Structural Modulation Of Silk Fibroin Microspheres For Controlled Drug Loading And Release In Gastrointestinal Fluids

With the development of basic biological sciences,protein drugs are widely used in disease prevention,diagnosis and treatment due to their convenient preparation methods,strong specificity,high sensitivity and good biocompatibility.However,protein drugs have problems like poor stability,easy acidolysis and enzymolysis,and short half-life in the body,which affect their clinical application.The use of polymer materials to embed and protect protein drugs is an effective means to solve the above problems.Silk fibroin is a natural polymer material extracted from silkworm cocoons.The silk fibroin carrier with high embedding rate can be prepared by gentle freeze-drying or natural air-drying.The nanocrystals formed in the carrier can be used for active substances such as protein drugs.The structure and performance of silk fibroin are controllable,resulting in controlled release of embedded drug molecules.In this study,rhodamine B and horseradish peroxidase(HRP)were used as model drugs,and the secondary structure of silk fibroin was modulated through blending silk with hydrophilic substances while preparing the carrier materials.The cross-sectional morphology and degradation properties of the material(membrane)were characterized,and the release of these two model drugs in vitro were determined.It was found that the silk fibroin film with addition of polysodium glutamate(PGA)showed porous cross-section,low β-sheet content and better degradation performance,facilitating the release of rhodamine B and HRP,proving that the medium content of silk β-sheets,highly porous structure and high degradability promoted drug release within a desired time frame(30 h).Silk fibroin microspheres have large specific surface area,good fluidity,and flexible administration routes,and are widely used in drug delivery systems.The soluble silk fibroin microspheres prepared by the freeze-drying method can achieve water insolubility after mild water vapor treatment,which,however,might cause non-specific binding and incomplete release of the protein drug from the microspheres.In order to improve the oral availability of the microparticulate drugs,it is necessary to extend the residence time of the silk fibroin microsphere carrier in the gastrointestinal juice environment as much as possible,and delay the release of protein drugs in the gastric fluid.Four kinds of silk fibroin microspheres added with different hydrophilic agents were prepared,and pure silk fibroin microspheres and PGA-silk fibroin microspheres with relatively low β-sheet content,higher porosity and higher degradation performance were screened out.Using horseradish peroxidase(HRP)and insulin(INS)as model drugs,studies of drug stability and in vitro release were carried out.It was found that the residual rates of drug activity of the spheres incubated in artificial gastric fluid for 2 hours were 23.1±0.7%and 48.5±3.4%,which were much higher than those in the free drug(2.2±0.3%).The cumulative release percentages of HRP and INS in the artificial gastric-intestinal fluid of PGA-silk fibroin microspheres were 2.3 times and 2.5 times of the cumulative release percentages of HRP and INS in pure silk fibroin microspheres,respectively.In summary,the silk fibroin microspheres with high drug embedding rate are prepared by freeze-drying method,and the stability of the model protein drug in the silk fibroin microspheres can be improved by the mild water vapor treatment.The introduction of PGA can change the secondary structure,cross-sectional pores,and degradation properties of silk fibroin microspheres to promote the release of protein drugs,laying the foundation for the oral delivery of silk fibroin microspheres.