Viscous Agents Research Articles

The effects of mucus glycoproteins on the bioavailability of tetracycline. I. Dissolution rate

The effects of a model mucus system on the dissolution rate of tetracycline hydrochloride have been assessed. The model is unique in containing only the rheologically active fraction of the secretion which is a large glycoprotein. A solution of mucus glycoprotein reduced the dissolution rate of tetracycline hydrochloride compared to that in simple acid media although the rate reduction was not the same as that observed in solutions of other viscous agents at the same viscosity. The nature of the results suggests that this occurs as a result of two separate viscosity-related effects. First, the presence of the glycoprotein causes an increased resistance to diffusion but this is less than that expected from the bulk viscosity. In this respect, the mucin resembles other large hydrophillic polymers in having a low, so-called “effective” viscosity. Second, the high viscosity causes a hydrodynamic effect of an increased diffusion layer thickness the maximum value of which is limited by the geometry of the dissolution vessel. Mucus glycoprotein also reduced the dissolution rate and final drug concentration at neutral pH, due to an enhanced build up of crystals of free base on the dissolving solid. This behaviour was altered by the bile salts sodium cholate, deoxycholate and taurodeoxycholate in a manner which can he rationalized in terms of the respective pK a values.

Evaluations on the usefulness of viscous agents in anterior segment surgery. I. The ability to maintain the deepness of the anterior chamber.

Maintenance of the deepness of the anterior chamber is necessary to prevent the direct contact of surgical instruments with the corneal endothelium. Therefore, in this study, we measured the ability of viscous agents to maintain the deepness of the anterior chamber in vitro and discussed the correlations between this ability and the viscosity or elasticity of the various viscous agents. A 1% solution of sodium hyaluronate with a molecular weight of 2160 X 10(3) which has the highest viscosity and elasticity showed the best ability to maintain deepness. A 2% solution of methylcellulose with a molecular weight of 86 X 10(3) and a 1% solution of sodium hyaluronate with a molecular weight of 790 X 10(3) were also useful in maintaining the deepness. On the other hand, a 50% solution of sodium chondroitin sulfate with a molecular weight of 30 X 10(3), which has a higher viscosity but a lower elasticity than methylcellulose or sodium hyaluronate with a molecular weight of 790 X 10(3), was unable to maintain sufficient deepness. A 1% solution of sodium hyaluronate with a molecular weight of 250 X 10(3) which has the lowest viscosity and elasticity was completely ineffective for maintaining deepness. These results suggest that the ability to maintain the deepness of the anterior chamber depends on the elasticity of the viscous agent rather than its viscosity.

Determination of Some Metal-EDTA Complexes by Capillary Type Isotachophoresis

To establish the optimum conditions for the simultaneous determination of EDTA, Mg(II)-EDTA and Ca(II)-EDTA complexes by capillary type isotachophoresis, effects of the length of the precolumn and the main column, kinds of viscous agents, counter ions and terminating electrolytes, pH of leading electrolyte and the amount of sample injected into the analyzer were studied. The isotachophoretic separation was performed with analyzer equipped with a potential gradient detector. The migration current was i zitially set at 200μA and then changed to 100μA. The best result was obtained with a main column (40cm in length and 0.5mm in inner diameter) connected to a precolumn (4cm in length and 1.0mm in inner diameter) using a leading electrolyte containing 0.01M hydrochloric acid and 0.5% methyl cellulose buffered at pH 8.5 with tris(hydroxymethyl)aminomethane, and a terminating electrolyte containing 0.01M hexanoic acid. Under these conditions, Cu(II)-EDTA and Mn(II)-EDTA were also determined successfully. The error in the determination of the mixtures of these EDTA complexes was less than ±14%.

二酸化チタン水分散系に対する分散剤および増粘剤の効果

二酸化チタン水分散系に対する分散剤および増粘剤の効果

Movement of microorganisms in viscous environments

SOME microorganisms swim well in solutions containing viscous agents (molecules with long unbranched chains, such as methylcellulose)1–7. Leptospira, a slender helical bacterium, swims more rapidly in such an environment than it does in water3, even at viscosities of several hundred centipoise (1 cP = 10−3 kg m−1 s−1). This behaviour is baffling until one realises that solutions of viscous agents are highly structured (gel-like). The solute forms a loose quasi-rigid network easily penetrated by particles of microscopic size. The network can exert forces normal to a segment of the body of a slender cell even when that segment does not possess a component of velocity in the normal direction; hydrodynamic treatments of the motion of microorganisms (or of cilia and flagella) do not apply. Solutions containing highly branched polymers, for example, Ficoll, are much more homogeneous. Here, we will review existing evidence for the gel-like character of viscous agents and describe experiments in which the motion of Leptospira or Escherichia coli are compared in solutions of methylcellulose and Ficoll of the same apparent viscosity. Our data show that solutions of methylcellulose are gel-like even when quite dilute, when the bulk viscosity is as small as 2 cP.