Combined Atomic Force Microscopy and Optical Microscopy Measurements as a Method To Investigate Particle Uptake by Cells

Abstract

We propose a combination of atomic force microscopy (AFM) and optical microscopy for the investigation of particle uptake by cells. Positively and negatively charged polymer microcapsules were chosen as model particles, because their interaction with cells had already been investigated in detail. AFM measurements allowed the recording of adhesion forces on a single-molecule level. Due to the micrometer size of the capsules, the number of ingested capsules could be counted by optical microscopy. The combination of both methods allowed combined measurement of the adhesion forces and the uptake rate for the same model particle. As a demonstration of this system, the correlation between the adhesion of positively or negatively charged polymer microcapsules onto cell surfaces and the uptake of these microcapsules by cells has been investigated for several cell lines. As is to be expected, we find a correlation between both processes, which is in agreement with adsorption-dependent uptake of the polymer microcapsules by cells.

Measuring Cell Adhesion Forces: Theory and Principles

“…In the experiments described here, the adhesion of cells to two different types of surfaces, positively (NH 2 ) and negatively (COOH) charged spheres, has been investigated. Two types of breast cancer cell lines were measured in this study, the noninvasive strain MCF-10A and the invasive strain MDA-MB-4355 (58). The analysis of the force traces with respect to adhesion probability and adhesion forces on the single molecular level (while maintained at 37°C in nutrient medium) showed a higher adhesion probability for the positively charged spheres.…”

Real-time, label-free monitoring of cell viability based on cell adhesion measurements with an atomic force microscope

“…AFM is a powerful tool to measure very small forces between a cantilever tip and a surface on the nanoscale, even if the surface to be inspected is soft and submerged in a liquid, e.g., cells in solution. With AFM binding forces between two molecules [26], adhesion of molecules to surfaces [27], adhesion of cells to surfaces [28], or cell to cell adhesion [29] can be recorded. As AFM also allows for lateral resolution also local properties of cell surfaces can be raster-scanned, such as topography [30], localization of adhesion sites [31], local electro-mechanical signaling [21], or local viscoelastic properties [32, 33].…”

Degradable Multilayer Films and Hollow Capsules via a ‘Click’ Strategy

“…Thanks to the introduction of hydrolytically degradable carbonate ester linkages, it is believed that this type of coating technique will become an important strategy for the design of, e.g., drug delivery systems, degradable drug formulations, tissue engineering scaffolds, and others. Moreover, as the wall of the hollow capsules was observed to be extremely thin they could be of interest for intracellular delivery as upon cellular internalization, they are expected to be largely deformed, [70] which could facilitate the release of their payload.…”