Shengwen Zou

Simple, Reversible Emulsion System Switched by pH on the Basis of Chitosan without Any Hydrophobic Modification

Chitosan without hydrophobic modification is not a good emulsifier itself. However, it has a pH-tunable sol-gel transition due to free amino groups along its backbone. In the present work, a simple reversible Pickering emulsion system based on the pH-tunable sol-gel transition of chitosan was developed. At pH > 6.0, as adjusted by NaOH, chitosan was insoluble in water. Chitosan nanoparticles or micrometer-sized floccular precipitates were formed in situ. These chitosan aggregates could adsorb at the interface of oil and water to stabilize the o/w emulsions, so-called Pickering emulsions. At pH < 6.0, as adjusted by HCl, chitosan was soluble in water. Demulsification happened. Four organic solvents (liquid paraffin, n-hexane, toluene, and dichloromethane) were chosen as the oil phase. Reversible emulsions were formed for all four oils. Chitosan-based Pickering emulsions could undergo five cycles of emulsification-demulsification with only a slight increase in the emulsion droplet size. They also had good long-term stability for more than 2 months. Herein, we give an example of chitosan without any hydrophobic modification to act as an effective emulsifier for various oil-water systems. From the results, we have determined that natural polymers with a stimulus-responsive sol-gel transition should be a good particulate emulsifier. The method for in situ formation of pH-responsive Pickering emulsions based on chitosan will open up a new route to the preparation of a wide range of reversible emulsions.

Mineralization and drug release of hydroxyapatite/poly(l-lactic acid) nanocomposite scaffolds prepared by Pickering emulsion templating

Biodegradable and bioactive nanocomposite (NC) biomaterials with controlled microstructures and able to deliver special drugs have gained increasing attention in bone tissue engineering. In this study, the hydroxyapatite (HAp)/poly(l-lactic acid) (PLLA) NC scaffolds were facilely prepared using solvent evaporation from templating Pickering emulsions stabilized with PLLA-modified HAp (g-HAp) nanoparticles. Then, in vitro mineralization experiments were performed in a simulated body fluid (SBF) to evaluate the bioactivity of the NC scaffolds. Moreover, in vitro drug release of the NC scaffolds using anti-inflammatory drug (ibuprofen, IBU) as the model drug was also investigated. The results showed that the NC scaffolds possessed interconnected pore structures, which could be modulated by varying the g-HAp nanoparticle concentration. The NC scaffolds exhibited excellent bioactivity, since they induced the formation of calcium-sufficient, carbonated apatite nanoparticles on the scaffolds after mineralization in SBF for 3 days. The IBU loaded in the NC scaffolds showed a sustained release profile, and the release kinetic followed the Higuchi model with diffusion process. Thus, solvent evaporation based on Pickering emulsion droplets is a simple and effective method to prepare biodegradable and bioactive porous NC scaffolds for bone repair and replacement applications.

Macroporous antibacterial hydrogels with tunable pore structures fabricated by using Pickering high internal phase emulsions as templates

Artemisia argyi oil (AAO)-loaded macroporous antibacterial hydrogels were prepared by polymerization of oil-in-water Pickering high internal phase emulsions (HIPEs). The HIPEs were stabilized by the synergy of hydrophilic silica nanoparticles (N20) and surfactant Tween 80. The void interconnectivity and pore size of the hydrogels could be tailored readily by varying the concentrations of N20 nanoparticles and Tween 80. The mechanical properties of the porous hydrogels were related to the pore structure of the materials. There was an optimal condition for the N20 particle and Tween 80 contents where the hydrogel exhibited high compressive stress and strain. The in vitro release of the AAO-loaded hydrogels with different inner morphologies was evaluated and showed controlled release activity. The antibacterial activity of the AAO-loaded hydrogel was evaluated against Staphylococcus aureus and Escherichia coli. This kind of hydrogel exhibited excellent and long-term antibacterial activity indicating its potential use in biomedical and infection prevention applications.

Surfactant-Free Multiple Pickering Emulsions Stabilized by Combining Hydrophobic and Hydrophilic Nanoparticles

A series of W/O/W or O/W/O emulsion stabilized solely by two different types of solid nanoparticles were prepared by a two-step method. We explored the option of particular emulsifiers for the multiple Pickering emulsions, and a variety of nanoparticles (silica, iron oxide, and clay) only differing in their wettability was used. The primary W/O emulsion was obtained by the hydrophobic nanoparticles, and then the hydrophilic nanoparticles were used as emulsifier in the secondary emulsification to prepare the W/O/W emulsion. In a similar way, the primary O/W emulsion of the O/W/O emulsion was stabilized by the hydrophilic nanoparticles, while the secondary emulsification to prepare the O/W/O emulsion was effected with the hydrophobic nanoparticles. The resultant multiple Pickering emulsion was stable to coalescence for more than 3 months, except the W/O/W emulsions of which the secondary emulsion stabilized by clay nanoparticles became a simple O/W emulsion in a day after preparation. Moreover, the temperature and pH sensitive poly(N-isopropylacrylamide-co-methacrylic acid) (P(NIPAm-co-MAA)) microgels were introduced as an emulsifier for the secondary emulsification to obtain the stimulus-responsive multiple W/O/W emulsion. Such microgel-stabilized multiple emulsions could realize the efficient controlled release of water-soluble dye, Rhodamine B (RB) on demand in a multiple-emulsion delivery system.

One-pot fabrication of rattle-like capsules with multicores by pickering-based polymerization with nanoparticle nucleation.

Rattle-like polymer capsules with multicores in one shell are facilely fabricated by oil-in-water Pickering emulsion polymerization for the first time. The oil phase contains hydrophobic silica nanoparticles dispersed in polymerizable monomer, styrene, and unpolymerizable solvent, hexadecane. The multicore rattle-like capsules are facilely produced after the polymerization of monomers in the oil droplets. The key point of this one-pot method lies in the nucleation of hydrophobic silica and the phase separation between the resulting polystyrene and hexadecane. The influences of the contents of silica, hexadecane, cross-linker, and stabilizer on the structure and morphology of rattle-like capsules are systematically investigated. Moreover, functionalization of the rattle-like capsules can be developed easily by varying hydrophobic nucleation nanoparticles in the oil phase. This work opens up a new route to fabricate multilevel capsules or spheres.

Synergistic Stabilization of High Internal Phase Pickering Emulsions by a Mixture of Nanoparticle and Polymer

In this paper, we have prepared high internal phase Pickering emulsions (Pickering HIPEs) with internal phase volume fraction 90% which are stabilized by a mixture of silica nanoparticles (H30) and poly(L-lactide-co-glycolide) (PLGA). HIPEs with an internal phase volume not more than 75% could be prepared solely by H30 nanoparticles. Using PLGA as stabilizer, phase separation takes place and stable emulsions are not formed. Synergistic interaction between H30 particles and PLGA molecules plays an im- portant part in preparation of HIPEs. Using inorganic particles and polymer as co-stabilizer will be a new and effective method to prepare HIPEs.