Upper Critical Solution Temperature Layer-by-Layer Films of Polyamino acid-Based Micelles with Rapid, On-Demand Release Capability
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2017 American Chemical Society. Here, we report on upper critical solution temperature (UCST)-type polyamino acid-based block copolymer assembled in a layer-by-layer system with a natural polyphenol. The UCST-type block copolymer, polyvinylpyrrolidone-b-polyureido(ornithine-co-lysine) (PVP-b-PUOL), was synthesized via ring opening polymerization followed by postpolymerization functionalization with ureido groups. PVP-b-PUOL exhibited UCST behavior that was controlled by both molecular weight and ornithine-to-lysine ratio. Importantly, PVP-b-PUOL with a UCST of 33 C assembled into block copolymer micelles below UCST and dissociated above UCST, yet this behavior was not repeatable in solution due to -sheet formation and large-scale aggregation. To overcome this limitation, UCST micelles (UCSTMs) were deposited within layer-by-layer (LbL) films via hydrogen bonding with tannic acid (TA). Significantly, the assembled TA/UCSTM films stabilized the micelles from desorption while maintaining their morphology and prevented -sheet formation even after continuous exposure to 40 C for 7 days. Moreover, these films demonstrated repeatable swelling-deswelling for up to five temperature cycles from 25 to 40 C. The thermo-switchable hydrophobicity of micellar cores was used for trapping of a model active molecule, pyrene, and its on-off temperature-controlled release, demonstrating the potential of TA/UCSTM films for controlled delivery of active molecules.
