Hollow multi-shelled structures (HoMSs) with hollow interior and multiple shells have been recognized as one type of promising material for applications in in energy conversion and storage, sensors, catalysis, electromagnetic absorption and drug delivery, etc. However, compared to their single- shelled counterparts, the synthesis of HoMSs is much more challenging due to the increased complexity of the structure.
Our group proposed a general and widely usable sequential templating approach (STA) to prepare HoMSs by utilizing carbonaceous spheres as templates to adsorb metal ions and heating them to remove the template and generate multiple shells. Numerous HoMSs of single metal oxides (such as α-Fe2O3, ZnO, Co3O4, SnO2, TiO2, Mn2O3 and V2O5), metal sulfides (Ni3S2, NiS, NiS2), binary metal oxides ((CO2/3Mn1/3)(Co5/6Mn1/6)2O4) and also heterogeneous mixed metal oxides (ZnO@ZnO/ZnFe2O4@ ZnO/ZnFe2O4) have been successfully prepared using STA. The concentration and radial distribution of metal ions can be adjusted by changing the corresponding experimental conditions, such as the metal salt concentration, the solvent, the adsorption temperature and duration, the heating temperature and rate, and so forth, thus controlling the geometric parameters of HoMSs.
The breakthrough of synthetic methodologies for HoMSs also provides opportunities to acquire unique physical or chemical properties and performance in specific applications by manipulating their geometric structures, such as shell numbers, shell thickness, inter-shell space as well as shell composition and morphology. Many successful examples have been well demonstrated in the specific fields, including dye-sensitized solar cells, lithium ion batteries, sodium-ion battery, alkaline rechargeable battery,[14,16, 19] photo detector, gas sensors, etc.
Pickering emulsion is a special emulsion stabilized by nanoparticles instead of surfactant, it has been studied since 1903. Pickering emulsion has many advantages, for example: it is more stable than normal emulsion; its properties can be modulated by nanoparticles. However, conventionally SiO2 or polystyrene (PST) nanoparticle was used for preparing Pickering emulsion because uniform SiO2 and PST nanoparticles are easily prepared. The bio-application study of Pickering emulsion was limited due to the preparation difficulty of uniform biodegradable nanoparticles.
In this study, we prepared uniform alginate/chitosan and poly(lactide-glycolide) (PLGA) biodegradable nanoparticles by membrane emulsification technique and other technique, and used them to prepare Pickering emulsion for Insulin oral delivery and advanced engineered vaccine.
Firstly, we prepared alginate nanoparticle by rapid membrane emulsification technique, then we obtained alginate/chitosan nanoparticle by layer-by-layer process. Then, we prepared Pickering double emulsion (W/O/W) with insulin solution as inner water phase, PLGA/ethyl acetate (EA)/Arlacel 83 as oil phase, and nanoparticle aqueous phase as outer water phase. Then, after removing EA, we can obtain microcapsule with nanoparticle on its surface, it is called colloidosome. This colloidosome showed pH-sensitivity, it was stable at pH 1.2 (stomach), but released insulin quickly at pH 6.8 (Intestine), due to the pH-sensitivity of alginate/chitosan nanoparticle. Finally, the blood glucose level can be decreased apparently after oral administration.
Secondly, we prepared Pickering emulsion (O/W) by using squalene as oil phase, and PLGA nanoparticle aqueous phase as outer phase. Then we assembled antigen in the gap among nanoparticles to form engineered vaccine. We found that this vaccine mimic pathogen behavior, it showed force-dependent deformation, and antigen can move at oil/water interface. As a result, compared with conventional emulsion, it exerted potent immune protections against influenza virus challenge, and enhanced therapeutic anti-tumor efficiency, when we loaded H1N1 or MUC1 antigen on this Pickering emulsion, respectively.
Polyacrylic acid–modified titanium peroxide nanoparticles (PAA-TiOx NPs) locally injected into tumors exhibit radiosensitizing activity in vivo, enhancing the therapeutic effect of X-ray irradiation. However, the underlying mechanism remains unclear except for the involvement of hydrogen peroxide (H2O2), which is continuously from the PAA-TiOx NPs. Thus, this study investigated the details of H2O2 release from PAA-TiOx NPs and the effect on radiosensitivity of cultured tumor cells in vitro using a clonogenic assay in comparison with H2O2 solution as a control. PAA-TiOx NPs were internalized by treated cells within 10 min and released H2O2 for at least 7 h. Interestingly, further experiments revealed a significant increase in the intracellular H2O2 concentration corresponding with PAA-TiOx NP internalization. Additional X-ray irradiation killed tumor cells that had internalized PAA-TiOx NPs more effectively than tumor cells treated only with H2O2. PAA-TiOx NPs represent a novel radiosensitizing system for generating H2O2 in tumor cells.