Nanoparticles (NPs) have shown their efficiency in increasing the oral bioavailability of macromolecular drugs, among them heparin. However, mechanisms of absorption are still unclear. Here, heparin-loaded NPs were prepared from different polymers (Eudragit ® RS, poly(lactic-co-glycolic acid) (PLGA), and their respective mixtures) and analysed for their mucoadhesive properties using a resonant mirror system. Subsequent binding and drug transport studies of the free heparin and heparin-loaded NPs were carried out on Caco-2 cells. Cationic NPs were found to be mucoadhesive, while pure drug and polyester NPs were not. The adsorption of anionic heparin masked the positive surface charge of the particles, thus partially diminishing the adhesiveness to mucin. Increased binding to Caco-2 cells was found for all NP formulation, with RS/PLGA NPs showing maximum binding. However, the transport of heparin was the same for the RS/PLGA NPs and the PLGA NPs and slightly higher than for the free drug. In all cases, no NP transport across the cell layer was observed. When Caco-2 cells were coated with an additional mucin layer, cell binding of RS NPs and RS/PLGA NPs was further increased. Transport across Caco-2 cells demonstrated similar tendencies to results obtained without mucin. In contrast, cationic NPs led to higher heparin transport in the presence of mucin. The mechanism of drug absorption associated with RS NPs was concluded to be independent of typical transcellular NP transport.

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