Hydrophilic thickeners

Protective colloids can be divided into synthetic and natural materials. Table 3 classifies the pharmaceutical gums, thickeners, and other hydrophilic polymers according to their origins [72]. Protective colloids of natural origin, such as gelatin, acacia, and tragacanth, have... 

Thickening agent. A hydrophilic substance used to increase the viscosity of liquid mixtures and solutions and to aid in maintaining stability of their emulsifying properties. 

A stable emulsion requires balancing of hydrophobic and hydrophilic components into a uniform suspension. The suspension may be a multicomponent system of emulsifiers, surfactants, stabilizers, and thickeners that are included only to make an aesthetically pleasing product — not for their clinical significance. 

All but the polyurethane are characterized by methylene backbones with ligands that are sufficiently polar to make them water soluble. Thus, upon dissolution in water, the polarity of the water molecule associates with the polarity of the acrylic or acrylamide groups to form a shell. We discussed hydrophilic polyurethanes that are typically cross-linked and are not (but could be) considered effective thickeners. Nevertheless they too have hydration shells developed due to the influence of the polyethylene glycol backbone. The extent of that shell is determined by the hydro-philicity of the ligand the acrylic > acrylamide > alcohol > polyurethane. The volume... 

This product contains no less than 19% and no more than 30% methoxy groups and no less than 3 % and no more than 12 % hydroxypropyl residues. It occurs as a white fibrous granular powder. Hydroxypropylmethylcellulose is employed as a suspending or a thickening agent and tablet excipient. Solutions of this hydrophilic polymer are used as topical protectants or as artificial tears for contact lenses. 

The epidermis plays a role in skin mechanics. Thereby, hydrophilic as well as hydrophobic substances affect mechanical properties of the skin. Changes in skin mechanics can be the result of either a direct influence of a substance on the intercellular matrix, or an epiphenomenona, for example, a physiological shift of water between the tissues aimed to maintain physiological homeostasis, 50 The hydration level of the SC affects its mechanical properties. Increased hydration of the SC influences its extensibility and elasticity.51-54 Examples from human diseases such as ichthyotic and xerotic disorders indicate that thickening of the SC due to hyperkeratosis and increased corneocyte cohesion is responsible for a marked decrease in the flexibility of the entire SC.55... 

Highly disperse silica is widely used in pharmaceutical formulations as a filler, adsorbent, thickener etc.5 Their high hydrophilicity and the absence of emulsifying ability restrict their application. In contrast to hydroxylated silica, partially or fully hydrophobized silica may exhibit improved properties as a drug carrier. The main goal of this work is to study hydrophobized silica nanocomposites with immobilized vitamins C and E. Investigations of adsorption-desorption processes which involve silica nanoparticles and the antioxidants are described. Factors affecting the antioxidant stability have also been carefully considered. 

Hydrophilic fumed silica aggregates will very strongly interact in a nonpolar medium by hydrogen-bonds between surface silanol groups of neighbouring particles. For that, hydrophilic silica is an excellent thickener and rheological additiv for nonpolar liquids. Less than 5 wt. % of hydrophilic fumed silica will thicken a liquid alkane or silicone oil to a cuttable rubber-like gel. 

The thickening ability of hydrophilic fumed silica in a highly polar liquid is also rather low. In a polar medium the hydrophilic silica surface will be effectively wetted, the particles are shielded from each other and their interaction is prevented. Hydrogen-bonds and other polar interactions within the liquid, between surface and liquid molecules or between particle surfaces are of the same order of strength - no energy results from hydrophilic particles that interact in a polar medium and consequently no thickening is reached. 

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