Novel and simple route for the synthesis of core–shell chitosan–gold nanocomposites

This work presents a novel and simple route for the synthesis of water-soluble core–shell chitosan–gold nanocomposites. The experimental procedure can be summarized by the following steps: (i) chitosan deacetylation, (ii) chitosan depolymerization, (iii) chitosan nanoparticles’ formation and (iv) chitosan–gold nanocomposite formation. FT-IR spectroscopic results indicate that the formation of chitosan nanoparticles (ChtNPs) occurs via NH₃⁺ and PO⁻ groups electrostatic interactions, while UV–vis spectra points to a possible embedding of gold nanoparticles into the ChtNPs. This feature was confirmed by electronic transmission microscopy measurements. Chitosan and gold are biocompatible materials. Added to this, the obtained chitosan–gold nanocomposites presented thermal and absorbance properties which strongly point to their potential use in phototherapeutic processes.     

Synthesis and characterization of chitosan–multiwalled carbon nanotubes/hydroxyapatite nanocomposites for bone tissue engineering

Chitosan–multiwalled carbon nanotubes/hydroxyapatite nanocomposites were synthesized by a novel in situ precipitation method. The electrostatic adsorption between multiwalled carbon nanotubes and chitosan was investigated and explained by Fourier transform infrared spectroscopy analysis. Morphology studies showed that uniform distribution of hydroxyapatite particles and multiwalled carbon nanotubes in the polymer matrix was observed. In chitosan–multiwalled carbon nanotubes/hydroxyapatite nanocomposites, the diameters of multiwalled carbon nanotubes were about 10 nm. The mechanical properties of the composites were evaluated by measuring their compressive strength and elastic modulus. The elastic modulus and compressive strength increased sharply from 509.9 to 1089.1 MPa and from 33.2 to 105.5 MPa with an increase of multiwalled carbon/chitosan weight ratios from 0 to 5 %, respectively. Finally, the cell biocompatibility of the composites was tested in vitro, which showed that they have good biocompatibility. These results suggest that the chitosan–multiwalled carbon nanotubes/hydroxyapatite nanocomposites are promising biomaterials for bone tissue engineering.     

Synthesis and characterization of chitosan–carbon nanotube composites

Acid functionalized single walled carbon nanotubes were covalently grafted to chitosan by first reacting the oxidized carbon nanotubes with thionyl chloride to form acyl-chlorinated carbon nanotubes which are subsequently dispersed in chitosan and covalently grated to form composite material, CNT–chitosan, 1, which was washed several times to remove un-reacted materials. This composite has been characterized by FTIR, 13C NMR, TGA, SEM and TEM and has been shown to exhibit enhanced thermal stability. The reaction of 1, with poly lactic acid has also been accomplished to yield CNTchitosan–g-poly(LA), 2 and fully characterized by the above techniques. Results showed covalent attachment of chitosan and chitosan–poly lactic acid to the carbon nanotubes.     

Synthesis and characterization of barium ferrite–silica nanocomposites

In this work, we prepared barium ferrite-silica (BaM-SiO₂) nanocomposites of different molar ratios by high-energy ball milling, followed by heat-treatment at different temperatures. The microstructure, morphology and magnetic properties were characterized for different synthesis conditions by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). The results indicate that 15 h of milling was enough to avoid the generation of hematite phase and to get a good dispersion of barium ferrite particles in the ceramic matrix. For milling periods beyond 15 h and heat treatment above 900 °C, the XRD patterns showed the presence of hematite phase caused by the decomposition of BaM. The agglomerate size observed through SEM analysis was around 150 nm with a good BaM dispersion into the SiO₂ matrix. The highest saturation magnetization (Ms) value obtained was 43 emu/g and the corresponding coercivity (Hc) value of 3.4 kOe for the composition 60BaM-40SiO₂ milled for 15 h and heat treated at 900 °C. This coercivity value is acceptable for the application in magnetic recording media.     

Synthesis and characterization of gold–polypyrrole film composite

Polypyrrole (PPy) coatings have potential applications in batteries, fuel cells, sensors, anti-corrosion coatings, and drug delivery systems. In this article, PPy film coating on the electrode of quartz crystal microbalance (QCM) was exposed to acidic aqueous HAuCl₄ solution. The reduction for gold ions took place and gold particles were produced at the film surface. The gold content at the PPy film was monitored by using QCM. The concentration of gold uptake increases as the original concentration of HAuCl₄ solution increases. The morphology of the film before and after the deposition of the gold particles was studied by the scanning electron microscopy coupled with energy dispersive X-ray spectrometry. The gold particles are of undefined shape and have diameters around 200–600 nm. However, the image of the composite powder shows that gold particles of sizes 100–120 nm are distributed over the surface of the polymer particles with some aggregation. Infrared spectroscopy and X-ray diffraction were used to characterize the composite.     

Preparation and characterization of hydroxyapatite/polycaprolactone–chitosan composites

Hydroxyapatite (HA)/polycaprolactone (PCL)–chitosan (CS) composites were prepared by melt-blending. For the composites, the amount of HA was varied from 0% to 30% by weight. The morphology, structure and component of the composites were evaluated using environmental scanning electron microscope, X-ray diffraction and Fourier transform infrared spectroscope. The tensile properties were evaluated by tensile test. The bioactivity and degradation property were investigated after immersing in simulated body fluid (SBF) and physiological saline, respectively. The results show that the addition of HA to PCL–CS matrix tends to suppress the crystallization of PCL but improves the hydrophilicity. Adding HA to the composites decreases the tensile strength and elongation at break but increases the tensile modulus. After immersing in SBF for 14 days, the surface of HA/PCL–CS composites are covered by a coating of carbonated hydroxyapatite with low crystallinity, indicating the excellent bioactivity of the composites. Soaking in the physiological saline for 28 days, the molecular weight of PCL decreases while the mass loss of the composites and pH of physiological saline increase to 5.86% and 9.54, respectively, implying a good degradation property of the composites.     

Development,optimization, and in vitro characterization of dasatinib-loaded PEG functionalized chitosan capped gold nanoparticles using Box–Behnken experimental design

Objective: The purpose of this research study was to develop, optimize, and characterize dasatinib loaded polyethylene glycol (PEG) stabilized chitosan capped gold nanoparticles (DSB-PEG-Ch-GNPs).

Methods: Gold (III) chloride hydrate was reduced with chitosan and the resulting nanoparticles were coated with thiol-terminated PEG and loaded with dasatinib (DSB). Plackett–Burman design (PBD) followed by Box–Behnken experimental design (BBD) were employed to optimize the process parameters. Polynomial equations, contour, and 3D response surface plots were generated to relate the factors and responses. The optimized DSB-PEG-Ch-GNPs were characterized by FTIR, XRD, HR-SEM, EDX, TEM, SAED, AFM, DLS, and ZP.

Results: The results of the optimized DSB-PEG-Ch-GNPs showed particle size (PS) of 24.39?±?1.82?nm, apparent drug content (ADC) of 72.06?±?0.86%, and zeta potential (ZP) of ?13.91?±?1.21?mV. The responses observed and the predicted values of the optimized process were found to be close. The shape and surface morphology studies showed that the resulting DSB-PEG-Ch-GNPs were spherical and smooth. The stability and in vitro drug release studies confirmed that the optimized formulation was stable at different conditions of storage and exhibited a sustained drug release of the drug of up to 76% in 48?h and followed Korsmeyer–Peppas release kinetic model.

Conclusions: A process for preparing gold nanoparticles using chitosan, anchoring PEG to the particle surface, and entrapping dasatinib in the chitosan-PEG surface corona was optimized.     

Properties and in vitro characterization of polyhydroxybutyrate–chitosan scaffolds prepared by modified precipitation method

Porous polyhydroxybutyrate (PHB)–chitosan biopolymer scaffolds were prepared by co-precipitation from biopolymer solutions with propylene carbonate and acetic acid as solvents. A change of the fibrous character of chitosan precipitates to globular shaped forms with a polyhydroxybutyrate addition was found in suspensions. Scaffolds differ by porosity and morphology of polymers in microstructures, while chitosan represented more compact plate-like fibers and PHB characterized mainly fine fibrous globular agglomerates. Two structurally dissimilar phase regions were verified in blended scaffolds. A rise in the number of smaller pores, and fine structured polymer forms with PHB content were observed in the scaffolds. A significant reduction in the average molecular weight of biopolymers was found in pure chitosan scaffold, this after precipitation of the chitosan in the presence of propylene carbonate and in blends after mutual biopolymer mixing. Interactions between shortened chitosan chains, PHB and chitosan biopolymers in the blends were observed. An excellent fibroblast proliferation was found in scaffolds prepared from biopolymer blends.     

Synthesis and characterization of polymetalate based photochromic inorganic–organic nanocomposites

A novel reversible photochromic nanocomposite film based on a hybrid inorganic–organic matrix in which heteropolyacid H₃PW₁₂O₄₀ (PWA) was entrapped was prepared. The structure, photochromic behaviors and mechanism of the film were investigated by means of infrared (IR) spectroscopy, UV-Vis absorption spectra and electron spin resonance (ESR). The results showed that heteropolyanion, i.e. PW₁₂O₄₀³⁻ (PW₁₂), maintained a Keggin structure in the film and there was a strong interaction between anion PW₁₂ and cation R–NH₃⁺ (R=link of hybrid composite). The photochromic properties of the composite film originated from the reversible charge transfer between the anions and cations. Under ultraviolet (UV) irradiation, the anion would be reduced via one-electron step with simultaneous oxidation of the cation, accompanied by a color change from colorless to blue. Then the bleaching could occur when the film was in contact with ambient air or O₂ in the dark.     

Broadband dielectric spectroscopy and small-angle neutron scattering investigations of chitosan–graphene–silver metacomposites

Journal of Materials Science: Materials in Electronics - Solid polymer electrolytes (SPE) are an important field of research. Creation of environmentally friendly SPEs is essential. In this...     

Dynamic light scattering and UV–vis spectroscopy of gold nanoparticles solution

Gold nanoparticles solution prepared in water by laser ablation at 1064 nm of a gold metal plate was characterized by dynamic light scattering and UV–vis spectroscopy. Polarized dynamic scattering allows the measurement of translational diffusivity of Au nanoparticles, while depolarized scattering yields simultaneously the characterization of translational and rotational diffusivities. From these measurements the size and shape of Au nanoparticles are determined. Dynamic light scattering yields an average radius of 32 nm for the spherical nanoparticles in as prepared solution. The same measurements performed in an aged solution reveal the formation of ellipsoidal nanoparticles with minor and major semi-axis of 36 nm and 69 nm, respectively. The measured values allow to fit the UV–vis spectra with the Mie-Gans model and to measure the concentration of Au nanoparticles obtaining a complete characterization of their nanostructure. Dynamic light scattering results a powerful technique to characterize the size and shape of gold nanoparticles.     

Low temperature,pH-triggered synthesis of collagen–chitosan–hydroxyapatite nanocomposites as potential bone grafting substitutes

A pH-triggered synthesis strategy at low temperature was developed to initiate collagen self-assembly, chitosan precipitation and hydroxyapatite synthesis by ammonia diffusion into the acidic homogeneous stock solution for preparing bone-like nanocomposites. FTIR and XRD analyses were used to confirm the molecular interactions and the formation of bone-like hydroxyapatite in collagen–chitosan–hydroxyapatite nanocomposites. A facile modulation of hydroxyapatite content in the obtained nanocomposites was further validated by thermogravimetric analysis. SEM observations revealed that the unique microstructure of obtained nanocomposites was composed of collagen fibrils and nano needle-like objects dependent upon the relative ratio of inorganic to organic components. This strategy is convenient and also feasible to prepare collagen based bone-like nanocomposites.     

Discrimination of matrix–fibre interactions in all-cellulose nanocomposites

All-cellulose nanocomposites are produced using dissolved microcrystalline cellulose (MCC) as the matrix and cellulose nanowhiskers (CNWs), produced by acid hydrolysis, as the reinforcement. These nanocomposites are then characterised using X-ray diffraction to determine their crystallinity, and Raman spectroscopy to discriminate the reinforcing phase (cellulose I) from the CNWs and the matrix phase (cellulose II) from the dissolved MCC. Mechanical testing of the composites shows that there is a significant systematic reinforcement of the matrix material with the addition of CNWs. Furthermore, Raman spectroscopy is used to show that distinct spectroscopic bands for each phase within the composite spectrum can be used to discriminate the effects of both reinforcement and matrix. It is shown that a Raman band located approximately at 1095 cm⁻¹ can be used to follow the micromechanical deformation of the CNWs and matrix, whereas another band located at 895 cm⁻¹ arises purely from the matrix. This spectroscopic fingerprint is used to gain insights into the complex interactions occurring in these potentially recyclable composite materials, and offers a way forward to optimising their properties.     

Analysis of polarization behavior in relaxation of BaTiO₃-based ferroelectrics using wideband dielectric spectroscopy

Wideband dielectric spectra from the kilohertz to terahertz range are discussed for BaTiO?-based ferroelectrics. Ceramics of BaTiO? (BT), Ba(0.6)Sr(0.4)TiO? (BST-0.6), and BaZr(0.25)Ti(0.75)O? (BZT-0.25) were selected as normal ferroelectrics, ferroelectrics with diffuse phase transition (DPT ferroelectrics), and relaxor ferroelectrics, respectively. The variation of ionic polarization in both BT and BST-0.6 ceramics with temperature could be explained by the softening of the soft phonon mode. In BZT-0.25, a permittivity anomaly at the dielectric maximum temperature (T(m)) at low frequencies is not attributed to the softening of the soft phonon mode, but originates from the permittivity derived from the dipole polarization (?(dipole)). Relaxor behavior in BZT-0.25 is derived from the increase in the depression of ?(dipole) on cooling across the T(m) with increasing frequency. In dipole polarization, BT, BST- 0.6, and BZT-0.25 all exhibited a similar tendency of ?(dipole) above the Curie temperature (T(c)) and T(m). However, behavior of ?(dipole) below the T(c) can be explained by the ferroelectric domains in BT, whereas the variation of ?(dipole) below the Tm could be explained by growth process of polar nanoregions (PNRs) in BST-0.6 and BZT-0.25. Regarding this, BT can be distinguished from BST-0.6 and BZT-0.25. Relaxation in BT could be interpreted as successive change in polarization mechanism from normal ferroelectrics to relaxor ferroelectrics via DPT ferroelectrics.     

Raman spectroscopy and AC conductivity of polyaniline montmorillonite (PANI–MMT) nanocomposites

A series of polyaniline/montmorillonite clay (PANI–MMT) nanocomposites were synthesised by in situ polymerisation of aniline in acidic medium in the presence of varying amounts (from 1 to 30 wt%) of MMT and a substoichiometric amount of ammonium persulfate (APS). For a preferred molar ratio of monomer to oxidant of 2:1, the aniline was polymerised and largely incorporated into the MMT. The PANI–MMT nanocomposites were characterised and compared by wide-angle powder X-ray diffraction and UV–Vis spectroscopy. Raman spectroscopy was used to investigate the interaction between clay layers and the intercalated polymer chains. Room temperature AC conductivity was measured in the frequency range 30 Hz to 1 MHz. Pure PANI and all the composites exhibited a low frequency region of frequency independent AC conductivity followed by a high frequency dispersive region where the AC conductivity obeyed a fractional power law of frequency dependence. The fractional exponent n for all the nanocomposites is significantly high as compared to that of pure PANI; n = 0.9 for all the composites whereas for pure PANI n = 0.2. In pristine PANI the onset of the dispersive region ω _c is at a much higher frequency (at 300 kHz) as compared to the nanocomposites in which ω _c is about 10 kHz.     

Synthesis of protein–gold nanoparticle hybrid and gold nanoplates in protein aggregates

A straightforward and economically viable approach was developed to biomimetic synthesis of gold nanocrystals by using casein micelles (CMs) without additional reductant. The UV–vis, TEM, SAED, FTIR, DLS and XRD techniques were employed to systematically characterize Au nanocrystals synthesized. Isotropic gold nanoparticle (GNP) and gold nanoplates in good yields (up to 90%) with different sizes can be obtained easily by adjusting the experimental condition. Spherical nanoparticles were obtained with tunable mean sizes at higher pH and casein concentrations. The high colloidal stability of the spherical GNP is attributed to the formation of CM/GNP hybrid under some experimental condition. At lower pH, reaction temperature and casein concentrations, single-crystalline gold nanoplates in good yields (up to 90%) are obtained. The growth of these nanostructures is attributed to an interplay between the faceting tendency of the protein molecules/micelles and the growth kinetics. More importantly, the morphological evolution of large gold nanoplates at different reaction times has been followed, and compared with some earlier protein systems, different formation mechanisms in casein micelles are obtained. The results demonstrate that both the property of individual protein molecules and protein aggregates play important roles in controlling the formation of gold nanocrystals by using amphiphilic protein.     

Supermacroprous chitosan–agarose–gelatin cryogels: in vitro characterization and in vivo assessment for cartilage tissue engineering

The study focuses on the synthesis of a novel polymeric scaffold having good porosity and mechanical characteristics synthesized by using natural polymers and their optimization for application in cartilage tissue engineering. The scaffolds were synthesized via cryogelation technology using an optimized ratio of the polymer solutions (chitosan, agarose and gelatin) and cross-linker followed by the incubation at sub-zero temperature (−12°C). Microstructure examination of the chitosan–agarose–gelatine (CAG) cryogels was done using scanning electron microscopy (SEM) and fluorescent microscopy. Mechanical analysis, such as the unconfined compression test, demonstrated that cryogels with varying chitosan concentrations, i.e. 0.5–1% have a high compression modulus. In addition, fatigue tests revealed that scaffolds are suitable for bioreactor studies where gels are subjected to continuous cyclic strain. In order to confirm the stability, cryogels were subjected to high frequency (5 Hz) with 30 per cent compression of their original length up to 1 × 10⁵ cycles, gels did not show any significant changes in their mass and dimensions during the experiment. These cryogels have exhibited degradation capacity under aseptic conditions. CAG cryogels showed good cell adhesion of primary goat chondrocytes examined by SEM. Cytotoxicity of the material was checked by MTT assay and results confirmed the biocompatibility of the material. In vivo biocompatibility of the scaffolds was checked by the implantation of the scaffolds in laboratory animals. These results suggest the potential of CAG cryogels as a good three-dimensional scaffold for cartilage tissue engineering.     

Numerical calculations of residual–stress relaxation in quenched plates

Abstract

Methods of thermal stress relief such as stretching and compression are compared for different thermal and mechanical properties during quenching. The heat equation for a simple geometric model, such as an infinite plate, is solved with an experimental surface conductance and a step–by–step method of determining the temperature field in the thickness of the plate. This field is introduced as data for the uncoupled thermal elastic–plastic model for quenching. In the calculation of the plastic–strain path, the thermal and mechanical properties are considered as temperature dependent for a homogeneous and isotropic material. Good agreement is found between the calculated residual stresses and experimental values for an aluminium alloy and a stainless steel. The predicted residual–stress distributions and strain history are then used as data for the numerical simulation of stress–relief methods with an incremental integration of the Prandtl–Reuss equation. This analysis allows the observation of the effects of small variations in mechanical properties during quenching on the residual–stress field after mechanical stress relief and the theoretical comparison of different processes.

MST/6