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.
Keywords: chitosan; ionotropic gelation; nanogels; nanoparticles; reverse emulsion.
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