Protrusion of nanospikes on cholesterol-containing microgels by reduction-responsive self-assembly in cell milieu and its influence on cell functions

Self-assembly in living systems is important for developing biological functional materials and regulating cellular processes, which have potential applications in disease diagnosis and treatment. However, the controllable fabrication of complex self-assemblies such as micro/nanocomposite structures and the direct observation of morphology-defined nanostructures in a cell milieu are still challenging. We report here a facile strategy for achieving the intracellular stimuli-responsive fabrication of micro/ nanocomposite structures by using reduction-responsive microgels as a platform. Amphiphilic polymers (CSEG-g-Chol) that contained disulfide bonds in side chains and grafted cholesterol groups (Chol) were synthesized and used to prepare microgels (MGs) by a method based on a calcium carbonate template, in which the template was removed after the polymer was loaded and crosslinked. In the presence of reductants such as glutathione (GSH) and dithiothreitol (DTT), nanospikes gradually protruded from the surface of CSEG-g-Chol MGs. After internalization into cells, reduction-responsive self-assembly and the protrusion of nanospikes in the cell milieu were observed. No obvious influence on the cytoskeleton and endoplasmic reticulum was observed via light microscopy. However, co-incubation of the MGs caused a certain extent of cytotoxicity depending on the co-incubation concentration and stimulated the secretion of tumor necrosis factor-alpha (TNF-alpha), which was several times higher than in the control group. This work may serve as a paradigm for the study of intracellular and in vivo self-assembly and may also provide important insights for the investigation of biological self-assembly and interactions between micro/nanomaterials and cells.