An In Situ Reversible Heterodimeric Nanoswitch Controlled by Metal‐Ion–Ligand Coordination Regulates the Mechanosensing and Differentiation of Stem Cells

Abstract In situ and cytocompatible nanoswitching by external stimuli is highly appealing for reversibly regulating cellular adhesion and functions in vivo. Here, a heterodimeric nanoswitch is designed to facilitate in situ switchable and combinatorial presentation of integrin‐binding cell‐adhesive moieties, such as Mg 2+ and Arg‐Gly‐Asp (RGD) ligand in nanostructures. In situ reversible nanoswitching is controlled by convertible coordination between bioactive Mg 2+ and bisphosphonate (BP) ligand. A BP‐coated gold‐nanoparticle monomer (BP‐AuNP) on a substrate is prepared to allow in situ assembly of cell‐adhesive Mg 2+ ‐active Mg‐BP nanoparticles (NPs) on a BP‐AuNP surface via Mg 2+ ‐BP coordination, yielding heterodimeric nanostructures (switching “ON”). Ethylenediaminetetraacetic acid (EDTA)‐based Mg 2+ chelation allows in situ disassembly of Mg 2+ ‐BP NP, reverting to Mg 2+ ‐free monomer (switching “OFF”). This in situ reversible nanoswitching on and off of cell‐adhesive Mg 2+ presentation allows reversible cell adhesion and release in vivo, respectively, and spatiotemporally controls cyclic cell adhesion. In situ heterodimeric assembly of dual RGD ligand‐ and Mg 2+ ‐active RGD‐BP‐Mg 2+ NP (switching “Dual ON”) further tunes and promotes focal adhesion, spreading, and differentiation of stem cells. The modular nature of this in situ nanoswitch can accommodate various bioactive nanostructures via metal‐ion–ligand coordination to regulate diverse cellular functions in vivo in reversible and compatible manner.