Cellular Mechanics
Micromechanical properties of biological cells are crucial for cells functions. Despite extensive study by a variety of approaches, an understanding of the subject remains elusive. We conducted a comparative study of the micromechanical properties of cultured alveolar epithelial cells with an oscillatory optical tweezer-based cytorheometer. In this study, the frequency-dependent viscoelasticity of these cells was measured by optical trapping and forced oscillation of either a submicron endogenous intracellular organelle (intra-cellular) or a 1.5μm silica bead attached to the cytoskeleton through trans-membrane integrin receptors (extra-cellular). Both the storage modulus and the magnitude of the complex shear modulus followed weak power-law dependence with frequency. These data are comparable to data obtained by other measurement techniques. The exponents of power-law dependence of the data from the intra- and extracellular measurements are similar; however, the differences in the magnitudes of the moduli from the two measurements are statistically significant.
Fig. (A) A sketch of optical tweezer-based cytorheometer. Optical tweezers were used to manipulate an intracellular granular structure (lamellar body, left circle), or an extracellular anti-body coated glass bead (right circle). (B) A bright-field image of lamellar bodies that abundantly exist in alveolar epithelial type II cells. |
Fig. (A) Power-law exponents of G' and G* for extracellular and intracellular data. Error bars represent standard deviation and means are not statistically different. (B) Magnitudes of prefactor G'o and G*o for extracellular and intracellular data. Error bars are 95% confidence intervals on log-scale and means are statistically different (p<0.01, log-transformed t-test). |
Fig. (A) Effect of Latrunculin treatment, Jasplakinolide treatment and 37ºC temperature on average power-law exponents for extracellular data. (B) Effect of Latrunculin treatment, Jasplakinolide treatment and 37ºC temperature on normalized elastic and shear modulus for extracellular data. Data are means ± SE. * indicates significant difference compared with untreated cells at 23℃ (p<0.05) and ^ indicates significant difference compared with Latrunculin treated cells (p<0.05). |
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