Chitosan-based nanocapsules: physical characterization, stability in biological media and capsaicin encapsulation

Abstract

This study addresses the effect of the degree of N-acetylation (DA ~1.4–56 %) of chitosan (CS) of low and medium molecular weight (M w ~ 9.5–13.2 and ~122–266 kDa, respectively) on the biophysical properties, colloidal stability and encapsulation efficiency of capsaicin (a lipophilic drug currently used in pain therapy) of CS-based nanocapsules (NCs). The average diameter of the NCs varied within the range of ~150–200 nm, but it was slightly higher for NCs comprising high M w CS than for those with low M w CS. The zeta potential (ζ) was highly positive and clearly dependent on the M w of CS, exhibiting a monotonic decreasing trend concomitant with the increase in DA. Both results suggest that M w and DA of CS have an effect on the disposition of the polysaccharide onto the phospholipidic surface. Synchrotron SAXS studies revealed a monotonic increase in Bragg interplanar distances (from ~55 up to ~67 A) as a function of the DA, a finding that agrees with previous results that are consistent with the capacity of hydrophobic domains to disturb the crystalline state of gelled phospholipidic membranes. Colloidal stability studies carried out in cell-culture biological media revealed the determinant role of hydration forces, a short-range repulsive interaction, on the stability of the NCs. Finally, M w and DA of CS both influenced the encapsulation efficiency of capsaicin, thus showing the effect of the harnessed NCs shell on its capacity to encapsulate lipophilic drugs.