In situ processing and properties of nanostructured hydroxyapatite/alginate composite

A series of hydroxyapatite/alginate (HA/Alg) nanocomposites with alginate amounts varying from 10 to 40 wt% were prepared through in situ hybridization technique. The inorganic phase in the composites was carbonate-substituted HA with low crystallinity. The crystallinity of HA decreased with the increase of alginate content. HA crystallites were needle-like in shape with a typical size of 20 to 50 nm in length and 5 nm in width. FT-IR spectroscopy indicated that the chemical interaction occurred between the mineral phase and the polymer matrix. As compared to pure HA without alginate, the composites showed more homogeneous microstructures, where HA nanocrystals were well embedded in alginate matrix. Among all the samples, the composite containing 30 wt% alginate exhibited a highly ordered three-dimensional network, similar to natural bone’s microstructure.     

Polishing behavior of PS/CeO2 hybrid microspheres with controlled shell thickness on silicon dioxide CMP

Organic-inorganic composite microspheres with PS as a core and CeO₂ nanoparticles as a shell were synthesized by in situ decomposition reaction of Ce(NO₃)₃ on the surfaces of PS microspheres prepared through soap-free emulsion polymerization. The shell thickness of the composite microspheres could be turned by varying the concentration of Ce(NO₃)₃ in the reaction solution. The whole process required neither surface treatment for PS microspheres nor additional surfactant or stabilizer. The as-synthesized PS/CeO₂ composite microsphere samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). Oxide chemical mechanical polishing (CMP) performance of the PS/CeO₂ composite abrasives with different shell thickness was characterized by atomic force microscopy (AFM). The results indicated that the as-prepared core-shell structured composite microspheres (220-260 nm in diameter) possessed thin shell (10-30 nm) composed of CeO₂ nanoparticles (particle diameter of 5-10 nm), and the final CeO₂ contents of the composite microspheres ranged from 10 to 50 wt%. A possible mechanism for the formation of PS/CeO₂ composite microspheres was discussed also. The CMP test results confirmed that the novel core-shell structured composite abrasives are useful to improve oxide CMP performance. In addition, there is an obvious effect of shell thickness of the composite abrasives on oxide CMP performance.     

Enantiomeric PLA–PEG block copolymers and their stereocomplex micelles used as rifampin delivery

A novelty approach to self-assembling stereocomplex micelles by enantiomeric PLA–PEG block copolymers as a drug delivery carrier was described. The particles were encapsulated by enantiomeric PLA–PEG stereocomplex to form nanoscale micelles different from the microspheres or the single micelles by PLLA or PDLA in the reported literatures. First, the block copolymers of enantiomeric poly(l-lactide)–poly(ethylene–glycol) (PLLA–PEG) and poly(D-lactide)–poly(ethylene–glycol) (PDLA–PEG) were synthesized by the ring-opening polymerization of l-lactide and d-lactide in the presence of monomethoxy PEG, respectively. Second, the stereocomplex block copolymer micelles were obtained by the self-assembly of the equimolar mixtures of enantiomeric PLA–PEG copolymers in water. These micelles possessed partially the crystallized hydrophobic cores with the critical micelle concentrations (cmc) in the range of 0.8–4.8 mg/l and the mean hydrodynamic diameters ranging from 40 to 120 nm. The micelle sizes and cmc values obviously depended on the hydrophobic block PLA content in the copolymer. Compared with the single PLLA–PEG or PDLA–PEG micelles, the cmc values of the stereocomplex micelles became lower and the sizes of the stereocomplex micelles formed smaller. And lastly, the stereocomplex micelles encapsulated with rifampin were tested for the controlled release application. The rifampin loading capacity and encapsulation efficiency by the stereocomplex micelles were higher than those by the single polymer micelles, respectively. The drug release time in vitro was depending on the composites of the block copolymers and also could be controlled by the polymer molecular weight and the morphology of the polymer micelles.     

Preparation of poly(styrene-glucidylmethacrylate)/Fe3O4 composite microspheres with high magnetite contents

Magnetic polymer composite microspheres with high magnetite contents were prepared by dispersion polymerization of styrene (St) and glucidylmethacrylate (GMA), in which Fe₃O₄ nanoparticles were co-stabilized by oleic acid and silane surfactants. The microstructure of the composite microspheres was characterized by Fourier transform infrared (FTIR) spectrometry, X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results demonstrated the presence of a hybrid morphology with organic polymer-encapsulated inorganic particles. Subsequently, thermogravimetric analysis (TGA) and vibrating sample magnetometry (VSM) were used to evaluate the magnetite content of the microspheres. It was found that an accordant magnetite content of about 70 wt%, could be obtained for the magnetic polymer microspheres, a value significantly higher than those reported thus far. The possible mechanism for the formation of the microspheres was proposed.     

Fabrication of surface‐enhanced Raman scattering‐active ZnO/Ag composite microspheres

We show in this paper how zinc oxide (ZnO)/silver (Ag) composite microspheres can be prepared by the reduction of Ag(NH₃)₂⁺ with the reducing agent formaldehyde in aqueous solution on the surface of ZnO microspheres. During the preparation, Sn²⁺ was absorbed on the surface of ZnO microspheres for sensitization and activation, and then Ag(NH₃)₂⁺ was reduced to Ag nanoparticles by the reducing agent to obtain ZnO/Ag composite microspheres. SEM and TEM images revealed silver nanoparticles with a diameter ranging from tens to 100 nm. X‐Ray photoelectron spectra (XPS), X‐ray diffraction (XRD) patterns and UV‐vis spectra were used to characterize the structure of the ZnO/Ag composite microspheres. The origin of the surface‐enhanced Raman scattering properties was traced to the surface of the ZnO/Ag composite microspheres. The enhancement factor was estimated in detail, and the enhancement mechanism for the SERS effect was also investigated. Copyright © 2007 John Wiley & Sons, Ltd.     

Gelatin–Chitosan composite capped gold nanoparticles: a matrix for the growth of hydroxyapatite

Growth of hydroxyapatite (HA) on gelatin–chitosan composite capped gold nanoparticles is presented for the first time by employing wet precipitation methods and we obtained good yields of HA. Fourier transform infrared spectroscopy (FTIR) spectrum has shown the characteristic bands of phosphate groups in the HA. Scanning electron microscopy (SEM) pictures have shown spherical nanoparticles with the size in the range of 70–250 nm, whereas ≥2–50 nm sized particles were visualized in high resolution transmission electron microscopy (HR-TEM). X-ray diffraction (XRD) spectrum has shown Bragg reflections which are comparable with the HA. Energy dispersive X-ray (EDX) studies have confirmed calcium/phosphate stoichiometric ratio of HA. The thermogravimetric analysis (TGA) has shown about 74% of inorganic crystals in the nanocomposite formed. These results have revealed that gelatin–chitosan capped gold nanoparticles, acted as a matrix for the growth of HA.     

Production of magnetic microspheres by ultrasonic atomisation

Magnetic microspheres, with mean particle sizes from 23 to 32 μm were produced by the ultrasonic atomisation of a suspension of magnetite particles, of approximately 200 nm diameter, in a solution of poly–l–lactic acid (PLLA). The mean particle diameter and the width of the particle diameter distribution both increased with increasing magnetite concentration. The particles appear to be suitable for magnetic hyperthermic treatment of liver cancers, with the hysteresis loop areas increasing linearly with nominal magnetite concentration up to 30 wt% magnetite.     

Co-precipitation of asiatic acid and poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactide) using rapid expansion of subcritical solutions into liquid solvents

Poly(l-lactide) (PLLA) nanoparticles loaded with asiatic acid (AA) were successfully produced by rapid expansion of a subcritical solution into an aqueous receiving solution containing a dispersing agent. A mixture of carbon dioxide (CO₂) and ethanol (EtOH) with a weight ratio of 1:1 was used as the solvent for AA and PLLA. Two surfactants, Pluronic F127 and sodium dodecyl sulfate were employed. The former was found to be more effective for stabilizing AA-loaded PLLA nanoparticles, as a rapid expansion into a 0.1 wt% Pluronic F127 solution produced a stable nanosuspension consisting mainly of well-dispersed, individual nanoparticles. The effects of rapid expansion-processing conditions—AA to PLLA weight ratio and pre-expansion temperature (T_pre)—on the size and morphology of composite nanoparticles, and the loading capacity and entrapment efficiency of AA in PLLA nanoparticles, were systematically investigated. It was found that AA-loaded PLLA nanoparticles with a size range of 30–100 nm were consistently fabricated by rapid expansion at T_pre of 70–100 °C and AA to PLLA weight ratios of 1:2 and 1:4, and with a constant pre-expansion pressure of 330 bar. The T_pre and AA to PLLA weight ratio had no significant effects on the size of the nanoparticles. The AA to PLLA weight ratio is a controlling parameter for both the loading capacity and the entrapment efficiency of AA in PLLA nanoparticles. The loading capacity and entrapment efficiency increased from 8–11 to 16–21 wt%, and 38–57 to 50–62 wt%, respectively, when the AA to PLLA weight ratio changed from 1:4 to 1:2. However, increasing the T_pre from 70 to 100 °C decreased both the loading capacity and entrapment efficiency of AA in PLLA nanoparticles by ~20–30%.     

Preparation and Characterization of Gelatin–Poly(L-lactic) Acid/Poly(hydroxybutyrate-co-hydroxyvalerate) Composite Nanofibrous Scaffolds

Poly(L-lactic) acid (PLLA) scaffolds, prepared by electrospinning technology, have been suggested for use in tissue engineering. They remain a challenge for application in biological fields due to PLLA's slow degradation and hydrophobic nature. We describe PLLA, PLLA/poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), and PLLA/PHBV/gelatin (Gt) composite nanofiberous scaffolds (Gt–PLLA/PHBV) electrospun by changing the electrospinning technology. The morphologies and hydrophilicity of these fibers were characterized by scanning electron microscopy (SEM) and water contact angle measurement. The results showed that the addition of PHBV and Gt resulted in a decrease in the diameters and their distribution and greatly improved the hydrophilicity. The in-vitro degradation test indicated that GT–PLLA/PHBV composite scaffolds exhibited a faster degradation rate than PLLA and PLLA/PHBV scaffolds. Dermal fibroblasts viabilities on nanofibrous scaffolds were characterized by [3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide] (MTT) assay and cell morphologies after 7 days culture. Results indicated that the GT–PLLA/PHBV composite nanofibers showed the highest bioactivity among the three scaffolds and increased with increasing time. The SEM images of cells/scaffolds composite materials showed the GT–PLLA/PHBV composite nanofibers enhanced the dermal fibroblasts's adhesion, proliferation, and spreading. It is suggested that the nanofibrous composite scaffolds of GT–PLLA/PHBV composites would be a promising candidate for tissue engineering scaffolds.     

Effect of radiation on conductivity of solid PVA–KOH–PC composite polymer electrolytes

The aim of this work is to enhance the room temperature conductivity of solid alkaline composite polymer electrolytes (ACPEs) based on polyvinyl alcohol/potassium hydroxide/propylene carbonate (PVA–KOH–PC) composites by cross-linking the PVA and bond scission of the PC by γ-radiation. The ACPEs were prepared by solvent-casting technique and irradiated with doses up to 200 kGy at room temperature. The microstructure of the ACPEs was measured using XRD spectrometer, and the results show the structural change from semicrystalline to amorphous, indicating that the cross-linking has been achieved at higher doses. It was found that the PKOH composite at 40 wt% KOH and PPC composite at 60 wt% PC show higher conductivities. The conductivity of the PKPC composites is dominated by dc conductivity at higher frequencies and that PC with 60 wt% has the highest conductivity at a dose of 200 kGy.Paper presented at the International Conference on Functional Materials and Devices 2005, Kuala Lumpur, Malaysia, June 6–8, 2005.     

One-pot fabrication and enhanced thermoelectric properties of poly(3,4-ethylenedioxythiophene)-Bi<Subscript>2</Subscript>S<Subscript>3</Subscript> nanocomposites

Bi₂S₃ nanotubes and de-doped poly(3,4-ethylenedioxythiophene) (PEDOT) composite nanopowders were synchronously synthesized by a one-pot self-assembly method. The powders were characterized by X-ray powder diffraction, infrared spectroscopy, and transmission electron microscopy, respectively. Thermoelectric properties of the Bi₂S₃–PEDOT composite nanopowders with different Bi₂S₃ contents after being cold pressed into pellets were measured at room temperature. The sample with 36.1 wt% Bi₂S₃ has a highest power factor of 2.3 μWm⁻¹K⁻², which is higher than that of both pure PEDOT (0.445 μWm⁻¹K⁻²) and Bi₂S₃ (1.94 μWm⁻¹K⁻²).     

One-pot hydrothermal synthesis of an assembly of magnetite nanoneedles on a scaffold of cyclic-diphenylalanine nanorods

The assembly of metal oxide nanoparticles (NPs) on a biomolecular template by a one-pot hydrothermal synthesis method is achieved for the first time. Magnetite (Fe₃O₄) nanoneedles (length: ~100 nm; width: ~10 nm) were assembled on cyclic-diphenylalanine (cFF) nanorods (length: 2–10 μm; width: 200 nm). The Fe₃O₄ nanoneedles and cFF nanorods were simultaneously synthesized from FeSO₄ and l-phenylalanine by hydrothermal synthesis (220 °C and 22 MPa), respectively. The samples were analyzed by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (IR), transmission electron microscopy (TEM), and superconducting quantum interference device (SQUID) magnetometry. Experimental results indicate that Fe₃O₄ nanoneedles were assembled on cFF nanorods during the hydrothermal reaction. The composite contained 3.3 wt% Fe₃O₄ nanoneedles without any loss of the original magnetic properties of Fe₃O₄.     

Nanocomposites of poly(l-lactide) and surface modified magnesia nanoparticles: Fabrication, mechanical property and biodegradability

A novel nanocomposite based on biodegradable poly(l-lactide) (PLLA) was prepared by the incorporation of surface modified magnesia (g-MgO) nanoparticles using a solution casting method. The mechanical properties, biodegradable properties and protein adhesion behavior of the g-MgO/PLLA nanocomposites were investigated. Scanning electron microscopy (SEM) results showed that g-MgO nanoparticles could comparatively uniformly disperse in PLLA matrix. The addition of g-MgO nanoparticles to PLLA matrix improved the tensile strength and elastic modulus, whereas reduced the elongation at break. The mass loss results showed that the nanocomposites with higher g-MgO content had faster degradation rates. The in vitro pH value determination results indicated that the g-MgO nanoparticles could neutralize effectively the lactic acid resulting from the degradation of PLLA. The g-MgO/PLLA nanocomposites exhibited enhanced protein adsorption, i.e., with the increase of g-MgO content, the amount of protein adsorption increased. The (5 wt%)g-MgO/PLLA nanocomposites adsorbed 33% more protein than the pure PLLA.     

Preparation of magnetic composite microspheres by surfactant free controlled radical polymerization: Preparation and characteristics

Submicron magnetic composite microspheres have been prepared by a new surfactant free controlled radical polymerization. This new approach is based on the use of diphenylethene (DPE) as radical controlling agent and no emulsifier is required. X-ray powder diffraction (XRD), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM), etc. were conducted to characterize the magnetite particles and magnetic composite microspheres. The average size of the magnetic composite microspheres prepared by this new approach is 265 nm and the magnetite content of the composite microspheres is around 20%. Furthermore, the magnetic composite microspheres which surfaces have epoxy groups were also prepared.     

Preparation and Characterization of Polyacrylonitrile and Polyacrylonitrile/β-cyclodextrins Microspheres

Polyacrylonitrile (PAN) and PAN/β-cyclodextrin (β-CD) microspheres were prepared via an electrospinning method. The PAN microspheres could be successfully obtained in a suitable range of concentrations of electrospun PAN solutions. When β-CD was added to the PAN solutions, electrospun PAN/β-CD composite spheres were prepared. The morphology of the spheres was characterized by scanning electron microscopy (SEM); it showed that the spheres had uniform diameter and a smooth surface. The composition of the composite microspheres was studied by Fourier transform infrared spectroscopy (FTIR). The results showed that the β-CD was incorporated in the polymer microspheres.     

Electrochemical sensing for the detection of 2,4-dichlorophenoxy acetic acid using molecularly imprinted polymer membrane

Molecularly imprinted polymer (MIP) membranes were used to develop highly sensitive chemical sensors for the detection of herbicide 2,4-dichlorophenoxy acetic acid (2,4-d). The 2,4-d imprinted composite MIP membranes were prepared, and the characterization was done by UV-VIS spectrophotometer, Fourier transform infrared spectroscopy, and scanning electron microscopy, and the same were fitted in a new electrochemical sensor model. Membrane electroconductivity measurements were performed by applying a small-amplitude alternating voltage (20 mV) with a varying frequency from 20 Hz to 80 kHz generated by a low-frequency wave form generator. The measured changes in the membrane ionic/electric conductivity as a function of 2,4-d concentration was allowed to evaluate the recognition properties of the prepared membrane. This sensor is useful in detecting 2,4-d herbicide having concentration range 10^-3 M to 10^-6 M. The cross-selectivity of the sensor, reproducibility of results, and reusability of MIP membrane were examined and found remarkable and recommendable.     

The impact of carbon shell on a Sn–C composite anode for lithium-ion batteries

Spherical Sn–carbon core-shell powders (CSCM/Sn) were synthesized through a resorcinol–formaldehyde microemulsion polymerization performed in the presence of SnO₂ powders, followed by carbonization in an inert atmosphere. Scanning electron microscope and X-ray diffractometry analyses showed that the Sn powders were thoroughly encapsulated within the carbon microspheres. The CSCM/Sn presented much better cyclability than the conventional Sn–carbon microsphere composite. In core-shell-structured composite, most of the Sn particles were encased inside carbon microspheres and not easy to aggregate or fall off from the microspheres. The carbon shell suppressed the aggregation of tin particles and alleviated the volume change of tin, and the conductive carbon shell effectively decreased the polarization during cycling, giving rise to better high rate performance and excellent capacity retention ability. It is shown that surface structure plays an important role in alloy/C composite anode materials for lithium-ion battery.     

Electrochemical and surface behavior of hydyroxyapatite/Ti film on nanotubular Ti-35Nb-xZr alloys

In this paper, we investigated the electrochemical and surface behavior of hydroxyapatite (HA)/Ti films on the nanotubular Ti-35Nb-xZr alloy. The Ti-35Nb-xZr ternary alloys with 3-10 wt.% Zr content were made by an arc melting method. The nanotubular oxide layers were developed on the Ti-35Nb-xZr alloys by an anodic oxidation method in 1 M H₃PO₄ electrolyte containing 0.8 wt% NaF at room temperature. The HA/Ti composite films on the nanotubular oxide surfaces were deposited by a magnetron sputtering method. Their surface characteristics were analyzed by field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS) and an X-ray diffractometer (XRD). The corrosion behavior of the specimens was examined through potentiodynamic and AC impedance tests in 0.9% NaCl solution. From the results, the Ti-35Nb-xZr alloys showed a solely β phase microstructure that resulted from the addition of Zr. The nanotubular structure formed with a diameter of about 200 nm, and the HA/Ti thin film was deposited on the nanotubular structure. The HA/Ti thin film-coated nanotubular Ti-35Nb-xZr alloys showed good corrosion resistance in 0.9% NaCl solution.     

Studies on PEO-based sodium ion conducting composite polymer films

A sodium ion conducting composite polymer electrolyte (CPE) prepared by solution-caste technique by dispersion of an electrochemically inert ceramic filler (SnO₂) in the PEO–salt complex matrix is reported. The effect of filler concentration on morphological, electrical, electrochemical, and mechanical stability of the CPE films has been investigated and analyzed. Composite nature of the films has been confirmed from X-ray diffraction and scanning electron microscopy patterns. Room temperature d.c. conductivity observed as a function of filler concentration indicates an enhancement (maximum) at 1–2 wt% filler concentration followed by another maximum at ∼10 wt% SnO₂. This two-maxima feature of electrical conductivity as a function of filler concentration remains unaltered in the CPE films even at 100 °C (i.e., after crystalline melting), suggesting an active role of the filler particles in governing electrical transport. Substantial enhancement in the voltage stability and mechanical properties of the CPE films has been noticed on filler dispersion. The composite polymer films have been observed to be predominantly ionic in nature with t _ion ∼ 0.99 for 1–2 wt% SnO₂. However, this value gets lowered on increasing addition of SnO₂ with t _ion ∼ 0.90 for 25 wt% SnO₂. A calculation of ionic and electronic conductivity for 25 wt% of SnO₂ film works out to be ∼2.34 × 10⁻⁶ and 2.6 × 10⁻⁷ S/cm, respectively.     

Fabrication and characterization of rod-like nano-hydroxyapatite on MAO coating supported on Mg-Zn-Ca alloy

The poor corrosion resistance of magnesium alloys is a dominant problem that limits their clinical application. In order to solve this challenge, micro-arc oxidation (MAO) was used to fabricate a porous coating on magnesium alloys and then electrochemical deposition (ED) was done to fabricate rod-like nano-hydroxyapatite (RNHA) on MAO coating. The cross-section morphology of the composite coatings and its corresponding energy dispersion spectroscopy (EDS) surficial scanning map of calcium revealed that HA rods were successfully deposited into the pores. The three dimensional morphology and scanning electron microscopy (SEM) image of the composite coatings showed that the distribution of the HA rods was dense and uniform. Atomic force microscope (AFM) observation of the composite coatings showed that the diameters of HA rods varied from 95 nm to 116 nm and the root mean square roughness (RMS) of the composite coatings was about 42 nm, which were favorable for cellular survival. The bonding strength between the HA film and MAO coating increased to 12.3 MPa, almost two times higher than that of the direct electrochemical deposition coating (6.3 MPa). Compared with that of the substrate, the corrosion potential of Mg-Zn-Ca alloy with composite coatings increased by 161 mV and its corrosion current density decreased from 3.36 × 10⁻⁴ A/cm² to 2.40 × 10⁻⁷ A/cm² which was due to the enhancement of bonding strength and the deposition of RNHA in the MAO pores. Immersion tests were carried out at 36.5 ± 0.5 °C in simulated body fluid (SBF). It was found that RNHA can induce the rapid precipitation of calcium orthophosphates in comparison with conventional HA coatings. Thus magnesium alloy coated with the composite coatings is a promising candidate as biodegradable bone implants.