Mesoporous silica particles as potential carriers for protein drug delivery: protein immobilization and the effect of displacer on γ-globulin release

The adsorption of gamma-globulin was evaluated with experiments with silica particles marketed as Syloid AL1-FP (S-AL), XDP-3150 (S-XDP), and 244FP (S-FP). The influence of pH, pore sizes, and degree of surface porosity on the extent of gamma-globulin immobilization was examined. Protein adsorption on these particles was largely related to their surface porosity and pore sizes. The adsorption capacity was established to be greater with mesoporous S-FP and S-XDP particles at 474 and 377 mg/g, respectively, when compared to significantly low-porosity S-AL (16 mg/g). Additionally, gamma-globulin immobilization was favored at pH closer to iso-electric point. A key aim of this work was to better understand and improve the limited reversibility of protein adsorption. Protein desorption was found to be lower in simulated intestinal fluid (SIF) in comparison to pH 7.4 phosphate buffer (PB). The use of displacer molecules (sodium dodecyl sulfate [SDS]/Tween 80/Pluronic F127 [PF127]) promoted protein desorption from the adsorbent surface by the exchange mechanism. The PF127 provided substantial release in both studied condition but the highest release of 83% of gamma-globulin from S-XDP was obtained with tween 80 in PB. The released protein was analyzed with circular dichroism (CD) spectroscopy which indicated that the secondary structure of desorbed gamma-globulin was dependent on the pH and displacer molecule. The conformation largely remained unchanged when desorption was carried out in SIF but changed markedly in PB specially in the presence of SDS.