Dissociation of chitosan/tripolyphosphate complexes into separate components upon pH elevation.

Ionically crosslinked chitosan/tripolyphosphate (Chit/TPP) particles have been widely tested in biomedical applications, particularly as potential carriers for controlled drug delivery. Since Chit/TPP particles are typically prepared under acidic conditions, their application in physiological environment and correct evaluation of biological data ultimately require knowledge on their physico-chemical properties and overall behaviour at physiological pH, as they may differ substantially from those exhibited after preparation. In this study, Chit/TPP complexes prepared at pH 4.43 were exposed to a physiological and slightly alkaline pH of 7.42 and 8.90, respectively, and analysed by inductively coupled plasma mass spectrometry and Fourier transform infrared spectroscopy with attenuated total reflectance for TPP content. In parallel, osmolarity measurements as well as theoretical calculations were used to interpret the composition and behaviour of Chit/TPP complexes upon pH elevation. Exposure of Chit/TPP complexes to a pH in the physiological range resulted in their practically complete dissociation into free chitosan chains. This leads to a significant consequence that Chit/TPP particles prepared at acidic pH do not exist under physiological conditions.