Carbomers properties

These stabilizers are added to the formulation in order to stabilize the emulsion formed during particle preparation. These stabilizers, however, can also influence the properties of the particles formed. The type and concentration of the stabilizer selected may affect the particle size. Being present at the boundary layer between the water phase and the organic phase during particle formation, the stabilizer can also be incorporated on the particle surface, modifying particle properties such as particle zeta potential and mucoadhesion (203). Other polymers have also been evaluated as stabilizers in earlier studies such as cellulosic derivatives methylcellu-lose (MC), hydroxyethylcellulose ( ), hydroxypropylcellulose (HPC), and hydroxypropylmethylcellulose (HPMC), as well as gelatin type A and B, carbomer and poloxamer (203). 

A slightly different approach is to deliver the active drug in a dry powder carrier system, for example microcrystalline cellulose, hydroxyethyl starch, cross-linked dextran, microcrystalline chitosan, carbomer, pectin, or alginic acid. The polymer absorbs water upon contact with the nasal mucosa and swells to become a viscous gel, often demonstrating bioadhesive properties. Such systems can remain in the nasal cavity for as long as six hours. For example, the bioavailability in rats of the somatostatin analogue, octreotide, was shown to be enhanced by the co-administration of alginic acid and cross-linked dextran as dry powders. 

Carbomer is also compatible with dimethyl sulfoxide. The veterinary product, Domoso (Syntex Veterinary Labs), is a topical gel consisting of carbomer 934 and 90% dimethyl sulfoxide. Carbomer 940 gels exhibit superior optical clarity compared with 934 gels, and can be used in ophthalmic preparations. However, only carbomer 934 is approved for internal use. The mucoadhesive properties of carbomer were studied with triamcinolone acetonide, with acyclovir and to improve protein uptake across the nasal mucosa. Pharmaceutical gel products containing carbomer in their formulations are listed in Table 6. All are dermatological gels except for Anbesol Gel (Whitehall) and Pilopine HS (Alcon). 

Vehicles that exhibit the unusual property of Bingham-type plastic rheological flow are characterized by the need to overcome a finite yield stress before flow is initiated. Permanent suspension of most pharmaceutical systems requires yield-stress values of at least 2-5 Pa (20-50 dyn/cm ). Bingham plastic flow is rarely produced by pharmaceutical gums and hydrophilic colloids. National Formulary (NF) carbomers exhibit a sufficiently high yield value at low solution concentration and low viscosity to produce permanent suspensions. The carbomers, however, require a pH value between 6 and 8 for maximum suspension performance. The polymer is essentially incompatible... 

Cosmetic suspensions are available in two types. The first comprises pigmented products that are suspended in essentially aqueous vehicles (liquid makeup, eyeliners, mascara, and blusher). These products have a high solids content, high density, impalpable powders, and pigments permanently suspended in a primary oil-in-water emulsion-type base or a complex system of hydrophilic cellulose derivatives, clays, and/or polymeric film formers, in which the gelling and suspending properties of the vehicle often are reinforced by a small amount of a Bingham-type plastic such as carbomer. 

Perez-Marcos B, Iglesias R, Gomez-Amoza JL, et al. Mechanical and drug-release properties of atenolol-carbomer hydrophilic matrix tablets. / Control Release 1991 17 267-276. 

Although it is used in lotions, the marked degreasing properties of isopropyl alcohol may limit its usefulness in preparations used repeatedly. Isopropyl alcohol is also used as a solvent both for tablet film-coating and for tablet granulation, where the isopropyl alcohol is subsequently removed by evaporation. It has also been shown to significantly increase the skin permeability of nimesulide from carbomer 934. ... 

Both of the types of polymer mentioned above can be modified by the incorporation of hydrophobic monomers onto the essentially hydrophilic acrylate backbone. The effect of this is to modify their characteristics by giving them so-called associative properties. These hydrophobes can interact or associate with other hydrophobes in the formulation (e.g., surfactants, oils, or hydrophobic particles) and thus build additional structures in the matrix [3-11]. These associative polymers are termed cross-polymers when they are based on carbomer-type chemistry [12] and hydrophobically modified alkali-soluble emulsions (HASEs) when based on ASE technology. 

The simplest system to consider is represented by a dispersion of the neutralized polymer in water. All show excellent clarity, but the carbomers (and the cross-polymers, not shown) are undoubtedly the most efficient in terms of their simple aqueous thickening properties, as indicated in Figure 5.4. The quantity of polymer required to achieve a given mid-shear rate viscosity is close to an order of magnitude less than that required for a crosslinked ASE thickener. The HASE polymers are generally found to have an efficiency between that of the ASE and the carbomer/cross-polymers. 

The shape of the aqueous rheology curve also varies with the nature of the polymer. Both the carbomers and the cross-polymers show fairly similar behavior. Crosslinked ASE polymers, as shown in Figure 5.4, show a profile close to that of the carbomers, giving highly shear-thinning properties, although this is to some extent dependent on molecular weight. A noncrosslinked ASE polymer shows a more Newtonian profile. The HASE polymers tend to show a behavior between that of a noncrosslinked ASE thickener and the carbomers or crosslinked ASE polymers. 

In this chapter the solid state extrusion of different grades of polyethylene is discussed. The term copolyethylene stands as well for short and long branched PE as for the nearly alternating 1 1 copolymer poly(ethylene-co-chlorotrifluoroethylene) (PECTFE). It is well known that even HOPE contains a certain amount of short branches. Therefore, it is of interest to note that already one butyl side group per thousand main chain carbom atoms effects the solid state extrusion properties of PE remarkably. 

Glass-ionomers not only release ions, but are capable of taking them up. Studies have shown that cements exposed to natural saliva take up calcium and phosphate ions, and develop a surface of significantly increased hardness [121]. Also, when used as pit and fissure sealants, they interact with saliva to form a substance with increased content of calcium and phosphate that is considerably more resistant to cutting with a dental drill than the original material. Under these circumstances, the cement had become transformed into a material with enamel-like optical and mechanical properties [122]. This observation is the basis of the development of glass-ionomer type materials with even further enhanced bioactivity, the so-called glass carbomers, which are discussed in Chapter 8. 

Overall, though there were only a limited amount of data reported in this study [27], it was useful because they showed that the properties of glass carbomer are at least comparable with those of a well-known conventional glass-ionomer. 

The glass carbomer has similar properties to conventional glass-ionomers in terms of mechanical strength, adhesion and fluoride release. It is somewhat tougher, though. There do... 

Properties M.w. 875.23 HLB 3.0 nonionic Uses Dispersant, emulsifier, wetting agent, solubilizer, emollient, conditioner, softener, detergent for cosmetics, toiletries, pharmaceuticals excipient, diluent, lubricant, binder, filler polymerization emulsifier for food-pkg. film emulsifier, softener, detergent for foods ManufJDistrib. CarboMer Trade Names Crodesta F-10 Crodesta F-50 Trade Names Containing Crodesta F-110... 

Properties Wh. cryst. sol. in water, glycerol insol. in alcohol, ether m.w. 150.13 dens. 1.585 (20/4 C) m.p. 158.5 C Precaution Combustible Uses Culture medium Manuf/Distrib. CarboMer http //www.carbomer.com] Fluka http //www.sigma-aldrich.com] Lonza http //www.lonza.com] Ruger http //www.rugerchemical.com] U.S. Biochemical... 

Synonyms Pectin sugar Empirical C5H10O5 Properties M.w. 150.13 Uses Culture medium natural sweetener for foods and pharmaceuticals Regulatory FEMA GRAS Japan approved Manuf./Distrib. CarboMer http //www.carbomer.com] Danisco Sweeteners... 

Manuf./Distrib. CarboMer http //www. carbomer. com Trade Name Synonyms Glucoplus C [Chemstar Prods, http //www.chemstar.com], Glucoplus P [Chemstar Prods. httpU/www. chemstar. com] Chloro-2-hydroxypropyl trimonium chloride CAS 3327-22-8 EINECS/ELINCS 222-048-3 Synonyms 3-Chloro-2-hydroxypropyltrimethyl ammonium chloride Classification Nonaromatic amine Empirical C6H15CI2NO Formula CICH2CHOHCH2N(CH3)3 Cr Properties M.w. 188.10 dens. 1.154 m.p. 189-190 C ref. index 1.4541... 

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