The storage stability of chitosan/tripolyphosphate nanoparticles in a phosphate buffer

The objective of this study is to investigate the effect of initial size and pH of the solution on the changes in size of chitosan/tripolyphosphate (CS/TPP) nanoparticles stored in a phosphate buffer at 25 °C. The size decreased with increasing pH of the storage phosphate buffer. The initial sizes of the nanoparticles themselves also affected storage stability—the larger ones decreased in size, however the smaller ones increased their size in a phosphate buffer with a pH of 7.5 at 25 °C for 10 days due to protonation or deprotonation effects on the chitosan molecules. The changes of nanoparticle sizes are classified into instantaneous, aging, and swelling/aggregation stages over the storage time of 97 days. Mechanisms for these size changes are discussed.