Meticulous Doxorubicin Release from pH‐responsive Nanoparticles Entrapped within an Injectable Thermoresponsive Depot

The dual stimuli‐controlled release of doxorubicin from gel‐embedded nanoparticles is reported. Non‐cytotoxic polymer nanoparticles are formed from poly(ethylene glycol)‐ b ‐poly(benzyl glutamate) that, uniquely, contain a central ester link. This connection renders the nanoparticles pH‐responsive, enabling extensive doxorubicin release in acidic solutions (pH 6.5), but not in solutions of physiological pH (pH 7.4). Doxorubicin loaded nanoparticles were found to be stable for at least 31 days and lethal against the three breast cancer cell lines tested. Furthermore, doxorubicin loaded nanoparticles could be incorporated within a thermoresponsive poly(2‐hydroxypropyl methacrylate) gel depot, which forms immediately upon injection of poly(2‐hydroxypropyl methacrylate) in DMSO solution into aqueous solution. The combination of the poly(2‐hydroxypropyl methacrylate) gel and poly(ethylene glycol)‐ b ‐poly(benzyl glutamate) nanoparticles yields an injectable doxorubicin delivery system that facilities near‐complete drug release when maintained at elevated temperatures (37 °C) in acidic solution (pH 6.5). In contrast, negligible payload release occurs when the material is stored at room temperature in non‐acidic solution (pH 7.4). The system has great potential as a vehicle for the prolonged, site‐specific, release of chemotherapeutics.