Abstract
Cytoplasmic viscosity (μc) is a key biomechanical parameter for evaluating the status of cellular cytoskeletons. Previous studies focused on white blood cells, but the data of cytoplasmic viscosity for tumour cells were missing. Tumour cells (H1299, A549 and drug-treated H1299 with compromised cytoskeletons) were aspirated continuously through a micropipette at a pressure of −10 or −5 kPa where aspiration lengths as a function of time were obtained and translated to cytoplasmic viscosity based on a theoretical Newtonian fluid model. Quartile coefficients of dispersion were quantified to evaluate the distributions of cytoplasmic viscosity within the same cell type while neural network-based pattern recognitions were used to classify different cell types based on cytoplasmic viscosity. The single-cell cytoplasmic viscosity with three quartiles and the quartile coefficient of dispersion were quantified as 16.7 Pa s, 42.1 Pa s, 110.3 Pa s and 74% for H1299 cells at −10 kPa (ncell = 652); 144.8 Pa s, 489.8 Pa s, 1390.7 Pa s, and 81% for A549 cells at −10 kPa (ncell = 785); 7.1 Pa s, 13.7 Pa s, 31.5 Pa s, and 63% for CD-treated H1299 cells at −10 kPa (ncell = 651); and 16.9 Pa s, 48.2 Pa s, 150.2 Pa s, and 80% for H1299 cells at −5 kPa (ncell = 600), respectively. Neural network-based pattern recognition produced successful classification rates of 76.7% for H1299 versus A549, 67.0% for H1299 versus drug-treated H1299 and 50.3% for H1299 at −5 and −10 kPa. Variations of cytoplasmic viscosity were observed within the same cell type and among different cell types, suggesting the potential role of cytoplasmic viscosity in cell status evaluation and cell type classification.
Highlights
The mechanical behaviour of biological cells is largely determined by their cytoskeletons [1,2]
Probes with fluorescent intensities regulated by the viscosity of surrounding medium are injected within biological cells, and the corresponding images are obtained by fluorescent microscopy to determine viscosity distributions within single cells [36,37]
Three quartiles and the quartile coefficient of dispersion were quantified as 16.7 Pa s, 42.1 Pa s, 110.3 Pa s and 74% for H1299 cells at 210 kPa; 144.8 Pa s, 489.8 Pa s, 1390.7 Pa s, and 81% for A549 cells at 210 kPa; 7.1 Pa s, 13.7 Pa s, 31.5 Pa s, and 63% for Cytochalasin D (CD)-treated H1299 cells at 210 kPa; and 16.9 Pa s, 48.2 Pa s, 150.2 Pa s, and 80% for H1299 cells at 25 kPa. These results reveal the significant variations of cytoplasmic viscosity within the same cell types
Summary
The mechanical behaviour of biological cells is largely determined by their cytoskeletons [1,2]. Compared with AFM, micropipette aspiration involves deformations of larger cellular portions, and it can characterize the mechanical properties of single cells in a more global manner [24,25,26,27,28]. In conventional micropipette aspiration, a low pressure was used to aspirate a single tumour cell partially into the pipette and after that, the cell being measured would be expelled out of the pipette. This procedure takes a considerable amount of time and suffers from the limitation of low throughput
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