Preparation And Properties Of Titanium-based Composite Liposomes Based On The Action Of Phospholipid Bilayer On The Limitation Of Organic Titanium Source

Liposomes are enclosed vesicles formed by the self-assembly of amphiphilic phospholipid molecules.The unique natural structure of the lipid endows the liposome with encapsulation properties of hydrophilic and hydrophobic substances.The use of liposomes in drug packaging,delivery and storage has been extensively explored because of a superior combination of their properties,including high biocompatibility,low toxicity or side effect,and capacity for controlled release of the encapsulated cargo.However,their practical applications are significantly constrained because of physical instability of the self-assembled structure,so the liposomes can be easily aggregated and destroyed due to the factors such as pollution,light,O₂ and sedimentation during preparation or storage.To improve the stability of liposome,various protection strategies have been developed.Material used of these strategies range from polymers?e.g.,chitosan,PEG?to inorganic materials?e.g.,silica,calcium phosphate,gold or titania?,which encapsulate and decorate liposomes to reinforce the structure and expand the functionality of the liposomes.Inorganic materil has become a popular choice for modified liposomes because of its excellent rigidity,toleration high temperature,abrasion and corrosion resistance in recent years.Among the inorganic materials,titania has been recognized as one of the most widely used semiconductor materials for photovoltaic,photocatalytic,and sensing applications because of its wide band gap,high activity and stability and low cost.Moreover,titania has become the preferred material for modified liposomes due to its high biocompatibility and biodegradability.To date,experimental strategies of combining the function of liposome with titania requires primary preparation of titania nanoparticles,or primary treatment of liposomal surfaces.These operation and process are complicated,and the modified liposomes are prone to phase separation when incorporate with inorganic particles due to the distinct surficial properties.Based on the accumulation of the works which our groups did before,and combined with the relevant reports at home and abroad,we provide a simple route to prepare a class of hybrid TiO₂-liposome composites.The natural amphiphilic structure of lipid bilayer was used to localize the precursor TBOT within the hydrophobic core of the bilayer.Subsequently,the TBOT was accompanied with quick hydrolysis and condensation reaction at the interface of the lipid bilayer/water layer in-situ,,then producing TiO₂-liposome composite microcapsule.The simple route,called "inner interface confined deposition way",exploiting interfacial sol-gel chemistry confined TBOT to the hydrophobic interior of the native bimolecular structure of the phospholipid bilayer drives titania formation in-situ.On the basis of the above,this research extensible investigated the co-assembly behavior of TBOT and chlorophyll within phospholipid bilayer.In such a way,composite liposome materials with photoelectric conversion function were prepared..In particular,we carried out the research as below:?1?TiO₂-lipsome composites were prepared by "outer deposition way" and "inner interface confined deposition way" respectively.Then the liposomes were compared and characterized by means of SEM,TEM et al.The results showed that compared with"outer deposition way",the TiO₂,lipsome composites prepared by the "inner interface confined deposition way" have high stability and excellent performance of sustained drug release.?2?An "inner interface confined deposition way" was raised to prepare a class of TiO₂-reinforced liposomes with hybrid core-shell nanostructures.The interaction between phospholipid bilayers and tetrabutyl titanate was systematically studied.The results of SEM,TEM,XRD,TG-DTA,FTIR showed that those lipotils maintained integrated morphology,uniform sizes and good dispersions.The shell of titania was formed inner lipid bilayer of liposomes.DSC measurements demonstrated that the TiO₂ inorganic coating hindered in the lateral mobility of the lipids and improved the phase temperature from free liposomes to lipotils,which provided another strong evidence for the formation of TiO₂-liposome composites.Embedded pyrene yield was used to monitor detailed information of fluorescence measurements on changes on the structural evolution during titania formation The results showed that the hydrophobic TBOT was located in the lipid bilayer and formed a Ti-O-Ti network inside the lipid bilayer.Moreover,a Two-Dimensional Langmuir membrane at the air-water interface was designed.The ?-A isotherms demonstrated that the increase of molecular area of TBOT-lecithin mixed membrane was smaller than that of pure lecithin molecular membrane,indicating that the cooperation of TBOT into mid-membrane of the lipid and titania in the core of the membrane strengthened the assembly of the lipid bilayer.The sensitivity of the sample to the surfactant TritonX-100 and in vitro release of drugs experiments indicated that the TiO₂-liposome composites formed by "inner interface confined deposition way" have high stability,,large drug encapsulation capacity and slow release of ability.?3?Based on the above work,chlorophyll/TiO₂/liposome composites were also prepared by "inner interface confined deposition way".According to the dissolution properties of the hydrophobic chlorophyll and titanium precursors in the hydrophobic region of the phospholipid bilayer,TBOT were encapsulated in the phospholipid bilayers and chlorophyll molecules were embedded in the lipid membrane while liposomal bilayer assemblies in the aqueous phase.The chlorophyll/TiO₂/liposome composites were prepared by exploiting interfacial sol-gel chemistry confined TBOT to the hydrophobic interior of the phospholipid bilayer.SEM,TEM,TGA,DLS and Surface tension meter were used to characterize the morphology,composition and performance of the prepared chlorophyll/TiO₂/liposome composites.The results showed that the samples remained well-dispersed,in a shape of spherical structure.Static fluorescence spectra monitoring results revealed that chlorophyll and titania were confined in the hydrophobic core of lipid bilayer and the feasibility of the inner interface confined deposition way was described.Electrochemical workstation results confirmed that chlorophyll/TiO₂/liposome composites can be used as the DSSC photo anode materials with photoelectric conversion properties.