Effect of drug molecular weight on niosomes size and encapsulation efficiency

Encapsulation into nanocarriers, such as niosomes, is a promising way to protect them from degradation, and allow controll and target delivery of bioactive compounds. For biotechnological applications, a tight control of particle size with acceptable encapsulation efficiencies (EE) is a technological challenge, especially for hydrophilic compounds due to its capability to diffuse across biological barriers. Niosomes formulated with mixture of surfactants represent promising nanocarriers due to the advantages of non-ionic surfactants, such as low cost, versatility and enhanced physico-chemical properties. In this work, the effect of both, composition of the hydrating solution and molecular weight of the loaded compound, on the particle size and EE of niosomes prepared by using the thin film hydration method was studied. Particularly, mili-Q water, glycerol solution and PEG-400 solution were tested for niosomes formulated with Span®80-Tween®80 with/without dodecanol as membrane stabilizer. It was found that particle size highly depends on hydration media composition and an interaction with compound MW could exist. Larger vesicles results in an increase in EE, which could be purely related with physical aspects such as vesicle loading volume capacity. The effect of hydration solution composition could be related with their ability to change the bilayer packing and physical properties, as observed by differential scanning calorimetry. Finally, it was possible to compare the suitability of dialysis and gel filtration as purification methods, demonstrating that gel filtration is not an adequate purification method when viscous solutions are used, since they could affect the particle vesicles retention and hence EE measurements would be misrepresentative.