Temperature and pH dual responsive 2-(dimethylamino)ethanethiol modified starch derivatives via a thiol-yne reaction for drug delivery

In this study, a novel type of temperature/pH dual responsive polymer PyHES- DMAET ((2-hydroxy-3-(2-propynyloxy) propyl hydroxyethyl starch (PyHES))-2-(dimethylamino) ethanethiol (DMAET)) was synthesized. First, the temperature-responsive polymer PyHES was prepared via hydrophobic modification of hydroxyl groups in hydroxyethyl starch (HES) with propynylglycidyl ether (PGE) subsequently; pH-responsive tertiary amine group was connected to the propynyl group via a thiol-yne click reaction. Because PyHES-DMAET has pH-responsive amino groups and hydrophobic thioether groups, its aqueous solution exhibits excellent temperature/pH dual sensitivity, i.e., a good transference between the hydrophobic (or self-assembly) and hydrophilic (or swelling) state along as a result of changing temperature/pH values; these properties can be exploited, for hydrophobic drug release. The drug release reached 96% at 37 °C and a pH of 6.5. The drug loading capacity of PyHES-DMAET was increased by increasing the degree of substitution (DS) of the hydrophobic propynyl groups in the PyHES. The highest drug loading capacity for doxorubicin (DOX) achieved in this study was 33 wt%.