In vitro studies of calcium phosphate silicate bone cements

A novel calcium phosphate silicate bone cement (CPSC) was synthesized in a process, in which nanocomposite forms in situ between calcium silicate hydrate (C–S–H) gel and hydroxyapatite (HAP). The cement powder consists of tricalcium silicate (C₃S) and calcium phosphate monobasic (CPM). During cement setting, C₃S hydrates to produce C–S–H and calcium hydroxide (CH); CPM reacts with the CH to precipitate HAP in situ within C–S–H. This process, largely removing CH from the set cement, enhances its biocompatibility and bioactivity. The testing results of cell culture confirmed that the biocompatibility of CPSC was improved as compared to pure C₃S. The results of XRD and SEM characterizations showed that CPSC paste induced formation of HAP layer after immersion in simulated body fluid for 7 days, suggesting that CPSC was bioactive in vitro. CPSC cement, which has good biocompatibility and low/no cytotoxicity, could be a promising candidate as biomedical cement.     

A novel method to low temperature synthesis of nanocrystalline forsterite

Nanocrystalline forsterite (Mg₂SiO₄) powder was synthesized using sucrose as a chelating agent and template material from an aqueous solution of magnesium nitrate and colloidal silica. The synthesized powders were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), simultaneous thermal analysis (STA), and scanning electron microscopy (SEM). The synthesized nano-powder had particle size smaller than 200 nm and average crystallite size of powders calcined at 800 °C for 3 h was in the range of 10-30 nm. Also the effect of addition 2 and 4 wt.% forsterite seed on nucleation temperature and crystallite size of forsterite was investigated. The presence of small amounts of Mg₂SiO₄ as seed obviously accelerated the crystallization of forsterite. According to DTA results the inceptive formation temperature of Mg₂SiO₄ without any seed was 760 °C, while this temperature for the specimen containing 4 wt.% seed was 700 °C.     

Structural characterization and strengthening mechanism of forsterite nanostructured scaffolds synthesized by multistep sintering method

In this study, highly porous forsterite scaffolds with interconnected porosities were synthesized using multi-step sintering (MSS) method. The starting powder was nanosized forsterite, which was synthesized from talc and magnesium carbonate powders. The phase composition, average particle size and morphology of the produced forsterite powder were characterized by X-ray diffraction technique (XRD) and transition electron microscopy (TEM). Forsterite scaffolds were produced by foamy method using polymeric sponges. MSS process including three steps was used to efficiently sinter the forsterite nanopowders without destroying the initial porous structure of polymeric sponges. The results showed that MSS technique is an efficient and appropriate procedure to produce highly porous forsterite scaffolds with pore size in the range of 100–300?μm. The compressive strength, compressive modulus and porosity of C12 specimen (sintered at 1650?°C for 1?h with subsequent annealing at 1000?°C for 1000?min) was 1.88?MPa, 29.2?MPa, and 72.4%, respectively, which is very close to that of cancellous bone. The approach studied in this research can be developed for other nanostructure ceramics to produce highly porous scaffolds with interconnected porosities for load bearing applications.     

Densification behaviour of oxide-coated silicon nitride powders

Powder coating has been explored as a method of incorporating sintering additives into a ceramic powder. This procedure has been explored in the case of Si₃N₄ powders coated with thin layers of MgO.The effectiveness of the powder coating technique has been evaluated by comparing the powder properties, densification behaviour, microstructure and mechanical properties of coated Si₃N₄ powders with identical powders in which the additive oxide has been added in particulate form. It is concluded that the powder coating technique is an excellent method of homogeneously incorporating minor amounts of sintering additive into a powder. The coated powder exhibited improved homogeneity, and gave good green compact density, high green strength, and faster densification rate. Moreover, coated powders densified more easily by pressureless sintering and showed a more homogeneous microstructure, higher strength and faster densification rates, compared with materials prepared using mixed oxide powders. Significant improvements in hardness and fracture toughness were observed for the coated powders.     

Bioactivity of CaSiO<Subscript>3</Subscript>/poly-lactic acid (PLA) composites prepared by various surface loading methods of CaSiO<Subscript>3</Subscript> powder

Mixing bioactive ceramic powders with polymers is an effective method for generating bioactivity to the polymer-matrix composites but it is necessary to incorporate up to 40 vol% of bioactive ceramic powder. However, such a high mixing ratio offsets the advantages of the flexibility and formability of polymer matrix and it would be highly advantageous to lower the mixing ratio. Since surface loading of ceramic powders in the polymer is thought to be an effective way of reducing the mixing ratio of the ceramic powder while maintaining bioactive activity, CaSiO₃/poly-lactic acid (PLA) composites were prepared by three methods; (1) casting, (2) spin coating and (3) hot pressing. In methods (1) and (2), a suspension was prepared by dissolving PLA in chloroform and dispersing CaSiO₃ powder in it. The suspension was cast and dried to form a film in the case of method (1) while it was spin-coated on a PLA substrate in method (2). In method (3), CaSiO₃ powder was surface loaded on to a PLA substrate by hot-pressing. The bioactivity of these samples was investigated in vitro using simulated body fluid (SBF). Apatite formation was not observed in the samples prepared by method (1) but some apatite formation was achieved by mixing polyethylene glycol (PEG) with the PLA, producing a porous polymer matrix. In method (2), apatite was clearly observed after soaking for 7 days. Enhanced apatite formation was observed in method (3), the thickness of the resulting apatite layers becoming about 20 μm after soaking for 14 days. Since the amount of CaSiO₃ powder used in these samples was only ≤0.4 vol%, it is concluded that this preparation method is very effective in generating bioactivity in polymer-matrix composites by loading with only very small amounts of ceramic powder.     

45S5 bioactive glass coatings by atmospheric plasma spraying obtained from feedstocks prepared by different routes

45S5 bioactive glass powders with the composition of 45 SiO₂, 6 P₂O₅, 24.5 CaO and 24.5 wt% Na₂O were melted and quenched in water to obtain a frit. The frit was milled using two different routes: dry milling followed by sieving to obtain glass particles and wet milling followed by spray drying to obtain a powder comprising porous agglomerates. All feedstocks showed adequate characteristics that make them suitable to be deposited by atmospheric plasma spraying. The powders and coatings were characterised by field-emission gun environmental scanning electron microscope and X-ray diffraction. The roughness and the contact angle of the coatings were also determined. The bioactivity of the powders and coatings was assessed by immersion in simulated body fluid. It was found that bioactive glass prepared from bioglass frit by dry milling exhibited similar bioactivity as that of a commercial bioactive glass. All coatings produced showed good adhesion to the substrate as well as suitable surface properties to ensure efficient contact with body fluid. Regardless of the characteristics of the feedstocks or plasma spray conditions used, all coatings were exclusively made up of an amorphous phase. On the other hand, micrographs revealed that the characteristics of the feedstock strongly impact on the final coating microstructure. The most homogeneous microstructure was obtained when the feedstock was prepared by fine dry grinding of the frit. For this coating, the formation of a bioactive layer was also proved by Fourier transform infrared spectroscopy and X-ray diffraction.     

Synthesis, characterization and formation mechanism of single-phase nanostructure bredigite powder

Single-phase nanocrystalline bredigite powder was successfully synthesized by mechanical activation of talc, calcium carbonate, and amorphous silica powder mixture followed by annealing. Simultaneous thermal analysis (STA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS),and Fourier transform infrared spectroscopy (FT-IR) techniques were employed to characterize various powders. Single-phase nanostructure bredigite powder with crystallite size of about 65 nm was synthesized by 20 h of mechanical activation with subsequent annealing at 1200 °C for 1 h. The bredigite formation mechanism was studied. During the formation process of nanostructure bredigite powder some intermediate compounds such as wollastonite (CaSiO₃), larnite (Ca₂SiO₄), merwinite (Ca₃MgSi₂O₈), and calcium magnesium silicate (Ca₅MgSi₃O₁₂) were formed. It was found that bredigite was not produced directly and that the formation of merwinite, enstatite and Ca₅MgSi₃O₁₂was unavoidable during the synthesis of bredigite.     

Bioactivity of CaSiO<Subscript>3</Subscript>/poly-lactic acid (PLA) composites prepared by various surface loading methods of CaSiO<Subscript>3</Subscript> powder

Mixing bioactive ceramic powders with polymers is an effective method for generating bioactivity to the polymer-matrix composites but it is necessary to incorporate up to 40 vol% of bioactive ceramic powder. However, such a high mixing ratio offsets the advantages of the flexibility and formability of polymer matrix and it would be highly advantageous to lower the mixing ratio. Since surface loading of ceramic powders in the polymer is thought to be an effective way of reducing the mixing ratio of the ceramic powder while maintaining bioactive activity, CaSiO₃/poly-lactic acid (PLA) composites were prepared by three methods; (1) casting, (2) spin coating and (3) hot pressing. In methods (1) and (2), a suspension was prepared by dissolving PLA in chloroform and dispersing CaSiO₃ powder in it. The suspension was cast and dried to form a film in the case of method (1) while it was spin-coated on a PLA substrate in method (2). In method (3), CaSiO₃ powder was surface loaded on to a PLA substrate by hot pressing. The bioactivity of these samples was investigated in vitro using simulated body fluid (SBF). Apatite formation was not observed in the samples prepared by method (1) but some apatite formation was achieved by mixing polyethylene glycol (PEG) with the PLA, producing a porous polymer matrix. In method (2), apatite was clearly observed after soaking for 7 days. Enhanced apatite formation was observed in method (3), the thickness of the resulting apatite layers becoming about 20 μm after soaking for 14 days. Since the amount of CaSiO₃ powder used in these samples was only ≤0.4 vol%, it is concluded that this preparation method is very effective in generating bioactivity in polymer-matrix composites by loading with only very small amounts of ceramic powder.     

Synthesis and characterization of nanostructured CaSiO3 biomaterial

Here we report a successful preparation of nanostructured calcium silicate by wet chemical approach. The synthesized sample was characterized by various physico-chemical methods. Thermal stability was investigated using thermo-gravimetric and differential thermal analysis (TG-DTA). Structural characterization of the sample was carried out by the X-ray diffraction technique (XRD) which confirmed its single phase hexagonal structure. Transmission electron microscopy (TEM) was used to study the nanostructure of the ceramics while homogeneous grain distribution was revealed by scanning electron microscopy studies (SEM). The elemental analysis data obtained from energy dispersive X-ray spectroscopy (EDAX) were in close agreement with the starting composition used for the synthesis. Superhydrophilic nature of CaSiO₃ was investigated at room temperature by sessile drop technique. Effect of porous nanosized CaSiO₃ on early adhesion and proliferation of human bone marrow mesenchymal stem cells (BMMSCs) and cord blood mesenchymal stem (CBMSCs) cells was measured in vitro. MTT cytotoxicity test and cell adhesion test showed that the material had good biocompatibility and promoted cell viability and cell proliferation. It has been stated that the cell viability and proliferation are significantly affected by time and concentration of CaSiO₃. These findings indicate that the CaSiO₃ ceramics has good biocompatibility and that it is promising as a biomaterial.     

Capability of mechanical alloying and SPS technique to develop nanostructured high Cr,Al alloyed ODS steels

Abstract

Oxide dispersion strengthened (ODS) Fe alloys were produced by mechanical alloying (MA) with the aim of developing a nanostructured powder. The milled powders were consolidated by spark plasma sintering (SPS). Two prealloyed high chromium stainless steels (Fe–14Cr–5Al–3W) and (Fe–20Cr–5Al+3W) with additions of Y₂O₃ and Ti powders are densified to evaluate the influence of the powder composition on mechanical properties. The microstructure was characterised by scanning electron microscope (SEM) and electron backscattering diffraction (EBSD) was used to analyse grain orientation, grain boundary geometries and distribution grain size. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) equipped with energy dispersive X-ray spectrometer (EDX) were used to observe the nanostructure of ODS alloys and especially to observe and analyse the nanoprecipitates. Vickers microhardness and tensile tests (in situ and ex situ) have been performed on the ODS alloys developed in this work.     

Mechanically activated crystallization of phase pure nanocrystalline forsterite powders

Pure nanocrystalline forsterite was successfully synthesized via a mechanical activation route assisted with heat treatment. X-ray diffraction (XRD), scanning electron microscopy (SEM) and simultaneous thermal analysis (STA) techniques were utilized to characterize the prepared powders. Results showed that pure nanocrystalline forsterite could be fabricated completely by 10 h of mechanical activation and post-heat treatment at 1000-1200 °C for 1 h. By 10 h mechanical activation, the initial temperature of forsterite crystallization was reduced to about 820 °C. The obtained nanocrystalline forsterite powder had crystallite size about 57 nm according to Williamson-hall approach and particle sizes smaller than 1000 nm. XRD patterns showed that pure forsterite could not be obtained by mechanical activation process alone and that enstatite could be fabricated by increasing the time of milling. Liberation of CO₂ gas increased the rate of forsterite formation by increasing contact surface between grains.     

Understanding phase stability,microstructure development and biocompatibility in calcium phosphate–titania composites,synthesized from hydroxyapatite and titanium powder mix

Some important issues in developing Calcium phosphate (CaP)-based composites are the thermo-chemical compatibility, dissociation and its influence on microstructure development as well as on biocompatibility property. In the present work, a planned set of sintering experiments have been carried out for different Hydroxyapatite (HAp, one of the materials in CaP group)–Titanium(Ti) starting powder mix (10–40 wt.% Ti) in the temperature range of 1000–1400 °C under air atmosphere. In all the sintered samples, β-tricalcium phosphate (β-TCP) and rutile (TiO₂) are the major crystalline phases irrespective of the sintering temperature; while other reaction products, like, CaTiO₃, CaO are also recorded for various HAp–Ti compositions. Based on the combined study of XRD, FT-IR, TGA and thermodynamic analysis, the feasibility of various possible sintering reactions are discussed. Based on SEM-EDS analysis, the microstructure development has been described in terms of matrix constituents of TCP/HAp phase, agglomerated TiO₂ grains and the presence of pores. The results of the cell culture experiments involving L929 mouse fibroblast cells reveal excellent bioactivity property and in particular, good cell adhesion as well as cell–cell interaction.     

Synthesis and characteristics of monticellite bioactive ceramic

Mono-phase ceramics of monticellite (CaMgSiO₄) were successfully synthesized by sintering sol–gel-derived monticellite powder compacts at 1,480 °C for 6 h. The mechanical properties and the coefficient of thermal expansion (CTE) of the monticellite ceramics were tested. In addition, the bioactivity in vitro of the monticellite ceramics was evaluated by investigating their bone-like apatite-formation ability in simulated body fluid (SBF), and the biocompatibility in vitro was detected by osteoblast adhesion and proliferation assay. The results showed that the bending strength, fracture toughness and Young’s modulus of the monticellite ceramics were about 159.7 MPa, 1.63 MPa m^1/2 and 51 GPa, respectively. The CTE was 10.76 × 10⁻⁶ °C⁻¹ and close to that of Ti-6Al-4V alloy (10.03 × 10⁻⁶ °C⁻¹). Furthermore, the monticellite ceramics possessed bone-like apatite-formation ability in SBF and could release soluble ionic products to significantly stimulate cell growth and proliferation. In addition, osteoblasts adhered and spread well on the monticellite ceramics, which indicated good bioactivity and biocompatibility.     

Synthesis and characterization of boron suboxide powder produced at ambient pressure condition

Boron suboxide (B₆O)?based materials have shown good properties which make them good candidates for cutting tool and other applications where abrasive wear resistance is important. The objective of this study was to optimize the production of B₆O at ambient pressure by varying reaction temperature and time. B₆O powders were produced from the reaction between boric acid and amorphous boron powders at the reaction temperatures between 300°C and 1400°C for 6 h. The powders produced were characterized in terms of particle size, phase analysis and composition, product yield, as well as morphology. Increase in temperature increased both the yield as well as the particle size of the produced powders. X-ray diffraction (XRD) pattern obtained also showed improved crystallinity of the produced powder as the temperature increases. Scanning electron microscopy (SEM) images of the synthesized powder at higher temperature clearly showed improved crystallinity (star-like crystals) as the reaction temperature was increased. The B₆O powders synthesized at 1300°C for 6 h had the optimum yield of over 95%.     

RF plasma synthesis of YBa2Cu3O7−x powders

Fine powders of YBa₂Cu₃O_7?x have been synthesized by injecting mixed nitrate solutions of yttrium, barium, and copper into an argon rf thermal plasma. In general, the as-produced powders were dark brown and nonconducting. To obtain superconductivity, the as-produced powders were annealed either in a flowing oxygen tube furnace (at ～900?C) or in a lowpressure oxygen rf plasma. X-ray powder diffraction, scanning electron microscopy, and centrifugal sedimentation were used for powder characterization. For resistance measurements, bulk samples were prepared by isostatic pressing and tube furnace sintering of the annealed powders. The superconducting transition temperature (at 50% drop of resistivity) was ～86 K.     

Analysis of powder flow and in-system rheology in a horizontal convective mixer with reclining blades

A prototypal convective mixer, designed and built for this work, allows investigating powder rheology under various geometrical configurations. The configuration chosen here is a horizontal vessel with four rectangular blades. Two blade inclinations (0–33°) and three filling ratios are studied for two powders of different kind: a free-flowing powder (semolina) and a cohesive powder (lactose). For the smaller agitation speeds, the flow regime of the powder is rolling and is characterized by surface powder avalanches. For greater agitation speeds, the flow regime is cataracting, with particle projections that follow the blade movement. These flow regimes are identified for both powders and do not depends on the filling ratio. Rheological measurements evidence that the blade inclination has little impact on the mechanical power needed to stir the free-flowing powder. It has an impact observable on cohesive powders, especially for high filling ratios. A correlation between the power number and the Froude number is established and compared to previous results obtained on a different technology. It is of the form: N_p?=?a.F_r^b. The dependencies of the coefficients a and b on the powder type and on the flow regime are quantified.     

Photoluminescence properties of a hollandite compound K2Ga2Sn6O16

A hollandite compound K₂Ga₂Sn₆O₁₆ (KGSO) has photocatalytic activity, although little is known about the optical properties of the compound. To design a higher quality photocatalyst, studies on its optical properties are required. In this study, a KGSO powder and a SnO₂ (rutile structure) powder were prepared by the sol—gel method. Photoluminescence (PL) and PL excitation spectra of the two powders were measured. To our knowledge, this is the first report of PL from a hollandite compound. It was found that the band gap energy of the KGSO powder is 3.6 eV, the value of which is identical with that of the band gap energy of SnO₂. This was confirmed by the result of the photoacoustic spectrum of the KGSO. The shapes of the PL excitation spectra of the two powders agreed. Moreover, the PL spectra of the two powders have one broad band around 600 nm. From these results, one can conclude that the mechanism of PL of KGSO is the same as that of SnO₂. In air with ethanol, however, the time-course of the KGSO powder was different from that of the SnO₂ powder. By adding ethanol vapor in air, the PL intensity of the SnO₂ powder increased, whereas the PL intensity of the KGSO powder remained unchanged. By comparing the PL time-courses of the two powders with those of a commercial rutile TiO₂ powder, it was concluded that the photodesorption of O₂ in air with ethanol occurs on the SnO₂ powder, not on the KGSO powder. This was supported by the results of the inorganic carbon concentrations on the two powders. These results indicate that the behavior of O₂ on the KGSO surface during a photocatalytic oxidation is different from that on the SnO₂ surface during the oxidation.

© 2003 Elsevier Ltd. All rights reserved.     

Photoluminescence properties of a hollandite compound K2Ga2Sn6O16

A hollandite compound K₂Ga₂Sn₆O₁₆ (KGSO) has photocatalytic activity, although little is known about the optical properties of the compound. To design a higher quality photocatalyst, studies on its optical properties are required. In this study, a KGSO powder and a SnO₂ (rutile structure) powder were prepared by the sol–gel method. Photoluminescence (PL) and PL excitation spectra of the two powders were measured. To our knowledge, this is the first report of PL from a hollandite compound. It was found that the band gap energy of the KGSO powder is 3.6 eV, the value of which is identical with that of the band gap energy of SnO₂. This was confirmed by the result of the photoacoustic spectrum of the KGSO. The shapes of the PL excitation spectra of the two powders agreed. Moreover, the PL spectra of the two powders have one broad band around 600 nm. From these results, one can conclude that the mechanism of PL of KGSO is the same as that of SnO₂. In air with ethanol, however, the time-course of the KGSO powder was different from that of the SnO₂ powder. By adding ethanol vapor in air, the PL intensity of the SnO₂ powder increased, whereas the PL intensity of the KGSO powder remained unchanged. By comparing the PL time-courses of the two powders with those of a commercial rutile TiO₂ powder, it was concluded that the photodesorption of O₂ in air with ethanol occurs on the SnO₂ powder, not on the KGSO powder. This was supported by the results of the inorganic carbon concentrations on the two powders. These results indicate that the behavior of O₂ on the KGSO surface during a photocatalytic oxidation is different from that on the SnO₂ surface during the oxidation.     

Effects of surface modification on the mechanical and structural properties of nanofibrous poly(ε-caprolactone)/forsterite scaffold for tissue engineering applications

Composite scaffolds consisting of polymers reinforced with ceramic nanoparticles are widely applied for hard tissue engineering. However, due to the incompatible polarity of ceramic nanoparticles with polymers, they tend to agglomerate in the polymer matrix which results in undesirable effects on the integral properties of composites. In this research, forsterite (Mg₂SiO₄) nanoparticles was surface esterified by dodecyl alcohol and nanofibrous poly(ε-caprolactone)(PCL)/modified forsterite scaffolds were developed through electrospinning technique. The aim of this research was to investigate the properties of surface modified forsterite nanopowder and PCL/modified forsterite scaffolds, before and after hydrolytic treatment, as well as the cellular attachment and proliferation. Results demonstrated that surface modification of nanoparticles significantly enhanced the tensile strength and toughness of scaffolds upon 1.5- and 4-folds compared to unmodified samples, respectively, due to improved compatibility between matrix and filler. Hydrolytic treatment of scaffolds also modified the bioactivity and cellular attachment and proliferation due to greatly enhanced hydrophilicity of the forsterite nanoparticles after this process compared to surface modified samples. Results suggested that surface modification of forsterite nanopowder and hydrolytic treatment of the developed scaffolds were effective approaches to address the issues in the formation of composite fibers and resulted in development of bioactive composite scaffolds with ideal mechanical and structural properties for bone tissue engineering applications.     

Influence of powder characteristics and powder processing routes on microstructure and properties of hot pressed silicon nitride materials

Four different commercial Si₃N₄ powders were hot pressed with the addition of La₂O₃ and Y₂O₃ as sintering aids. Two powder processing routes were set up: addition of sintering aid powders by ultrasonic dispersion, addition of nanodispersed amorphous additive species by chemical coprecipitation. The following aspects were analyzed: characteristics of starting powders and powder mixtures, with reference to surface modification (electrokinetic behaviour and surface properties) induced by the powder treatment; sintering behaviour of the powder mixtures; influence of raw powders characteristics and processing route on microstructure and properties of dense materials. The microstructural characteristics of hot pressed materials (grain size, aspect ratio, grain boundary phases) were found to be dependent on powder characteristics and its process history. Significant variation of the mechanical properties (Young modulus, hardness, toughness and strength) were related to microstructural features. Strength, for example, ranges from 600 to 1200 MPa at room temperature and from 400 to 1000 MPa at 1200°C; toughness ranges from about 4 to about 6 MPam^1/2.