulose-hydroxyapatite (BC-HA) nanocomposite membranes for bone regeneration. Nanocomposites were prepared from bacterial cellulose membranes sequentially incubated in solutions of CaCl2 followed by Na2HPO4. BC-HA membranes were evaluated in noncritical bone defects in rat tibiae at 1, 4, and 16 weeks. Thermogravimetric analyses showed that the amount of the mineral phase was 40%–50% of the total weight. Spectroscopy, electronic microscopy/energy dispersive X-ray analyses, and X-ray diffraction showed formation of HA crystals on BC nanofibres. Low crystallinity HA crystals presented Ca/P a molar ratio of 1.5 (calcium-deficient HA), similar to physiological bone. Fourier transformed infrared spectroscopy analysis showed bands assigned to phosphate and carbonate ions. In vivo tests showed no inflammatory reaction after 1 week. After 4 weeks, defects were observed to be completely filled in by new bone tissue. The BC-HA membranes were effective for bone regeneration.

Effect of trisodium citrate on electrolytic deposition of hydroxyapatite coatings

Hydroxyapatite coatings were deposited on the titanium substrate by using various content Na₃Cit as an organic modifier in electrolytes. The influence of the Na₃Cit on the sizes of the HA crystals during electrolytic deposition was investigated under different molar ratio of Na₃Cit to calcium ions. The experimental results showed that the size of HA crystal was well controlled by the addition of Na₃Cit. When the molar ratio of Na₃Cit to calcium ions was equal or greater than five, the obtained HA coating consisted of nanosized crystals. The HA nanoparticles were precipitated without a precursor phase when the molar ratio of Na₃Cit to calcium ions was five; otherwise, the CaP coating experienced a phase conversion from octacalcium phosphate (OCP) to HA during the ELD. The effect of pH on saturation indexes with respect to hydroxyapatite, OCP, and dicalcium dihydrogen phosphate of these electrolytes was calculated by a computer program PHREEQC. The calculation showed the nucleation of OCP as the precursor during the deposition could be inhibited with increasing Na₃Cit content in the electrolytes.

Facile fabrication of nano-hydroxyapatite/silk fibroin composite via a simplified coprecipitation route

Nano-hydroxyapatite/silk fibroin (n-HA/SF) composite was successfully fabricated based on a simplified coprecipitation route. In detail, the degummed SF was first dissolved in CaCl2 aqueous/ethanol solution without desalting procedure, and then (NH4)2HPO4 solution and NH4OH were dropped into the above solution to form n-HA/SF composite. The structure and morphology of n-HA/SF composite were investigated by Transmission electron microscopy, Fourier transform infrared spectrometry, energy dispersive X-Ray spectrum, X-ray diffraction, and thermogravimetric analyses. Results indicate that the inorganic phase is carbonate-substituted HA with low crystallinity and similar to the crystals of human bone. The HA crystals have diameter of around 20–30 nm and length of about 200–500 nm. The content of SF in the composite is about 30%, and the two phases bonded each other strongly. In addition, a formation mechanism of n-HA/SF was proposed.

Constitution and morphology of hydroxyapatite whiskers prepared using amine additives

Currently-available HA particle-reinforced composites are not suitable for use in large stress-bearing restorations and biomedical substitution due to low strength and poor durability. HA is the most promising because of good biocompatibility and bioactivity, and since reinforcement efficacy is greatly affected by length and aspect ratio, the preparation of long HA whiskers could be important for biomedical applications. Acetamide, formamide, and carbonyl diamide were tested as precipitation agents to modify crystal growth habit. The morphology and composition of the whiskers showed a sensitive dependence on the additive used. Carbonyl diamide and formamide led to contaminated HA; crystals were needle-like but contained carbonate or formate, respectively. In comparison, acetamide showed a low hydrolysis rate under hydrothermal conditions, giving rise to a rapid growth of HA crystals at a low supersaturation. Furthermore, the hydrolysis products of AA affected neither the composition nor the growth habit of the HA.

Synthesis and characterization of hydroxyapatite whiskers by hydrothermal homogeneous precipitation using acetamide

Long and uniform HA whiskers with high crystallinity, controlled morphology and high aspect ratio were successfully synthesized by hydrothermal homogeneous precipitation using acetamide. Compared with the additive urea, which is commonly used to raise the pH to drive nucleation and growth of HA crystals, acetamide has a low hydrolysis rate under the required hydrothermal conditions. This allows better and easier control, giving rise to rapid growth of whiskers at a low supersaturation. Whisker length and width were in turn determined by solution conditions, including the concentration of Ca and PO(4). Whiskers had a mean length of 60-116 microm and an aspect ratio of 68-103 for starting solutions containing 42-84 mmolL(-1) Ca and 25-50 mmolL(-1) PO(4) with a fixed Ca/P ratio of 1.67. Such whiskers are favourable for their improved bone bonding and bioactivity, as well as their mechanical properties. Whiskers were slightly Ca-deficient with Ca/P=1.60-1.65, with the preferred direction of growth along the c-axis. Variation of acetamide concentration did not affect the constitution, the crystallinity or the crystal growth habit.

Effects of ultrasonic and dispersants on shape and composition of hydroxyapatite by reflux method

Hydroxyapatite with needle-like shape has been successfully synthesized by reflux method with the aid of ultrasonic treatment and different dispersants. As-synthesized samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electron microscope. The effects of ultrasonic and dispersants on formation, composition and morphology of the products have been investigated in detail. It is shown that ultrasonic treatment is favorable for the rapid nucleation and growth of HA crystal and the selected dispersants contribute to form needle-like HA crystal. The formation mechanism has also been preliminarily explained.

Co-Synthesis and Drug Delivery Properties of Mesoporous Hydroxyapatite-Silica Composites

In this work, mesoporous hydroxyapatite-silica (HA-silica) composite materials with four different Si:Ca:P ratios were sol-gel derived through self-assembly using triblock copolymer Pluronics P123 as template. The composition and mesoporous structure formed were characterized by X-ray diffraction and electron microscopy. The XRD patterns indicated that the intensity of the HA phase becomes stronger as the Ca/Si ratio of the composite increases. From nitrogen gas analysis at 77 K, type IV isotherm plots for typical mesoporous materials were observed for all of the samples. However, the mesoporous structure of HA-silica tends to becomes less ordered as the Ca/Si ratio increases. Promising consistency between the pore sizes from the Barrett, Joyner and Halenda (BJH) method, Transmission Electron Microscopy (TEM) and Small Angle X-ray diffraction (SAXRD) was also observed. The formation mechanism of mesoporous HA-silica composites was proposed, where the interaction between the crystallization of HA and the surfactant liquid crystal determines the regularity of the meso-structure. In vitro drug loading and release studies showed that drug loading capacity is dependent on the pore volume of the sample, and the mesoporosity of the samples were responsible for the sustained release of drugs. In vitro cell culture of the samples showed promising biocompatibility where osteosarcoma cells were observed to grow favourably on the synthesized composites.

Biomimetic synthesis and biocompatibility of nano-hydroxyapatite/chitosan scaffold for bone tissue engineering

Objective To evaluate the physicochemical properties and biocompatibility of nano-hydroxyapatite/chitosan (n-HA/CS) scaffolds. Methods n-HA/CS scaffolds were generated by in situ hybridization and freeze-drying technology. The microscopic morphology and components of the composite were analyzed by scanning electron microscopy (SEM), morphology, X-ray diffraction (XRD) examination and Fourier transformed infrared spectroscopy (FTIR) . The effects of u-HA/CS scaffolds on adherence and proliferation of human bone marrow stromal cells (hBMSCs) were evaluated by leaching liquor and scaffolds surface seeding methods. After being implanted into back muscle pockets of New Zealand rabbits, the histo-compatibility of n-HA/CS was observed by histological staining. Results n-HA/CS composite showed abundant homogeneous pores with (112.63 ± 20.47) μm diameter and (88.65 ± 2.34)% porosity. HA particles were distributed on the pore walls homogeneously with (200 ～ 700 nm) nanoscale. XRD and FTIR results showed that the HA crystals were carbonate-substituded and not well-crystallized. Cytocompatibility teat showed that the seeded hBMSCs could adhere to the scaffolds, and their proliferation ability was not affected by n-HA/CS composite and its leaching liquor. In addition, histocompatibility test found that tissue inflammatory reactions of n-HA/CS composite implanted decreased significantly at 4 w, and the composite was degraded mostly and was substituted by new tissue at 12 w. Conclusion The n-HA/CS scaffolds could be successfully used in the bone tissue engineering, as it has good physicochemical properties and fine biocompatibility. Key words: Hydroxyapatites; Chitosan; Tissue engineering; Scaffold; Nanocomposites

Kinetics of hydrothermal crystallization under saturated steam pressure and the self-healing effect by nanocrystallite for hydroxyapatite coatings

Hydroxyapatite coatings (HACs) with a low crystalline state were prepared using the plasma spraying process followed by hermetic autoclaving hydrothermal treatment at 100, 150 and 200 °C. Experimental evidence confirmed that the HACs became significantly crystallized and the content of amorphous calcium phosphate decreased by performing the autoclaving hydrothermal treatment in an ambient saturated steam pressure system. The obvious chemisorbed hydroxy groups (OH) peak in the X-ray photoelectron spectra detected from the hydrothermally crystallized HAC specimens means that the hydroxyl-deficient state of plasma-sprayed HACs is significantly improved by the abundant replenished OH groups. The HA nanocrystallite observed from scanning electron microscopy and transmission electron microscopy images within hydrothermally treated HACs is the result of nucleation and grain growth through the replenishment of OH groups into the hydroxyl-deficient HA crystal structure. The microstructural self-healing effect is a result of reduction in defects (pores, microcracks and lamellar boundaries) due to new-growth HA nanocrystallite. According to the systematic derivation of the Arrhenius equation, the HA crystallization is a second-order Arrhenius reaction kinetics. Besides the effects of heating temperature and an atmosphere with abundant water molecules, the saturated steam pressure is a crucial factor which significantly improves the crystallization rate constant and further reduces the activation energy for the hydrothermal HA crystallization.

Systemic injection of planktonic forms of mammalian-derived nanoparticles alters arterial response to injury in rabbits

Experiments were designed to test the hypothesis that the systemic delivery of planktonic forms of nanoparticles (NPs) derived from calcified, diseased human tissue or bovine blood are transmissible particles that exacerbate arterial response to injury. New Zealand White rabbits in which the endothelium was mechanically removed from one carotid artery were injected intravenously with either saline (control), lipopolysaccharide (LPS; surrogate for subclinical infection), hydroxyapatite crystals (HA; surrogate for NP shell), HA crystals exposed to culture media, or planktonic forms of bovine- or human-derived NPs. Carotid arteries were monitored by ultrasonography for 5 wk and then removed for histological examination. Uninjured arteries from all animals in each group remained patent with a normal anatomy. Injured arteries from 6 of 11 animals injected with human-derived NPs occluded and/or calcified; none of the injured arteries from animals in the other groups occluded (n = 28; P < or = 0.05). Injured arteries of rabbits injected with LPS or HA crystals developed eccentric hyperplasia. Discontinuous internal elastic laminae and thinning media characterized arteries from animals injected with bovine-derived NPs or cultured HA crystals. In conclusion, the systemic administration of planktonic forms of human-derived NPs exacerbated arterial response to injury distinct from that of bovine-derived NPs and other inflammatory agents.

The Effects of Different Hydroxyapatite/TiO&lt;sub&gt;2&lt;/sub&gt; Composite Coatings on Protein Expression of Osteoblast

Hydroxyapatite/TiO2 composite material was coated onto Ti25Nb3Mo2Sn3Zr (TLM) alloy substrate. To study the effects of hydroxyapatite/TiO2 composite coatings on bone-related protein expression, the osteoblast were cultured with composite coatings for different times. The phase transformation and compound formation of the HA/TiO2 coatings were investigated using XRD (X-ray diffraction). The mRNA expression of Type I collagen, alkaline phosphatase (ALP) and osteocalcin were studied by RT-PCR (reverse transcriptional polymerase chain reaction). The titania delayed the crystallization of HA. The mRNA expressions of Type I collagen are decreased as the increasing of TiO2 percentage. The mRNA expressions of osteocalcin are approached. The ALP expression on H4 coating (HA/TiO2 mol ration is 5) after the osteoblast cultured with composite coating for 6 days is the highest. The increasing of TiO2 amount decreases the bioactivity of the composite coatings.