Influence of size and cross-linking density of microgels on cellular uptake and uptake kinetics

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 PNIPAM-based 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.

Victoria K. Switacz, Sarah K. Wypysek, Rudolf Degen, Jérôme J. Crassous, Marc Spehr, and Walter Richtering

Biomacromolecules, 2020, DOI: 10.1021/acs.biomac.0c00478