Mucus-penetrating nanoparticles based on chitosan grafted with various non-ionic polymers: Synthesis, structural characterisation and diffusion studies.

Transmucosal administration offers numerous advantages for drug delivery as it usually helps to avoid first pass metabolism, provides rapid onset of action, and is a non-invasive route. Mucosal surfaces are covered by a viscoelastic mucus gel layer which acts as a protective barrier preventing the entrance of harmful substances into the human tissues. This function of mucus also inhibits the diffusion of drugs and nano-formulations and can result in a significant reduction of their efficacy. The design of mucus-penetrating nanoparticles can overcome the barrier function of mucus which may lead to better therapeutic outcomes. In this study, chitosan was chemically modified by grafting short chains of poly(ethylene glycol), poly(2-hydroxyethyl acrylate), poly(2-ethyl-2-oxazoline), or poly(N-vinyl pyrrolidone) and the resulting chitosan derivatives were used to prepare nanoparticles using an ionic gelation method with sodium tripolyphosphate. These nanoparticles were characterised using dynamic light scattering, transmission electron microscopy, small-angle neutron scattering and nanoparticle tracking analysis. Small-angle neutron scattering data revealed the presence of a large amount of water inside these nanoparticles and lack of a heterogeneous internal structure. The nanogel model with low crosslinking density is suggested as the most feasible model to describe the structure of these nanoparticles. The studies of the behaviour of these nanoparticles in bovine submaxillary mucin solutions and their penetration into sheep nasal mucosa indicated greater diffusivity of modified chitosan nanoparticles compared to unmodified chitosan nanoparticles with the best results achieved for the chitosan grafted with poly(N-vinyl pyrrolidone).