Direct encapsulation of proteins into calcium silicate microparticles by water/oil/water interfacial reaction method and their responsive release behaviors

The direct encapsulations of proteins such as lysozyme, bovine serum albumin (BSA) and ovalbumin into calcium silicate microparticles were examined by interfacial reaction method using water/oil/water emulsion (W/O/W emulsion), which was effective for the preparations of silica and calcium carbonate microcapsules encapsulating biomacromolecules. Those proteins added to the sodium silicate solution of the W/O/W emulsion were successfully encapsulated into the microparticles, which were ascertained by diffuse reflectance ultraviolet (UV) and infrared spectra. The encapsulation efficiency of the proteins depended on the molecular weight of proteins, which were also observable in the protein encapsulations into silica and calcium carbonate microcapsules. No discharge of encapsulated proteins by simple washing with deionized water indicated the secure packing of proteins into calcium silicate matrix. Ethylenediamine-N,N,N′,N′-tetraacetic acid, tetrasodium salt (EDTA·4Na) effectively extracted calcium ions from the microparticles to serve as a trigger for the release of proteins, indicating that the elimination of calcium ion initiated the discharge of encapsulated proteins. The ion exchange between calcium and sodium ions also achieved the release of proteins into aqueous solutions. The release rate of proteins such as lysozyme and BSA increased with the concentration of sodium chloride less than 1 M. In diluted solutions, potassium chloride accelerated the protein release more than sodium chloride. These characteristic release behaviors must be applied to drug delivery systems that respond to the concentration of alkaline ions in body fluid.