Preparation and optimization of Pickering emulsion stabilized by chitosan-tripolyphosphate nanoparticles for curcumin encapsulation
Graphical abstract
Introduction
Emulsions stabilized by solid particles instead of surfactants are known as “Pickering emulsions”. These emulsions have drawn increasing interest because of their wide range of application in foods, pharmaceuticals and cosmetics, against conventional emulsions using surfactants where toxicity is an issue (Dickinson, 2010, Frelichowska et al., 2009). In these emulsions unlike surfactants, the particles due to their high energy of attachment irreversibly adsorb at the interface, making the resultant Pickering emulsions more stable for months or even years (Binks, 2002). To prepare Pickering emulsions, a variety of colloidal particles have been successfully employed including inorganic and polymeric colloids such as silica (Binks & Lumsdon, 2000), polymer latex (Binks & Lumsdon, 2001), magnetic particle (Zhang, Su, Ramakrishna, & Lim, 2008), grapheme (Song, Yang, Liu, & Zhao, 2011) and clays and poly methyl methacrylate particles (Yu, Lin, & Li, 2013). Chitosan (CS) the second most abundant biopolymer in nature next to cellulose, derived from the exoskeleton of shrimps and other crustaceans is one of the very few positively charged natural biopolymers existing in the world. Due to its unique characteristics of biodegradability, biocompatibility, bio-adhesion and non-toxicity, CS nanoparticles (NPs) are used as drug delivery systems, nanofibers, biosensors, and edible films (Sogias, Williams, & Khutoryanskiy, 2008). A series of methods are used for producing stable CS NPs for different applications. Preparation of CS NPs by ionic gelation technique has attracted more attention since this process is non-toxic, organic solvent free, convenient and controllable (Agnihotri, Mallikarjuna, & Aminabhavi, 2004). Ionic gelation technique involves the ionic interactions between the positively charged primary amino groups of CS and the negatively charged groups of poly anion, such as TPP, which is the most extensively used ion cross-linking agent due to its non-toxic and multivalent properties (Shu & Zhu, 2002). It is considered that CS–TPP NPs are formed mainly through the electrostatic interaction between positively charged CS and negatively charged TPP molecules. This interaction requires only mild conditions in terms of temperature and pH (Zhang, Oh, Allen, & Kumacheva, 2004) and the NPs size can be controlled by varying the CS: TPP ratio, pH and the molar mass of the CS (Hu et al., 2008, Tsai et al., 2011). The physical cross-linking process between CS and TPP not only avoids the use of chemical cross-linking and emulsifying agents which are often toxic to organisms, but also prevents the possibility of damage to drugs, particularly biological agents (Berger et al., 2004).
Curcumin, a naturally occurring polyphenol derived from Curcuma longa has been used in traditional medicine for many Centuries in countries such as India and China (Shishodia, Sethi, & Aggarwal, 2005). Recently, it is reported that curcumin has a wide range of pharmacological applications such as anti-inflammation, anti-human immuno-deficiency virus, anti-microbial, anti-oxidant, anti-parasitic, anti-mutagenic and anti-cancer with low or no intrinsic toxicity (Yallapu, Jaggi, & Chauhan, 2010). But the clinical advancement of this promising natural compound is hampered by its poor water solubility and short biological half-life resulting in low bioavailability in both plasma and tissues. In this context nanotechnology has been employed in an attempt to increase its retention time and enhance its bioavailability (Cui et al., 2009). However, to the best of authors' knowledge, no such study has been conducted so far that focuses on encapsulation ability, stability and in vitro release of curcumin using tripolyphosphate cross linked CS NPs stabilized Pickering emulsion. Therefore, in the current study, we prepared and optimized CS-TPP NPs stabilized Pickering emulsion in an attempt as a curcumin delivery system.
Section snippets
Materials
Chitosan (CS, Mw 5 × 105–7 × 105 Da) was purchased from Qingdao Yunzhou biochemistry Co., Ltd. (Shandong, China). Medium chain triglyceride (MCT) was purchased from Boxing 145 Chemical Reagent Co., Ltd. (Wuhan, China). Curcumin (95.0% purity), was purchased from National Medicine Group Chemical Reagent Co., Ltd. Sodium Tripolyphosphate (TPP), Glacial acetic Acid, NaCl, CaCl2, NaOH and HCl were purchased from Sinopharm chemical reagent Co., Ltd. (Beijing, China). All the reagents were of
Synthesis and characterization of CS-TPP NPs
- 1.
Chitosan (CS) nanoparticles (NPs) were prepared by ionotropic gelation with the drop-wise addition of tripolyphosphate (TPP) to a chitosan solution. Here we performed preliminary experiments for the selection of the optimal ratios in the formation of CS-TPP NPs. For this purpose, the appearance of opalescence from transparent solution was used as an indicator of NPs formation, which was also confirmed by means of dynamic light scattering. The particles formed with CS:TPP mass ratio of 5:5
Conclusion
We optimized the preparation of CS-TPP NPs stabilized Pickering emulsion. The particles were prepared with different CS:TPP ratios and were characterized. For the optimization of the emulsion, the emulsion was prepared under varying conditions. CS concentration showed positive effect on the emulsion stability. The emulsions droplet size changed greatly over a period of storage time, when the CS concentration was 0.2 wt%. Also the emulsion was not very stable when different emulsifier (CS-TPP
Acknowledgment
This work was financially supported by the National Natural Science Foundation of China (No. 31071607). The authors would like to express their sincere gratitude to many conveniences offered by colleagues of Key Laboratory of Environment Correlative Dietology of Huazhong Agricultural University. The author is also grateful to Chinese Scholarship Council for granting PhD scholarship.
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