The development of materials capable of varying macroscale ligand distributions can emulate an extracellular matrix (ECM) remodeling and regulate the adhesion and polarization of macrophages. In this report, negatively charged slidable nano‐ligands are assembled and then conjugated to a positively charged substrate via electrostatic interaction. The negatively charged slidable nano‐ligands are prepared by coating magnetic nanoparticles with a polymer linker and negatively charged RGD ligand. The nano‐ligand sliding is characterized under an external magnetic field, which spatiotemporally alters macroscale ligand density. To the best of knowledge, this is the first demonstration that magnetic maipulation of the macroscale ligand density inhibits inflammatory M1 phenotype but stimulates the adhesion and regenerative M2 phenotype of host macrophages. Furthermore, it is elucidated that the magnetic attraction of the slidable nano‐ligand facilitates the assembly of adhesion structures in macrophages, thereby stimulating their regenerative M2 phenotype. The design of ECM‐emulating materials that allow remote, spatiotemporal, and reversible controllability of macroscale ligand density provides an appealing strategy in the spatiotemporal regulation of immunomodulatory tissue‐regenerative responses to implants in vivo.
The spotlighted dual functions of pyridine as a denaturant and as a stabilizer for duplex DNA are thoroughly investigated using spherical nucleic acids (SNAs). At neutral pH, pyridine destabilizes the duplex interconnects of assembled SNAs, resulting in a gradual decrease in their melting temperature (T) as a function of the pyridine concentration. This result is in good agreement with the conventional role of pyridine as a powerful denaturant for free duplex DNA. On the contrary, the addition of pyridine dramatically increases the T of hybridized SNAs under acidic conditions, which could be a striking result of pyridine's stabilizing effect for DNA duplex as previously suggested on the basis of the pyridine-nucleobase interactions. After comprehensive and quantitative investigation based on the analysis of the sharp melting transitions of SNAs, however, we report that, in fact, the pH increase induced by pyridine is also an essential parameter accounting for pyridine's DNA-stabilizing effects under acidic conditions. Importantly, we prove that pyridine, particularly at a low concentration, does not increase the T of hybridized SNAs even under acidic conditions, if the pH increase by pyridine is corrected to maintain the same initial pH.
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