Investigation On The Stability Of Drug-Loaded Polymersomes And Its Influencing Factors

Polymersomes are a class of hollow spheres formed by self-assembly of amphiphilic block copolymers in solution with size ranging from tens of nanometers to tens of microns.Due to their unique structure and functional features,they have garnered great interest in the fields of drug delivery,medical diagnosis,food industry and cosmetics.In the application,the stability of polymersomes is a key parameter that determines the effect of their practical application.Previous literature mostly focused on studying the stability of polymersomes under routine laboratory conditions,however,ignored the influence of different storage methods during practical applications.Based on this,we investigated various factors in the process of film rehydration used to prepare polymersomes and optimized the technical scheme to obtain narrow-distributed nanopolymersomes.Furthermore,considering the practical application scenarios,long-term stability of polymersomes in different forms(liquid,lyophilized products)and under different storage conditions was studied by exploring morphology,diameter and drug loading content of them.The main research contents as follows:(1)Study on the factors affecting the preparation of PEG-b-PLA polymersomes by film rehydration.We prepared polymersomes by film rehydration using amphiphilic polyethylene glycol-block-polylactic acid(PEG-b-PLA)copolymer,and studied various influencing factors on the self-assembly of PEG-b-PLA.The challenge of the self-assembly of PEG-b-PLA into polymersomes was investigated by exploring the block ratio and molecular weight of the block copolymer,types of film-forming organic solvents,and rehydration conditions.Finally,the optimal hydration conditions were preferably obtained and a convenient,stable and efficient preparation method for narrow-distributed polymersomes was developed,which lays the foundation for the practical application of polymersomes.(2)Study on the stability of PEG-b-PLA polymersomes.In order to meet the practical needs of long-term storage of polymersomes in the form of liquid and lyophilized products,stability of PEG-b-PLA polymersomes under various storage conditions was studied and the feasibility of long-term storage of lyophilized polymersomes was further investigated by exploring the effect of lyophilization and reconstitution on morphology,structure and diameter of polymersomes.The results show that storing at low temperature are conducive to long-term storage of polymersomes,repeated freeze-thawing cycles leads more uniform diameter of polymersomes.Finally,the lyophilized polymersomes that can be efficiently reconstituted was obtained by using lyoprotectants.(3)Study on the preparation and influencing factors of lyophilized drug-loaded PEG-b-PLA polymersomes.Firstly,three kinds of drug-loaded polymersomes including hydrophilic doxorubicin,hydrophobic nile red and biomacromolecular hemoglobin were prepared by film rehydration and solvent exchanging methods.Then,we used organic solvent to dissolve polymersomes and release encapsulated drug in attempt to calculate drug loading efficiency accurately.Finally,different freeze-dried drug-loaded polymersomes were prepared by adding various lyoprotectants,and then the changes of various parameters(morphology,diameter and drug loading content)of them after reconstitution were evaluated and analyzed.It is found that using hydroxypropyl-?-cyclodextrin as lyoprotectant can maintain the morphology,diameter and drug loading content of freeze-dried drug-loaded polymersomes after lyophilization and reconstitution.In this study,we obtained the methods for the stable preparation and storage of PEG₁₁₃-b-PLA₁₆₇ polymersomes and provided a new way of long-term storage of drug-loaded polymerspmes.It provided theoretical and technical support for the clinical application of polymersomes.