Rheological properties of sodium alginate in an aqueous system during gelation in relation to supermolecular structures and Ca binding

Gelation behavior of sodium alginate was investigated in an aqueous system at various CaCO₃ doses using two alginate samples of different mannuronate (M)/guluronate (G) ratios but with comparable molecular masses. Macroscopic rheological properties of the polysaccharide were discussed during gelation in relation to microscopic supermolecular structures imaged by atomic force microscopy and Ca²⁺ binding. At fixed concentrations of the polysaccharide (0.5 w/v%) and glucono-δ-lactone (15 mM) as an acidic material, the G-rich sample was higher in elasticity with rod-like molecular assemblies at the highest CaCO₃ dose; 15 mM, while the M-rich sample was higher in elasticity with network-like molecular assemblies at the lowest CaCO₃ dose; 3.75 mM. Gelation behavior near the sol-to-gel transition was generally described by the percolation model, except for the M-rich sample at the lowest CaCO₃ dose. A critical CaCO₃ dose corresponded to 7.5 mM at which both alginate samples showed essentially the same gelation kinetics. In an equilibrium state, it was estimated that the G-rich sample was bound to larger amount of Ca²⁺ at the lowest CaCO₃ dose, while the M-rich sample was bound to larger amount of Ca²⁺ at the highest CaCO₃ dose. The amount of bound Ca²⁺ did not directly relate to elasticity of the system. Based on these results, dominant block structures are suggested for gelation.     

Electrochemical formation of viologen nano/microsized wires and tubes by potential sweep technique combined with micellar disruption method

The first bottom-up electrochemical approach for the preparation of viologen (1,1′-didodecyl-4,4′-bipyridinium salt) nano/microsized wires and tubes are described. This approach involves film formation of the viologen using the micellar disruption method followed by transformation of the film into the nano/microstructures using a potential sweep technique. The hexagonal cross-section of the wires and tubes has a 400 nm-30 μm width and >1 mm length. The formation mechanism of the nano/microstructures was discussed on the basis of the X-ray photoelectron spectroscopic analyses, FT-IR spectra, scanning electron microscopic observation, UV-vis spectra, and cyclic voltammograms before and after the transformation.     

In situ pH-decrease-induced gelation of sodium alginate/carboxymethylated konjac glucomannan

The gelation kinetics and rheological properties of a mixture system containing two anionic polysaccharides, sodium alginate and carboxymethylated konjac glucomannan, in the presence of glucono-delta-lactone were investigated with dynamic viscoelastic measurements. The slow release of protons induced by glucono-delta-lactone gave birth to partly uncharged polymer chains and partly shielded electrostatic repulsion, resulting in an interpolymer association. This segregative interaction brought about a significant improvement in the elastic modulus of the resultant gel. The strongest synergism occurred at a carboxymethylated konjac glucomannan concentration of 29.9 wt %, exhibiting the highest gel strength. Increasing the content or the degree of substitution of carboxymethylated konjac glucomannan resulted in slower gelation kinetics. The fractal dimension of the incipient gel, which was not greatly affected by the mixing ratio or the degree of substitution of carboxymethylated konjac glucomannan, reflected a rather compact gel structure network. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Viscoelastic and fragmentation characters of model bolus from polysaccharide gels after instrumental mastication

Model bolus from polysaccharide gels was investigated by the stress-relaxation tests and particulate size analyses. Using two gelling agents, gellan gum and a composite of gellan/psyllium seed gums, gels with different physical properties (i.e., elastic gellan single gels and plastic composite gels) and gel hardness were prepared. Gels were masticated instrumentally in the presence or absence of artificial saliva to prepare model bolus. Data from the stress-relaxation tests analyzed by 5-element mechanical model showed that difference between two Maxwell-bodies in the elasticity for the composite gels was generally smaller than that for gellan single gels when compared at equivalent gel hardness and was less influenced by the addition level of saliva. For each gel sample, cumulative particulate size distribution of model bolus was reduced logarithmically with a normal curve regardless of the addition level of saliva. Mean particulate size of model bolus from the composite gels was generally larger than that for gellan single gels when compared at equivalent gel hardness and was less influenced by the addition level of saliva. Based on the particulate size distribution of model bolus, coefficients of skewness and kurtosis calculated for the composite gels tended to be larger than those for gellan single gels when compared at equivalent gel hardness. Results indicated higher structural homogeneity of model bolus from the composite gels, which is related to higher miscibility with saliva. Structural homogeneity should be the key for texture design of nursing-care foods, particularly for dysphagia.     

Swallowing profiles of food polysaccharide solutions with different flow behaviors

The relationship between physiological response and sensory perceived scores in swallowing was investigated using food polysaccharide solutions. Solutions from xanthan gum (0.3–0.9%) and locust bean gum (0.5–0.8%) were used as specimen with different flow behaviors identified by static and dynamic rheological methods. Acoustic analysis and sensory evaluation were carried out to investigate the swallowing profiles using the same human subjects. From acoustic analysis, time required for bolus to transfer through the pharyngeal phase t₂ decreased with increasing concentration of xanthan gum despite the viscosity increase. Also, the acoustic balance for the swallowing sound shifted to a higher frequency range with increasing concentration. The t₂ for locust bean gum was much less concentration-dependent and consistently larger than that for xanthan gum when compared at equivalent shear viscosity at 10 s⁻¹. Also, the acoustic balance for the swallowing sound was less concentration-dependent than that for xanthan gum. From sensory evaluation, 0.6% xanthan gum was scored the highest in perceived swallowing ease, while 0.75% locust bean gum was scored the lowest. Both t₂ and the acoustic balance correlated well with perceived swallowing ease. Results indicate that xanthan gum solutions flow as one coherent bolus through the pharyngeal phase with smaller variation of flow velocity than locust bean gum solutions, leading to a greater sensation of swallowing ease. “Structured fluid”, defined as fluid with yield stress such as xanthan gum solutions, is a rheological nature that allows bolus to be swallowed in one go, relating to perceived swallowing ease of liquid foods.     

Powder metallurgy magnesium composite with magnesium silicide in using rice husk silica particles

By using the solid-state reaction of rice husk silica particles with magnesium powder, P/M magnesium based composites dispersed with the magnesium silicide (Mg₂Si) and magnesium oxide (MgO) were fabricated. High-purity silica particles were originated from rice husks, one of the major agricultural wastes, via the citric acid leaching treatment and combustion in air. The effects of the silica particle characteristics such as size, crystalline and porous structures, on the reactivity of silica and magnesium to synthesize Mg₂Si intermetallics were discussed. As the results by DTA and XRD analysis, finer silica particles were more effective for the solid-state reaction at low temperature due to the increase of their surface area contacted with magnesium powder. Amorphous silica was also more useful for this reaction than the crystalline one. The reactivity of rice husk silica was superior to that of the conventional mineral silica particles not only because of its amorphous structure but also the larger specific surface area due to their pore structures. In the case of the green compact of the elemental mixture of silica particles and Mg powder, the silica particle size was not effective on the reactivity because the coarse particles were fractured into fine ones by cold compaction. The distribution of Mg₂Si intermetallics of magnesium powder composites consolidated by SPS process was investigated by XRD and SEM-EDS analysis. When the sintering temperature was over the exothermic temperature of the mixture in the DTA profile, the synthesis of Mg₂Si completely occurred during sintering. The sinterability of the elemental mixture powder was improved when employing the amorphous rice husk silica particles. The density and hardness of their composites sintered over the ignition temperature of the DTA profile were remarkably high because of the good densification by the high reactivity and the distribution of Mg₂Si hard compounds.     

A Kinematic Analysis of Joint Synergy of the Lower Limb in Human Locomotion

This paper deals with the mode analysis of the kinematic structure of human locomotion. The authors investigated synergy mechanism of human locomotion from motion-captured data and EMG signal data. The authors extracted some common basic movements and residual modes, and analyzed the kinematical structures of limit cycle in joint angle space. The authors also implemented the numerical simulation analyses by using the motion captured data and EMG signal data to investigate the mechanical activities of human joints and to extract the mechanical structure of the limit cycle. The results show the joint synergy that is derived by the common basic modes, which expresses an inverted pendulum mode in support phase, and ballistic mode in swing phase with the kick-off motion in the most effective direction. This result can be guessed that the control strategy of human locomotion is simply based on the minimal control principle.     

Cytoprotective effects of nicorandil on hypothermic injury to immature cardiac myocytes--comparison with nitroglycerin, diltiazem and prostaglandin E1

The purpose of this study was to evaluate the functional and biochemical effects of nicorandil (NRD), nitroglycerin (NTG), diltiazem (DTZ) and prostaglandin E1 (PGE) on cardiac myocytes incubated under hypothermic conditions. Cardiac myocytes were isolated from neonatal rat ventricles and cultured for 4 days with MCDB 107 medium. Myocytes (12.5 x 10(5) myocytes/flask) were then incubated at 4 degrees C for 24 h in media containing various concentrations of NRD, NTG, DTZ or PGE. After hypothermic incubation, creatine kinase (CK) and lactate dehydrogenase (LDH) were measured. The myocytes were cultured for an additional 24 h at 37 degrees C to evaluate the recovery of myocyte beating rate. In the nicorandil groups, 10(-4) M NRD showed a significantly increased beating rate recovery compared to the control (44% vs 25% respectively, as a percentage of the baseline values; i.e., beating rate prior to hypothermic incubation). Although treatment with 10(-6) M diltiazem showed no beneficial effects (10(-6) M; 25%, control; 30%), beating was not observed at all with 10(-4) M or 10(-5) M DTZ. There were no significant changes among the NTG and PGE groups. The release of CK and LDH was significantly suppressed with 10(-4) M NRD (10(-4) M: 24.1 mIU/flask, 257.2; control: 125.4, 459.5, respectively). In contrast, 10(-4) M DTZ showed significantly increased CK and LDH levels compared to its respective control (10(-4) M: 203.3 mIU/flask, 883.4; control: 112.3, 457.4, respectively). There were no significant differences in CK and LDH levels among the NTG and PGE groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Antegrade or retrograde blood cardioplegic method: comparison of postsurgical right ventricular function and conduction disturbances

This study was undertaken to compare postsurgical right ventricular function and the occurrence of conduction disturbances after employing cold blood antegrade or retrograde cardioplegia during open heart surgery. Thirty-four patients were divided into AC (antegrade) and RC (retrograde) groups for the difference of route for delivery of cardioplegic solutions. Preoperative evaluation of cardiac and respiratory function revealed to be equal characteristics between the groups. Postoperatively, A-aDO2 and respiratory index (RI) as functional parameters of oxygenation capacity, LVSWI, RVSWI, dosage of dopamine and conduction disturbances were monitored at 0, 3, 6, 12 hours after termination of cardiopulmonary bypass and at extubation period. Although the recovery of respiratory function and left ventricular function were similar in both groups, temporal suppression of right ventricular function was indicated in RC group during early period after surgery, and then recovered to the same values of AC group within 3 hours. In RC group, several type of conduction disturbances were detected in 28 per cent of patients. But none of the persistent conduction disturbances were remained in all patients. We suggest retrograde coronary sinus perfusion may emerge as a valuable alternative to antegrade methods for delivery of cardioplegia.