Abstract: In some aspects, the present disclosure pertains to tissue bulking compositions that comprise: (a) solid particles comprising a pH-sensitive polymer that has a pH-dependent solubility such that the solid particles dissolve upon an increase or decrease in pH, (b) a crosslinking agent for the pH-sensitive polymer and (c) a pH modifying agent that generates acid or base in vivo, wherein when the tissue bulking composition comprises solid particles that dissolve upon a decrease in pH, the pH modifying agent generates acid in vivo and wherein when the tissue bulking composition comprises solid particles that dissolve upon an increase in pH, the pH modifying agent generates base in vivo. Other aspects of the present disclosure pertain to kits that comprise such compositions, to methods of forming injectable dispersions that comprise such compositions and to methods of treatment comprising injecting injectable dispersions that comprise such compositions into a subject.