Novel pH-sensitive microgels prepared using salt bridge

pH-sensitive microgels were prepared by crosslinking carboxymethylcellulose (CMC) and polymeric β-cyclodextrin (PβCD) using (2-hydroxyethyl)trimethylammonium chloride benzoate (TMACB) as a crosslinker. PβCD was prepared by reacting epichlorohydrin and β-CD in an aqueous phase (NaOH solution, 30% (w/w)). TMACB will interact with CMC by an electrostatic interaction and it will also interact with PβCD by a hydrophobic interaction. The size of microgel was tens of nanometers to several micrometers. The degree of calcein release in 24 h from the microgels was as low as 23% at pH 8.0. The degree of release at pH 3.0 was almost 100%. The carboxyl groups of CMC will lose their charge in an acidic condition and they would lose their ability to form salt bridges with TMACB, leading to the disintegration of microgels. The degree of release at pH 11, about 47%, was less than the value at pH 3.0 but it was greater than the value at pH 8.0. The CMC will be strongly electrostatically charged in the alkali condition, so the microgels would swell due to the electrostatic repulsion among CMC molecules, which could promote the release of their contents.