It is believed that mucoadhesive surface properties on particles delivered to the gastrointestinal (GI) tract improve oral absorption or local targeting of various difficult-to-deliver drug classes. To test the effect of nanoparticle mucoadhesion on distribution of nanoparticles in the GI tract, we orally and rectally administered nano- and microparticles that we confirmed possessed surfaces that were either strongly mucoadhesive or non-mucoadhesive. We found that mucoadhesive particles (MAP) aggregated in mucus in the center of the GI lumen, far away from the absorptive epithelium, both in healthy mice and in a mouse model of ulcerative colitis (UC). In striking contrast, water absorption by the GI tract rapidly and uniformly transported non-mucoadhesive mucus-penetrating particles (MPP) to epithelial surfaces, including reaching the surfaces between villi in the small intestine. When using high gavage fluid volumes or injection into ligated intestinal loops, common methods for assessing oral drug and nanoparticle absorption, we found that both MAP and MPP became well-distributed throughout the intestine, indicating that the barrier properties of GI mucus were compromised. In the mouse colorectum, MPP penetrated into mucus in the deeply in-folded surfaces to evenly coat the entire epithelial surface. Moreover, in a mouse model of UC, MPP were transported preferentially into the disrupted, ulcerated tissue. Our results suggest that delivering drugs in non-mucoadhesive MPP is likely to provide enhanced particle distribution, and thus drug delivery, in the GI tract, including to ulcerated tissues.

Aims We previously demonstrated that nanoparticles (NPs) densely coated with low molecular weight (MW, 2-5 kDa) polyethylene glycol (PEG) rapidly diffused through various mucus secretions, whereas NPs coated with 10 kDa PEG were mucoadhesive due to presumed polymer interpenetration and entanglement with mucins. Here, we demonstrate that PEG with MW as high as 40 kDa can be used as a mucoinert NP surface coating if sufficient surface density is achieved. Materials and Methods We compared two sets of reaction conditions for coating model polystyrene NPs with 10 kDa PEG and used the optimized reaction conditions to coat various sized NPs with PEG with MW as high as 40 kDa. We then characterized NP transport in human cervicovaginal mucus (CVM) ex vivo. We further administered PEG-coated NPs to the mouse cervicovaginal tract and colorectum to assess mucosal distribution in vivo. Results and Conclusions We demonstrate here that PEG with MW as high as 40 kDa can be densely grafted to the surface of NP to prevent interactions with mucus. NP coated with 10-40 kDa PEG rapidly diffused through human CVM ex vivo, and uniformly lined the mouse colorectal and vaginal epithelium in vivo. This not only suggests that the density of PEG on the NP surface, and thus the conformation, is key for preventing interactions with mucus, but also redefines and broadens the design criteria for drug and gene delivery systems for improved mucosal delivery.