Formation of nano-hydroxyapatite crystal in situ in chitosan–pectin polyelectrolyte complex network

Hydroxyapatite (HA)/polysaccharide composites have been widely used in bone tissue engineering due to their chemical similarity to natural bone. Polymer matrix-mediated synthesis of nano-hydroxyapatite is one of the simplest models for biomimetic. In this article, the nano-hydroxyapatite/chitosan–pectin (nHCP) composites were prepared through in situ mineralization of hydroxyapatite in chitosan–pectin polyelectrolyte complex (PEC) network. The formation processes of nHCP were investigated by X-ray diffraction (XRD) analysis. The interactions between nHA crystal and chitosan–pectin PEC networks were studied using Fourier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC). The morphology and structure of nHA crystal were characterized by XRD and Transmission Electron Microscope (TEM). Results suggested that the interfacial interactions between nano-hydroxyapatite crystal and chitosan–pectin PEC network assist the site specific nucleation and growth of nHA nanoparticles. The nHA crystals grow along the c-axis. In this process, pH value is the main factor to control the nucleation and growth of nHA crystal in chitosan–pectin PEC networks, because both the interactions' strength between nHA crystal and chitosan–pectin and diffusion rate of inorganic ions depend on the pH value of the reaction system. Apart from the pH value, the chitosan/pectin ratio and [Ca²⁺] also take important effects on the formation of nHA crystal. An effective way to control the size of nHA crystal is to adjust the content of pectin and [Ca²⁺]. It is interesting that the Zeta potential of nHCP composites is about ? 30 mV when the chitosan/pectin ratio ≦ 1:1, and the dispersion solution of nHCP composites has higher stability, which provides the possibility to prepare 3D porous scaffolds with nHCP for bone tissue engineering.     

Nanohydroxyapatite–chitosan–gelatin polyelectrolyte complex with enhanced mechanical and bioactivity

A wet chemical approach was used to synthesis HAp–chitosan–gelatin nanocomposites at different wt.% of chitosan–gelatin (CG) ratios such as CG-00, CG-40, CG-31, CG-22, CG-13 and CG-04. XRD analysis confirms the formation of HAp on nanocomposite matrix and the decreased crystallite size was found with the decrease in chitosan and increase in gelatin compositions. FTIR study reveals that the presence of characteristic bands of HAp and CG. The decrease in chitosan in CG leads to band shift of organic phase towards a higher wave number side due to the intimate bonding with an inorganic phase. FE-SEM images show that the particles had a short nanorod-like morphology. The bioresorbability and microhardness test indicate that the composites have better resorbability and hardness than pure HAp. It was inferred that particle size, morphology, resorbability and hardness of the composite can be altered by tuning the composition.     

Thermoreversible behavior of κ-carrageenan and its apatite-forming ability in simulated body fluid

Osteoconductive materials with self-setting ability have received much attention because their properties allow developing injectable materials for bone defects. Thermosensitive hydrogel with ability of bone-like apatite formation in a body environment is a candidate of injectable bone fillers with osteoconductivity because the apatite formation on materials is an essential to show osteoconduction. The present study focused on the development of a thermosensitive hydrogel through modifications of the sulphonic groups of the polysaccharide, κ-carrageenan, with potassium chloride (KCl) and calcium chloride (CaCl₂). We found that the gelation temperature of κ-carrageenan solutions increased with increasing amounts of K⁺ ions. Apatite formation was observed on the gel after exposure to simulated body fluid for 0.5 day when the gel was prepared with a molar ratio of Ca²⁺/sulfonic groups = 1.5. These results indicate that a thermosensitive κ-carrageenan hydrogel with apatite-forming ability was obtained through the incorporation of K⁺ and Ca²⁺ ions into the solution.     

Sol-gel transition of a mixture of gelatin and κ-carrageenan

Abstract

The characteristics of sol-gel transition of a mixture made by mixing two kinds of gelling agents of different nature, i.e. gelatin and carrageenan were examined. The sample solutions consisted of 3.00 wt % gelatin solution, 1.00 wt % κ-carrageenan solution and 4.00 wt% mixed solution which was prepared by mixing the said gelatin and carrageenan solutions in the ratio 3:1. In the experiment, the optical rotation and the dynamic viscoelasticity were measured under the same temperature change program. As the sample solutions were cooled, the carrageenan solution started to show a change in the specific rotation in the first place, followed by the mixed solution and finally the gelatin solution. The gelatin and the mixed solutions had the same increasing tendency in the specific rotation, whereas the carrageenan solution changed a little. When the mixed solution was chilled to set, it turned into a highly elastic gel. In the mixed solution, the gelation of carrageenan was found to precede that of gelatin.     

In vitro study in the endothelial cell compatibility and endothelialization of genipin-crosslinked biological tissues for tissue-engineered vascular scaffolds

To overcome the cytotoxicity of the chemical reagents used to fix bioprostheses, genipin, a naturally occurring crosslinking agent, was used to fix biological tissues in present study. We prepared the biological vascular scaffolds through cell extraction and fixing the porcine thoracic arteries with 1% (by w/v) genipin solution for 3 days, and then examined their mechanical properties and microstructures; glutaraldehyde- and epoxy-fixed counterparts were used as controls. HUVECs were seeded on the type I collagen-coated surface of different modified acellular vascular tissues (fixed with different crosslinking agents), and the growths of HUVECs on the specimens were demonstrated by means of MTT test, the secretion of PGI₂ and vWF by HUVECs on the various specimens was also measured. Finally, HUVECs were seeded on the luminal surface of acellular biological vascular scaffolds (<6 mm internal diameter) which were, respectively, treated in the same manner described above, and then cultured for 9 days. On the ninth day, the HUVECs on the luminal surface of these vascular scaffolds were examined morphologically and by immunohistochemistry. Genipin-fixation can markedly diminish antigenicity of the vascular tissues through partially getting rid of cell or reducing the level of free amino groups in the vascular tissues. Genipin-fixed acellular vascular tissues mimicked the natural vessels due to the maintenance of the integrity of total structure and the large preservation of the microstructures of collagen fibers and elastic fibers; therefore, it appeared suitable to fabricate vascular scaffolds in mechanical properties. Compared to controls, the genipin-fixed acellular vascular tissues were characterized by low cytotoxicity and good cytocompatibility. The HUVECs can not only proliferate well on the genipin-fixed acellular vascular tissues, but also preserve the activities and function of endothelial cells, and easily make it endothelialized in vitro. The results showed that the genipin-fixed acellular porcine vascular scaffolds should be promising materials for fabricating vascular grafts or the scaffolds of tissue-engineered blood vessels.     

Use of к-carrageenan,chitosan and Carbopol 974P in extruded and spheronized pellets that are devoid of MCC

The search for excipients to replace microcrystalline cellulose (MCC) in the production of pellets by extrusion-spheronization in cases of drug incompatibility or the lack of pellet matrix disintegration forms the basis of this study. A combination of к-carrageenan as a spheronization aid, chitosan as a diluent and Carbopol^® 974P as a binder in the production of pellets containing no MCC has been investigated using acetaminophen as a model drug. Design of experiments allowed assessment of formulation and processing effects on pellet responses that included size, shape, fines, yield and friability. Statistical analysis revealed that the main factors and some of the two-factor interactions had a significant effect on pellet characteristics. Formulations containing high levels of к-carrageenan required more water to produce a wetted mass with good extrudability and extrudate capable of being spheronized. Although only a low level of Carbopol was used in the formulation, it imparted cohesiveness to the wetted mass as well as the extrudate. Furthermore, it was discovered that Carbopol could act as an extrusion aid, enabling the wetted mass to flow easily through the extruder screen holes without building up heat. Spherical and rugged pellets were produced that met the immediate release criterion.     

Precipitation of complex carbonitrides in a Nb–Ti microalloyed plate steel

Complex carbonitrides precipitated in base metal and heat-affected zone (HAZ) in Nb–Ti hot-rolled microalloyed steel plates have been identified to be Ti-rich (Nb, Ti)(C, N). As the reheating temperature is decreased from 1,200 to 1,150 °C, the average particle size in base metal is decreased from 40 to 20 nm. The morphology of complex carbonitrides in the HAZ, however, is transformed from cuboidal to rectangle shape with length of over 500 nm. Reheating at low temperature 1,150 °C may improve the toughness of HAZ by reducing the austenite size at large heat input welding.     

Determination of residual stresses in components of complex shape – correction of measurements using finite element method

Abstract

A method by which measured values of residual stresses in a component of complex shape may be corrected using the finite element is presented. The surface of the component is removed layer by layer and the residual stresses after removal of each layer are measured using X-ray diffraction; the correction factors are calculated using the finite element method, thereby obtaining the distribution of internal stresses in the complex component. In addition, methods of verifying the final values of the internal stresses are suggested. As examples, the distributions of the residual stresses, within several cross-sections of two types of heat treated shaft are calculated using the above method. Finally, the reliability of the results is discussed.

MST/16     

Optimal 3D printing of complex objects in a 5–axis printer

Optimization and Engineering - Three-dimensional (3D) printing, also known as additive manufacturing (AM), has emerged in the last decades as an innovative technology to build complex structures....     

The excitation of one-dimensional plasmons in Si and Au-Si complex atom wires

An atom-scale quantum wire array at the Au adsorbed Si(111) surface is studied by electron energy loss spectroscopy. Clear one-dimensional metallicity is verified by the observation of low-energy plasmonic excitation which exhibits a strong anisotropic dispersion. Our theoretical analysis using a quantum-mechanical nonlocal response theory shows that the plasmons are most probably supported in conductive channels made of Si honeycomb wires rather than those made of Au-Si complex wires.     

Evolution properties of the complex degree of coherence of a partially coherent Laguerre–Gaussian beam in turbulent atmosphere

Evolution properties of the complex degree of coherence of a partially coherent Laguerre–Gaussian beam (LGB) on propagation in free space and turbulent atmosphere are studied comparatively with the help of the general propagation formula for such beam. It is found that the behavior of the complex degree of coherence of a partially coherent LGB on propagation in turbulent atmosphere is much different from that in free space and is closely related to the initial beam parameters and the structure constant of the turbulent atmosphere. The distribution of the modulus of the complex degree of coherence of the partially coherent LGB finally becomes of Gaussian distribution at long propagation distance in turbulent atmosphere, and it becomes of Gaussian distribution more slowly with the increase of the mode orders, beam width and wavelength. Our results will be useful in long-distance free-space optical communications.     

Studies in the setting of polyelectrolyte cements: Part VII The effect of divalent metal chlorides on the properties of zinc polycarboxylate and glass–ionomer dental cements

A study is reported in which a zinc polycarboxylate and a glass polyalkenoate dental cement, were prepared from aqueous solutions of divalent metal chlorides, namely ZnCl2, CaCl2, MgCl2 and SrCl2, all at 1.0 mol dm-3 concentration, as well as from pure water. Calcium chloride was employed at additional concentrations, i.e. 2.0, 0.5 and 0.1 mol dm-3. As was previously found for monovalent salts, setting of the zinc polycarboxylate was speeded up and water uptake generally enhanced by the presence of the divalent metal salts. However, the divalent salts were found to reduce the compressive strength at 24 h (from 86 MPa to about 60 MPa). The glass polyalkenoate showed broadly similar effects to those observed in the presence of monovalent salts, with the setting time being increased, water uptake inhibited and compressive strength at 24 h reduced; however, by contrast, the working time was generally reduced. These results occur because the rate of the neutralization process is increased by the divalent salts, a consequence of the reduced pH of the poly(acrylic acid) caused by these salts. Infrared spectroscopy demonstrated interactions between the metal chlorides and poly(acrylic acid), with various chelate structures being apparent from the position of the asymmetric carbonyl stretch. © 1998 Chapman & Hall     

A microemulsion of puerarin–phospholipid complex for improving bioavailability: preparation,in vitro and in vivo evaluations

Puerarin is a phytochemical with various pharmacological effects, but poor water solubility and low oral bioavailability limited usage of puerarin. The purpose of this study was to develop a new microemulsion (ME) based on phospholipid complex technique to improve the oral bioavailability of puerarin. Puerarin phospholipid complex (PPC) was prepared by a solvent evaporation method and was characterized by X-ray diffraction and infrared spectroscopy. Pseudo-ternary phase diagrams were constructed to investigate the effects of different oil on the emulsifying performance of the blank ME. Intestinal mucosal injury test was conducted to evaluate safety of PPC-ME, and no sign of damage on duodenum, jejunum and ileum of rats was observed using hematoxylin-eosin staining. In pharmacokinetic study of PPC-ME, a significantly greater C_max (1.33?µg/mL) was observed when compared to puerarin (C_max 0.55?µg/mL) or PPC (C_max 0.70?µg/mL); the relative oral bioavailability of PPC-ME was 3.16-fold higher than puerarin. In conclusion, the ME combined with the phospholipid complex technique was a promising strategy to enhance the oral bioavailability of puerarin.     

Rapid growth of nanotubes and nanorods of würtzite ZnO through microwave-irradiation of a metalorganic complex of zinc and a surfactant in solution

Large quantities of single-crystalline ZnO nanorods and nanotubes have been prepared by the microwave irradiation of a metalorganic complex of zinc, in the presence of a surfactant. The method is simple, fast, and inexpensive (as it uses a domestic microwave oven), and yields pure nanostructures of the hexagonal würtzite phase of ZnO in min, and requires no conventional templating. The ZnO nanotubes formed have a hollow core with inner diameter varying from 140–160 nm and a wall of thickness, 40–50 nm. The length of nanorods and nanotubes varies in the narrow range of 500–600 nm. These nanostructures have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The ZnO nanorods and nanotubes are found by SAED to be single-crystalline. The growth process of ZnO nanorods and nanotubes has been investigated by varying the surfactant concentration and microwave irradiation time. Based on the various results obtained, a tentative and plausible mechanism for the formation of ZnO nanostructures is proposed.     

Microencapsulation of Ibuprofen by A Coacervation Process Using Eudragit L100–55 as An Enteric Polymer

Abstract

Ibuprofen microcapsules were prepared using Eudragit as enteric coating material and a simple coacervation method as coating process. Preliminary experiments based on results published with cellulose acetate phthalate led to the formation of a precipitate rather than a coacervate. Adjusting the polarity of the solvent in the Eudragit system by the addition of cosolvents enabled the transformation of the precipitate into a coacervate. This behaviour was qualitatively explained using the solubility parameter approach. The coacervate phase obtained from a system containing 2-propanol as cosolvent was assayed quantitatively in the absence and in the presence of ibuprofen. Due to the increased solubility of the drug in the cosolvent containing system, the composition of the coacervate phase was significantly altered when compared to a system without drug. The surface morphology of the microcapsules was assessed by scanning electron microscopy. The enteric properties of the microcapsules were tested according to the USP XXII test procedures. The permeability of the wall was evaluated by a dissolution test performed at pH 4. During stability testing over a period of 6 months the quality of the ibuprofen microcapsules remained almost unchanged.     

A novel ion-activated in situ gelling ophthalmic delivery system based on κ-carrageenan for acyclovir

The aim of this study was to prepare and evaluate ion-activated in situ gel ophthalmic drug delivery system based on κ-carrageenan (KC), using acyclovir as a model drug, hydroxypropyl methylcellulose (HPMC) as the viscosity agent and hydroxypropyl-β-cyclodextrin (HP-β-CD) as the penetration enhancer. The two ternary phase diagrams exhibited the effect of K⁺ and Ca²⁺ on the sol-to-gel transition, which turned out that KC was more sensitive to K⁺. The optimal ophthalmic matrix (prepared from KC and HPMC) was optimized with in vitro drug release test. The apparent permeability coefficient of acyclovir under 2% HP-β-CD was found to have dramatically increased (2.16-ploid) than that of conventional eye drops (p?in situ gel based on KC significantly delayed drug release and its bioavailability could be improved in comparison with the conventional eye drops. Hence, it has the potential to be a novel kind of ocular drug delivery system.     

Annealing kinetics of gold and iron–gold complex

Thermally induced defects in heat treated and then quenched in water n-silicon samples have been studied using deep level transient spectroscopy. Two deep levels at energies E _c-0.55 eV, and E _c-0.23 eV are observed in high concentration. The emission rate signature and annealing characteristics of energy state E _c-0.55 eV identify it as Au(A). During annealing a level emerges at energy position E _c-0.35 eV. This level has been identified as Au–Fe complex. Au(A) and Au–Fe showed an interesting reversible reaction in temperature range 175 °C–325 °C which follows the following theoretical relation that adds a new parameter in identifying Au(A) and Au–Fe complex.

Welding simulation of complex structures – possibilities and limits

The possibilities of predicting welding distortions are extensive. The boundary conditions used in industrial production play an important role in choosing the right strategy. Not only the right abstraction of the welding process is essential for correct and useful results, the clamping conditions and pre-tack welding are also very important. This article reviews experiments and FEM calculations of welded complex structures of industrial relevance. The examined structure comes from a railway vehicle and contains u-profiles with a sheet thickness of 4 mm. The review starts with the explanation of the researched structure and shows different welding situations, like unclamped and clamped manufacturing. Then the FE model with several weld seams is explained and the used boundary conditions are shown. Finally, the measured and calculated distortions are compared and discussed.