The unique pH and temperature responsiveness of PNIPAM-based microgels make them a promising target for novel biomedical applications such as cellular drug delivery systems. However, we lack a comprehensive understanding of how the physicochemical properties of microgels relate to their interaction with cells. Here, we show that HEK293T cells take up PNIPAMbased microgels on a second-to-minute time scale. Uptake rates are determined by microgel size and cross-linker content. Using fluorescence confocal live-cell microscopy, we observe microgel uptake in real time and describe cellular uptake kinetics. Experiments reveal that small and less cross-linked microgels show faster uptake kinetics than microgels of larger size or higher cross-linker content. Only microgels that are larger than 800 nm in diameter and have cross-linking contents of 10−15 mol % do not show translocation into cells. Together, these results provide insight into microgel−cell interactions and generate quantitative information on the deterministic role of microgel architecturei.e., size and rigidityfor uptake by a prototypical human cell line.

The 3D structure and the local environment of stimuli-responsive microgels were investigated with the superresolution fluorescence microscopy method PAINT using Nile Red as solvatochromic dye.

The authors demonstrate how the size and structure of the cavity of hollow charged microgels may be controlled by varying pH and ionic strength. Hollow charged microgels based on N‐isopropylacrylamide with ionizable co‐monomers (itaconic acid) combine advanced structure with enhanced responsiveness to external stimuli. Structural advantages accrue from the increased surface area provided by the extra internal surface. Extreme sensitivity to pH and ionic strength due to ionizable moieties in the polymer network differentiates these soft colloidal particles from their uncharged counterparts, which sustain a hollow structure only at cross‐link densities sufficiently high that stimuli sensitivity is reduced. Using small‐angle neutron and light scattering, increased swelling of the network in the charged state accompanied by an expanded internal cavity is observed. Upon addition of salt, the external fuzziness of the microgel surface diminishes while the internal fuzziness grows. These structural changes are interpreted via Poisson–Boltzmann theory in the cell model.

Controlling the distribution of ionizable groups of opposite charge in microgels is an extremely challenging task, which could open new pathways to design a new generation of stimuli‐responsive colloids. Herein, we report a straightforward approach for the synthesis of polyampholyte Janus‐like microgels, where ionizable groups of opposite charge are located on different sides of the colloidal network. This synthesis approach is based on the controlled self‐assembly of growing polyelectrolyte microgel precursors during the precipitation polymerization process. We confirmed the morphology of polyampholyte Janus‐like microgels and demonstrate that they are capable of responding quickly to changes in both pH and temperature in aqueous solutions.