Understanding how cells adhere to and detach from different material interfaces is critical to fundamental biology and biofouling processes as well as to various biomaterial applications. Compared to other measurement options, QCM-D analysis can provide unprecedented insights into these interfacial processes. In this blog post, we present an example where the QCM-D technique was used for time-resolved analysis of cell adhesion and detachment, including the study motivation, measurement concepts, data analysis, and future possibilities.
Both cell-cell and cell-material interactions are important, especially when designing materials for medical implant and biosensing applications. In some cases, it is favorable to engineer material interfaces to resist cell adhesion while, in other cases, it is advantageous to promote the selective adhesion of certain cell types. QCM-D technology is highly useful for studying cell adhesion and detachment because the technique works with a wide range of organic and inorganic material surface types, is label free, operates under static and flow conditions, and provides high kinetic resolution. In addition, QCM-D data analysis can aid viscoelastic characterization of adhered cell states.
The adsorption kinetics of model eukaryotic cells (S. cerevisiae yeast) and model prokaryotic cells (E. coli bacteria) onto gold and silicon dioxide surfaces, which have different surface free energies, was studied by the QCM-D technique. The experiments were conducted at different cell concentrations in phosphate-buffered saline with physiologically relevant salt concentrations, and cell adhesion was initially studied under flow conditions before flow was stopped to further probe cell attachment stability in static conditions over longer periods of time—all in the same measurement run. Time-independent plots of the resonance frequency vs. energy dissipation shifts were also prepared to analyze cytoskeletal changes in the adhered cell cytoskeletal structures. Similar experiments were also run with human embryonic kidney (HEK) cells as a more biologically complex eukaryote model.
The results showed that S. cerevisiae yeast cells adsorbed to a greater extent on silicon dioxide surfaces than on gold surfaces (Figure 1). Interestingly, in both cases, cell detachment readily occurred during long-term incubation and the extent of detachment was in fact greater in the silicon dioxide case. Similar result trends were also obtained with HEK cells as a second type of tested eukaryotic cell. By contrast, E. coli bacterial cells adsorbed much more strongly to both surface types. The overall extent of bacterial cell attachment to gold surfaces was greater than on silicon dioxide surfaces and there was only minor cell detachment even after long-term incubation. Different stages of the cell attachment and detachment processes could also be identified by analysis of the frequency-dissipation plots.
Figure 1: Measuring attachment of prokaryotic and eukaryotic cells to inorganic surfaces. E. coli bacterial cells and S. cerevisiae yeast cells served as model prokaryotes and eukaryotes, respectively, and were added to gold and silicon dioxide surfaces. The corresponding attachment and detachment kinetics were monitored under static and flow conditions.
While various experimental techniques such as microscopy-based options can analyze cell attachment on certain solid surfaces, the QCM-D approach has several key advantages related to quantifying surface adsorption. The QCM-D technique works with various types of optically transparent and opaque surface coatings and does not require cell labeling. This latter point is particularly advantageous when considering that this one study was able to study yeast, bacterial, and human cells using the same protocol. Another advantage of the QCM-D technique is the ability to monitor cell attachment/detachment in a well-controlled environment for long time periods while being able to controllably adjust the flow conditions.
The biofouling of material surfaces is an important part of biological recognition processes and can influence the biocompatibility level. This measurement approach is also important for developing antifouling coatings that resist nonspecific cell adhesion, in which case the QCM-D technique can sensitively detect the degree of fouling in a quantitative manner, even if very small. In addition to studying cell-material interactions related to inorganic surfaces, cell interactions with different material surfaces such as lipid membrane and protein coatings can also be monitored and are relevant to tissue engineering and regenerative medicine applications.
Download the overview to learn more about how QCM-D can be used to measure molecular interactions at surfaces and interfaces in biotechnology and biophysics.
Malin graduated in engineering physics in 2006, where her research focused on the QCM-D technology. Since then, she has been scrutinizing the how’s and why’s of the world in general, and the world of QCM-D in particular.
