Light-responsive polyurethanes: classification of light-responsive moieties, light-responsive reactions, and their applications

Stimuli responsiveness has been an attractive feature of smart material design, wherein the chemical and physical properties of the material can be varied in response to small environmental change. Polyurethane (PU), a widely used synthetic polymer can be upgraded into a light-responsive smart polymer by introducing a light-sensitive moiety into the polymer matrix. For instance, azobenzene, spiropyran, and coumarin result in reversible light-induced reactions, while o-nitrobenzyl can result in irreversible light-induced reactions. These variations of light-stimulus properties endow PU with wide ranges of physical, mechanical, and chemical changes upon exposure to different wavelengths of light. PU responsiveness has rarely been reviewed even though it is known to be one of the most versatile polymers with diverse ranges of applications in household, automotive, electronic, construction, medical, and biomedical industries. This review focuses on the classes of light-responsive moieties used in PU systems, their synthesis, and the response mechanism of light-responsive PU-based materials, which also include dual- or multi-responsive light-responsive PU systems. The advantages and limitations of light-responsive PU are reviewed and challenges in the development of light-responsive PU are discussed.

Doxorubicin-loaded polypyrrole nanovesicles for suppressing tumor metastasis through combining photothermotherapy and lymphatic system-targeted chemotherapy

The lymphatic system provides a main route for the dissemination of most malignancies, which was related to high mortality in cancer patients. Traditional intravenous chemotherapy is of limited effectiveness on lymphatic metastasis due to the difficulty in accessing the lymphatic system. Herein, a novel lymphatic-targeting nanoplatform is prepared by loading doxorubicin (DOX) into sub-50 nm polypyrrole nanovesicles (PPy NVs). The PPy NVs possessed hollow spherical morphologies and a negative surface charge, leading to high drug loading capacity. These vesicles can also convert near-infrared (NIR) light into heat and thus can be used for tumor thermal ablation. DOX loaded PPy NVs (PPy@DOX NVs) along with NIR illumination are highly effective against 4T1 breast cancer cells in vitro. More importantly, following subcutaneous (SC) injection, a direct lymphatic migration of PPy@DOX NVs is confirmed through fluorescence observation of the isolated draining nodes. The acidic conditions in metastatic nodes might subsequently trigger the release of the encapsulated DOX NVs based on their pH-sensitive release profile. In a mouse model bearing 4T1 breast cancer, lymphatic metastases, as well as lung metastases, are significantly inhibited by nanocarrier-mediated trans-lymphatic drug delivery in combination with photothermal ablation. In conclusion, this platform holds great potential in impeding tumor growth and metastasis.