pH-sensitive release of insulin-loaded mesoporous silica particles and its coordination mechanism

In this work, we investigated the feasibility of employing metal ion that coordinated with amino group grafted mesoporous silica as a pH-sensitive release carrier of insulin. Mesoporous silica particles were firstly grafted with amino groups. After coordination of metal ions onto the surface of mesoporous pore, insulin was loaded onto mesoporous silica particles through coordination bonds with metal ions. Insulin-loaded mesoporous silica particle with an acid sensitivity between the pH range of physiological environment (pH 7.4) and diabetic acidosis (pH 7.0) and with an insulin encapsulation rate of 74.50% was identified by investigating the influence factors of pH response value. The morphology of particles was confirmed by different analytical methods, indicating that insulin-loaded mesoporous silica particles maintained the rod-like and orderly hexagonal phase mesoporous structure. The coordination mechanism results showed that half of the amino groups on the carrier were coordinated with Cu²⁺, and insulin was successfully coordinated with Cu²⁺ without any damage on the secondary structure. The amount of insulin coordination with Cu²⁺ was positively correlated with the pH of the reaction solution. The cytotoxicity result shows that SBA₁₅-NH₂-Cu²⁺-Ins was biocompatible with cells in the concentration ranging from 25 to 100 μg·mL^-1. In vivo study preformed on rats showed that the insulin-loaded particles elicited a period hypoglycemic response. Furthermore, fluorescence and UV methods revealed that insulin-loaded mesoporous silica particles had no significant effect on the secondary structure of serum albumin.