Light and temperature dual stimuli-responsive micelles from carbamate-containing spiropyran-based amphiphilic block copolymers: Fabrication, responsiveness and controlled release behaviors

With the increasing demand for treating cancer and cardiovascular diseases in recent years, drug delivery therapy using intelligent nanocarriers has been investigated intensely. Usually, hydrophobic dyes were used as drug models for the development of drugrelease carriers. In this study, light and temperature dualresponsive micelles were designed and fabricated, and the controlled release property was investigated using the hydro-phobic fluorescent dye coumarin 102 as the model. A carbamate-containing spiropyran methacrylate monomer (SPMA) was adopted as the photosensitive unit because it is more conducive to stabilize the micelle structure compared to traditional spiropyran. Firstly, a light and temperature dual-responsive copolymer P[DMA50-b- (SPMA20-co-NIPAAm17)] was synthesized through reversible addition-fragmentation chain transfer (RAFT) polymerization. Then, the copolymer was self-assembled into micelles with coumarin 102 encapsulated in the hydrophobic core above the lower critical solution temperature (LCST) and under visible light (Vis) irradiation. When the visible light was switched to ultraviolet (UV) radiation, the micelles' permeability increased as a result of the change from closed, three-dimensional spiropyrans (SP) to open, planar merocyanines (MC), resulting in the release rate of 51% for coumarin 102 in 15 min with "low" release capability. Lowering the temperature to room temperature (RT), the hydrophobic nuclei were partially destructed as a result of the changing of PNIPAAm segment from hydrophobicity to hydrophilicity. Meanwhile, the release rate was observed to be 77% in 15 min showing "medium" release capability. The micelles were almost wholly disintegrated under the dual stimulation of both UV irradiation and RT, achieving the release rate of 96% within the same time exhibiting "high " release capability. This study offered an approach for the construction of controllable drug release carriers.