Chemical functionalization of chitosan biopolymer and chitosan-magnetite nanocomposite with sulfonic acid for acid-catalyzed reactions

Chemical functionalization of chitosan biopolymer and chitosan-magnetite nanocomposite was performed with sulfonic acid functional groups to achieve new solid acid materials. The sulfonic acid functional groups were created through the ring opening nucleophilic reaction of amine groups of chitosan with 1,4-butane sultone. Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopies (XPS) verified the successful sulfonic acid functionalization of chitosan. The obtained sulfonic acid functionalized chitosan-magnetite nanocomposite showed superparamagnetic properties according to the vibrating sample magnetometry analysis and exhibited magnetic separation feature from dispersed mixtures. Nitrogen adsorption-desorption analysis indicated the increase in surface area after formation of chitosan-magnetite nanocomposite and functionalization with sulfonic acid. Both of the prepared solid acids exhibited high catalytic activities in the acid-catalyzed acetic acid esterification with n-butanol and benzaldehyde acetalization with ethylene glycol as model reactions. Furthermore, they can be reused several times without considerable loss of their activities.     

Lipid Nanotechnology

Nanotechnology is a multidisciplinary field that covers a vast and diverse array of devices and machines derived from engineering, physics, materials science, chemistry and biology. These devices have found applications in biomedical sciences, such as targeted drug delivery, bio-imaging, sensing and diagnosis of pathologies at early stages. In these applications, nano-devices typically interface with the plasma membrane of cells. On the other hand, naturally occurring nanostructures in biology have been a source of inspiration for new nanotechnological designs and hybrid nanostructures made of biological and non-biological, organic and inorganic building blocks. Lipids, with their amphiphilicity, diversity of head and tail chemistry, and antifouling properties that block nonspecific binding to lipid-coated surfaces, provide a powerful toolbox for nanotechnology. This review discusses the progress in the emerging field of lipid nanotechnology.     

Synthesis,characterization and in-vitro behavior of natural chitosan-hydroxyapatite-diopside nanocomposite scaffold for bone tissue engineering

Composite materials based on a combination of biodegradable polymers and bioactive ceramics, including chitosan and hydroxyapatite are discussed as suitable materials for scaffold fabrication. Diopside is a member of bioactive silicates; it is a good choice for hard tissue engineering because of its biocompatibility with host tissue and high mechanical strength. Chitosan and hydroxyapatite were extracted from shrimp shell and bovine bone, respectively and diopside nanoparticles were prepared by the sol-gel method. The present study reports on a chitosan composite which was reinforced by hydroxyapatite and diopside; the scaffolds were fabricated by the freeze-drying method. The so-produced chitosan-hydroxyapatite-diopside (CS-HA-DP) scaffolds were further cross-linked using tripolyphosphate (TPP) to achieve enhanced mechanical strength. The ratios of the ceramic components in composites were 5-58-37, 10-55-35, and 15-52-33 (diopside-hydroxyapatite-chitosan, w/w %). The physicochemical properties of scaffolds were investigated using Fourier-transform infrared spectrometry (FT-IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) techniques. The effect of scaffolds composition on bioactivity and biodegradability were studied well. To investigate mechanical properties of samples, compression test was done. Results showed that the composite scaffold with 5% DP has the highest mechanical strength. The porosity of composites dropped from 92% to 76% by increasing the amount of DP. Cytocompatibility of the scaffolds was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, alkaline phosphatase (ALP) activity, and cell attachment studies using human osteoblast cells. Results demonstrated no sign of toxicity and cells were found to be attached to the pore walls within the scaffolds; moreover, results illustrated that the developed composite scaffolds could be a potential candidate for tissue engineering.     

UV-induced synthesis of chitosan-<Emphasis Type="Italic">g</Emphasis>-polyacrylamide semi-IPN superabsorbent hydrogels

Superabsorbent hydrogels of chitosan-g-polyacrylamide with N,N′-methylene-bis-acrylamide as a crosslinker were prepared via UV irradiation in the absence of photoinitiator under homogeneous conditions. The product was characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy to confirm the formation of hydrogels. The transparent hydrogels have been observed to exhibit as much as 2987% swelling in acidic solution. In addition, the hydrogel which hydrolyzed for 6 h (0.24 × 10³ min) can have a water uptake of 106 times its weight (5300% swelling for 0.5 g hydrogel). The effect of several variables such as time, temperature, pH, acrylamide/chitosan ratio, crosslinker amount, and different media was explored. Finally, the prepared hydrogel have been used in adsorption of Zn(II) ions from water with high removal efficiency (0.636 meq g⁻¹ or 20.8 mg g⁻¹) at pH = 7. The experimental data of the adsorption equilibrium from Zn(II) solution fit well with the pseudo-second-order model.     

Fiber‐reinforced nanocomposite seismic isolators: Design and manufacturing

Fiber‐reinforced elastomeric isolator (FREI) is a new generation of seismic isolation device in which steel plates are replaced by fiber reinforcement. The essential characteristic of the elastomeric isolator is a very large ratio of the vertical to horizontal stiffness. This is somehow provided in FREI by resembling to steel reinforced elastomeric isolators (SREI). In this work, a comparative experimental analysis is presented to evaluate the performance of fiber‐reinforced nanocomposite elastomeric isolator (FRNEI) with FREI. FRNEI was manufactured based on nanocomposite rubber compound. The results clearly indicate an increase of 20% in the ratio of the vertical to horizontal stiffness for FRNEI when compared with FREI. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Effects of dopants and copolymerization on Schottky barriers of polypyrrole and polyindole/metal interfaces

Schottky-barrier diode devices were fabricated in a sandwich configuration with poly(pyrrole-co-indole) copolymer semiconducting films prepared by electropolymerization. Effect of different dopants of ClO₄ ^?, BF₄ ^?, C₇H₇SO₃ ^? and [Fe(CN)₆]^3? on the electronic properties of the fabricated devices was followed using Ag, In, Al and Cu metal junctions. Current?Cvoltage and capacitance?Cvoltage characteristics were recorded for making a comparative evaluation of the electronic and junction properties of the devices. The electrical characteristics of the junctions were analyzed based on the standard thermionic emission theory. Polymer doped by ClO₄ ^? showed lower reverse saturation currents and ideality factor but higher potential barriers and rectification ratios. Effect of dopant ions and copolymerization on the optical band gaps (E _g) of the films were investigated and the optical transmissions of the doped copolymer films were measured in the wavelength range of 250?C900?nm. It was shown that the energy gap of copolymers laid between those of corresponding homopolymers and polyindole (PIN) doped by [Fe(CN₆)]^?3 had E _g less than that of polymer doped by other anions whereas E _g of polypyrrole was independent of dopant ions. Also, the morphology of the polymeric films revealed the surface of the PIN doped with ClO₄ ^? was very smooth which created a good contact with indium metal.     

Evaluation of antibacterial property of hydroxyapatite and zirconium oxide‐modificated magnetic nanoparticles against Staphylococcus aureus and Escherichia coli

In the first section of this research, superparamagnetic nanoparticles (NPs) (Fe₃ O₄) modified with hydroxyapatite (HAP) and zirconium oxide (ZrO₂) and thereby Fe₃ O₄ /HAP and Fe₃ O₄ /ZrO₂ NPs were synthesised through co‐precipitation method. Then Fe₃ O₄ /HAP and Fe₃ O₄ /ZrO₂ NPs characterised with various techniques such as X‐ray photoelectron spectroscopy, X‐ray diffraction, scanning electron microscopy, energy dispersive X‐ray analysis, Brunauer–Emmett–Teller, Fourier transform infrared, and vibrating sample magnetometer. Observed results confirmed the successful synthesis of desired NPs. In the second section, the antibacterial activity of synthesised magnetic NPs (MNPs) was investigated. This investigation performed with multiple microbial cultivations on the two bacteria; Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Obtained results proved that although both MNPs have good antibacterial properties, however, Fe₃ O₄ /HAP NP has greater antibacterial performance than the other. Based on minimum inhibitory concentration and minimum bactericidal concentration evaluations, S. aureus bacteria are more sensitive to both NPs. These nanocomposites combine the advantages of MNP and antibacterial effects, with distinctive merits including easy preparation, high inactivation capacity, and easy isolation from sample solutions by the application of an external magnetic field.Inspec keywords: nanocomposites, X‐ray chemical analysis, microorganisms, magnetic particles, scanning electron microscopy, precipitation (physical chemistry), nanomagnetics, X‐ray diffraction, X‐ray photoelectron spectra, nanoparticles, superparamagnetism, iron compounds, antibacterial activity, biomedical materials, nanomedicine, calcium compounds, nanofabrication, Fourier transform infrared spectra, magnetometers, zirconium compoundsOther keywords: antibacterial effects, antibacterial property, superparamagnetic nanoparticles, X‐ray photoelectron spectroscopy, X‐ray diffraction, X‐ray analysis, antibacterial activity, bactericidal concentration, S. aureus bacteria, Staphylococcus aureus, Escherichia coli, hydroxyapatite, coprecipitation method, scanning electron microscopy, energy dispersive X‐ray analysis, Brunauer‐Emmett‐Teller method, Fourier transform infrared spectroscopy, vibrating sample magnetometer, microbial cultivations, nanocomposites     

Aligned Carbon Nanotube–Based Flexible Gel Substrates for Engineering Biohybrid Tissue Actuators

Muscle‐based biohybrid actuators have generated significant interest as the future of biorobotics but so far they move without having much control over their actuation behavior. Integration of microelectrodes into the backbone of these systems may enable guidance during their motion and allow precise control over these actuators with specific activation patterns. Here, this challenge is addressed by developing aligned carbon nanotube (CNT) forest microelectrode arrays and incorporating them into scaffolds for cell stimulation. Aligned CNTs are successfully embedded into flexible and biocompatible hydrogels exhibiting excellent anisotropic electrical conductivity. Bioactuators are then engineered by culturing cardiomyocytes on the CNT microelectrode‐integrated hydrogel constructs. The resulting cardiac tissue shows homogeneous cell organization with improved cell‐to‐cell coupling and maturation, which is directly related to the contractile force of muscle tissue. This centimeter‐scale bioactuator has excellent mechanical integrity, embedded microelectrodes, and is capable of spontaneous actuation behavior. Furthermore, it is demonstrated that a biohybrid machine can be controlled by an external electrical field provided by the integrated CNT microelectrode arrays. In addition, due to the anisotropic electrical conductivity of the electrodes provided by aligned CNTs, significantly different excitation thresholds are observed in different configurations such as the ones with electrical fields applied in directions parallel versus perpendicular to the CNT alignment.     

Antibacterial flexographic ink containing silver nanoparticles

The current work deals with the effects of incorporation of silver nanoparticles on the antibacterial and the thermal properties of a flexographic ink. The stable and uniform dispersion of silver nanoparticles in the ink were confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The thermal properties of the pure and nanoparticle loaded ink films were also evaluated using TGA and DSC techniques. The results from this study proved acceptable dispersion characteristics, wherein, the flexographic ink showed a significant antibacterial activity against Gram-positive and Gram-negative bacteria     

Estimation of reactivity ratios of styrene/butyl acrylate copolymer by ordinary and generalized least square methods

A novel generalized least square (GLS) estimator program was employed for determination of styrene (STY)/butyl acrylate (BA) reactivity ratios synthesized by solution copolymerization method. The monomer reactivity ratios as well as the 95 % individual confidence limits were determined by application of conventional linear methods like Finemann–Ross, Ezrielev–Brokhina–Roskin, Joshi–Joshi, Kelen–Tudos, modified Kelen–Tudos, extended Kelen–Tudos and Mao–Huglin. The estimation process was performed by applying techniques based on ordinary least square (OLS) and GLS approaches and the results were compared. The results showed a fairly good agreement between the experimental and calculated copolymer compositions. The model was then successfully validated through handling regression models with error terms that are heteroskedastic or autocorrelation, or both and clearly showed that the model was able to predict the reactivity ratios by accounting response error structure. Based on the copolymer compositions determined by ¹H NMR, the reactivity ratios of STY and BA were found to be 0.886634 and 0.216369, respectively, by Mao–Huglin method through the GLS approach, and this new estimation method shows the best linear estimations for the monomer reactivity ratios. The present paper shows a new estimation integral approach for determining the monomer reactivity ratios by different conventional linear methods at low and high conversions in EViews software and the calculated values are discussed in terms of regression models.