Fabrication of flower-like hydroxyapatite agglomerates with the assistant of bamboo membrane

Flower-like hydroxyapatite agglomerates formed on a bamboo membrane were investigated in the mimic biological environment with pH of 7.4 and temperature of 37 °C by using a uniquely designed crystallizer. The influences of holding time on the morphology and crystallinity of the agglomerates were studied in detail. It was observed that the crystal growth experienced a process that transformed from calcium hydrophosphate to octacalcium phosphate then to hydroxyapatite. The sheet-like crystals become thinner, longer, and wirelike in the end. The mechanism of crystal growth was discussed.     

Pulsed laser deposition of silicon-substituted hydroxyapatite coatings

Thin films of Si-substituted hydroxyapatite (Si-HA) were deposited on Si and Ti substrates by pulsed laser deposition (PLD), in the presence of a water vapour atmosphere. The PLD ablation targets were made with different mixtures of commercial carbonated HA and Si powder, in order to produce the Si-HA thin films. The physicochemical properties of the coatings and the incorporation of the Si into the HA structure was studied by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The Si atoms were successfully incorporated into the HA structure, and were found to be in the form of SiO₄⁴⁻ groups, principally displacing carbonate groups off the HA structure.     

Solid solution formation at the sintering of hydroxyapatite–fluorapatite ceramics

Fluorhydroxyapatite ceramics are increasingly studied for the use as biomaterials due to their good integration ability in the bone tissue and higher resorption resistance compared to the common hydroxyapatite (HA) ceramics. This study is aimed at the X-ray diffraction investigation of the interaction between HA and fluorapatite (FA) particulates in the sintering temperature range up to 1300 °C. The lattice parameters were calculated in dependence of both the FA content in the powder mixtures and the sintering temperature. From those data, the solid solution formation is concluded, at least in the temperature range from 1200 to 1300 °C. Energy-dispersive X-ray microanalysis confirmed the fluorine distribution to be almost uniform in the sintered at 1300 °C ceramics.     

Biodegradable and bioactive properties of a novel bone scaffold coated with nanocrystalline bioactive glass for bone tissue engineering

The development of the new technologies of bone tissue engineering requires the production of bioactive and biodegradable macroporous scaffolds. Hydroxyapatite (HA) ceramics are useful bone substitutes, but they degrade minimally. Tricalcium phosphates also show poor ability of Ca-P formation both in-vitro and in-vivo, although they are degradable. The present study introduces a biodegradable, bioactive, and macroporous scaffold with suitable mechanical properties. The prepared hydroxyapatite scaffold was coated with a nanocrystalline bioactive glass layer to be subsequently sintered at different temperatures. The bioactivity and degradability of the coated scaffolds were investigated by standard procedures. The ability to induce Ca-P formation in SBF (simulated body fluid) was also investigated semi-quantitatively. BS1 scaffolds (scaffolds sintered at 800 °C with a holding time of 2 h) showed remarkable bioactivity and degradability simultaneously. Formation of a nanocrystalline phase (Si₂PO₇) during the sintering considerably decreased the capability of BS1 scaffolds for Ca-P formation and the rate of degradation but enhanced their mechanical properties. The BS1 scaffolds showed not only significant bioactivity but also good degradability and suitable mechanical property.     

The adsorption characteristics of osteopontin on hydroxyapatite and gold

The adsorption of osteopontin on hydroxyapatite (HA) and reference gold (Au) surfaces was studied at different protein bulk concentrations over the temperature range 295-317 K, using quartz crystal microbalance with dissipation (QCM-D) and X-ray photoelectron spectroscopy (XPS). The QCM-D protein adsorption studies were complemented with polyclonal antibodies to examine the availability of protein sequences on the resulting protein layer. The QCM-D and XPS results show that the osteopontin surface mass uptake is larger on Au as compared to HA surfaces within the range of experimental conditions examined (protein bulk concentrations and temperature range), in accordance with the formation of a more compact protein film on Au. The specific antibody binding to the resulting adsorbed osteopontin layer as measured by QCM-D further confirms that the protein packing and conformational/orientational changes occurring during OPN adsorption on Au and HA are different, since fewer antibodies are observed to bind per OPN molecule on Au as compared to HA. The adsorption process on the respective surfaces was modeled using both the Langmuir and Hill adsorption isotherms, and from these isotherm curves, the Gibbs free energy, ?G, of the osteopontin adsorption was determined. The estimated ?G values indicate that the osteopontin molecules have a high affinity towards Au, while a lower affinity is observed between osteopontin and HA. By examining the changes in ?G as a function of temperature, we additionally find that the osteopontin adsorption on HA and Au is endothermic and driven by an increase in entropy.     

Effect of supersaturation on the morphology of hydroxyapatite crystals deposited by electrochemical deposition on titanium

Cathodic deposition of calcium phosphate coating on titanium using electrochemical method was investigated in our study and well-defined hexagonal rod-like hydroxyapatite (HAp) crystals were synthesized. Scanning electron microscopic photographs of HAp coatings under different deposition durations revealed the morphology change of the HAp crystals in the coating film with the experimental process: from cone-like structure to hexagonal prism with sharp-angled tip, and finally turns to rod-like one with regular hexagonal cross section. It was suggested that both morphology and longitudinal length of the HAp crystals in the coating could be regulated by an accurate control of the degree of supersaturation of the aqueous system.     

Preparation of nanocrystalline MgO by surfactant assisted precipitation method

Nanocrystalline magnesium oxide with high surface area was prepared by a simple precipitation method using pluronic P123 triblock copolymer (Poly (ethylene glycol)-block, Poly (propylene glycol)-block, Poly (ethylene glycol)) as surfactant and under refluxing conditions. The prepared samples were characterized by X-ray diffraction (XRD), N₂ adsorption (BET) and scanning and transmission electron microscopies (SEM and TEM). The obtained results revealed that the refluxing time and temperature and the molar ratio of surfactant to metal affect the structural properties of MgO, because of the changes in the rate and extent of P123 adsorption on the prepared samples. The results showed that the addition of surfactant is effective to prepare magnesium oxide with high surface area and affects the morphology of the prepared samples. With increasing the P123/MgO molar ratio to 0.05 the pore size distribution was shifted to larger size. The sample prepared with addition of surfactant showed a plate-like shape which was completely different with the morphology of the sample prepared without surfactant. The formation of nanoplate-like MgO was related to higher surface density of Mg ions on the (0 0 1) plane than that on the other planes of the Mg(OH)₂ crystal. The (0 0 1) plane would be blocked preferentially by the adsorbed P123 molecules during the growing process of Mg(OH)₂ nanoentities and the growth on the (0 0 1) plane would be markedly restricted, and the consequence is the generation of nanoplate-like MgO. In addition, increase in refluxing temperature and time increased the specific surface area of the prepared MgO samples.     

Highly porous gelatin–silica hybrid scaffolds with textured surfaces using new direct foaming/freezing technique

Highly porous gelatin–silica hybrid scaffolds with high porosity, large pores and large interconnections, as well as tailored surface textures were produced using a newly developed direct foaming/freezing. Two different types of precursors as the silica source, 3-glycidoxyproyltrimethoxysilane (denoted as “GS”) and sol–gel derived silica (denoted as “SS”), were used for producing the porous GLA–GS and GLA–GS–SS hybrid scaffolds. In this method, air bubbles could be vigorously incorporated into the GLA–GS and GLA–GS–SS mixtures and then stabilized by rapid freezing of the foamed mixtures at −70 °C. Both the porous GLA–GS and GLA–GS–SS hybrid scaffolds produced herein had a highly porous structure (porosity > 90 vol%, pore size = 200–500 μm, interconnection size = 100–200 μm) with a uniform distribution of the silica phase in the gelatin matrix. In addition, surface textures with a rugged morphology could be created after immersion of the porous GLA–GS and GLA–GS–SS hybrid scaffolds in ethanol at −20 °C for 24 h. The porous GLA–GS and GLA–GS–SS hybrid scaffolds showed much higher mechanical properties than the porous GLA scaffold, while preserving excellent in vitro biocompatibility, demonstrating potential application as the bone scaffold.     

Synthesis of mesoporous hydroxyapatite using a modified hard-templating route

Mesoporous polycrystals of hydroxyapatite-calcium are synthesized via a modified hard-templating route. The structure properties of hydroxyapatite-calcium are characterized by means of X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and N₂ adsorption-desorption isotherms. Wide-angle X-ray diffraction and Fourier transform infrared spectroscopy measurements reveal that the crystalline grains consist of highly crystalline pure hydroxyapatite phases. Transmission electron microscopy results show that rod-like hydroxyapatite-calcium grains with an average diameter of about 100 nm long and about 20 nm wide are uniformly distributed, which are also observed with an average pore size of 2-3 nm. Based on N₂ adsorption-desorption isotherms investigation, the pore size, surface area and pore volume of mesoporous hydroxyapatite-calcium are 2.73 nm, 42.43 m² g⁻¹ and 0.12 cm³ g⁻¹, respectively.     

A novel in situ synthesis of dicalcium phosphate dehydrate nanocrystals in biodegradable polymer matrix

In the paper, we found a novel method to synthesize dicalcium phosphate dehydrate (DCPD) nanocrystals by in situ reaction in biodegradable PDLLA matrix. Calcium hydrid was selected as calcium source of DCPD, which is different from general methods. The method is not only simple and effective to synthesize Ca–P particles, but also can avoid the aggregation of inorganic nanoparticles in the course of their being dispersed into polymer matrix.     

The affect of densification and dehydroxylation on the mechanical properties of stoichiometric hydroxyapatite bioceramics

This paper reports the effects of processing densification on the mechanical properties of hydroxyapatite bioceramics. Densification of synthetic hydroxyapatite is conducted in the range 1000-1300 °C. X-ray diffraction and SEM microscopy are used to check the microstructure transformations. Vickers hardness, toughness and Young's modulus are analyzed versus the density and grain size. The sintering temperature and the particle size influence strongly the densification and the resulting mechanical properties. In addition, the critical sintering temperature appears around 1200 °C and the declined strength at the temperature up to 1200 °C is found sensitive to the dehydroxylation process of hydroxyapatite.     

Synthesis of organic derived hydroxyapatite scaffold from pig bone waste for tissue engineering applications

Micro porous hydroxyapatite (HAp) had drawn great attention in the field of tissue engineering due to its numerous applications such as tissue regeneration, dental, drug delivery, and adsorption and desorption of substances etc. The chemical synthesis of HAp is often faced with the high cost of starting materials and often lacks the presence of beneficial ions which can promote biological reactions. This paper examined a novel application of pig bone waste for the synthesis of HAp via heat treatment between 600 and 1000 °C. Thus synthesized powder was characterized by X-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FT-IR), Thermogravimetric analysis (TGA), Scanning electron microscopy (SEM), Energy dispersive X-ray analysis (EDX) and Transmission electron microscopy (TEM). XRD results revealed the main characteristic peaks of single phase HAp powder, while the presence of various functional groups such as PO₄^3?, CO₃^2? and OH^? corresponding to HAp were observed by FT-IR analysis. The elemental composition of as-synthesized HAp powder as observed by EDX showed the presence of Ca and P in addition to some beneficial metals such as Na, K, Mg and Si which plays vital roles in biological applications. SEM and TEM observation confirmed the microscopic sctructure of the as-synthesized HAp to be rod-like morphology with 38–52 nm in length. Porous HAp scaffold up to 65% porosity could be prepared using ammonium bicarbonate as pore forming agent. Therefore, bio-waste such as pig bones can be utilized in the synthesis of porous hydroxyapatite scaffold which can serve as an alternative for the conventional chemical method.     

Rapid microwave assisted synthesis of hydroxyapatite

A fast, efficient and novel method of preparation of hydroxyapatite using microwaves has been described. Contribution No. 1252 from Solid State and Structural Chemistry Unit     

Electrolytic deposition of magnesium-substituted hydroxyapatite crystals on titanium substrate

Electrolytic deposition of magnesium-substituted hydroxyapatite (Mg-HAp) coatings on titanium was investigated and Mg-HAp crystals with up to 2 wt.% Mg²⁺ were deposited in electrolytes with various Mg²⁺ concentration. The incorporation of Mg substantially changed the morphology of the HAp crystals and decreased the crystal size and crystallinity of the HAp. The similarity with natural dentin and bone in composition and the increased specific surface of the Mg-HAp coatings on the Ti substrates were believed to benefit the bioactivity and the drug-carrying properties of the coatings.     

Structural,microstructural and magneto-electric properties of single-phase BiFeO3 nanoceramics prepared by auto-combustion method

Polycrystalline nano BiFeO₃ powders were synthesized by auto-combustion method using urea as fuel and metal nitrates (Fe(NO₃)₃·9H₂O, Bi(NO₃)₃·5H₂O) as oxidizers. In order to optimize the single-phase synthesis condition of BiFeO₃, different fuel to oxidizer ratios have been investigated. The preliminary structural investigation using X-ray diffraction shows the samples were of single phase and crystallize in rhombohedral structure (R3c). The ferroelectric and antiferromagnetic ordering temperatures of BiFeO₃ were found to be 832 °C and 364 °C respectively, from differential thermal analysis. The temperature dependent dielectric study shows an anomaly around 215 °C which corresponds to magneto-electric coupling in the material. Field-emission scanning electron micrographs show effect of fuel to oxidizer ratio on grain size evolution. The ferroelectric hysteresis loops for all the samples were measured at a frequency of 100 Hz confirming the ferroelectric nature. An evidence of magneto-electric coupling was also observed at room temperature from magneto-capacitance measurements.     

Synthesis and sintering of nanocrystalline hydroxyapatite powders by citric acid sol-gel combustion method

The citric acid sol-gel combustion method has been used for the synthesis of nanocrystalline hydroxyapatite (HAP) powder from calcium nitrate, diammonium hydrogen phosphate and citric acid. The phase composition of HAP powder was characterized by X-ray powder diffraction analysis (XRD). The morphology of HAP powder was observed by transmission electron microscope (TEM). The HAP powder has been sintered into microporous ceramic in air at 1200 °C with 3 h soaking time. The microstructure and phase composition of the resulting HAP ceramic were characterized by scanning electron microscope (SEM) and XRD, respectively. The physical characterization of open porosity and flexural strength have also been carried out.     

Influence of fluorine substitution on the morphology and structure of hydroxyapatite nanocrystals prepared by hydrothermal method

Hydroxyapatite (HAp) nanocrystals with different levels of fluorine substitution (P/F = 0, 6, 4 and 2) on the OH sites were produced via hydrothermal method. The fluorine substitution was found to alter the morphology of crystals appreciably. The aspect ratio and the crystallinity of HAp crystals increased with increasing fluorine substitution. The presence of broad ring and hallow ring patterns in electron diffraction suggests the low-crystalline nature of HAp crystals. With increasing fluorine substitution, the diffraction patterns exhibited discrete rings and numerous diffraction spots, implying the increased crystallinity. Raman spectra from the HAp nanoparticles also support the less-crystalline nature of the pristine HAp and the enhanced crystallization by fluorine substitution. In HAp crystals processed with no fluorine substitution, surface energy and planar Ca²⁺ density are less sensitive to the crystallographic orientation because of its low-crystalline nature, favoring equi-axed or slightly elongated particles. The addition of fluorine apparently increased the crystallinity, enhancing the orientation dependent growth and accordingly the aspect ratio. Osteoblast proliferation was observed to be enhanced by fluorine substitution in HAp. In vitro biological data support that the excellent osteoblastic cell viability and functional activity of the fluoridated apatite.     

Influence of the precipitation pH on the compositions and properties of Bi-based oxyiodide photocatalysts

A series of Bi-based oxyiodide photocatalysts with different compositions were synthesized via a precipitation-filtration process followed by hydrothermal treatment. The compositions of the bismuth oxyiodides could be controlled by adjusting the precipitation pH values. The effects of the precipitation pH values on the compositions and photocatalytic activities of the bismuth oxyiodides were investigated and the relationship between structure and photocatalytic property is discussed. All the as-prepared powders exhibit photocatalytic activity on decomposing methyl orange under visible light irradiation. The activity increases with increasing content of iodine in the bismuth oxyiodides.     

Effect of the powder precursor characteristics in the reaction sintering of aluminum titanate

Aluminum titanate precursor powders, containing 2.5 wt.% MgO additive, were prepared by two powder processing methods, the hydrolysis of alkoxides and coprecipitation of inorganic salts. The hydrolysis-derived precursor powder showed a higher chemical homogeneity than the coprecipitated-derived precursor powder. Dilatometric analysis, accomplished with XRD and microscopy, was a very good method to study both phase transformation and sintering processes. Different phase transformation paths of TiO₂ and Al₂O₃ were observed in the two powders. The formation of aluminum titanate solid solution began at ∼1220°C in both, but in the hydrolysis-derived powder compact the aluminum titanate grains grew faster, leading to incomplete reaction and a non-uniform microstructure of large grains with small residual inclusions.     

Effect of Fe on the synthesis and electrochemical performance of nanostructured MnO2

Different MnO₂ nanostructures were synthesized in stoichiometric KMnO_4/MnSO₄ aqueous solutions in the absence/presence of Fe³⁺ at temperature ranging from 30 °C to 180 °C. The phase structures, morphologies and electrochemical properties of the as-prepared MnO₂ products were investigated using X-ray powder diffraction, scanning electron microscope, N₂ physical adsorption and cyclic voltammetry techniques. The results showed that the presence of Fe³⁺ addition had a significant effect on the phase structural evolution, morphological features and electrochemical properties of the MnO₂ products. Fe³⁺ was found to greatly prevent the epitaxial growth and crystallization of MnO₂ nucleus, which in turn influenced textual characteristics. The electrochemical performance of the nanostructured MnO₂ products had a complex relationship with the phase structures, specific surface area as well as pore characteristics. MnO₂ prepared in the presence of Fe³⁺ (KMF-MnO₂) showed relatively higher specific capacitance compared to that of MnO₂ prepared in the absence of Fe³⁺ (KM-MnO₂). Maximum capacitance of 214 F g⁻¹ was obtained for KMF-MnO₂ prepared at 30 °C at a scan rate of 2 mV s⁻¹ in 0.1 M Na₂SO₄ electrolyte.