Influence of Size and Cross-Linking Density of Microgels on Cellular Uptake and Uptake Kinetics

Abstract

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.

Nanoparticles in the Biological Context: Surface Morphology and Protein Corona Formation

“…It is, for example, well known that nanogels can penetrate through pores that are much smaller than the nanogels diameter and even very large microgels can be taken up by cells if they have a low cross linker content. [ 53–56 ]…”

“…It is, for example, well known that nanogels can penetrate through pores that are much smaller than the nanogels diameter and even very large microgels can be taken up by cells if they have a low cross linker content. [53][54][55][56] The concept of zeta-potential is not well-defined for soft objects as charged groups as well as their counter-ions can be distributed inside the object. Despite the fact that models for soft, penetrable charged objects have been developed, [57] one should rather report electrophoretic mobilities instead of zeta-potential, which are calculated using models for rigid nanoparticles with a sharp surface.…”

Endocytosis of abiotic nanomaterials and nanobiovectors: Inhibition of membrane trafficking

“…Charged microgels had fast cellular uptake, in the range of seconds to minutes. Microgels that were larger than 800 nm in diameter and had cross-linking densities of 10–15 mol% could not be translocated into cells [160] .…”

“…For example, microgels with cross-linking densities between 1.7 and 15 mol% were internalized into cells through several mechanisms, which result in high uptake rates [159] . In another study, poly( N -isopropylacrylamide)-based microgels were used to investigate the effects of nanoparticles with different cross-linking densities on interaction with the plasma membrane [160] Microgels with low cross-linking densities were softer than those with high cross-linking densities. Charged microgels had fast cellular uptake, in the range of seconds to minutes.…”

Adhesion of Epithelial Cells to PNIPAm Treated Surfaces for Temperature-Controlled Cell-Sheet Harvesting

“… 16 More recently, Switacz et al found that depending on the size and softness of the polymer, the HEK293T cells could take up PNIPAm based microgels. 31 Additionally, a correlation of protein adsorption of ECM of cells and the water content of the grafted PNIPAm brushes was investigated. 34 Even though these recent reveals could be the partial determinant for cell-sheet detachment, to fully apply the advantages of functional substrates for cell-sheet harvesting, systematic and consistent evaluation of cell–substrate and cell–cell adhesion on a well-characterized PNIPAm surface is required.…”