An investigation into the role of mucus thickness on mucoadhesion in the gastrointestinal tract of pig

Mucoadhesion in the gastrointestinal tract is a complex phenomenon and both formulation and physiological features need to be well understood and considered. Mucus thickness has been inferred to play a role in this process; however no definitive influence has been established. This study aimed to investigate the influence of mucus thickness on the mucoadhesion process, using a large animal (pig) as a model to closely resemble the human physiological features. The mucus thickness of different regions of the gastrointestinal tract of pig was fully measured by means of a histochemical method (hematoxilin/eosin) employing cryostat sections. Mucoadhesion was evaluated ex vivo on porcine mucosa by tensiometry using a polyacrylic acid polymer (Carbopol 974P NF) as a mucoadhesive model material, both in a dry and swollen state. Mucus was thickest in the stomach (body 67.9 +/- 54.7 mu m) and mucus thickness increased from proximal to distal segments in both the small intestine (duodenum 25.9 +/- 11.8 mu m, ileum 31.0 +/- 15.7 mu m) and large intestine (caecum 19.4 +/- 8.7 mu m, ascending colon 31.9 +/- 17.2 mu m, descending colon 35.1 +/- 16.0 mu m and rectum 40.8 +/- 12.5 mu m). Swollen polymer exhibited lower mucoadhesion than the dry form in all sections analysed. Mucus thickness plays a role on the mucoadhesion, as thicker mucus provides deeper polymer chain diffusion and entanglements; however, other factors are also involved in this complex process. (c) 2010 Elsevier B.V. All rights reserved.