An experimental investigation of the stability of ethylcellulose latex: Correlation between zeta potential and sedimentation

Department of Applied Physics, University of Granada, Granata, Andalusia, Spain
European Journal of Pharmaceutical Sciences (Impact Factor: 3.35). 11/2005; 26(2):170-5. DOI: 10.1016/j.ejps.2005.05.008
Source: PubMed


This paper aims at explaining the experimental observations of the stability and redispersibility of an aqueous ethylcellulose latex through the electrokinetic characterization of the particles. The surface charge and the electrical double layer thickness play an essential role in the stability of the system, hence the need for a full characterization of the polymeric particles. The effect of both pH and ionic strength of the dispersion medium were investigated. It was found that at acid pH values the latex displays "delayed" or "hindered" sedimentation: in such conditions, the electrophoretic mobility and zeta potential are rather low, indicating a small electrokinetic charge on the particles. At alkaline pH, when the dissociation of ionizable surface groups must be complete, the zeta potential is high and negative. The electrostatic repulsion between polymer particles is responsible for the low sedimentation volume and poor redispersibility of the latex. The effect of NaCl and CaCl(2) concentration on both the zeta potential and stability of the latexes was also investigated: it was found that CaCl(2) has the greatest influence, yielding flocculated, easily re-dispersible systems when its concentration in the dispersion medium is high enough. There qualitative observations were ascertained by means of calculations of the potential energy of interaction between particles. In the case of NaCl solutions, a high and relatively wide potential energy barrier was predicted, that may prevent the particle aggregation. Above 5mM NaCl a shallow minimum in the potential energy curves must lead to the formation of aggregates. Similar results were found with CaCl(2) solutions, although in this case the secondary minima are deeper and appear at lower concentrations.

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    • "The loading of ACZ molecules inside the liposomes did not altered the zeta potential (−10.3 ± 3.9 SD mV). The low value of zeta potential associated with the ACZ loaded neutral liposomes is indicative of insufficient stability (Gallardo et al., 2005; Wang et al., 2011 "
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    ABSTRACT: In the present work comparative evaluation of acetate and pH gradient techniques for effective drug loading in liposomes has been investigated. The acetazolamide (ACZ) loaded liposomes prepared by two methods were analyzed by vesicle size analysis, zeta potential, percent encapsulation efficiency, in vitro drug release studies and intraocular pressure lowering activity. ICH guidelines were followed for determining stability of the prepared liposomes. The superiority of acetate gradient method for active loading of acetazolamide has been established. The prepared acetate gradient positive liposomes showed extended hypotensive effect when compared to other liposomal formulations. Thus ACZ loaded liposomes prepared by acetate gradient technique may serve as promising ocular delivery system in the treatment of glaucoma. The current work emphasizes the fact that the techniques used for active drug loading into liposomes strongly influence the pharmaceutical performance of the final formulation.
    Full-text · Article · Nov 2013 · International Journal of Pharmaceutics
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    • "Zeta potential values are used to predict particles’ stability, stable particles presenting a zeta potential more negative than -30 mV or more positive than +30 mV [16]. All this considered, the PU structures obtained in the first two experiments (using Cremophor EL and Cremophor A6 as emulsifiers) are considered the most stable products. "
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    ABSTRACT: Background Emulsifiers have a significant role in the emulsion polymerization by reducing the interfacial tension thus increasing the stability of colloidal dispersions of polymer nanostructures. This study evaluates the impact of four emulsifiers on the characteristics of polyurethane hollow structures used as drug delivery system. Results Polyurethane (PU) structures with high stability and sizes ranging from nano- to micro-scale were obtained by interfacial polyaddition combined with spontaneous emulsification. The pH of PU aqueous solutions (0.1% w/w) was slightly acidic, which is acceptable for products intended to be used on human skin. Agglomerated structures with irregular shapes were observed by scanning electron microscopy. The synthesized structures have melting points between 245-265°C and reveal promising results in different evaluations (TEWL, mexametry) on murine skin. Conclusions In this study hollow PU structures of reduced noxiousness were synthesized, their size and stability being influenced by emulsifiers. Such structures could be used in the pharmaceutical field as future drug delivery systems.
    Full-text · Article · Apr 2013 · Chemistry Central Journal
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    • "The Zetasizer results (Table 1) show large values for the diameter of each sample (over 500 nm) which could be attributed to the particle aggregation process. The zeta potential values are significant because if all the particles have a zeta potential more negative than −30 mV or more positive than +30 mV the dispersion should remain stable [19]. All this considered, the product obtained in the second experiment, when isophorone diisocyanate (IPDI) was used, is regarded as the most stable. "
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    ABSTRACT: Background Polymers have been considered as important materials in fabrication of microstructures for various medical purposes including drug delivery. This study evaluates polyurethane as material for hollow microstructures preparation. Results Polyurethane microstructures were obtained by interfacial polyaddition combined with spontaneous emulsification and present slightly acid pH values. Scanning electron microscopy revealed the existence of irregular shapes and agglomerated microstructures. The material is heat resistant up to 280°C. Good results were recorded on murine skin tests in case of polyurethane microstructures based on isophorone diisocyanate. Mesenchymal stem cells viability presents good results for the same sample after 48 hours based on the Alamar Blue test. Conclusions The research revealed the reduced noxiousness of this type of microstructures and consequently the possibility of their use for therapeutic purposes.
    Full-text · Article · Aug 2012 · Chemistry Central Journal
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