The aim of the present study was to develop zeta potential-changing polyphosphate nanoparticles (pp-NPs) in order to overcome the diffusion barrier of the mucus gel layer and to provide an enhanced cellular uptake. pp-NPs were obtained by in situ gelation between cationic polyethylene imine and anionic polyphosphate. The resulting pp-NPs were characterized with regard to size and zeta potential. Phosphate release studies were carried out by incubation of pp-NPs with isolated as well as cell-associated intestinal alkaline phosphatase (IAP) and quantified by malachite green assay. Correspondingly, change in the zeta potential was measured, and pp-NPs were analyzed by scanning electron microscopy studies. Mucus permeation studies were performed with porcine intestinal mucus via the transwell insert method and rotating tube method. Furthermore, cell viability and cellular uptake were investigated on Caco-2 cells. The resulting pp-NPs displayed a mean size of 269.16 ± 1.12 nm and a zeta potential between −9 and −10 mV in the characterization studies. Within 4 h, a remarkable amount of phosphate was released from pp-NPs incubated with isolated IAP as well as cell-associated IAP and zeta potential raised up from −9.14 ± 0.45 to −1.75 ± 0.46 mV. Compared with dephosphorylated polyphosphate nanoparticles (de-pp-NPs), a significantly enhanced mucus permeation of pp-NPs was observed. Moreover, pp-NPs did not exhibit cytotoxicity. Cellular uptake increased 2.6-fold by conversion of pp-NPs to de-pp-NPs following enzymatic cleavage. Taking the comparatively simple preparation method and the high mucus-permeating properties of pp-NPs and high cellular uptake properties of de-pp-NPs into account, these nanocarriers might be promising novel tools for mucosal drug delivery.

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