Synthesis and characterization of triple-responsive PNiPAAm-S-S-P(αN₃CL-g-alkyne) copolymers bearing cholesterol and fluorescence monitor

Real-time monitoring and controlled release of drugs are key factors in drug delivery. In this study, versatile fluorescence triple-responsive block-graft copolymers PNiPAAm-S-S-P(αN₃CL-g-alkyne)_n with a disulfide (S–S) bond as a junction point between the hydrophilic and hydrophobic chains bearing cholesteryl- and pyrenyl- side groups were synthesized. The polymer was temperature-sensitive with a lower critical solution temperature in the range of 36 °C to 44 °C. When the polymer solution was treated with reducing agents and exposed to ultrasound, significant hydrolysis of the amide bonds was noted. The partial destruction of micelles in the presence of a reducing agent and ultrasound was observed through transmission electron microscopy. The copolymers containing cholesteryl and pyrenyl possessed highly drug loading content and entrapment efficiency. Above the lower critical solution temperature, the release rate could be greatly increased and adjusted remotely under high- intensity focused ultrasound in the presence of dithiothreitol. The nanoparticles exhibited slight toxicity against HeLa cells in the concentration range of 10–300 μg mL⁻¹. Doxorubicin (DOX)-loaded micelles facilitated the uptake of DOX by HeLa cells and were predominantly retained in the cytoplasm.