Synthesis of silica-alginate nanoparticles and their potential application as pH-responsive drug carriers.

Composite silica-alginate nanoparticles were prepared via silica sol-gel technique using a water-in-oil microemulsion system. In our system, cyclohexane served as the bulk oil phase into which aqueous solutions of sodium alginate were dispersed as droplets that confined nanoparticle formation after addition of tetraethylorthosilicate (TEOS). Our studies showed that much of the particle growth is completed within the first 24 hours and reaction times up to 120 hours only resulted in an additional 5% increase in particle diameter. Average particle size was found to decrease with increasing water-to-surfactant molar ratio (R) and with increasing cocentration of alginate in the aqueous phase. The potential for drug loading during particle formation was demonstrated using rhodamine B as a model drug. In vitro release studies showed that particles incubated in pH 2.5 phosphate buffer released only about 7% of the drug load in 27 days, while 42% was released in pH 7.5 phosphate buffer over the same period. Analysis of the release profile suggested that rhodamine B was homogeneously distributed throughout the particle and that the drug diffusivity was 40-fold greater in pH 7.5 buffer compared to that at pH 2.5. These results suggest that silica-alginate nanoparticles could be used as a pH-responsive drug carrier for controlled drug release.

Immobilized thermolysin for highly efficient production of low-molecular-weight protamine--an attractive cell-penetrating peptide for macromolecular drug delivery applications.

Macromolecules present a remarkable potential as future therapeutics. However, their translation into clinical practice has been hampered by an inherently low bioavailability. Cell-penetrating peptides (CPP) have been recently shown to significantly improve on the bioavailability of macromolecules. Yet, the high cost associated with development and production of these peptides is a major factor hindering their rapid deployment beyond the laboratory. Here, we describe a facile and robust methodology for efficient and large-scale production of low-molecular-weight protamine-a potent CPP of great clinical potential. Our methodology is based on the immobilization of thermolysin, an enzyme catalyzing digestion of native protamine, on chemically surface-modified gels produced by silica sol-gel chemistry. Thermolysin was immobilized at extremely high matrix loading of 733 mg/g matrix and exhibited good thermal and pH stability, indicating robustness with respect to processing conditions. The mechanical properties of the silica matrix further allowed utilization of the immobilized thermolysin in both batch and packed-bed reactor systems to produce the LMWP peptide in high yields. Results presented here are of high significance as this efficient and cost-effective production of high purity LMWP could enable clinical translation of many potential macromolecular drugs.