Release Mechanisms and Properties of pH-responsive Drug Nanocarriers

pH-responsive drug nanocarriers are a kind of important multifunctional nanocarriers due to their intelligent properties of acid sensitive or alkali sensitive release, and have received extensive attention from researchers. Especially, acid sensitive nanocarriers can be applied for controlled release at weak acid microenvironment of tumor, with play an active role at some biomedicine application such as targeted delivery of drugs and targeted therapy for cancer. In this paper, the typical fabrication methods for pH-responsive drug nanocarriers in recent years have been summarized, and the pH-responsive drug release mechanisms triggered by three ways have been systematically introduced. Firstly, pH-responsive mechanism triggered by covalent bond, in which imine bond, acetal bond, ester bond, coordination bond and others covalent bond can be used individually as pH initiator. Secondly, pH-responsive mechanisms triggered by intermolecular forces, in which both electrostatic interaction and hydrogen bond are applied for pH-responsive release drug. Thirdly, pH-responsive mechanism triggered by physical structure of nanocarries, in which both polymer swelling at diffirent pH values and calcium phosphate dissolving in the acid environment can result in controlled drug release. The loading properties, release properties in vitro, cytotoxicity in vitro, anticancer properties in vivo and distribution properties in vivo of pH-responsive drug nanocarriers are also expounded. Various experimental parameters of pH-responsive drug nanocarriers have been enumerated in detail, which provide the performance and methodological references for the in-depth studies of pH-responsive nanocarries.