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Disulfide-Bridged Organosilica Frameworks: Designed, Synthesis, Redox-Triggered Biodegradation, and Nanobiomedical Applications
Over the past few years, silicaâbased nanotheranostics have demonstrated their great potential for nano/biomedical applications. However, the uncontrollable and difficult degradability of their pure silica framework and longâtime in vivo retention still cause severe and unpredictable toxicity risks. Therefore, it is highly desirable to design and synthesize materials with safer framework structures and compositions. To this aim, the introduction of disulfide bonds into the silica framework can not only maintain high stability in physiological conditions, but also achieve a stimuliâresponsive biodegradation triggered by intracellular reducing microenvironment in living cells, especially in cancer cells. Once nanotheranostics with disulfide (i.e., thioether)âbridged silsesquioxane framework are taken up by tumor cells via passive or active targeting, the disulfide bonds in the hybrid silica matrix can be cleaved by a high concentration of intracellular glutathione, enabling redoxâtriggered biodegradation of the nanosystems for both concomitant release of the loaded therapeutic cargo and in vivo clearance. It is envisioned that such hybrid materials comprised of disulfideâbridged silsesquioxane frameworks can become promising responsive and biodegradable nanotheranostics. This review summarizes the recent advances in the synthesis of hybrid organosilicas with disulfideâbridged silsesquioxane frameworks, and discuss their redoxâtriggered biodegradation behaviors combined with their biocompatibility and nanobiomedical applications.© 2018 The Author