Preparation and characterization of gelatin/hydroxyapatite nanocomposite for bone tissue engineering

Homogeneous gelatin/hydroxyapatite (GEL/HA) nano‐composites were synthesized by a novel in situ precipitation method, and its corresponding characterizations, including composition, morphology, pore structure, thermal stability, mechanical strength, and biocompatibility, were carried out. High‐magnified scanning electron microscope (SEM) images indicated that nano‐HA with particle size ranging from 20 to 50 nm were uniformly distributed in GEL matrix and tightly integrated with organic phase. Wide angle X‐ray diffraction (XRD) analysis and transmission electron microscope (TEM) images showed that, during the process of mineralization, there existed preferred oriented growth of HA crystals along (002) and (211) crystal planes. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) indicated that, the thermal stability of GEL molecules enhanced by hybridizing with HA nanocrystals. Interconnected porous GEL/HA nanocomposites with pore size ranging between 50 and 350 μm were prepared by a freeze‐drying method. This pore size was adequate for bone tissue engineering (BTE) applications. In addition, in vitro MG63 osteoblast‐like cell culture illuminated that GEL/HA nanocomposites had excellent cytocompatibility and could promote proliferation of cells. These results suggested that GEL/HA nanocomposite might be an ideal bone substitute. POLYM. COMPOS., 38:1579–1590, 2017. © 2015 Society of Plastics Engineers     

Fabrication of Nanostructured Hydroxyapatite via Hydrothermal Synthesis and Spark Plasma Sintering

Hydrothermal synthesis has been used to produce hydroxyapatite (HA) particles with high crystallinity. Such particles of nanorods were used to fabricate HA ceramic by using spark plasma sintering. X-ray diffraction, transmission electron microscope, scanning electron microscope, and the BET method have been used to examine crystallite size, crystallite shape, and the surface area of particles, and grain size of sintered HA ceramics. It was found that the morphology of the nanorods in the HA particles changed to a more equiaxed shape during sintering.     

Growth of calcium bilirubinate crystal controlled by functional polymer

Calcium bilirubinate (CaBR) particles were synthesized in three systems, such as pure water, glucan and polyethylene glycol (PEG) aqueous solutions, respectively. The polymorph and morphology of the particles were investigated using Fourier transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM) and X-ray diffraction spectroscopy (XRD). The results revealed that the CaBR formed in pure water was amorphic and quasi-spherical with a mean diameter of about 80 nm.The glucan in solutions made the size of spheric CaBR particles increased obviously, but the crystallinity of particles was not improved apparently. The oriented growth of fusiform CaBR crystals was induced by PEG successfully. The average length of the crystals was 170 nm and the diameter 26 nm. The formation mechanism of CaBR crystal controlled by PEG was also discussed in this article.     

Influence of temperature,ripening time and calcination on the morphology and crystallinity of hydroxyapatite nanoparticles

Nano-sized hydroxyapatite (HA) particles were prepared by chemical precipitation through aqueous solutions of calcium chloride and ammonium hydrogenphosphate. The influence of temperature, ripening time and calcination on the crystallinity and morphology of the HA nanoparticles were investigated. It was found that the crystallinity and crystallite size increased with the increase of synthetic temperature and ripening time. XRD and TEM results showed that the morphology change of HA nanoparticles was related to their crystallinity. High crystallinity of HA led to regular shape and smooth surface of the nanoparticles. The crystallinity of HA powders increased greatly after calcination at 650 °C for 6 h but the change of the crystallite size after calcination was dependent on the crystallinity and crystallite size of “as prepared” HA nanoparticles.     

Nanoparticles formation for metallocene catalyzed cyclic olefin copolymer via a continuous supercritical anti-solvent process

Nanoparticles of the metallocene catalyzed cyclic olefin copolymer (mCOC) were prepared with a lab scale continuous supercritical anti-solvent (SAS) apparatus. Several experimental parameters were investigated to explore their influences on the morphology and the mean size of the products. These parameters included the character of carbon dioxide injector, precipitation pressure and temperature, anti-solvent density, the polymer concentration, the flow rate of feed, and the nature of organic solvents. The phase states of the mixtures of solvent + anti-solvent in precipitation stage may govern the mean size of the resulting particles. Nanoparticles of mCOC were obtained in the homogeneous compressed liquid or supercritical region, while sub-micrometric particles were formed in the vapor–liquid coexistence region. The morphology of precipitates was also significantly changed, turning from spherical nanoparticles to microfibrils, as the polymer concentration of feed was increased from 2 to 4 wt.%. Under 15 MPa and 306.2 K, the mean size of the resultant primary mCOC particles as small as 39 nm with a standard deviation of about 6 nm could be produced. The residual solvent was about 1.6 wt.% in the sample after SAS processing by analyzing with a thermogravimetric analyzer (TGA), and the particle samples exhibited sub-glass transition behavior according to the thermal histograms of differential scanning calorimeter (DSC).     

Sintering properties of hydroxyapatite powders prepared using different methods

In the present work, the sintering behaviour of HA particles prepared via the wet precipitation method (HAp) and wet mechanochemical technique (HAwm) was investigated. The sintering behaviour of a commercial HA powder (HAc) was also studied for comparison purpose. All the three powders were characterised in terms of particle size, Ca/P ratio and crystal size. Green samples were prepared and sintered in air at temperatures ranging from 1000 °C to 1400 °C. The sintered bodies were studied in terms of the phase stability, relative density, Young's modulus, Vickers hardness, fracture toughness and grain size. The results indicated that HAwm samples suffered phase decomposition while the HAp and HAc sintered samples showed no phase disruption throughout the temperature range employed. The HAp samples exhibited the overall best densification and properties when compared to the HAc and HAwm samples. Furthermore, the results showed that mechanical properties of sintered samples were governed by both the bulk density and the grain size.     

Preparation of hydroxyapatite/poly(vinyl alcohol) composite film with uniformly dispersed hydroxyapatite particles using citric acid

Biocompatible hydroxyapatite (HA)/poly(vinyl alcohol) (PVA) composites and their transparent films were prepared by the coprecipitation and solvent casting method. The formation of HA in PVA composite powder was confirmed by the characteristic phosphate bands at 1100–1032 and 565 cm^?1 at FT‐IR spectra, and the weight ratio of HA to PVA was 50/50 examined by TGA. The crystal melting temperature of HA/PVA decreased compared with that of pure PVA. HA/PVA (50/50) composite powder and pure PVA were dissolved in dimethyl sulfoxide to obtain a film with HA/PVA weight ratio of 10/90. To improve HA particles' dispersity, which is one of the major factors affecting the mechanical properties of composite materials, various contents of citric acid were used for the preparation of HA/PVA films. At a citric acid concentration of 5 wt %, HA/PVA film with good dispersity of HA particles was obtained. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Synthesis of barium fluoride nanoparticles by precipitation in ethanol-aqueous mixed solvents

In this work, the BaF₂ nanopowders with different particle size were synthesized by precipitation in the ethanol/water mixed solvents. Five kinds of compositions of mixed solvents, including pure water, 25 vol.%, 50 vol.%, 67.5 vol.%, and 75 vol.% of ethanol were used. The effects of aging and the volume percentage of ethanol in the mixed solvents on the resultant BaF₂ nanoparticles were under investigation. The size and morphology of the BaF₂ particles were characterized by TEM, FSEM and XRD analyses. The results show that after aging for 2 h the particle size of the BaF₂ precipitates in the 50% mixed suspension changes little. The prepared BaF₂ particles all exhibit cubic fluorite structures no matter what kind of composition is used. In pure water environment, the size of BaF₂ particles is about 70 nm, whereas it reduces to 33 nm in the 75% mixed solution. As the vol.% of ethanol increases the particle size decreases, and other properties such as the size distribution, dispersion, oriented growth et al. are also modulated. These alterations can be interpreted by varying the dielectric constant of mixed solvent.     

Polymer-assisted precipitation of ZnO nanoparticles with narrow particle size distribution

Zinc oxide nanoparticles were produced by aqueous precipitation in mild hydrothermal conditions (90 °C). Well crystallized regular roundish particles were obtained, with a very narrow size distribution. The influence of soft templates (organic species) to control size and size distribution in the final product was investigated. No effect was observed with polyvinylpyrrolidone (PVP M_w 8000 and 40,000), (d?)fructose and hydroxypropylmethylcellulose (HPMC). A significant decrease of the particle size towards 100 nm, while conserving a very narrow size distribution was observed for poly(acrylic acid) (PAA M_w 2000), Dispex A40 (commercial PAA from CIBA M_w ～10,000), and sodium dodecylsulfate (SDS). The influence of the pH was also investigated with PAA. By increasing the pH from slightly acidic to basic conditions, the morphology was spectacularly modified from roundish nanoparticles to micronic branched flower-like particles, with an elongated primary crystal morphology.     

Effect of surfactant and heat treatment on morphology,surface area and crystallinity in hydroxyapatite nanocrystals

Hydroxyapatite (HA) powders were synthesized by the wet precipitation method, with and without surfactant, under identical processing parameters. These powders were then heat treated at 900 °C for 3 h in air. The detailed characterization of the powders was done by using SEM, dynamic light scattering, nitrogen adsorption, XRD, Raman spectroscopy, and FTIR techniques. The HA phase, identified by well defined PO₄^3? and OH^? ion peaks in Raman and FTIR spectra, was observed in all the powder samples. The addition of surfactant changed the morphology of the particles from spherical to needle/rod-like structure and increased the surface area up to three times (from 33 to 96 m²/g). Also, suppression in the evolution of β-TCP phase was observed along with decrease in the crystal size and crystallinity of the powder due to the addition of surfactant. Synthesized nano-HA crystals were found to have diameters and lengths in the range 10–25 nm and 75–150 nm, respectively. The heat treatment changed the architecture of the particles, increased the crystallinity and reduced the surface area to ≈7 m²/g. However, the relative increase in crystallinity was much higher for the powder synthesized with surfactant. The ratio of the average crystallite size to the crystallinity degree was about 0.53±0.07 for all the powders. The particle size distribution was bimodal and coarser for the powder synthesized without surfactant. The pore size analysis showed transformation of a predominantly mesoporous structure into a meso- plus macroporous one on heat treatment. The intensity of OH^? group peak in Raman spectra was found to be highly sensitive to the crystalline state of the HA powder and may be used to assess crystallinity.     

Selenium-substituted hydroxyapatite particles with regulated microstructures for osteogenic differentiation and anti-tumor effects

Selenium-substituted HA (Se/HA) particles with special micro/nanohybrid morphologies were prepared hydrothermally. With increasing Se substitution, Se/HA transitioned from a ribbon-like morphology, to a radical form, and further to microspheres (diameters: ∼10 μm) assembled from nanosheets (thickness: 2–5 μm; length and width: ∼100 nm). Chemical analyses confirmed increasing incorporation of Se in Se/HA particles, with increasing Se/(Se + P) molar ratio of the raw materials for their synthesis. Rat calvarial osteoblasts (RCOBs) adhered and spread on the Se/HA particles with Se/(Se + P) ratios ranging 0–0.05. Particles synthesized at Se/(Se + P) = 0.05 showed increased alkaline phosphatase activity of bone marrow mesenchymal stem cells, likely due to their micro/nano-sized surface morphology. Se released from particles effectively inhibited human osteosarcoma cell growth by inducing apoptosis. Therefore, Se/HA prepared at Se/(Se + P) = 0.05 presented a potential material for bone defect repair after surgical tumor removal, offering safety, increased osteogenic differentiation of stem cells, and inhibition of tumor cell growth. These results also suggest that trace element substitution is an effective approach to simultaneously imparting desirable microstructures and biological functions to bio-ceramics.     

Hydroxyapatite coating on titanium surface with titania nanotube layer and its bond strength to substrate

A vertically aligned titania nanotube layer on titanium surface was prepared by electrochemical anodic oxidation in an F⁻-containing electrolyte, followed by annealing at 450 °C. Bioactive hydroxyapatite (HA) coatings on as anodized titania nanotube layer were obtained by a biomimetic method without other surface treatment. The morphology, crystal structure, and components of the titania nanotube layer and bioactive coatings were examined by scanning electron microscopy, thin film X-ray diffraction, and Fourier transform infrared spectroscopy. The bond strength between the HA coatings and substrates was tested using a mechanical tester. The diameter of the titania nanotubes was about 100 nm, the wall thickness about 19 nm and the height about 1 μm. HA rapidly deposited on the as anodized nanotube surface after immersion in a biomineral solution only for 1 day. The HA coatings were carbonated apatite and composed of a number of column-like crystals with nanometer size. Tensile test shows that the bond strength between the HA coating and the nanotube layer was larger than 15.3 MPa.     

Precipitation of pharmaceuticals using a supercritical anti‐solvent (SAS) dechnique: A preliminary study

The aims of this research were to investigate the applicability of the supercritical anti‐solvent (SAS) process on the precipitation of pharmaceuticals (andrographolide and acetaminophen). In particular, the goal of this research was to study the influence of pressure at 10 and 24 MPa on particle characteristics (morphology, crystalline structure, polymorphic form, size, size distribution, and precipitation yield), and to compare the precipitation efficiency of SAS process and evaporation process. Scanning electron microscope (SEM), X‐ray diffraction (XRD), and high performance liquid chromatography (HPLC) showed a significant change in particle size, size distribution, morphology, and precipitation yield, respectively. From an analysis of the results it was found that the crystal size of andrographolide and acetaminophen decreased with increasing pressure. The morphology of andrographolide particles changed from slice‐like to column‐like when the pressure was increased. On the other hand, the acetaminophen particles obtained were found to be monoclinic form (I) under both operating pressures. The SAS process produced small uniform shaped crystals, with a narrow size distribution, high precipitation yield and selective precipitation were also observed.     

Precipitation kinetics of PMMA sub-micrometric particles with a supercritical assisted-atomization process

Sub-micrometric particles of PMMA were successfully prepared via a supercritical assisted-atomization (SAA) process using acetone as a solvent and supercritical carbon dioxide as a spraying medium. The effects of several key factors on the particle size were investigated. These factors included the concentration of polymer solution, temperature in saturator and volumetric flow rate ratio of carbon dioxide to polymer solution. The shape of the polymer's primary particles is spherical with the arithmetic mean size ranging from 82 nm to 176 nm and the mass-weighted mean size ranging from 127 nm to 300 nm. As evidenced from the experimental results, the lower concentrations of polymer solution, optimized volumetric flow rate ratios, and higher temperatures in saturator can effectively reduce the mean particle size. The precipitation kinetic parameters were determined from the particle size distributions with the aid of the population balance theory. This study found the primary nucleation to be dominant in the precipitation and diffusion may govern particle growth.     

Preparation of equiaxed α-Al2O3 by adding oxalic acid

The preparation of α-Al₂O₃ powders with equiaxed architecture for the fabrication of advanced ceramics is of great importance but still challenging. A new and facile approach for the fabrication of equiaxed α-Al₂O₃ adopting alumina hydroxide and oxalic acid as the raw materials was reported in this paper for the first time. The current work demonstrated that the adding 0.16 mol/L oxalic acid solution made α-Al₂O₃ heterogeneously nucleate at a temperature as low as 800 °C, and the amount of nucleation was high enough to remove the vermicular microstructures during the morphology evolution of α-Al₂O₃, resulting in the formation of equiaxed α-Al₂O₃ particles with an average size of 205.72 nm at 1300 °C.     

Effect of process parameters on the microstructure and property of hydroxyapatite precursor powders and resultant sintered bodies

Nanocrystalline hydroxyapatite (HA) ceramic could have better potential in biomedical application due to its high bioactivity and mechanical strength. This study aimed at investigating on the relationship between the starting HA powders and resultant HA ceramics. The synthesized HA crystals using chemical precipitation showed different morphology, size, and crystallinity under different reaction temperature and aging time. The spray-dried HA powders from the different HA slurries synthesized at 40, 60, and 80°C had spherical shapes and similar particles size but different specific surface area (SSA). Lower synthesizing temperature resulted in lower crystallinity and need-like shape of the HA crystals, and thus higher SSA of the spray-dried HA powders. After cold isostatic pressing of the HA powders, the HA green compacts were sintered at 1000, 1050, and 1150°C, respectively, and they presented different sinterability, compactness, and mechanical strength, which were tightly dependent on the starting HA powders. As compared to 80°C synthesized powders, 40 and 60°C synthesized powders exhibited better sinterability due to the lower crystallinity and higher SSA, leading to the relatively high compactness and mechanical strength, but small grain size below 100 nm of the resultant HA ceramics even at low sintering temperature of 1050°C.     

Pulsed discharge production of nano- and microparticles in ethanol and their characterization

Nanoparticles were synthesized using a pulsed arc submerged in ethanol. Two electrode configurations, (a) a 1×4 mm and a 10×10 mm graphite electrodes, and (b) Ni, W, and steel rod electrode pairs, were used. The liquid was arc treated for 5 min with 100 A peak current, 20 μs duration pulses, at a repetition rate of 100 Hz. Samples were obtained by extracting liquid from the top of the treatment vessel, and by allowing the liquid to evaporate from the vessel, and collecting the residue. The samples were examined by HRTEM, HRSEM, XRD, and X-ray photoemission spectroscopy (XPS). Carbon nanoparticles with an onion-like structure, i.e., composed of concentric spherical layers, were found in the samples from the top of the liquid vessel after arcing with either C or Ni electrode pairs. These particles typically had an o.d. of 15-20 nm, and the diameter of the interior void was approximately 5-8 nm. In some cases, the onions were clustered together, such that a typical cluster size was 50-60 nm. Ni and W nanoparticles were produced by treatment with Ni and W electrodes, respectively. The particles could be electrically collected by applying a potential difference between a pair of collection electrodes submerged in the fluid. The Ni particles with sizes of ∼15 μm drifted in the direction generally towards the positive electrode with velocities of approximately ∼2.5-3.5 mm/s in a d.c. electric field of 100 V/mm.     

Synthesis of nanoscale hydroxyapatite particles using triton X-100 as an organic modifier

Nano-sized rod like hydroxyapatite (HA) particles were synthesized using Ca(NO₃)₂·4H₂O and (NH₄)₂HPO₄ as precursors with varying contents of non-ionic surfactant viz., p-(1,1,3,3-tetramethylbutyl)phenoxypoly(oxyethylene)glycol (triton X-100) as organic modifer. The crystalline phase, chemical composition, surface area and morphology of the prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), BET surface area analysis, high resolution scanning electron microscopy (HRSEM) and transmission electron microscopy (TEM). The above studies indicate the presence of nanoscale hydroxyapatite (HA) phase. Triton X-100 does not appear to affect the crystallinity of the samples. Increase of BET surface area and the consequent decrease in particle size of HA were observed as a function of surfactant content. Probable mechanism for the role of the surfactant in the synthesis of nanoscale HA has also been discussed.     

Onion-like fullerenes synthesis from coal

Onion-like fullerenes (OLFs) were synthesized in high yields from coal by radio frequency plasma. The morphologies and structures of the products were characterized by high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) technique. Results reveal that OLFs can be prepared from coal with high purity. The particles display a clear polyhedral or quasi-spherical morphology with hollow center, having an average diameter ranging from 10 nm to 35 nm and high degree of graphitization.     

Effects of the doping concentration of boron on physicochemical,mechanical, and biological properties of hydroxyapatite

Ion doping is an approach to modify properties of materials, like hydroxyapatite (HA), that contributes to designing biomaterials with desired characteristics applicable in bone defect treatments. Recently, boron (B) has been noticed in biomaterial fields due to its beneficial effects on formation, growth, and quality of bone. In this study, B-doped HA nanoparticles with different molar concentrations of B (0.05, 0.1, 0.25, and 0.5) were synthesized through microwave-assisted wet precipitation. The effects of B content on various properties of HA were evaluated. The results demonstrated that the size of HA particles reduced from 106 nm to 89-85 nm in B doped materials. Meanwhile, the crystallinity degree of B doped HA (BHA) samples was between 89.90% and 93.77%, compared to 95.19% of HA. Diametral tensile strength of samples was measured in the ranges of 2.51 and 3.61 with no significant difference among groups. The micro-hardness of HA was 0.88 GPa, whilst doped ones had hardness values of 0.5 GPa–0.68 GPa. Biodegradability of samples increased from less than 1% to approximately 4% after 28 days, while B-doping did not make any change in the degradation rate. Doping dosages were appropriate in terms of bioactivity and cell viability, and B doping caused higher bioactivity and cell proliferation. All changed properties were dose-dependent and more effective in doped groups with a higher amount of B. Despite proliferative effect, 260 μg/l and 770 μg/l of B release in two groups with the highest dopant concentrations did not positively influence the osteogenic activity of cells. Our results demonstrated that doping concentrations that resulted in B release ≤260 μg/l seem more appropriate dosage, especially for bone tissue engineering and substitute applications due to promoted bioactivity and proliferation, as well as no obstructive effects on mechanical properties and osteogenic activities of HA.