We here performed an in-depth investigation of the behavior of microgels (μgels) and their associated physicochemical transformations under shear force. Thermo-and mechanoresponsive poly(N-vinylcaprolactam) (PVCL) μgels (d ∼ 400 nm) cross-linked with a force-responsive mechanofluorophore in different crosslinking degrees were synthesized and examined. Fluorescence spectroscopy (FS), confocal laser scanning microscopy (CLSM), dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryoTEM), high-resolution magic-angle sample spinning (HRMAS) nuclear magnetic resonance (NMR), Fourier-transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) are used to characterize the μgels before, during, and after shearing with different shear rates and intensities. The obtained results suggest nonuniform structural features consisting of a softer outer "corona" and a harder particle "core" (cross-linker-rich). Upon shearing, the μgels rapidly lose their corona and the cores agglomerate altering μgel functionality. Surprisingly, μgels degrade promptly, even when subjected to low shear forces, such as the extrusion through a needle. This has potential implications for all applications in which shear forces in solution are expected, including extrusion, injection, and filtration processes involving colloidal μgel solutions as well as circulation within the bloodstream of living organisms.

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The unique response of microgels to force can be measured by AFM, tailored by synthesis, and used for activating functionality.

Microgels (μgels) swiftly undergo structural and functional degradation when they are exposed to shear forces, which potentially limit their applicability in, e.g., biomedicine and engineering. Here, poly( N ‐vinylcaprolactam) μgels that resist mechanical disruption through supramolecular hydrogen bonds provided by (+)‐catechin hydrate (+C) are synthesized. When +C is added to the microgel structure, an increased resistance against shear force exerted by ultrasonication is observed compared to μgels crosslinked by covalent bonds. While covalently crosslinked μgels degrade already after a few seconds, it is found that μgels having both supramolecular interchain interactions and covalent crosslinks show the highest mechanical durability. By the incorporation of optical force probes, it is found that the covalent bonds of the μgels are not stressed beyond their scission threshold and mechanical energy is dissipated by the force‐induced reversible dissociation of the sacrificial +C bonds for at least 20 min of ultrasonication. Additionally, +C renders the μgels pH‐sensitive and introduces multiresponsivity. The μgels are extensively characterized using Fourier‐transform infrared, Raman and quantitative nuclear magnetic resonance spectroscopy, dynamic light scattering, and cryogenic transmission electron microscopy. These results may serve as blueprint for the preparation of many mechanically durable μgels.

We have developed a simple and versatile polymer coating method that provides excellent non-biofouling properties.