Understanding Gel-Powers: Exploring Rheological Marvels of Acrylamide/Sodium Alginate Double-Network Hydrogels

This study investigates the rheological properties of dual-network hydrogels based on acrylamide and sodium alginate under large deformations. The concentration of calcium ions affects the nonlinear behavior, and all gel samples exhibit strain hardening, shear thickening, and shear densification. The paper focuses on systematic variation of the alginate concentration-which serves as second network building blocks-and the Ca²⁺-concentration-which shows how strongly they are connected. The precursor solutions show a typical viscoelastic solution behavior depending on alginate content and pH. The gels are highly elastic solids with only relatively small viscoelastic components, i.e., their creep and creep recovery behavior are indicative of the solid state after only a very short time while the linear viscoelastic phase angles are very small. The onset of the nonlinear regime decreases significantly when closing the second network (alginate) upon adding Ca²⁺, while at the same time the nonlinearity parameters (Q₀, I₃/I₁, S, T, e₃/e₁, and v₃/v₁) increase significantly. Further, the tensile properties are significantly improved by closing the alginate network by Ca²⁺ at intermediate concentrations.

Rheology of graphene oxide stabilized Pickering emulsions

Pickering emulgels stabilized by graphene oxide (GO) with didodecyldimethylammonium bromide (DDAB) as an auxiliary surfactant and liquid paraffin as the oil phase have proved to be an excellent 3D printable ink. This paper elucidates the structure of such emulgels by a combination of microscopy before and after intensive shear as well as broadband dielectric spectroscopy and rheology in the linear and nonlinear regime. An increase of the DDAB surfactant and GO-contents leads to a systematic increase of modulus and viscosity, a reduction of the limits of the nonlinear regime and a more complicated variation of the normal forces, with negative normal forces at high shear rate  for low GO-contents and positive normal forces at high GO-contents. The interfacial jamming behavior studied by morphology, rheology and dielectric spectroscopy is explained based on droplet deformation, jamming and recovery phenomena.

Influence of Cellulose Nanofibers on the Behavior of Pickering Emulsions. Part 1. Microscopy and Startup Flow Test

The dispersibility of flexible polymer chains present at the emulsion's interface between the dispersed and continuous phase has obvious effects on rheology and dielectric properties of the whole emulsion. Cellulose nanofiber (CNF)-based Pickering emulsions are good systems to research these properties with respect to their microscopic phase structure, dielectric, and rheological properties by using CNF as a water-dispersible Pickering emulsifier, liquid paraffin as an oil phase, and didodecyldimethylammonium bromide (DDAB) as a cationic auxiliary surfactant. The CNF and DDAB contents were systematically varied while the water-to-paraffin oil ratio was kept constant to discern the influence of the Pickering emulsifiers. Polarized optical microscopic images reveal that the droplets tend to shrink at higher CNF content but grow bigger when increasing the DDAB content, which is proved by fluorescence analysis of the CNF dispersibility with varying DDAB content. The dielectric damping exhibits a minimum, whose value decreases with increasing DDAB and CNF content. Increasing the DDAB content promotes the solubilization of CNF in the aqueous phase, which will increase the overall viscosity and yield points. Similarly, a higher CNF content leads to a higher viscosity and yield point, but at high DDAB contents, the viscosity function exhibits an S-shape at intermediate CNF contents. To evaluate the results further, they were compared with CNF dispersions (without oil phase), which showed a surfactant effect slightly on maximum stress but strongly on yield stress τy, indicating that DDAB can promote the formation of a CNF network rather than the viscosity of the whole system. This paper provides information on how a systematical variation of the composition influences morphology and physico-chemical interactions as detected by broadband dielectric spectroscopy and rheological behavior.

[Effects of occupational cadmium exposure on workers' cardiovascular system]

Objective: To investigate the effects of cadmium exposure on cardiovascular system of occupational workers. Methods: Cross-sectional study was applied to 992 workers in a nickel-cadmium battery plant in November, 2011, of which 749 were cadmium exposed workers and 243 were controls without cadmium and other expose. Urinary cadmium、electrocardiogram (ECG) and blood pressure were examined simultaneously among 992 workers. The risk factors of ECG abnormality rate and hypertension rate were analyzed by Logistic regression. Results: The level of urinary cadmium in cadmium exposed workers was significantly higher than controls (8.89±4.00 vs 1.34±1.18 μg/g creatinine, P<0.01) . Urinary cadmium level in women was significantly higher than men in both exposure and control group (P<0.05) . According to the group of working years, Urinary cadmium level raised with the increase of working years (F=28.272, P<0.001) . The ECG abnormality rate and hypertension rate of cadmium exposed workers were higher than that of control group, the differences were all statistically significant (P<0.01) . The abnormal rate of ECG and the hypertension rate increased with the prolonging of working years and demonstrated dose-response relationship. With the increase of urinary cadmium level, the abnormal rate of ECG and hypertension rate raised (OR=1.11, P<0.01) and (OR=1.15, P<0.01) respectively. Conclusion: Occupational cadmium exposure increased the abnormal rate of ECG and blood pressure and therefore damaged cardiovascular system of workers. This study provided base data for protecting health of cadmium exposed workers.

Maximum-biomass concentration prediction for Bifidobacteria in the pH-controlled fed-batch culture

Our objective was to systematically study the relationship between maximum biomass concentration of different Bifidobacteria and total-acid anions accumulation, and develop a prediction equation for the maximum biomass concentration in the fed-batch culture at pH-controlled 7·0. The accumulation of acid anions and the consumption of nutrients of various strains were evaluated. In addition, minimum inhibitory concentrations (MICs) of acid anions on a range of strains were examined at pH 7·0. The inhibition of acid anions, which had the same MIC as sodium chloride, was due to the osmotic pressure under pH 7·0 conditions. Moreover, the concentration of total-acid anions completely inhibiting each strain in the fed-batch culture at pH-controlled 7·0 had no significant differences with the MIC of acid anions for the corresponding strains. The osmotic pressures under two conditions were not significantly different. Finally, the maximum biomass concentration of Bifidobacteria was found to be closely related to biomass yield per unit of acid anion produced (YX/P ) and MIC (C) which were needed for the prediction, and different strains exhibited marked correlation (P ˂ 0·01, R = 0·985). An equation for the prediction of the maximum biomass concentration was developed as follows: Xmax -X0  = (0·71 ± 0·03)·YX/P ·C.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides further insights into the inhibition of Bifidobacteria by dissociated acid anions (the dissociated form) at pH 7·0. The high correlation between different strains suggested that the equation established in this paper is appropriate for different strains of Bifidobacteria. The prediction equation could be used to guide practical production in the preparation of materials, the control of the end of fermentation and production plans for further products such as freeze-dried powder of Bifidobacteria or food fermentation.

[Study on the release mechanism of fenoprofen calcium from hydrophillic sustained-release matrix]

AIM

To study the release mechanism of fenoprofen calcium (FC) from hydroxypropylmethylcellulose (HPMC) matrices.

METHODS

The release of FC and the erosion properties of hydrophillic matrices containing HPMC was examined at different paddle speed. The release mechanism of FC was further confirmed by evaluating the n value in Peppas equation.

RESULTS

The results indicate that the release of FC and the erosion of matrices exhibit zero order kinetic equation, and it exhibits line relationship between them.

CONCLUSION

In the first 40 min, FC mainly released by diffusion and erosion from HPMC matrix, while it was controlled by the rate of tablet erosion after 50 min.