Surface functionalization of porous glass networks: Effects on bovine serum albumin and porcine insulin immobilization

Biomolecules can be immobilized in many different ways. They can also be entrapped or tightly adsorbed within porous gels, clays, membranes, resins, and several other materials, but it is crucial that they retain their active conformation after the incorporation procedure. Porous gel matrixes with functionalized surfaces offer unlimited possibilities to control the protein-substrate interaction behavior. In the present work, we have studied the adsorption and the relative stability of bovine serum albumin (BSA) and porcine insulin (PI) incorporated in gels of SiO2 glass matrixes. The porous gel matrixes were obtained using tetramethoxysilane (TMOS)/methanol and functionalized with (3-mercaptopropyl)trimethoxysilane and (3-aminopropyl)triethoxysilane. The relative adsorption kinetics and stability of BSA and PI incorporated in glass networks were evaluated by immersion in phosphate buffer saline (PBS) and alkaline elution media for different periods of time. The kinetics of protein release from the gel matrix was monitored by UV-visible spectroscopy. A significantly larger PI release was observed compared to BSA in PBS solutions. We believe this is mainly associated with the difference on protein interactions with the modified surface, according to the characterization results of porosity, surface area, and contact angle of different functionalized gel matrixes. We could not observe any evidence of denaturation with either proteins after their desorption from gel matrixes using the ultraviolet spectroscopy technique. These results have also been confirmed with the strong bioactivity response from "in vivo" tests conducted in rats, where porous gels with PI incorporated were implanted, showing that released proteins retained their native conformation.