Ionically crosslinked chitosan micro- and nanoparticles attract keen interest as potential drug carriers, and are typically prepared by crosslinking chitosan with tripolyphosphate (TPP). To broaden the range of particle characteristics that can be achieved through ionic crosslinking, we have examined the formation and properties of particles prepared using pyrophosphate (PPi) instead of TPP. Light scattering analysis of chitosan/PPi mixtures revealed that, to form micro- and nanoparticles, the PPi:chitosan charge ratio must be at least near-stoichiometric. This formation behavior differs significantly from that of chitosan/TPP particles, which begin forming even at very low TPP concentrations. Moreover, unlike the chitosan/TPP micro- and nanoparticles, which coagulate and precipitate when TPP is in excess, chitosan/PPi particles remain colloidally-stable at both near-stoichiometric and high PPi:chitosan charge ratios. Once the PPi concentration is high enough for particles to fully form, their size distributions are insensitive to further PPi addition; the average particle volume, however, scales roughly linearly with the chitosan concentration used in their preparation. Furthermore, we have investigated the dissolution of chitosan/PPi micro- and nanoparticles by systematically diluting the particles while keeping the overall chitosan concentration constant (i.e., lowering the PPi:chitosan charge ratio). This revealed hysteresis in the particle formation/dissolution cycle, where portions of the chitosan/PPi particles remain stably intact even when the PPi concentrations are below those required for particle formation. This irreversible behavior likely reflects the cooperativity of chitosan/PPi binding and was qualitatively modeled using the Bragg-Williams theory.

Formation and properties of chitosan/pyrophosphate micro- and nanoparticles

246th National Meeting (2013)

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