Fig. 6: Loss angle comparison of the generalized Maxwell viscoelastic model and power law rheology (PLR) models for various adherent human skin cell types.

The generalized viscoelastic models showcase non-monotonic behavior for all human skin cell lines across a wide frequency range when compared with the relatively smooth and monotonic PLR model prediction for human lung epithelial cells. Loss angles have been provided for each cell type and showcase nonlinear, non-monotonic action as a function of frequency. This is in contrast to the inset data, which was reproduced from the literature⁵ using a PLR model for human lung epithelial cells and shows a completely monotonic response with increasing frequency. While the frequency ranges for the primary axis and inset do not overlap, the PLR model is clearly lacking in frequency domain features and is merely provided to represent a typical PLR model prediction. Observed confidence intervals are shaded in matching colors for each model. When comparing all three skin cell types, the melanocyte and fibroblast models showed noticeably tighter confidence intervals than the melanoma. As with Fig. 4, these loss angle estimates were obtained by analyzing an average of 70, 71, and 193 force curves from the melanoma, melanocyte, and fibroblast cell conditions, respectively. In total, the averaged datasets contain curves collected from 13 unique melanoma cells, 12 unique melanocytes, and 33 unique fibroblasts.