pH-responsive controlled release characteristics of solutes with different molecular weights diffusing across membranes of Ca-alginate/protamine/silica hybrid capsules.

Ca-alginate/protamine/silica (APSi) hybrid capsule membranes with pH-responsive controlled release characteristics are successfully prepared by combining co-extrusion minifludics, adsorption and biosilicification under different pH conditions from 3 to 7. The microstructures of the prepared capsule membranes are characterized by optical photography, CLSM and SEM. The pH-responsive permeability of APSi hybrid capsule membranes is controlled by the electrostatic interactions between Ca-alginate networks and protamine molecules. Four kinds of solute molecules with different molecular weights including methylene blue, VB 12 , 4 kDa and 10 kDa FITC-dextran molecules are selected as solute molecules to comparatively study the diffusional permeability characteristics of solutes across APSi hybrid capsule membranes. The results show that, for the solutes with suitable molecule sizes such as VB 12 and 4 kDa FITC-dextran, the diffusional permeabilities across the capsule membranes at pH 4 are lower than those at pH 5; however, for the solutes with too small molecule size such as methylene blue or too large molecule size such as 10 kDa FITC-dextran, the diffusional permeabilities across the capsule membranes at pH 4 are very close to those at pH 5. The results in this study provide valuable guidance for fabrication and application of APSi capsule membranes in the various fields including controlled release of drugs and immobilization of enzymes and so on. [ABSTRACT FROM AUTHOR]