Statistical optimization of chitosan-based synthesis strategies to generate albumin nanoparticles

Albumin-based nanoparticles (NPs) are typically synthesized by harsh conditions-based methods that limit their application in clinics and can seriously damage the entrapped drug and even their base material. Despite the potential of the use of chitosan (CS) as stabilizing agent by adapting the ionic gelation method or by adding CS as a coating to albumin NPs generated by desolvation, the influential factors of these methods have not yet been studied. In this article, these synthesis approaches have been optimized by a 2-step DoE-based methodology (a screening process with fractional designs plus a response surface methodology using central composite designs). The application of the ion gelation method to produce albumin-based NPs generates sizes from 66 to 1017 nm, PDI (polydispersity index) values of 0.3-0.6 and surface charges (ZP) from neutral to positive (> 20 mV). The fitted models of the responses depend on four factors (albumin and CS concentration, CS pH and CS:albumin mass ratio). On the other hand, the modification of the desolvation method using CS as a stabilizing coating generates 37-1305 nm NPs, with PDI between 0.4 and 0.7 and highly positive ZP (20-40 mV). In this case, the approximate models for the responses depend on four main effects (albumin and CS concentration, pH of CS and albumin:EtOH volume ratio). Furthermore, in this work the best combinations of factors and levels that allow minimizing PDI and obtaining the minimum and maximum expected values for mean size and ZP of NPs were determined for both synthesis methods. Focusing on the minimum possible PDI, the predicted values for the ion gelation- and desolvation-based methods are 0.363 and 0.341, respectively, which are achieved with values of [BSA] (mg/ml), [CS] (mg/ml), CS pH and CS:BSA or BSA:EtOH ratios (mL:mL) of {2.3,1.4,2.2,1:7.3} and {10,0.5,1.8,1:1}, respectively. These optimized conditions yield acceptable size and ZP values for the ion gelation-based (27.7 nm; 16.4 mV) and optimal values for the desolvation-based (146.2 nm; 29.5 mV).