Physical Properties and Stability of Soft Gelled Chitosan-Based Nanoparticles.

We addressed the role of the degree of acetylation (DA) and of Mw of chitosan (CS) on the physical characteristics and stability of soft nanoparticles obtained through either ionic cross-linking with sodium tripolyphosphate (TPP), or reverse emulsion/gelation. Each of these methods affords nanoparticles (NPs) or nanogels (NGs), respectively. The size of CS-TPP NPs comprising CS of high Mw (≈123-266 kDa) increases with DA (≈1.6%-56%), while it do not change for CS of low Mw (≈11-13 kDa); the zeta potential (ζ) decreases with DA regardless of Mw (ζ ≈+34.6 ± 2.6 to ≈+25.2 + 0.6 mV) and the NPs appear as spheres in transmission electron microscopy. Stability in various cell culture media (pH 7.4 at 37 °C) is greater for NPs made with CS of DA ≥ 27%. In turn, NGs exhibit larger sizes (520 ± 32 to 682 ± 27 nm) than do CS-TPP NPs, and can only be formed with CS of DA < 30%. The average diameter size for these NGs shows a monotonic increase with CS's Mw . The physical properties and stability of these systems in biological media depend mostly on the DA of CS and its influence on the balance between hydrophilic/hydrophobic interactions.