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At least 37 records · Page 2Linked to original sources
PubMed1996

Rheological studies of creams. II. Effect of water content on rheological characteristics.

25 creams with different water content was prepared by means of five self-emulsifying waxes. The variables were the ratio of the structure forming components of the lipophilic phase, the hydrophilic emulsifier and the water content. It was concluded from the flow curves, that the investigated creams were thixotropic systems independently of the water content. The yield value, the initial, the equilibrium and the plastic viscosity decreased exponentially with the concentration of the emulsified water. The slope of the linearized exponential curve is an important structural parameter. The measure of the this parameter provides information about the position of water in the gel structure.

Emulsions↗
PubMed2003

Rheological and mucoadhesive characterization of polymeric systems composed of poly(methylvinylether-co-maleic anhydride) and poly(vinylpyrrolidone), designed as platforms for topical drug delivery.

This study examined the rheological and mucoadhesive properties of polymeric systems composed of the bioadhesive copolymer poly(methylvinylether-co-maleic anhydride), PMVE/MA and poly(vinylpyrrolidone, PVP) as candidate platforms for improved drug delivery to the oral cavity. Aqueous, neutral formulations were prepared containing PMVE/MA (10 or 15% w/w) and PVP (0-9% w/w). The rheological properties were examined at 20 +/- 0.1 degrees C using both oscillatory rheometry (0.01 to 1.0 Hz at a constant strain of 1.0 x 10(-3) rad) and controlled stress flow rheometry using a Carri-Med CSL(2)-100 rheometer. The mechanical properties were examined using texture profile analysis (15-mm depth of insertion, 9 mm s(-1) rate of insertion, 15 s delay period between the end of the first and beginning of the second compressions). The interaction of the various formulations with mucin was examined using oscillatory rheometry. All formulations exhibited pseudoplastic flow with minimal thixotropy. Increasing the concentration of each polymeric component increased the zero-rate viscosity (calculated using the Cross model), hardness, compressibility, the storage (G') and loss (G") moduli, and decreased the loss tangent. These observations may be due to greater polymeric entanglement between adjacent polymer chains. Specifically, rheological synergy was observed between PMVE/MA and PVP, evidence of complexation between these two polymers. From the relationship between the viscoelastic properties and oscillatory frequency, and the mathematical comparison of steady and oscillatory shear response of formulations using the Cox-Merz equation, it may be concluded that formulations containing 15% w/w PMVE/MA and either 6 or 9% w/w PVP exhibited rheological properties that were consistent with gel behavior. All other formulations exhibited rheological properties that resembled polymeric liquids. Increasing the concentrations of PMVE/MA and PVP significantly increased the interaction with mucin, the rheological synergy between the polymeric formulations and mucin and, in addition, the adhesiveness of the formulations. This is evidence of the muco/bioadhesive properties of the formulations. Conversely, the time of contact between each formulation and mucin did not affect their resultant interaction. In conclusion, this study has uniquely described the rheological and mucoadhesive properties of aqueous systems composed of PMVE/MA and PVP. In particular, the concentrations required for gel formation have been defined and the interaction between these two polymeric components illustrated using rheological methods. Furthermore, the simultaneous analysis of rheological, mechanical, and mucoadhesive data provided an insight into their potential utility as platforms for drug delivery systems for application to the oral cavity.

Adhesives↗
PubMed1998

A rheological examination of the mucoadhesive/mucus interaction: the effect of mucoadhesive type and concentration.

The ability of mucoadhesive polymers to produce a large increase in the resistance to deformation when incorporated into a mucus gel, relative to when the mucus gel and test materials are evaluated separately at the same concentrations, has been reported in several previous studies. It has been proposed that this phenomenon, termed rheological synergism, can be used as a measure of the strength of the mucoadhesive interaction. In this investigation rheological synergism was investigated for a large range of putative mucoadhesive gels by dynamic oscillatory rheology. Changes in the storage modulus (G'), loss modulus (G"), and loss tangent (tan-delta) were found and the relative rheological synergism calculated. Rheological synergism was evident for a range of materials with known mucoadhesive properties giving behaviour between that of strongly cross-linked polymers gels and a physically entangled system. This effect was most marked with materials known to be of high mucoadhesive strength even when fully hydrated. Hence, polymers like sodium carboxymethylcellulose and high molecular weight poly(ethylene oxide) showed limited rheological synergism. When the effect of mucoadhesive concentration was investigated, relative rheological synergism occurred within a limited concentration range only, the values of which varied between materials. It was concluded that macromolecules possessing numerous hydrogen bond-forming groups and an open expanded network in the test environment gave pronounced rheological synergism, and the relevance of this to mucoadhesion studies will be investigated in further work. This study also confirmed the advantages of dynamic oscillatory rheology over simple viscosity measurement in the study of these systems.

Adhesiveness↗
PubMed2002

Study of effect of excipient source variation on rheological behavior of diltiazem HCl-HPMC wet masses using a mixer torque rheometer.

In the wet massing of powders and powder blends, the rheological behavior of the wet powder masses not only plays a critical role in the unit process but also influences the attributes of the product. The physical properties of the powder excipients, such as particle size and size distribution, shape, surface area, bulk and tapped density and surface morphology, are a major source of variability in the rheological behavior of wet powder masses and the quality attributes of the final product. The objective of the present investigations was to study the rheological behavior of wet masses containing hydroxypropyl methylcellulose (HPMC) obtained from two sources (Methocel from Dow and Pharmacoat from Shin-Etsu) using a mixer torque rheometer. In order to simulate a real formulation, diltiazem HCl (DTZ) (40% loading) was used as part of the substrate powder mass. Hydroxypropyl cellulose (HPC) was used as the binder. Since HPMC is water-soluble, isopropyl alcohol (IPA) was used as the wet massing liquid. The rheological behavior of the wet powder masses was studied as a function of mixing time and amount of wet massing liquid (IPA). The rheological profiles obtained for DTZ-Methocel and DTZ-Pharmacoat exhibited same magnitude for mean torque, however, for DTZ-Pharmacoat the peak was more extended than that for DTZ-Methocel. The extended peak for DTZ-Pharmacoat indicated that the wet mass will stay suitable during the process for larger quantities of the wet massing liquid before turning into paste and becoming unsuitable for the process as compared with the DTZ-Methocel system. The mixing kinetics of the two powder systems appeared to be quite different. These differences in the rheological behavior of the wet masses may be attributed to the difference in the particulate and surface properties of the two HPMCs. Some of the properties of the two HPMCs, such as particle size and size distribution, surface area, surface morphology and DSC thermograms, explain the difference observed in their rheological behavior. The difference in the rheological profiles of the two DTZ-HPMC systems indicated superiority of Pharmacoat over Methocel considering their wet massing behavior.

Calorimetry, Differential Scanning↗
PubMed1992

Blood rheology in arterial hypertension.

DETERMINANTS OF BLOOD RHEOLOGY: Blood flow depends on driving pressure and a resistance factor, the latter being related to geometrical hindrance and to the intrinsic viscosity of the blood. Since whole blood is non-Newtonian in nature, blood viscosity is strongly dependent on shear conditions. Low-shear areas occur in cardiovascular disease, and therefore the interaction between blood viscosity and flow conditions may affect vascular disorders. Increased shear stress secondary to increased viscosity may produce endothelial activation and release of endothelium-derived relaxing factors, leading to flow-dependent vasodilation. All the determinants of blood rheology, including plasma protein and erythrocyte factors may be altered in patients with arterial hypertension. BLOOD RHEOLOGY IN HYPERTENSION: A hyperviscosity state is created which is associated with an unfavourable prognosis, since it is correlated with blood pressure levels and the severity and complications of the disease including left ventricular hypertrophy. The mechanisms of haemorheological abnormalities in hypertension are still unclear. It is not known whether blood rheology is an independent variable in patients with hypertension or whether it is a covariable with other established indices of heterogeneity. However, many aetiopathological changes identified in hypertensive disease may contribute to the observed changes in blood rheology. Haemorheological changes in hypertension, through complex interactions with platelet activation and endothelial function, may contribute to the development of thrombosis and atherosclerosis. Moreover, in acute and chronic ischaemia and other conditions where compensatory mechanisms such as collateral formation and vasodilation are limited, rheological factors may become important determinants of blood flow and tissue oxygenation. TREATMENT EFFECTS: Many antihypertensive agents have direct or indirect potential effects on haemorheological variables. However, to date, most studies that have investigated the effects of therapy on rheological variables have not been performed in clinically relevant situations. Controlled studies that monitor both the acute and longterm effects of antihypertensive drugs on relevant haemorheological variables are required to show whether specific therapeutic approaches can correct abnormalities in blood rheology.

Antihypertensive Agents↗
PubMed1984

[Rheologic disorders in myocardial infarct complicated by acute left ventricular failure].

Thirty-six patients with acute myocardial infarction aggravated by acute left ventricular failure (pulmonary edema, cardiogenic shock) were studied for their blood rheologic properties. The impairments of the blood rheologic properties were classified as Stage I and II syndromes of high and low blood viscosity and were characterized by a phasic nature of their course. The rheologic disorders associated with pulmonary edema and reversed cardiogenic shock were decompensated (Stage II syndrome of high blood viscosity--Stage I syndrome of low blood viscosity), but reversible following intensive rheologic therapy. Irreversible cardiogenic shock was characterized by Stage II syndrome of low blood viscosity which was intractable. In acute myocardial infarction without concomitant acute left ventricular failure, rheologic disorders were characterized by Stage I syndrome of high blood viscosity, i. e. they were compensated and did not require intensive rheologic therapy. The management of rheologic impairments attending acute left ventricular failure should be combined, the intensity of therapeutic measures, the nature of combinations and the dosage of drugs being dependent on the degree and phase of rheologic disturbances.

Acute Disease↗