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Background/Objectives: Understanding the interactions between nanoparticles and mucosal tissues is crucial for the development of advanced drug delivery systems, as the diffusion behavior of nanoparticles through mucus is strongly influenced by their size and surface properties, and the viscoelastic nature of the hydrogel matrix. In this study, we investigated the impact of nanoparticle size, surface charge, and hydrogel crosslinking density on nanoparticle diffusion in a mucus model in vitro. Method: Citrate-stabilized and PEGylated 30 and 100 nm gold nanoparticles were used as a model of nanoparticle and their diffusion through mucus-mimicking mucin-based hydrogels of two different crosslinking densities was assessed. Results: Citrate-stabilized 30 nm nanoparticles demonstrated greater diffusion in hydrogels mimicking native mucus compared to more densely crosslinked ones, reaching approximately 50.3 ± 0.2% diffusion within the first 5 min of the assay. This size-dependent effect was not observed for the 100 nm citrate-stabilized nanoparticles, which showed limited diffusion in both hydrogel types. To confer different surface charge, gold nanoparticles were functionalized by the conjugation of poly(ethylene glycol) (PEG) derivatives of identical molecular weight with different terminal moieties (neutral, and positively and negatively charged) to modulate the surface charge and assess their interaction with the negatively charged mucin matrix. PEGylated particles exhibited significantly greater mobility than their citrate-stabilized counterparts, regardless of size or hydrogel density owing to the muco-penetration effect of PEG. Among PEGylated particles, the neutral and negatively charged 30 nm variants demonstrated higher diffusion than the positively charged ones due to weaker interactions with the negatively charged mucin hydrogel. For the 100 nm particles, the neutral PEGylated nanoparticles exhibited greater diffusion than their positively charged counterparts. Conclusions: Overall findings could provide valuable insights into the more rational design of nanoparticle-based drug delivery systems targeting mucosal tissues.
Porfiryeva et al. (Sun,) studied this question.