Thermorheology of living cells—impact of temperature variations on cell mechanics

Abstract

Upon temperature changes, we observe a systematic shift of creep compliance curves J (t) for single living breast epithelial cells. We use a dual-beam laser trap (optical stretcher) to induce temperature jumps within milliseconds, while simultaneously measuring the mechanical response of whole cells to optical force. The cellular mechanical response was found to differ between sudden temperature changes compared to slow, long-term changes implying adaptation of cytoskeletal structure. Interpreting optically induced cell deformation as a thermorheological experiment allows us to consistently explain data on the basis of time-temperature superposition, well known from classical polymer physics. Measured time shift factors give access to the activation energy of the viscous flow of MCF-10A breast cells, which was determined to be ≈ 80 kJ mol −1 . The presented measurements highlight the fundamental role that temperature plays for the deformability of cellular matter. We propose thermorheology as a powerful concept to assess the inherent material properties of living cells and to investigate cell regulatory responses upon environmental changes.

Investigation of temperature effect on cell mechanics by optofluidic microchips

“…(2)) on temperature is reported in Fig. 4(a), showing that higher values of Var are observed at higher temperatures, in agreement with results recently reported in literature [10,11]. In order to evaluate the significance of the differences, Mann-Whitney U-test was performed as the population was non-normal according to the Kolmogorov-Smirnov test.…”

“…The obtained results on optical deformability showed a statistically significant difference (p < 10 −3 ) between all the five temperatures. As known from literature [10,21,22], laser power can induce a sudden increase of the cell temperature, making it difficult to compare the deformation values obtained at different optical power levels. As in our case the same optical power is applied to all OS measurements, we expect an increase of about 30°C in the irradiated region for all the samples, provided that absorption coefficient changes due to the different temperatures are negligible.…”

“…Different techniques for cell-mechanics study, ranging from micropipette aspiration to atomic force microscopy and optical stretching, have been extensively studied and summarized in literature [9]. Thermo-rheological experiments have been recently reported in literature [10], and optical stretchers have been exploited to analyze cell deformability as a function of environmental temperature, allowing to obtain detailed data about temperature-sensitive transient receptor potential vanilloid (TRPV2) and thermal unbinding of transient cross-links [11]. In this study, we investigate the temperature impact on cell mechanics by focusing on long-term temperature effect in a wide range of temperatures (~0 -35 °C), especially in the low-temperature range.…”

Myosin II Activity Softens Cells in Suspension

“…Owing to the fact that the OS, operated at a wavelength of 1064 nm, might introduce additional heating effects that can impact cell rheology (34,38,39), we employed a MMM to confirm the impact of changes to suspended cell mechanical properties free from heating artifacts (see Materials and Methods). In this setup, cells were advected sequentially through a long microchannel with many constrictions smaller than the cell diameter using driving pressures within physiological range (50 mbar) (Fig.…”

Physical probing of cells

“…Interestingly, cells became effectively stiffer with blebbistatin treatment, which is in contrast to measurements by AFM and the dual optical trap [43]. Recently, it was shown that next to the optical deformation of a cell, there is also a significant thermal effect on the sample that allows to induce rapid changes in temperature [44]. Exploiting this thermal effect, the optical stretcher setup therefore allows a new class of experiments called 'thermorheology' that go beyond purely mechanical deformation.…”