Intrinsic viscosity and viscoelastic properties of xanthan/guar mixtures in dilute solutions: Effect of salt concentration on the polymer interactions

Ion-sensitive in situ hydrogels of natamycin bilosomes for enhanced and prolonged ocular pharmacotherapy: in vitro permeability, cytotoxicity and in vivo evaluation

Delivery of therapeutic molecules into the deeper ocular compartments is mainly hampered by short precorneal residence and limited transmembrane permeability of topically administered drugs. Hence, the current study was undertaken to fabricate the ion-sensitive in situ gels of natamycin (NT) bilosomes (NB) for efficient ocular delivery. The effect of cholesterol and sodium taurocholate proportion on the properties of the bilosomes were studied and the formulation with better physicochemical properties was optimized and utilized to derive the in situ gelling system (IG). The impact of type/composition of gelling agent on the formation and characteristics of the hydrogel was investigated. The hydrogel formed from IG with 0.3% w/v gellan gum showed optimal viscoelastic and adhesive characteristics. The ocular safety and cytocompatibility of NB and its IG was confirmed by corneal histology and in vitro cytotoxicity evaluation. A 6- to 9-fold enhancement in the transcorneal flux of NB demonstrated efficient ocular penetration of bilosomes. Moreover, the superior mean dose normalized NT levels in the ocular tissues of rabbits treated with optimized NB and IG illustrated the effectiveness of bilosomes loaded ion-sensitive in situ hydrogels as a potential platform for the improved and prolonged ocular pharmacotherapy.

Physical, Rheological, Functional, and Film Properties of a Novel Emulsifier: Frost Grape Polysaccharide from Vitis riparia Michx

A novel emulsifier, Frost grape polysaccharide (FGP), isolated from natural exudate of the species Vitis riparia Michx, was physically and rheologically characterized. The determination of the physical, structural, thermodynamic, emulsification, film, and rheological properties of FGP provide essential details for the commercial adoption of this novel plant polysaccharide. FGP is capable of producing exceptionally stable emulsions when compared with the industrially ubiquitous gum arabic (GA). The FGP isolate contained a negligible amount of nitrogen (0.03%), indicating that it does not contain an associated glycoprotein, unlike GA. Solutions of FGP have a high degree of thermostability, displaying no loss in viscosity with temperature cycling and no thermal degradation when held at 90 °C. FGP is an excellent film former, producing high tensile strength films which remain intact at temperatures up to 200 °C. This work identified a number of potential food and pharmaceutical applications where FGP is significantly superior to GA.

Rheological behavior of xanthan gum solution related to shear thinning fluid delivery for subsurface remediation

Xanthan gum solutions are shear thinning fluids which can be used as delivery media to improve the distribution of remedial amendments injected into heterogeneous subsurface environments. The rheological behavior of the shear thinning solution needs to be known to develop an appropriate design for field injection. In this study, the rheological properties of xanthan gum solutions were obtained under various chemical and environmental conditions relevant to delivery of remedial amendments to groundwater. Higher xanthan concentration raised the absolute solution viscosity and increased the degree of shear thinning. Addition of remedial amendments (e.g., phosphate, sodium lactate, ethyl lactate) caused the dynamic viscosity of xanthan solutions to decrease, but they maintained shear-thinning properties. Use of mono- and divalent salts (e.g., Na(+), Ca(2+)) to increase the solution ionic strength also decreased the dynamic viscosity of xanthan and the degree of shear thinning, although the effect reversed at high xanthan concentrations. A power law analysis showed that the consistency index is a linear function of the xanthan concentration. The degree of shear thinning, however, is best described using a logarithmic function. Mechanisms to describe the observed empiricism have been discussed. In the absence of sediments, xanthan solutions maintained their viscosity for months. However, the solutions lost their viscosity over a period of days to weeks when in contact with site sediment. Loss of viscosity is attributed to physical and biodegradation processes.

The Rheological Properties of Konjac Glucomannan (KGM) Solution

The rheological properties of konjac glucomannan (KGM) solution were measured by HAAKE Rotational Rheometer, and the results indicated that KGM solution began to transform from Newtonian fluid to non-Newtonian fluid above 0.10 wt%, which represented the overlap of molecular chains. When the concentration exceeded 1.00 wt%, the entanglements of molecular chains became obvious, and the KGM sol formed. Furthermore, the rheological formulas of KGM solution were simulated very regularly, and the parameters of viscosity (η) and non-Newtonian index (n) held the relationship of exponential function to concentration (C), however, the consistency coefficient (κ) displayed a power function, then their concentration-dependence functions were as follows: η=-0.33+1.17e16.80C, n=0.29+0.79e-2.56C, and κ=29.11C3.17. Finally, the rheological properties from diluted solution to KGM sol were revealed.

Rheological interactions between Lallemantia royleana seed extract and selected food hydrocolloids

BACKGROUND

Lallemantia royleana (Balangu) is a mucilaginous endemic plant which is grown in different regions of world. The flow behaviour of Balangu seed extract (BSE) and its mixture with xanthan, guar and locust bean gums at 1:3, 1:1 and 3:1 ratios, in addition to control samples (0% BSE), were evaluated. To describe the rheological properties of samples, the power law model was fitted on apparent viscosity-shear rate data. To evaluate the interaction between BSE and selected hydrocolloids in dilute solutions, the relative viscosity was also investigated.

RESULTS

There was no significant difference between the consistency coefficient of guar and locust bean solutions and their blends substituted with 250 g kg(-1) BSE. The BSE-xanthan mixture at 1:3 and 1:1 ratios had consistency index equal to xanthan solution. BSE-locust bean gum at all ratios, BSE-xanthan at 1:3 ratio and BSE-guar gum at 1:1 and 3:1 ratios indicated relative viscosity lower than values calculated assuming no interaction. The intrinsic viscosity value of BSE was determined 3.50 dL g(-1) .

CONCLUSION

The apparent viscosities of BSE, selected hydrocolloids and their blends were the same at a shear rate of 293 s(-1) and the commercial gums can be substituted by 250 g kg(-1) and 500 g kg(-1) BSE.

Stratification of foam films containing polyelectrolytes. Influence of the polymer backbone's rigidity

We studied the stratification behavior of free-standing foam films which are stabilized by nonionic surfactants and contain polyelectrolytes with different backbone flexibilities, namely sulfonated polyacrylamide (PAMPS), carboxymethyl-chitin (CM-Chitin), Xanthan, and DNA. Stratification is due to a specific arrangement of the polymer chains in the confined environment of the thin films. While stratification is easily observed for films containing PAMPS and CM-Chitin, it is more difficult to observe with Xanthan and DNA. We will discuss this effect in terms of different polymer backbone rigidities, which, in turn, are expected to lead to different time scales for polymer network relaxation.