Study On Pickering Emulsions For Drug Release And Enzymatic Catalysis

Pickering emulsions which are emulsions stabilized by solid particles instead of molecular surfactants.Using Pickering emulsions as vehicles for drug release and enzymatic catalysis is an attractive field due to the characteristic of high stability,adjustable wettability and environmental friendliness.Surface active Ti02 nanoparticles?NPs?self-assemble onto the oil-water interface to form rigid layers around the droplets could be particularly efficient as an inherent barrier in storage stability,drug protection,and controlled release.Based on above issue,this research focuses on the light-responsive Pickering emulsions destabilization mechanism according to UV-induced wettability transition of the TiO₂ NPs emulsifiers and studied its application in drug release and biphasic interface catalysis reactions.For drug release:a new strategy for developing light-triggered Pickering emulsions as smart soft vehicles for on-demand release and emulsions destabilization mechanism is proposed.UV-induced tailored wettability allows anchoring of TiO₂ NPs at the interface to prepare stable water in oil emulsions.Such emulsions show the ability of microencapsulation and controlled release by demulsification due to the hydrophilic conversion of the TiO₂ NPs using a noninvasive light irradiation trigger.Once the TiO₂ NPs at the water-oil interface are treated with UV,hydrophilicity changes due to the adsorption of hydroxyl groups on particle surface,disabling their stabilizing properties:the particles are expelled out of the interface,the W/O emulsions show instability and phase separation,and ultimately the encapsulated molecule is released.A molecule of interest is selected as a model cargo to quantitatively evaluate the as-prepared Pickering emulsions for their encapsulation and release behaviors.Moreover,light-responsive emulsion destabilization mechanism is studied as a function of particle concentration,light wavelength and light intensity,respectively,determined by drop diameter evolution and droplet coalescence kinetics plots.Herein,when the concentration of TiO₂ NPs increases from 1 to 2 and to 3 wt%,respectively,the W/O emulsions exhibit decreasing initial diameters of?280,?180 and?130 ?m,and the time of complete demulsification and phase separation prolongs from?12 to?24 and to?48 h;in case 1 wt%s-TiO₂ NPs used,only UV light with energy can be used as the driven force for emulsion destabilization and coalescence via wettability transition of s-TiO₂ NPs,whereas visible light and dark storage cannot;the release occurs at a longer UV light-irradiation time with the wavelength of 365 nm?36 h?;moreover,the intensity of UV irradiation inversely correlates with the time of light-triggered release of 12 h(200 ?w.cm^-2),32 h(100 ?w·cm^-2),and 72 h(50 ?w·cm^-2),respectively.For consideration of application in life sciences,Pickering emulsions sensitive to visible light are also established based on nitrogen doping of TiO₂ NPs emulsifiers.TiO₂ NPs is an effective and safe skin-protective UV-filter,widely used in cosmetic formulation,simultaneously,The author takes advantage of emulsion destabilization mechanism and provides a new method for make a kind of green,easy-clean,highly effective UV-Screening and controlled drug-delivery for cosmetic formulation.This research has promising potential as a powerful technique for pharmaceutical engineering and fine chemicals field.For interface catalysis:Based on the study of emulsion destabilization mechanism,the author has tried a series of chloroalkylsilanes commercially available to modify mesoporous SiO₂ particles with various alkyls to obtain suitable wettability and immobilize lipase.In the systems of Pickering interfacial catalysis,where enzyme immobilized in mesoporous SiO₂ particles are employed to stabilize emulsions and catalyze enzymatic reactions at the interface of the two immiscible solvents.The Pickering emulsions systems enable biphasic reactions to proceed efficiently through changing interfacial area only by the means of adjusting the wettability of particles.The results show the three phase contact angles are 25°,109°,118°,95°,130° and 145°;when chain length are CO?with 0 carbons?,C3?with 3 carbons?,C6?with 6 carbons?,C8?with 8 carbons?,CIO?with 10 carbons?,C12?with 12 carbons?and the conversion efficiency behaves C8>C3>C6>C10>C12>CO.Mesoporous SiO₂ particles?with 8 carbons?with oil-water interfacial contact angles around 90° are surface active and promise to stabilize emulsions with the smallest droplet size,the most thick emulsion layer and the largest interface area.Such a high level of oil-water mixing and a large interfacial area guarantee reaction efficiency.Moreover,the convenient and effective recycling of lipase could be achieved through simple low-speed centrifugation,thus indicating an ease of separation for the substrate?in the oil phase?,product?in the aqueous phase?and enzyme?as the solid phase?.As evidenced by a 6-cycles reaction,the robust protection can effectively avoid from the organic solvent stress that often causes damage to the activity of enzyme.This study demonstrates that Pickering emulsions system is an innovative and controllable platform to efficiently process enzymatic reactions and this method can further applied for a wide range of biphasic catalytic reactions.