ABSTRACT
Herein, we demonstrate for the first time the synthesis of ultra-stable, spherical, nematic liquid crystal (LC) droplets of narrow size polydispersity coated by sustainable, biodegradable, plant-based materials that trigger a typical bipolar-to-radial configurational transition in dynamic response to chemical and biological analytes. Specifically, a highly soluble polymer, potato protein (PoP) and a physically-crosslinked potato protein microgel (PoPM) of â¼100 nm in diameter, prepared from the PoP, a byproduct of the starch industry, were compared for their ability to coat LC droplets. Although both PoP and PoPM were capable of reducing the interfacial tension between water and n-tetradecane <30 mN m-1, PoPM-coated LC droplets showed better stability than the PoP-coated droplets via a Pickering-like mechanism. Strikingly, the Pickering LC droplets outperformed PoP-stabilized droplets in terms of dynamic response with 5× lower detection limit to model chemical analytes (sodium dodecyl sulphate, SDS) due to the difference in SDS-binding features between the protein and the microgel. To eliminate the effect of size polydispersity on the response, monodisperse Pickering LC droplets of diameter â¼16 µm were additionally obtained using microfluidics, which mirrored the response to chemical as well as biological analytes, i.e., primary bile acid, an important biomarker of liver diseases. We demonstrate that these eco-friendly microgels used for creating monodisperse, ultra-stable, LC complex colloids are powerful templates for fabricating next generation, sustainable optical sensors for early diagnosis in clinical settings and other sensing applications.
ABSTRACT
The aim of this study was to investigate the fate of curcumin (CUR)-loaded Pickering emulsions with complex interfaces during in vitro gastrointestinal transit and test the efficacy of such emulsions on improving the bioaccessibility and cellular uptake of CUR. CUR-loaded Pickering emulsions tested were whey protein nanogel particle-stabilized Pickering emulsions (CUR-EWPN) and emulsions displaying complex interfaces included 1) layer-by-layer dextran sulphate-coated nanogel-stabilized Pickering emulsions (CUR-DxS+EWPN) and 2) protein+dextran-conjugated microgel-stabilized Pickering emulsions (CUR-EWPDxM). The hypothesis was that the presence of complex interfacial material at the droplet surface would provide better protection to the droplets against physiological degradation, particularly under gastric conditions and thus, improve the delivery of CUR to Caco-2 intestinal cells. The emulsions were characterized using droplet sizing, apparent viscosity, confocal and cryo-scanning electron microscopy, zeta-potential, lipid digestion kinetics, bioaccessibility of CUR as well as cell viability and uptake by Caco-2 cells. Emulsion droplets with modified to complex interfacial composition (i.e. CUR-DxS+EWPN and CUR-EWPDxM) provided enhanced kinetic stability to the Pickering emulsion droplets against coalescence in the gastric regime as compared to droplets having unmodified interface (i.e. CUR-EWPN), whereas droplet coalescence occurred in intestinal conditions irrespective of the initial interfacial materials. A similar rate and extent of free fatty acid release occurred in all the emulsions during intestinal digestion (p > 0.05), which correlated with the bioaccessibility of CUR. Striking, CUR-DxS+EWPN and CUR-EWPDxM significantly improved cellular CUR uptake as compared to CUR-EWPN (p < 0.05). These results highlight a promising new strategy of designing gastric-stable Pickering emulsions with complex interfaces to improve the delivery of lipophilic bioactive compounds to the cells for the future design of functional foods.
ABSTRACT
The aim of this study was to restrict the degree of gastric destabilization of Pickering emulsions by using electrostatic deposition of a biopolymeric layer at the proteinaceous particle-laden oil-water interface. Pickering emulsions (20 wt% oil) were prepared using whey protein nanogel particles (WPN, Dh⼠91.5 nm) (1 wt%) and the emulsions were coated by a layer of anionic polysaccharide, dextran sulphate (DxS) of molecular weight (MW) of 40 or 500 kDa, respectively. The hypothesis was that DxS coating on the protein nanogel particle-laden interface would act as a steric barrier against interfacial proteolysis of WPN by pepsin. During static in vitro gastric digestion, the droplet size, ζ-potential, microstructure (confocal microscopy with fluorescently labelled dextran) and protein hydrolysis were monitored. The ζ-potential measurements confirmed that 0.2 wt% DxS was sufficient to coat the WPN-stabilized emulsion droplets with clear charge reversal from +35.9 mV to -28.8 (40 kDa) and -46.2 mV (500 kDa). Protein hydrolysis results showed a significantly lower level of free amino groups upon addition of 0.2 wt% DxS of either 40 or 500 kDa MW to the WPN (p < 0.05). Emulsions coated with DxS-500 kDa presented stable droplets with lower degree of pepsin hydrolysis of the adsorbed layer as compared to those coated with DxS-40 kDa or uncoated protein nanogel-stabilized interface after 120 min of digestion, highlighting the importance of charge density and molecular weight of the polymer coating. Insights from this study could enable designing gastric-stable emulsions for encapsulation of lipophilic compounds that require delivery to the intestine.
