Hydrothermal synthesis of magnetite nanoparticles as MRI contrast agents

Magnetite (Fe₃O₄) nanoparticles prepared using hydrothermal approach were employed to study their potential application as magnetic resonance imaging (MRI) contrast agent. The hydrothermal process involves precursors FeCl₂·4H₂O and FeCl₃ with NaOH as reducing agent to initiate the precipitation of Fe₃O₄, followed by hydrothermal treatment to produce nano-sized Fe₃O₄. Chitosan (CTS) was coated onto the surface of the as-prepared Fe₃O₄ nanoparticles to enhance its stability and biocompatible properties. The size distribution of the obtained Fe₃O₄ nanoparticles was examined using transmission electron microscopy (TEM). The cubic inverse spinel structure of Fe₃O₄ nanoparticles was confirmed by X-ray diffraction technique (XRD). Fourier transform infrared (FTIR) spectrum indicated the presence of the chitosan on the surface of the Fe₃O₄ nanoparticles. The superparamagnetic behaviour of the produced Fe₃O₄ nanoparticles at room temperature was elucidated using a vibrating sample magnetometer (VSM). From the result of custom made phantom study of magnetic resonance (MR) imaging, coated Fe₃O₄ nanoparticles have been proved to be a promising contrast enhanced agent in MR imaging.     

Preparation of hydroxyapatite coating on smooth implant surface by electrodeposition

A novel process for the deposition of a hydroxyapatite (HA) coating on a smooth implant surface has been developed. Specimens were firstly subjected to electrodeposition at −1.8 V (versus Ag/AgCl) in a mixed solution of 0.042 M Ca(NO₃)₂·4H₂O and 0.025 M NH₄H₂PO₄ at 85 °C for 5 s, and then post-treated in 1 M NaOH solution for 30 min. The experimental results showed the specimens prepared by the designed process to have better adhesion properties than those prepared by the traditional electrodeposition process.     

Calcium phosphate growth on sintered α-alumina treated with piranha solution using a wet-chemical procedure

Two alumina samples, a high surface powder γ-alumina and a sintered α-alumina have been studied as substrates for apatite growth. In the first case, the initial stage was the calcium adsorption in an alkaline solution, followed by phosphate uptake. On the other hand, the α-alumina was firstly subjected to an acid piranha treatment at 80 °C for four hours, before alternate immersions on calcium and phosphate solutions. Next, the alumina samples were immersed repeatedly in a glycine buffer, pH 10.2, and then in tris buffer solutions, pH 7.4 at 32 °C. The resultant solids were studied by means of XRD, TEM or SEM. Calcium phosphate growth was observed in both cases. An almost uniform and continuous layer was formed on the sintered α-alumina. The results suggest that pretreatment with piranha solution seems to be a fast and efficient alternative to bioactivate the α-alumina surface.     

Improvement of luminescent properties of GdPO4 doped with optimal europium concentration by Co-doping with lanthanum

Hexagonal gadolinium Phosphate Hydrate doped with different europium amounts (Gd_1-xPO₄:Eu_x·H₂O; x = 0.01, 0.05, 0.10, 0.15, and 0.20) was synthesized by hydrothermal synthesis method and the obtained samples were analyzed giving the optimal dopant concentration. Furthermore, gadolinium was additionally replaced by Lanthanum Gd_0.85-yLa_yPO₄:15%Eu (y = 0.25, 0.5, 0.75) in hopes of improving luminescence properties even more. This may be possible due to the fact that LaPO₄ exhibits a monoclinic crystal structure, which usually shows better luminescence properties. All of the synthesized compounds were analyzed by X-ray diffraction in order to investigate their crystal structure. SEM analysis was used to characterize the morphology of synthesized particles, while surface area and the pore size of Gd_0.85-xLa_xPO₄:15%Eu samples were measured using Nitrogen adsorption by the BET method and BJH method. The luminescence properties were also characterized and discussed in detail. Lastly, the cytotoxicity study demonstrated that the replacement of gadolinium with lanthanum leads to a reduction in the toxicity of the samples.     

Heat treatment-improved bond strength of resin cement to lithium disilicate dental glass-ceramic

This study investigated the influence of different hydrofluoric acid (HF) concentrations and heat treatments applied to a lithium disilicate dental glass-ceramic (EMX) on surface morphology and micro-shear bond strength (μSBS) to resin cement. Five HF concentrations (1%, 2.5%, 5%, 7.5% and 10%) and four different heat treatments applied before etching were assessed: 1. etching at room temperature with no previous heat treatment (control group); 2. HF stored at 70 °C for 1 min applied to the ceramic surface at room temperature; 3. HF at room temperature applied after a hot air stream is applied perpendicularly to the ceramic surface for 1 min; 4. the combination of previously heated HF and heated EMX surface. The etching time was fixed for 20 s for all groups. Etched EMX specimens were analyzed on field-emission scanning electron microscope (FE-SEM) and the μSBS was carried out on a universal testing machine at a crosshead speed of 1 mm/min until fracture. For the control groups, FE-SEM images showed greater glassy matrix dissolution and higher μSBS for 7.5% and 10% HF concentrations. The previous heat treatments enhanced the glassy matrix dissolution more evidently for 1%, 2.5% and 5% and yielded increased μSBS values, which were not statistically different for 7.5% and 10% HF concentrations (control group). HF concentrations and previous heat treatments did show to have an influence on the etching/bonding characteristics to lithium disilicate dental glass-ceramic.     

Formation of hexagonal plate shaped ZnO microparticles – A study on antibacterial and magnetic properties

The focus of this work is to realize ZnO microparticles with simultaneously enhanced antibacterial and magnetic properties through a double cationic (Mg+Co) doping. Undoped and magnesium (Mg)+ cobalt (Co) doped ZnO microparticles were synthesized using a cost-effective simple soft chemical route. Their surface morphological, magnetic, antibacterial and structural properties were investigated. Antibacterial studies of the prepared samples were carried out against a Gram Positive and Gram Negative bacteria. From the antibacterial studies, it is found that the double cationic doped ZnO microparticles exhibit superior antibacterial efficiency compared with undoped and single cationic doped ZnO microparticles. The FESEM images show that the undoped and single cationic (Mg/Co) doped ZnO particles have hexagonal block structures of micro scale dimensions whereas the double cationic doping causes the formation of hexagonal plate structures having near nanoscale thickness (~150 nm), thereby increasing the effective reactive surface area. The magnetization curves show that the coexistence of Mg²⁺ and Co²⁺ ions in the ZnO lattice causes a pronounced increase in the ferromagnetic behavior, already present in the undoped and single cationic doped ZnO material. The XRD, FTIR and PL results support the discussion on the antibacterial and magnetic results. The EDAX profiles and the compositional mapping images confirm the presence of expected proportions of the constituent elements and their uniform distribution in the final product. Structural studies show that the products exhibit hexagonal wurtzite structure of ZnO without any secondary phases.     

Porous boron nitride nanofibers/PVA hydrogels with improved mechanical property and thermal stability

Polyvinyl alcohol (PVA) hydrogel is a promising material possessing good chemical stability, high water absorption, excellent biocompatibility and biological aging resistant. However, the poor mechanical performance of PVA hydrogel limits its applications. Here we report the utilization of one-dimensional (1D) BN nanofibers (BNNFs) as nanofillers into PVA matrix to prepare a novel kind of BNNFs/PVA composite hydrogel via a cyclic freezing and thawing method. For comparison, the composite hydrogels using spherical BN nanoparticles i.e. BN nanospheres (BNNSs) as fillers were also prepared. The mechanical properties, thermal stabilities and swelling behaviors of the composite hydrogels were investigated in detail. Our study indicates that the mechanical properties of the hydrogels can be improved by adding of BNNFs. After loading of BNNFs into PVA with content of 0.5?wt%, the compressive strength of the composite hydrogel increases by 252% compared with that of pure PVA hydrogel. The tensile performance of BNNFs/PVA composite hydrogels has also been improved. Impressive 87.8% increases in tensile strengths can be obtained with 1?wt% BNNFs added. In addition, with the increase of BNNFs content, the thermal stability and the swelling ratio of hydrogels are increased gradually. The swelling ratio of hydrogel increases by 56.3% with only 1?wt% BNNFs added. In comparison, the improvement effects of the BNNS fillers on the mechanical strengths and swelling ratios are much weaker. The enhanced effects of BNNFs can be ascribed to the strong hydrogen bond interaction between BNNFs and PVA. The high aspect ratios of the nanofibers should also be took into account.     

Two-step modification process to improve mechanical properties and bioactivity of hydroxyfluorapatite scaffolds

Porous ceramic scaffolds are synthetic implants, which support cell migration and establish sufficient extracellular matrix (ECM) and cell-cell interactions to heal bone defects. Hydroxyapatite (HA) scaffolds is one of the most suitable synthetic scaffolds for hard tissue replacement due to their bioactivity, biocompatibility and biomimetic features. However, the major disadvantages of HA is poor mechanical properties as well as low degradability rate and apatite formation ability. In this study, we developed a new method to improve the bioactivity, biodegradability and mechanical properties of natural hydroxyfluorapatite (HFA) by applying two-step coating process including ceramic and polymer coats. The structure, morphology and bioactivity potential of the modified and unmodified nanocomposite scaffolds were evaluated using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and energy dispersive spectroscopy (EDS). The scaffold with optimized mechanical properties was HFA-30?wt%HT (HT stands for hardystonite) with a total porosity and pore size of 89?±?1 and 900–1000?µm, respectively. The compressive modulus and strength of HFA (porosity ~ 93?±?1) were improved from 108.81?±?11.12–251.45?±?12.2?MPa and 0.46?±?0.1–1.7?±?0.3?MPa in HFA-30?wt%HT sample, respectively. After applying poly(ε-caprolactone fumarate) (PCLF) polymer coating, the compressive strength and modules increased to 2.8?±?0.15 and 426.1?±?15.14?MPa, respectively. The apatite formation ability of scaffolds was investigated using simulated body fluid (SBF). The results showed that applying the hardystonite coating improve the apatite formation ability; however, the release of ions increased the pH. Whereas, modified scaffolds with PCLF could control the release of ions and improve the apatite formation ability as well.     

Synthesis and characterization of CaFe2O4 nanoparticles via co-precipitation and auto-combustion methods

In this paper, the techniques for the synthesis of CaFe₂O₄ nanoparticles using the auto-combustion and co-precipitation methods are discussed. The effects of both methods on the microstructure and magnetic properties of the CaFe₂O₄ nanoparticles were compared. The CaFe₂O₄ powder was obtained after drying the synthesized sample via co-precipitation overnight in an oven at 80 °C. For auto-combustion method, the sol that was initially formed was gradually converted into a gel, which was then combusted at 250 °C. Finally, the CaFe₂O₄ nanoparticles were calcined at 550 °C. The different synthesis methods produced nanoparticles with different physical and magnetic properties in order to find an optimum size to be utilized for drug delivery applications. The results of the X-ray diffraction showed that both processes produced nanocrystals with an orthorhombic crystalline structure. It was noted from the measurements made with a transmission electron microscope (TEM) that the synthesis using the co-precipitation method produced nanoparticles with a size of about 10–20 nm, which was comparable with the size that was obtained when the auto-combustion method was used. The magnetic properties were investigated using a vibrating sample magnetometer (VSM), where the magnetic saturation (M_s) of CaFe₂O₄ for the sample synthesized using the co-precipitation method was 47.279 emu/g, which was higher than the magnetic saturation (M_s) of 31.10 emu/g obtained when the auto-combustion method was used. The hysteresis loops (Hc) for the samples were 17.380 G and 6.1672 G, respectively. Additionally, the elaborate properties mentioned above, such as the size and superparamagnetic properties of the synthesized CaFe₂O₄ nanoparticle size, were the characteristics required for drug delivery because the targeted therapy required nanoparticles with good magnetic properties, a suitable size, and which were non-toxic in order to have a potential application in targeted drug delivery systems.     

Structural,mechanical, and in vitro characterization of freeze-cast scaffolds prepared using a sol-gel-derived bioactive glass from the SiO2–CaO–Na2O–P2O5–K2O–MgO system

This work deals with the preparation of freeze-cast scaffolds using a bioactive glass from the SiO₂–CaO–Na₂O–P₂O₅–K₂O–MgO system. This material could be sintered at lower temperatures (650 °C) than other variations of bioactive glasses, which is an important advantage in terms of energy and cost savings. This behavior represents a great advantage in terms of energy and cost savings. The freeze-casting step was conducted using water as a solvent and liquid nitrogen as a coolant. The prepared samples were examined according to their pore structure, thermal behavior, mechanical stability, and bioactivity. The glass transition temperature (T_g), crystallization onset temperature (T_x), and maximum crystallization temperature (T_c) evaluated for this bioactive glass were about 660 °C, 690 °C, and 705 °C. Consequently, the freeze-cast scaffolds could be sintered at 650 °C for 2–8 h, which favored viscous flow sintering without crystallization. Bioactivity assays were conducted by soaking the scaffolds in simulated body fluid for up to 21 days, showing that these materials present a bioactive behavior, inducing hydroxyapatite formation. These materials' mechanical properties and biocompatibility make them promising candidates for use in trabecular bone repair.     

Structures of organic additives modified magnetite nanoparticles

Magnetite (Fe₃O₄) nanoparticles and magnetite-based inorganic–organic hybrids are attracting increasing attention in biomedicine, as thermoseeds for hyperthermia and contrast media in magnetic resonance imaging. Controlling the size of Fe₃O₄ thermoseeds is important, as particle size affects their heat generation under alternative magnetic fields. Fe₃O₄ is easily synthesized via aqueous processes. We previously demonstrated that adding organic polymers during synthesis affected the size and crystallinity of the resulting Fe₃O₄. However, the relationship of the chemical structure of the low-molecular-weight organic additive of its effect on the product has not been elucidated. In this study, organic compounds containing varying functional groups and surface charges were added to the precursor solution of Fe₃O₄. Crystalline Fe₃O₄ formed in the presence of neutral acetone, cationic ethylenediamine, and anionic acetic acid. These nanoparticles had slightly smaller particle sizes than those prepared in the absence of additives. The presence of oxalic acid and tris(hydroxymethyl)aminomethane inhibited Fe₃O₄ nucleation, instead yielding lepidocrosite- or akaganeite-type FeOOH. These differences were attributed to the ability to form complexes between iron ions and the organic additives. The saturation magnetizations of the products were consistent with Fe₃O₄. This indicated that the crystal phase of the iron oxide products differed, even when prepared in the presence of organic additives of the same functional group. It is concluded that state of ion-organic molecule complex in the solutions is a key factor governing nanostructure of the resultant iron oxide.     

Preparation of the reticulated hydroxyapatite ceramics using carbon-coated polymeric sponge with elongated pores as a novel template

This paper proposes a novel, simple way to improve the compressive strength of reticulated porous hydroxyapatite (HA) ceramics using carbon-coated polymeric sponges with elongated pores as a novel template. This template allowed samples to have two interconnected pore networks with a preferential orientation, in which an addition pore network was newly formed by removing the carbon-coated polymeric struts, while preserving the pre-existing pore network. The compressive strength of the sample was as high as 2.9 ± 0.3 MPa with a porosity of 76% when tested parallel to the direction of pore elongation. In addition, the in vitro cell test using a pre-osteoblast cell line revealed the samples to have good biocompatibility.     

Sol-gel coated enamel for steel: 250 days of continuous high-temperature stability

Two types of thermally durable and heat-resistant enamel coatings were applied to steel alloys. Three-layer TiO₂-SiO₂ sol-gel films were grown by a dip-coating method on an enamelled metal alloy to maintain and protect their properties from undesired environmental impact.The enamel coatings withstood 6000 h at 600 °C, retaining their colour while staying hard and adhering firmly to the metal surface. A three-layer sol-gel coating improved the chemical resistance of the enamelled metal by 6% (0 h), 29% (3000 h), and 28% (6000 h) at 600 °C. Throughout the whole treatment at 600 °C, the enamel coatings maintained their microhardness and even increased it from 3.6 to 4.4 GPa.     

A comparative physico-chemical study of bioactive glass and bone-derived hydroxyapatite

This study aimed at comparing the physico-chemical properties of bioactive glass and bone-derived hydroxyapatite (HA). 63S bioglass particles were obtained by sol-gel process and HA samples were derived from bovine bone. The chemical composition and the crystalline structure of both bioceramics were evaluated. Then the zeta potential in physiological saline and at different pH values was determined. It was found that the negativity of zeta potential for 63S bioglass is higher than that of bone-derived HA. The exothermal behavior through the hydration process was evaluated by isothermal microcalorimetry. The results showed that the librated heat during bioactive glass hydration process and its rate are almost ten times higher than HA. It could be related to different hydration mechanisms of bioglass and HA. However, for both bioglass and HA, this value is in the safe range and cannot be harmful for the adjacent tissues in the body.     

Magnetic and catalytic properties of copper ferrite nanopowders prepared by a microwave-induced combustion process

Copper ferrite nanopowders were successfully synthesized by a microwave-induced combustion process using copper nitrate, iron nitrate, and urea. The process only took a few minutes to obtain CuFe₂O₄ nanopowders. The resultant powders were investigated by XRD, SEM, VSM, and surface area measurement. The results revealed that the CuFe₂O₄ powders showed that the average particle size ranged from 300 to 600 nm. Also, it possessed a saturation magnetization of 21.16 emu/g, and an intrinsic coercive force of 600.84 Oe, whereas, upon annealing at 800 °C for 1 h. The CuFe₂O₄ powders specific surface area was 5.60 m²/g. Moreover, these copper ferrite magnetic nanopowders also acted as a catalyst for the oxidation of 2,3,6-trimethylphenol to synthesize 2,3,5-trimethylhydrogenquinone and 2,3,5-trimethyl-1,4-benzoquinone for the first time. On the basis of experimental evidence, a rational reaction mechanism is proposed to explain the results satisfactorily.     

Preliminary studies on the valorization of animal flour ash for the obtainment of active glasses

Animal flour ash, rich in phosphorous, calcium and alkaline oxides, has been used to formulate (i) controlled-release fertilizers, since they manage to release the nutrient elements (P, K) at a low rate, and (ii) bioactive glasses.     

Potassium-based composition for a bioactive glass

The increasing need for biomedical devices, required to face dysfunctions of natural tissues and organs caused by traumatic events, diseases and simple ageing, has drawn attention onto new materials, that could be able to positively interact with the human body. Among them, Bioglass^® is firmly diffused in medical practice, thanks to its high bioactivity. In particular, due to its brittleness, it is mainly applied as a coating onto tougher bionert substrates; nevertheless, its bioactivity may be altered by the crystallization phenomena that could be involved by its processing. With the aim of reducing the tendency to crystallize, a new glass composition, inspired by the 45S5 Bioglass^®, was formulated by substituting the sodium oxide with potassium oxide. A parallel characterization of the new glass and the 45S5 Bioglass^® was carried out in order to define the effect of the potassium oxide on the thermal behaviour, mechanical properties and bioactivity. The results proved that the thermo-mechanical properties, as well as the in vitro response of the two glasses were comparable; however, preliminary tests to produce glass coatings by enamelling evidenced a higher stability of the new glass that, unlike the 45S5 Bioglass^®, did not crystallize during processing.     

Nanoindentation study of microplasma sprayed hydroxyapatite coating

The microplasma sprayed (MPS) hydroxyapatite (HAP) coating on surgical grade SS316L, is an emerging material for bio-ceramic based implant application involving higher reliability. For this purpose, a 200 μm thick MPS-HAP coating was developed on SS316L substrate and characterized by XRD, SEM and FE-SEM techniques. The local mechanical properties of the coating, e.g. nano-hardness and Young's modulus were evaluated by nanoindentation technique carried out with a Berkovich indenter at various depths in the range of about 170–3000 nm on a polished top surface. The characteristic values of nano-hardness (1.5–5 GPa) and Young's modulus (∼60–100 GPa) obtained through the application of Weibull statistics to the experimentally measured data revealed a strong indentation size effect (ISE). Attempts were made to explain the genesis of ISE on the basis of some existing and some new concepts.     

PMMA composite bone cement containing bioactive and ferrimagnetic glass-ceramic particles: Effect of temperature and of the additional phase on some physical and mechanical properties

In this work, PMMA-based composite bone cements, embedding bioactive and ferrimagnetic glass-ceramic particles, have been prepared and characterized. Bioactivity, wettability, density, curing parameters, viscoelastic behaviour, bending strengths and creep have been investigated at 37 °C. The growth of a layer of HA on the samples surface after immersion in SBF has been confirmed. The presence of glass-ceramic particles improved the wetting behaviour of the composite cements. Shorter curing times and lower maximum temperatures for the three composite cements, in comparison to the plain one, have been detected. Almost unaffected mechanical properties of the composite bone cements have been found in comparison to those of the plain commercial cement both at room and at 37 °C. A little increase of the viscous flow has been evidenced in the composite samples at 37 °C. Radiographic imaging confirmed the intrinsic radiopacity of the composite cements.     

In-vitro corrosion inhibition mechanism of fluorine-doped hydroxyapatite and brushite coated Mg–Ca alloys for biomedical applications

Magnesium alloys have received great attention as a new kind of biodegradable metallic biomaterials. However, they suffer from poor corrosion resistance. In this study, Mg–Ca alloy was coated with nano-fluorine-doped hydroxyapatite (FHA), and brushite (DCPD); via electrochemical deposition (ED). Coatings were characterized by X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results revealed that nano-fluorine-doped hydroxyapatite coating produced more dense and uniform coating layer, compared to the brushite coating. The compression tests of the ED-coated Mg alloy samples immersed in simulated body fluid for different time periods showed higher yield strength (YS) and ultimate tensile strength (UTS), compared to those of the uncoated samples. The degradation behavior and corrosion properties of the ED-coated Mg alloy samples were examined via electrochemical measurements and immersion tests. The results showed that FHA coating could effectively induce the precipitation of more Ca²⁺ and PO₄³⁻ ions than DCPD coating, because the nanophase can provide higher specific surface area. It was also found that FHA and DCPD coatings can significantly decline the initial degradation rate of the alloy. A corrosion mechanism of the ED-coated alloy is proposed and discussed in this paper.