A novel cell-stiffness-fingerprinting analysis by scanning atomic force microscopy: comparison of fibroblasts and diverse cancer cell lines

Differing stimuli affect cell stiffness while cancer metastasis is associated with reduced cell stiffness. Cell stiffness determined by atomic force microscopy has been limited by measurement over nuclei to avoid spurious substratum effects in thin cytoplasmic domains, and we sought to develop a more complete approach including cytoplasmic areas. Ninety mu m square fields were recorded from ten separate sites of cultured human dermal fibroblasts (HDF) and three sites each for melanoma (MM39, WM175, and MeIRMu), osteosarcoma (SAOS-2 and U2OS), and ovarian carcinoma (COLO316 and PEO4) cell lines, each site providing 1024 measurements as 32 x 32 square grids. Stiffness recorded below 0.8 mu m height was occasionally influenced by substratum, so only stiffness recorded above 0.8 mu m was analysed, but all sites were included for height and volume analysis. COLO316 had the lowest cell height and volume, followed by HDF (p < 0.0001) and then PEO4, SAOS-2, MeIRMu, WM175, U2OS, and MM39. HDF were more stiff than all other cells (p < 0.0001), while in descending order of stiffness were PEO4, COLO316, WM175, SAOS-2, U2OS, MM39, and MeIRMu (p < 0.02). Stiffness fingerprints comprised scattergrams of stiffness values plotted against the height at which each stiffness value was recorded and appeared unique for each cell type studied, although in most cases the overall form of fingerprints was similar, with maximum stiffness at low height measurements and a second lower peak occurring at high-height levels. We suggest that our stiffness-fingerprint analytical method provides a more nuanced description than previously reported and will facilitate study of the stiffness response to cell stimulation.