Pharmaceutical polymer-surfactants systems

Interactions between water vapor and amorphous pharmaceutical solids were evaluated using isothermal microcalorimetry. " The desorption of water from theophylline monohydrate has been investigated using microcalorimetric approaches.The properties of surfactants and surface-active drugs in solution were studied by Attwood et al. " using calorimetry, while titration microcalorimetry has been utilized to elucidate the nature of specific interactions in several pharmaceutical polymer-surfactants systems. " Drug decomposition was evaluated as a function of different... 

Polymer-surfactant systems have found wide-spread practical applications, e.g., in paints, in pharmaceutical formulations, and in systems for enhanced oil recovery. Their practical importance and the fundamental intricacies in these systems have triggei extensive studies of the interactions between polymers and surfactants, and several reviews have appeared [1-6]. The sodium dodecylsulfate (SDS)-poly(ethylene oxide) (PEO) system has been particularily well studied, both by classical [7,8] and modem methods [9-12]. 

Owing to its chemically highly aggressive nature, fluorine is difficult and hazardous to handle and it can be manufactured only via the electrolytic oxidation of fluoride. Fluorine gas has been produced commercially since 1946 and has found applications in many areas of fluorine chemistry (polymers, surfactants, lubricants, thermally stable liquids, blood replacement and pharmaceuticals, propellants, etc.). Inorganic fluorides such as Sp6 and UFe [21] have technical applications. Fluorous solvent systems [22] provide novel reaction environments fundamentally different from both aqueous and hydrocarbon media [23] and fluorine has been employed as a marker or spin label [24]. 

The most common emulsions used in dermatological therapy are creams. These are two-phase preparations in which one phase (the dispersed or internal phase) is finely dispersed in the other (the continuous or external phase). The dispersed phase can be either hydrophobic based (oil-in-water creams, O/W) or aqueous based (water-in-oil creams, W/O). Whether a cream is O/W or W/O is dependent on the properties of the system used to stabilize the interface between the phases. Given the fact that there are two incompatible phases in close conjunction, the physical stability of creams is always tenuous, but may be maximised by the judicious selection of an appropriate emulsion stabilizing system. In most pharmaceutical emulsions, stabilizing systems are comprised of either surfactants (ionic and/or non-ionic), polymers (non-ionic polymers, polyelectrolytes or biopolymers) or mixtures of these. The most commonly used surfactant systems are sodium alkyl sulphates (anionic), alkylammonium halides... 

Surfactants constitute some of the most important (in terms of function, not quantity) ingredients in cosmetic and toiletry products, foods, coatings, pharmaceuticals, and many other systems of wide economic and technological importance. In many, if not most, of those applications, polymeric materials, either natural or synthetic, are present in the final product formulations or are present in the targets for their use. Other surfactant applications, especially in the medical and biological fields, also potentially involve the interaction of polymers (including proteins, nucleosides, etc.) with surfactant system. 

Concepts of controlled, or slow, release are now well established in the pharmaceutical industry, but they are not yet practiced widely in the personal care field where, in principle, they should be equally applicable. Ingredients such as flavors, colorants, perfumes, biologically active ingredients, and so on are potential candidates for controlled release. While the literature on such systems is extremely limited, it is appropriate to cite one or two references from the pharmaceutical field to illustrate possibilities. In particular, one can cite the work of Alii et al. (42), who employed a combination of rheological and other methods, including DSC, to study the relevant polymer/surfactant release systems. 

Studies on the interaction between surfactants and styrene-ethylene oxide block co-polymers, however, indicate that the polymers exhibit, in the presence of surfactant, typical polyelectrolyte character. This, it has been suggested [264], is due to interaction repulsions between like charges of the NaDS ions adsorbed onto the polyoxyethylene blocks. Investigating the interaction of the same detergent with methylcellulose and poly(vinyl alcohol), Lewis and Robinson [265] also observed the polyelectrolyte character of the polymer-surfactant complexes. A complex between non-ionic surfactants and a polycarboxylic acid in water can solubilize oil-soluble dyes below the surfactant CMC [268]. The complex containing the solubilizate can be precipitated the solubilizate remains in the precipitated complex and is leached out only slowly on placing the precipitate in fresh solvent. This has potential pharmaceutical implications. Halothane uptake by coacervate systems of gelatin-benzalkonium [269] has... 

A pulsed system, called Time-Clock System, has been developed. It comprises a solid dosage form coated with a hydrophobie surfactant layer to which a water-soluble polymer is attached to improve adhesion to the core [66]. The thickness of the outer layer determines the time required to disperse in an aqueous environment. Following the dispersion of the outer layer, the eore becomes available for dispersion. An advantage is that eommon pharmaceutical excipients can be used to manufacture this system. Studies performed on human volunteers showed that the lag time was not affeeted by gastrie residence time. Furthermore, the dispersion of the hydrophobic film was not influenced by the presence of intestinal digestive enzymes or by the mechanieal aetion of the stomach. 

To sum up, the choice of operating conditions for a specific FFF application is made in a way that recalls the general criteria used in chromatography. An accurate search of literature addressed to similar samples that have been already analyzed by FFF techniques is very useful. A number of specific reviews have been published concerning, for example, enviromnental, pharmaceutical, and biological samples (see Section 12.5). As previously mentioned above, one of the most important factors is the stability of the considered colloidal system, for which a great deal of information can be obtained from specialized literature, such as colloid, polymer, and latex handbooks [33], For example, the use of the proper surfactant (e.g., Fl-70) is common for SdFFF applications. Polymer analysis with ThFFF requires solvent types similar to those employed in size exclusion chromatography. 

Aqueous solutions containing both polymers and surfactants are encountered In a number of Industrially Important areas such as detergents, cosmetics, pharmaceutics, paints, EOR, metal working/ hydraulic fluids, and mineral/ceramlc/materlal processing systems. 

Now consider the problems which occur In the surfactant field, e.g. In detergency, cosmetics or pharmaceuticals, where polymers are usually associated with detergents to control the surface activity of the formulations (17). In these systems the polymers are known to Interact with surfactant micelles or mlcroemulslon droplets the Interaction can be beneficial, but most often It Is a real nuisance. 

From a physical point of view, suspensions are usually unstable systems, as the solid phase almost always tends to form a sediment. One of the most important aims with this type of dosage form must therefore be to prevent sedimentation. As this ideal condition can usually not be achieved, it is at least attempted to reduce the sedimentation rate and, above all, to make any sediment easy to redisperse. A number of auxiliaries are used in pharmaceutical technology to achieve this. They include thickeners, hydrophilic polymers, sugars and sugar alcohols, surfactants and electrolytes [296]. In spite of its insolubility, crospovidone can be classed as a hydrophilic polymer. 

Hydrogen bonding is a subject of remarkable diversity as it is present in and dictates the behavior of an enormous number of systems including aqueous solutions, systems of biological/biomedical interest, pharmaceuticals, colloids and surfactants, physical networks and gels, adhesives and pastes, extractives and binders, polymer alloys and blends. There are many reviews of the subject in the... 

The titration cell for an isothermal microcalorimeter provides an excellent way of following complex interactions for biomaterials, polymers, and surfactants. Thus, this approach will see increasing use in the pharmaceutical sciences in the years to come. As with other calorimetric methods, there will often be parallel processes that will need to be corrected for. Furthermore, the more information that is known about a system from other methods, the easier it will be to understand the microcalorimetry data. 

From a theoretical point of view, adsorption at interfaces, either solid-liquid (S/L). liquid-vapor (L/V>, or liquid-liquid (L/L), is one of the topic.s of highest interest in the physical chemistry of colloidal systems due to the increasing number of important technological areas in which it finds application. We will only be here concerned with solid-liquid interfaces and. in particular, with the two main ways of favoring stabilization of pharmaceutical suspensions, which are the adsorption of surfactants and of polymers as additives in suspension. Let us first consider the fundamentals of these processes and later some results will be discussed. 

Colloidal systems and dispersions are of great importance in oil recovery, waist water treatment, coating, food and beverage industry, pharmaceutical industry, medicine, environmental protection etc. Colloidal systems and dispersions are always multi-component and multiphase systems. In these systems at least one dimension is in a range of colloidal forces action colloidal dispersions/emulsions are examples of three dimensional colloidal systems, while thin liquid films are examples of one dimensional colloidal systems. Mostly colloidal systems are stable because their properties are substantially enhanced by the presence of surfactants and or polymers. The distribution and redistribution of the latter molecules is of the crucial importance for colloidal systems. 

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