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Nanocarrier Technologies for Enhancing the Solubility and Dissolution Rate of Api
Published in Debarshi Kar Mahapatra, Sanjay Kumar Bharti, Medicinal Chemistry with Pharmaceutical Product Development, 2019
Ashwini Deshpande, Tulshidas S. Patil
Purpose of surfactants is to provide good stability against coalescence. Ideal requirements of surfactants are: – They must be able to lower interfacial surface tension to a very low value (below 10 dynes/cm).– They must form the complete deformable flexible film which is of sufficient lipophilic character to avoid coalescence of the globules.– They must impart appropriate zeta potential and viscosity to the carrier system for development of optimally stable formulations.– They must be nontoxic and their organoleptic properties should be compatible with the product.
Surfactants in Cosmetic Products
Published in Heather A.E. Benson, Michael S. Roberts, Vânia Rodrigues Leite-Silva, Kenneth A. Walters, Cosmetic Formulation, 2019
Ricardo Pedro, Kenneth A. Walters
Any discussion of emulsion stability should be approached not only on the stabilization mechanism, but also on the stability time and emulsion preparation conditions. The main factors related to coalescence are the physical nature of the interfacial film, the existence of electrical and steric barriers against the coalescence of the dispersed phase, the formation of liquid crystals in the interfacial film, the viscosity of the continuous phase, the volume ratio between phases and the temperature. Surfactants are, of course, crucial for the stabilization of emulsions. The droplets of dispersed liquid within the emulsion are constantly moving and colliding. Thus, it is very important to form an interfacial film of densely packed molecules of surfactant adsorbed around the droplets of the emulsion, with properties of strong intermolecular forces between them and the aqueous solution and high elasticity of the film, aiming at greater mechanical stability of the emulsion. For better packing of the surfactant molecules, it is important to use mixtures of at least two different surfactants in the emulsion system: one preferentially soluble in the oil phase, with long hydrophobic groups, preferably linear alkyl chains, and the other preferentially soluble in the aqueous phase, with stronger polar hydrophilic groups. The presence of electric charges in the interfacial films around the emulsion droplets constitutes a barrier to the approach of these droplets, a very important factor for O/W emulsions. The electric charge source is generally the surfactant layer adsorbed onto the droplets with their ionic hydrophilic group oriented towards the aqueous phase. The negative or positive charge created around the oil droplets delays the coalescence of the droplets in the same way that anionic surfactants in detergents keep the dirt in suspension, by the formation of a double electric layer, which acts against the force of attraction between the emulsified droplets.
Emulsion Rheology
Published in Laba Dennis, Rheological Proper ties of Cosmetics and Toiletries, 2017
Coalescence occurs when the particles of the dispersed phase come together to form larger particles. Ultimately, phase separation occurs. An exception is called limited coalescence, where the amount of emulsifier is insufficient to maintain a small particle size, but adequate to prevent flocculation or further coalescence of an emulsion with a larger particle size distribution (deNavarre, 1975).
Recent developments on foaming mechanical and electronic techniques for the management of varicose veins
Published in Expert Review of Medical Devices, 2019
C. Davide Critello, Salvatore A. Pullano, Thomas J. Matula, Stefano De Franciscis, Raffaele Serra, Antonino S. Fiorillo
Once a liquid has turned into foam, it is important to understand how long the foam can persist, since the duration of its contact with the endothelium inside the vessel determines treatment efficacy [32]. Although foam has complex physics, stability over time can be described by three major factors: Drainage, coalescence and coarsening [33]. Upon its formation, the first factor causing instability is the drainage of liquid between bubbles due to gravitational and capillary forces. Consequently, a visible phase separation between liquid (downward) and foam (upward) occurs. Coalescence represents the merging of bubbles caused by the rupture of the liquid films that separate bubbles. Finally, bubble coarsening is the gas diffusion that occurs between bubbles with different sizes (from smaller to bigger ones), determining an overall increase of bubble size. All these factors are mutually interrelated leading foams to evolve spatially and temporarily, but drainage is usually the main influence on stability [34].
Preparation and characterization of bee venom-loaded PLGA particles for sustained release
Published in Pharmaceutical Development and Technology, 2018
Min-Ho Park, Hye-Suk Jun, Jong-Woon Jeon, Jin-Kyu Park, Bong-Joo Lee, Guk-Hyun Suh, Jeong-Sook Park, Cheong-Weon Cho
PVA is the most commonly used emulsifier for the formulation of PLGA particles because the particles formed are relatively uniform and small in size18. During the evaporation process of the organic solvent, the viscosity of the emulsion droplets increased. This affects the droplet size equilibrium, and causes the coalescence and agglomeration of the droplets during the early stages of solvent removal19. This problem can be solved by adding a steric stabilizer, such as PVA, into the outer water phase, thereby providing a thin protective layer around the droplets and hence reducing their coalescence20. PVA molecular weight affected the encapsulation efficiency, drug loading, and particle size (V2 and V7). This might be attributed to the outer water phase containing PVA of a higher molecular weight, which increased the water phase viscosity. In addition, the increase in viscosity and osmosis in the outer water phase might prevent leakage. This is consistent with the results of previous studies, which found that the particle size and encapsulation efficiency are affected not only by the viscosity of organic phase but also by that of the outer water phase21,22. Stronger viscosity and osmosis during the outer water phase tend to produce lager particles, and result in higher encapsulation efficiency and drug loading.