Preparation Of PH-responsive Mesoporous Silica For Controlled Release Of Insulin Complex

Diabetes mellitus is a chronic metabolic disease that currently affects more than 530million people worldwide.The treatment of type Ⅰ diabetes or advanced type Ⅱ diabetes often relies on subcutaneous insulin injections,and long-term injections are associated with various side effects,resulting in poor patient compliance.Therefore,there is an urgent need to develop non-invasive insulin delivery methods,and oral administration is the most widely used modality because of its painlessness and convenience.Currently,there are no commercial products for oral insulin preparations,mainly due to the presence of barriers such as degradation of gastric proteases,poor intestinal mucus layer and membrane permeability,which seriously hinder the oral absorption efficiency of insulin.In this paper,we firstly prepare a complex of insulin and permeation enhancer,and then combine pH-stimulating responsive polymer with mesoporous silica as an oral delivery vehicle,and investigate the preparation process of pH-responsive mesoporous silica and in vitro release performance on insulin complex.（1）In response to the barrier of poor intestinal fluid layer and membrane permeability,permeation enhancers（PEs）can transiently open tight intercellular junctions and promote cellular bypass absorption of drugs.In this chapter,insulin-sodium decanoate complexes were prepared by hydrophobic ion-pairing method to increase the permeability of insulin.To improve the complexation rate of insulin with sodium decanoate,the pH of sodium decanoate solution,molar ratio of sodium decanoate to insulin,reaction time and reaction temperature were investigated to optimize the preparation process of insulin-sodium decanoate complexes.The experimental results showed that when sodium decanoate:insulin=6:1（molar ratio）,sodium decanoate solution was slowly added dropwise to insulin solution and stirred for 1h at 25℃,the maximum complexation rate of insulin and sodium decanoate could reach 92.5±1.4%.The insulin-sodium decanoate complex(INS-C₁₀)was successfully produced by FT-IR,DSC,XRD and Zeta characterization analysis,and its lipid solubility was improved as determined by the apparent oil-water partition coefficient,and INS-C₁₀was almost insoluble in simulated gastric fluid,while completely soluble in simulated intestinal fluid.The results of circular dichroism（CD）analysis showed that INS-C₁₀ still maintained the secondary structure of the protein and was biologically active.（2）Mesoporous silica nanoparticles（MSN）are widely used as drug carriers because of their safety and non-toxicity,orderly adjustable pore size and easy surface modification.In this thesis,a pH-responsive mesoporous silica is designed and prepared,and an amino-modified mesoporous silica needs to be prepared first.In this chapter,based on the classical SBA-15 synthesis method,a positively charged amino-modified mesoporous silica is prepared by Post-synthesis（PS）and One-pot synthesis（OPS）methods（NH₂-SBA-15）and investigated the effect of surface charge of NH₂-SBA-15 on insulin loading and in vitro release.The experimental results showed that the prepared NH₂-SBA-15（PS）loaded insulin at pH=6 with higher encapsulation rate（90.3%）and drug loading（20.5%）with zeta potential（24.3±2.3 mV）.However,the cumulative release of drug-loaded samples（INS@NH₂-SBA-15）in simulated gastric fluid（SGF,pH=1.2）and simulated intestinal fluid（SIF,pH=7.4）was 61.5%and 46.1%,with incomplete drug release and no pH-responsive release.（3）To overcome the incomplete release of INS@NH₂-SBA-15 in a simulated in vitro environment and the lack of pH-responsive release,a pH-responsive mesoporous silica loaded insulin-sodium decanoate complex(INS-C₁₀@PAA/SBA-15)was designed and prepared in this chapter.The pH-stimulating responsive polymer,polyacrylic acid（PAA）,was firstly used to further chemically modify NH₂-SBA-15（PS）,and the resulting PAA/SBA-15 was loaded with INS-C₁₀.In order to improve the encapsulation efficiency and loading capacity of INS-C₁₀ by PAA/SBA-15,the drug loading capacity of PAA/SBA-15 loaded with INS-C₁₀ was increased to 21.3±1.5%by the solvent self-diffusion method（repeated three times）.The cumulative release of the drug-loaded sample(INS-C₁₀@PAA/SBA-15)was reduced to 22.7%in SGF,while the cumulative release in SIF was increased to 81.3%with significant pH-responsive release and greatly increased in SIF.The cytotoxicity of PAA/SBA-15 drug loading and blank carrier was tested by CCK-8 method.The results showed that the carrier had a cell survival rate of more than 90%and had good biocompatibility.It is expected to be used for oral insulin administration.