A simple pathway in preparation of controlled porosity of biphasic calcium phosphate scaffold for dentin regeneration

A simple pathway in preparation of biphasic calcium phosphate scaffold of hydroxyapatite/beta-tricalcium phosphate with controlled pore size, shape and porosity using phosphoric acid and calcium carbonate was successfully developed. Microporosity was controlled by adjusting temperature and soaking time of the sintering process while macroporosity was obtained through addition of polyethylene spherical particles. The advantage of this method is that a highly pure biphasic calcium phosphate scaffold consisting of hydroxyapatite/beta-tricalcium phosphate in a controlled ratio of 20/80 with a mean pore size of 300 μm and 65% porosity can be produced. These properties of scaffold are of high potential for use in dentin regeneration.     

Octacalcium Phosphate for Bone Tissue Engineering: Synthesis,Modification, and In Vitro Biocompatibility Assessment

Octacalcium phosphate (OCP, Ca₈H₂(PO₄)₆·5H₂O) is known to be a possible precursor of biological hydroxyapatite formation of organic bone tissue. OCP has higher biocompatibility and osseointegration rate compared to other calcium phosphates. In this work, the synthesis of low-temperature calcium phosphate compounds and substituted forms of those at physiological temperatures is shown. Strontium is used to improve bioactive properties of the material. Strontium was inserted into the OCP structure by ionic substitution in solutions. The processes of phase formation of low-temperature OCP with theoretical substitution of strontium for calcium up to 50 at.% in conditions close to physiological, i.e., temperature 35–37 °C and normal pressure, were described. The effect of strontium substitution range on changes in the crystal lattice of materials, the microstructural features, surface morphology and biological properties in vitro has been established. The results of the study indicate the effectiveness of using strontium in OCP for improving biocompatibility of OCP based composite materials intended for bone repair.     

Mesoporous Calcium Phosphate Via Post-Treatment of α-TCP

α-Tricalcium phosphate (α-TCP) macroporous ceramic scaffold was chemically treated with a buffered solution at pH=4. Mesopores were formed in the scaffold after the treatment to result in a remarkable increase in surface area of the scaffold. The increase in the surface area is caused by precipitation of octacalcium phosphate (OCP). Bimodal pore size distribution consisting of mesopores and macropores obtained by the treatment of α-TCP scaffold having higher initial porosity brought about high adsorption of bovine serum albumin (BSA) than monomodal pore size distribution of mesopores. Adsorption of BSA, acidic protein, was suggested to result from crystallographic characters of OCP.     

Designing slurry conditions to control size distribution of spray-dried dense YSZ granules

This study suggests approaches to achieve the desired size and size distribution of highly dense spherical granules by investigating the effect of slurry conditions on size distribution. Highly dense spherical granules were prepared with a solid content of over 77 wt% by spray-drying the slurry. A prolonged deagglomeration time of 64 h provided adequate flowing ability by breaking up almost all aggregates and improved dispersibility, resulting in reduced granule sizes and narrow size distributions. The optimum slurry conditions for maintaining dispersibility were 1 wt% of the dispersant and a strong basic pH, which had the greatest effect on size distribution. Based on these considerations, the 10.6 µm sized 3 mol% yttria-stabilized zirconia granules were synthesized with 99.83% density, 97.17% sphericity, and uniform size with fraction yield of 80.01% at 10–20 µm. These dense granules have significantly higher hardness and modulus values of 19.19 and 206.68 GPa, respectively, than that of pellet and film types. To the best of our knowledge, the relationship between the slurries and the span of the size distribution of ceramic granules during spray-drying has been demonstrated for the first time.     

Sol–gel-derived mesoporous γ-alumina granules

Synthesis of stable boehmite sols and structural properties of the sol–gel-derived γ-alumina using alkoxides, commercial boehmite powders, and aluminum chloride were studied for cost-effective preparation of high quality γ-alumina granules. Stable boehmite sols could be prepared from aluminum butoxide, aluminum isopropoxide, and commercial boehmite powders but not from aluminum chloride. The stable sol-derived γ-alumina has large surface area and nanopore size with uniform pore size distributions. Mesoporous spherical γ-alumina granules were prepared by an oil-drop process from aluminum butoxide, aluminum isopropoxide and a commercial boehmite powder under specific conditions. The sol–gel-derived γ-alumina granules are better than the commercial γ-alumina granules in terms of the pore structure and mechanical strength. The successful synthesis of γ-alumina granules by the sol–gel method from the commercial boehmite powder provides a basis for large-scale, cost-effective production of the high quality γ-alumina granules for use as sorbents or catalysts in industrial processes.     

Spray-dried hydroxyapatite-5-Fluorouracil granules as a chemotherapeutic delivery system

This study describes the preparation and characterization of hydroxyapatite-5-Fluorouracil (5FU) granules, which are intended to be used as chemotherapeutic delivery matrices and bone regeneration templates. Suspensions of hydroxyapatite (Hap) nanoparticles in 5FU solution are spray dried as micro sized granules having donut type shape. Several spray drying temperatures are studied 80 °C being the optimized condition for obtaining granules composed by Hap and 5FU without secondary phases. The produced granules at 80 °C reveal a fast releasing rate of 5FU when soaked in buffer phosphate solution maintained at physiological temperature (37 °C), thereby indicating the potential application of the produced Hap matrices for drug delivery systems (DDSs).     

Comparative analysis and antibacterial properties of thermally sintered apatites with varied processing conditions

Hydroxyapatite (HA) and biphasic hydroxyapatite/beta-tricalcium phosphate (biphasic HA/β-TCP) were synthesized using thermal sintering. The parameters- sintering temperature (600°C, 900°C, and 1200°C), biological source used (fish bone, egg shells, and fish scales), and soaking time (2, 6, and 10 hours) were permuted to study their effects on the properties of the resultant apatite. Morphological study revealed that the smallest (60 nm) spherical particle and the largest (470 nm) irregular shaped particle were obtained from the fish bone sample sintered at 600°C and at 1200°C respectively. FTIR and XRD results showed that as the sintering temperature is increased, the phase transformation from HA to β-TCP takes place. Only the final products from fishbone sample at 600°C are pure carbonated HA. The crystallinity of synthesized particles ranged from 79% to 98%. Soaking time has no effect on phase composition of the apatite but has significant effect on crystallite size; increase in soaking time increases crystallite size and particle shape becomes more spherical. Interestingly, the fish bone sample sintered at 900°C has higher crystallinity and crystallite size compared to the fish scale sample sintered at the same temperature. EDX confirmed that non-stoichiometric apatite with Ca/P ratio ranging from 1.47 to 1.91 can be obtained by varying the sintering conditions. The antibacterial test revealed that both calcium apatite obtained from fish bones and fish scales have inhibited bacterial growth; apatite from fish bone works faster than fish scales. The in vitro cytotoxicity test ensured that all the calcium apatite except for eggshell are non-cytotoxic. Thus, apatite with excellent microbial activity can be obtained by using fish wastes, and by tuning the sintering parameters, the apatite with desired types and properties can be synthesized for different biomedical applications.     

Porous Ceramic Granules of Hydroxyapatite

A technology for fabrication of porous spherical granules from hydroxyapatite is reported, and the structure and properties of granules prepared under different process conditions are described. The granules prepared range in size from 50 to 2000 m and contain open pores of diameter mainly 2 – 3 nm. The granules can be used to heal defective bones and as vehicles for targeted drug.     

球形PE粒子的合成与马来酸酐固相接枝反应

采用负载型高效球形催化剂催化乙烯淤浆聚合得到了高孔隙率的球形聚乙烯(PE)颗粒。用光学显微镜、扫描电子显微镜等方法对所得PE的形貌、结构、粒径分布等进行了表征。实验表明,PE颗粒的粒径分布窄、形貌规整、孔隙率高。以球形PE为基体,研究了马来酸酐在PE颗粒中的接枝反应,考察了反应条件对接枝率和酸值的影响。     

Biomimetic Preparation and Characterization of Bioactive Coatings on Alumina and Zirconia Ceramics

For the preparation of bioactive coatings on alumina and zirconia ceramic surfaces a fast biomimetic method using a supersaturated solution containing Na⁺, Ca²⁺, Cl⁻, HCO₃⁻, and PO₄³⁻ ions was used. The coatings were analysed with the use of an X-ray diffraction spectrometer and a transmission electron microscope equipped with an energy-dispersive spectroscopy detector. After the precipitation both coatings were composed of poorly crystallized, nanosized, plate-like particles with the octacalcium phosphate (OCP) crystal structure. The adhesion of the coatings was improved by a heat treatment at 1050°C for 1 h. During this heat treatment the calcium phosphate layer, deposited from a supersaturated solution onto the surface of the substrates, was sintered to form a dense coating. At the same time the OCP crystal structure was transformed into that of hydroxyl apatite, the coating's crystallinity was increased, and the particles grew isotropically up to 300 nm in size. The bioactivity of the coated ceramic was confirmed before and after the heat treatment using a simple simulated body fluid test.     

Synthesis of zirconia toughened alumina nanopowders as soft spherical granules by combining co-precipitation with spray drying

The nanopowders of zirconia toughened alumina (ZTA) as soft spherical granules were directly synthesized by combining co-precipitation with spray drying (CPSD). The co-precipitation of alumina (Al₂O₃) and yttria-stabilized zirconia (YSZ) was performed together in one step to obtain the ZTA precipitate. Spray drying, which is the most preferred industrial processing way to produce the nanopowders as spherical granules, was used to atomize, dry and granulate the suspension like milk prepared from the synthesized ZTA precipitate under previously optimized spray drying conditions. However, the important and complex processing parameters of spray drying such as the solid-liquid ratio and the feeding rate of the suspension, the inlet temperature and the flow rate of the hot air have to be optimized depending on the moll mass and volume of the component in the prepared suspension. The ZTA nanopowders containing 4–20 wt% YSZ synthesized by the CPSD method have a crystalline structure of alumina and YSZ, an average nanoparticle size between 26.64 and 46.70 nm with a very high specific surface area (SSA) between 77.43 and 112.41 m² g⁻¹ in a soft spherical granule form, which were determined by XRD, BET and SEM, respectively. The preparation and drying conditions of the synthesized precipitate, the solid-liquid ratio of the suspension and the molar mass ratio of YSZ in Al₂O₃ matrix have a significant effect on the crystallinity, morphology, particle size, SSA, and granule form of the synthesized ZTA nanopowders.     

Preparation of dense spherical AlN fillers by aqueous granulation and post-sintering process

Herein, an innovative two-step method was proposed to prepare dense spherical aluminum nitride (AlN) fillers for the application of insulating encapsulants, involving spray granulation from AlN-based suspensions and subsequent sintering process to achieve full density. According to investigations on the dispersing ability of powders, the AlN-based aqueous suspensions with various solid loading were firstly prepared for spray granulation. It was indicated that a low-viscosity and high-concentration suspension could enhance the sphericity and uniformity of green granules and simultaneously facilitate the high green density. The spherical AlN green granules were further sintered with boron nitride (BN) powders, which played a role as the interval material to retain the spherical morphology and hinder the agglomerations of AlN granules. The distinct impacts of BN powders, sintering temperatures and additive species on the overall properties of resultant AlN fillers were further studied and rationally uncovered. Based on these results, spherical AlN granules with superior dispersion, low porosity and an average particle size of more than 40 µm were successfully fabricated via the newly-developed two-step method, showing promising potentiality for the application as thermal-conductive fillers.     

Multiphase zinc and magnesium mono-substituted calcium phosphates derived from cuttlefish bone: A multifunctional biomaterials

Biomimetic calcium phosphate (CaP) systems mono-substituted with zinc (Zn²⁺) and magnesium (Mg²⁺) ions were prepared from a biogenic source (cuttlefish bone) by wet precipitation method. The results revealed that the as-prepared powders were composed of calcium-deficient carbonated hydroxyapatite (HAp), octacalcium phosphate (OCP), and amorphous calcium phosphate (ACP), while the heat-treated powders consisted of HAp, α-tricalcium phosphate (α-TCP), and β-tricalcium phosphate (β-TCP). In addition to Zn²⁺ and Mg²⁺ ions, the presence of CO₃^2?, Sr²⁺ and Na ⁺ ions was detected with elemental analysis, which can be attributed to the use of cuttlefish bone as a natural precursor of Ca²⁺ ions. The data obtained by XRD study demonstrated the decrease in lattice parameters in the OCP and β-TCP phases for Zn-substitution and Mg-substitution in the HAp, OCP, and β-TCP phases. Zn²⁺ occupies the Ca(1,3,4,6,7,8) sites in OCP and Ca(1,2,3,4) sites in β-TCP, while Mg²⁺ occupies the Ca(2) sites in HAp and the Ca(4,5) sites in β-TCP. Phase transformation study under simulated physiological conditions for 7 days showed the transformation of OCP and ACP into the thermodynamically more stable HAp. Characterization of the zeta-potential showed positively charged populations for all prepared CaP powders, while all samples showed high bovine serum albumin adsorption capacity. The culture of human embryonic kidney cells showed that the prepared CaPs are non-cytotoxic and that viability of the cells increases during the culture period. All powders obtained showed antibacterial activity towards Gram-negative Escherichia coli and low antibacterial effect against Gram-positive Staphylococcus aureus, as determined by viability analysis during 48 h. Inhibition zone analysis and observation of the morphology after 24 h showed no antibacterial properties.     

Highly dense spinel ceramics with completely suppressed grain growth prepared via SPS with NaF as a sintering additive

For the preparation of transparent spinel ceramics it is common practice to use LiF as a sintering additive to achieve transparency. However, it is well known that in this case the grain size exhibits a significant increase compared to pure spinel ceramics, which can lead to a deterioration in mechanical properties. The findings of this paper indicate that when NaF is used as a sintering additive for the preparation of spinel ceramics via spark plasma sintering (SPS) translucent materials with a high level of densification can be obtained without observable grain growth. It is shown that the grain size after SPS at 1500 °C with 1 h dwell is essentially the same as the primary particle size of the spinel powder, whereas pure spinel ceramics prepared via SPS under the same conditions exhibit grain growth by approximately a factor 5.     

Hydrolysis Control of AlN Powders for the Aqueous Processing of Spherical AlN Granules

Spherical granules of aluminum nitride (AlN) with an average particle size of about 50 μm were produced from aqueous suspensions using an AlN powder surface treated against hydrolysis with aluminum dihydrogenphosphate [Al(H₂PO₄)₃]. Two different amounts of Al(H₂PO₄)₃ were tested and the effects of surface treatment and aging time were evaluated by various techniques (XRD, TG‐DTA, zeta potential and pH measurements). The treated powder exhibited antihydrolytic property and good dispersing behavior, enabling the preparation of low‐viscosity and high‐concentration aqueous AlN slurries for freeze granulation. The spherical AlN granules were sintered in a boron nitride (BN) powder bed followed by ultrasonic washing of the AlN granulates/BN mixture to remove BN. The sintered spherical AlN granules present excellent crystallinity and high sphericity as observed from SEM micrographs.     

Preparation and characterization of spherical activated carbons from oil agglomerated bituminous coals for removing organic impurities from water

A new and simple method of producing of spherical activated carbons (SACs) from different bituminous coals, i.e., gas coal, gas-coking coal and orthocoking coal, is presented. Coal agglomerates of spherical shape obtained by oil agglomeration using rapeseed oil and linseed oil, were subjected to carbonization and activation with steam at 850 °C. The SACs prepared from gas-coking coal (hvAb) agglomerates were characterized by the best developed porous structure with surface area S_BET of about 800 m²/g and pore volume of 0.40 cm³/g. The adsorption capacity of the produced SACs was determined in terms of substituted phenolic compounds. The adsorption of 2-chlorophenol (OCP), 4-chlorophenol (PCP) and 4-nitrophenol (PNP) from aqueous solutions was studied under a static conditions on the SAC prepared from gas-coking coal agglomerated using rapeseed oil. At high concentrations of the solute the adsorption behavior of OCP was found to be different in comparison to PCP and PNP. The adsorption of the two last phenolic compounds on the selected SAC is very well described by Langmuir adsorption model. For OCP a two-stepped adsorption isotherm was obtained. The Langmuir isotherm equation fits very well only for the first stage of the OCP adsorption.     

Morphological study of spherical MgCl2.nEtOH supported TiCl4 Ziegler‐Natta catalyst for polymerization of ethylene

Spherical MgCl₂·nEtOH was prepared by adducting ethanol to MgCl₂ using melt quenching method. Effect of molar ratio of [EtOH]/[MgCl₂] = 2.8–3.05 on the morphology and particle size of the MgCl₂·nEtOH were studied. The best adduct of spherical morphology was obtained when 2.9 mol ethanol to 1 mol MgCl₂ was used. An emulsion of dissolved MgCl₂ in ethanol was prepared in a reactor containing silicon oil. Stirrer speed of the emulsion and its transfer rate to quenching section that work at ?10 to ?40°C are affected by the particle size of the adduct particle. The adducted ethanol was partially removed with controlled heat primary to catalyst preparation (support). Treatment of the support with excess TiCl₄ increased its surface area from 13.1 to 184.4 m²/g. Heterogeneous Ziegler‐Natta catalyst system of MgCl₂ (spherical)/TiCl₄ was prepared using the spherical support. Scanning electron microscopy studies of adduct, support, and catalyst obtained shown spherical particles, however, the polyethylene particles obtained have no regular morphology. The behavior indicates harsh conditions used for catalyst preparation, prepolymerization, and polymerization method used. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3829–3834, 2006     

Radio Frequency Thermal Plasma Treatment for Size Reduction and Spheroidization of Glass Powders Used in Ceramic Electronic Devices

Radio frequency (RF) thermal plasma treatment is studied for the size reduction and the spheroidization of coarse glass particles to change them into submicrometer-sized powders of spherical shape. Such ultra-fine spherical powders are the key ingredients of a sintering aid to achieve efficient package and high performance in ceramic electronic applications. The coarse glass powders injected into the high-temperature RF thermal plasma undergo rapid heating, melting, and evaporation, followed by quenching, and then condense to very fine spherical powders. In the thermal plasma treatment with high RF powers of 18–23 kW at a powder feeding rate of 3 g/min, the scanning electron microscopy images and the particle size distribution graphs obtained from the treated glass powders indicate that most glass powders with initial average diameters of around 2 μm are reformed into spherical ones with sizes of below 500 nm. It is also observed in a 4 MHz RF thermal plasma reactor that the maximum size of particles decreases down to 200 nm when the reactor is operated under conditions of reduced pressure, low powder feeding rate, and high RF power. The compositions of glass powders before and after the plasma treatment are compared by using the wet and the inductively coupled plasma-optical emission spectroscopy analyses. Negligible composition changes appear within a range of <2 wt% during the RF thermal plasma process, which demonstrates the successful preparation of submicrometer-sized glass powders in spherical shape applicable to the advanced ceramic electronic devices.     

Effects of glutamic acid shelled PAMAM dendrimers on the crystallization of calcium phosphate in diffusion systems

Second generation poly(amidoamine) (PAMAM) dendrimers were synthesized and peripherally modified with glutamic acid (PAMAM-MG) as a shell. The effect of the dendrimers on the crystallization of different calcium phosphate compounds was investigated in both double and one way diffusion systems. It was found that the crystals of calcium phosphate showed tape-like morphology in the presence of PAMAM-MG, and the crystals’ thickness and width decreased compared to those grown without dendritic molecules. Such a result might be due to the interaction of electric charges between dendritic molecules and octacalcium phosphate (Ca₈H₂(PO₄)₆·5H₂O, OCP), which led to the adsorption of PAMAM-MG in the 100 and 010 surfaces of OCP. Moreover, PAMAM-MG showed an affinity for gelatin, and it could cause the formation of amorphous calcium phosphate (Ca₉(PO₄)₆·nH₂O, ACP) at a concentration of 5 mg/mL of PAMAM-MG. These results suggest that PAMAM-MG could be used for regulating the morphology of OCP and changing the composition of minerals in gels.     

Preparation of spherical AlN powders by combined microemulsion method and carbothermal method

In this study, a two-step strategy for the preparation of micron-sized spherical aluminium nitride (AlN) powder by the combined micro-emulsion method in conjunction with the carbothermal reduction nitridation (CRN) route was designed. The spherical AlN powder with perfect dispersibility was prepared after a heat treatment at 1550 °C for 2 h in flowing N₂. The effects of the aluminium fluoride (AlF₃) content, reaction temperature and the introduction of yttrium oxide (Y₂O₃) on the nitridation ratio and on the morphology of granules, in particular, were investigated by XRD analysis and SEM. Additionally, the promotion mechanism of AlF₃ and Y₂O₃ on the nitridation reaction was also discussed. Specifically, one of the underlying formation mechanisms of the spherical granules with the aid of AlF₃ and Y₂O₃, and suggestions on the selection of additives for the CRN synthesis of spherical AlN powder were logically proposed.