Fingerprinting circulating tumor cell with characteristic membrane viscoelasticity by atomic force microscopy

Atomic Force Microscopy (AFM) is a powerful tool that can resolve nanoscale cell surface features (e.g. re- ceptors, channels) as well as perform the mechanical characterization of living cells and tissues. Anecdotal observations suggest that metastasized tumor cells bear their phenotypical “telltale” signatures in their mem- brane characteristics, i.e prostate cancer cells are often stiffer and more elastic than breast cancer. In this talk, we present a new methodology allowing us to quantify mechanical properties of cells through force- deformation relations (F-D curves) by nano-indentation, as well as develop a novel mathematical framework to quantify cell membranes’ viscoelasticity by performing Ting’s integral over F-D measurements to differen- tiate cancer phenotypes. We have developed a custom-made flow cell that enables simultaneous microscopic observation and AFM experimentation. Three cell lines, prostate cancer (PC3), breast carcinoma (T47D), and lung a-carcinoma (A549), are used for this kernel study. Cells are split once reaching a confluence of 70% and a 10% dilution of cells are plated on 12 mm diameter wafer. After 24-hour growth, the plated slides are transferred to in-house flow cell containing the corresponding culture medium. With an integrated LED illuminator sealed within a polydimethylsiloxane matrix underneath the wafer, simultaneous observation of live cells can be achieved by an integrated upright microscope. Indentation measurements are conducted with a “wet” AFM. Gold coated probes (k=0.03N/m) are used to allow measurement on soft cell membrane. Differing from past studies, we probe the membrane with large indentation. Standard Linear Solid model are fitted over measurements to obtain viscoelasticity parameters. Preliminary results show distinctive hys- teresis between loading and unloading of the membrane. It is also found that multi-power law model is more suitable for cancer characterization. Model parameters of three phenotypes show clear distinction and great potential to develop membrane viscoelasticity as a biomarker for cancer cell diagnostics and characterization.