pH-Responsive Cellulose-Based Microspheres Designed as an Effective Oral Delivery System for Insulin.

Functional modified cellulose microsphere (CMs) materials exhibit great application potential in drug various fields. Here, we designed pH-responsive carboxylated cellulose microspheres (CCMs) by the citric/hydrochloric acid hydrolysis method to enhance oral bioavailability of insulin by a green route. The CMs were high purity cellulose that dissolved and regenerated from a green solvent by the green sol-gel method. The prepared microspheres were characterized by spectroscopic techniques, such as field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectrum (FT-IR), X-ray diffraction (XPS), etc. The spherical porous structure and carboxylation of cellulose were confirmed by FESEM and FT-IR, respectively. Insulin was loaded into the CCMs by electrostatic interactions, and the insulin release was controlled through ionization of carboxyl groups and proton balance. In vitro insulin release profiles demonstrated the suppression of insulin release in artificial gastric fluid (AGF), while a significant increase at artificial intestinal fluid (AIF) was observed. The insulin release profile was fitted in Korsmeyer-Peppas kinetic model, and insulin release was governed by the Fickian diffusion mechanism. The stability of the secondary structure of insulin was studied by dichroism circular. Excellent biocompatibility and no cytotoxicity of designed CCMs cast them as a potential oral insulin carrier.