Microrheology for cell elasticity and viscosity measurements
Cell elasticity and viscosity characterization is now possible using the built-in active microrheology routine of our SENSOCELL optical tweezers. The system performs the analysis of the local viscoelastic properties of your cells, hydrogels or other biological material in an automatized and straightforward manner.
Microrheology measurements of local cell elasticity and cell viscosity
Perform active micro-rheology experiments in viscoelastic media like the cell’s cytoplasm or the cell nucleus with SENSOCELL optical tweezers and obtain the local storage and loss shear modulus G’ and G”. Here, the stored energy term G’ represents the elastic behavior and the (heat) energy dissipation term G” represents the viscous behavior of the sample, thus giving values of the local cell elasticity and viscosity. Using our automatized active microrheology routine, you will obtain local and direct measurements of G’ and G” in your region of interest, decoupling the results from the contribution of other regions of your sample cell. The system can optically trap native structure such as vesicles, lipid droplets or use internalized microspheres as handles to impose an active oscillatory perturbation while tracking the exerted force and the particle’s position to compute G’ and G”.
Active microrheology in cells, extracellular matrix, gels or tissues
With SENSOCELL optical tweezers you will be able to measure the viscoelastic properties inside living cells, in extracellular matrix, gels or tissues with stiffnesses ranging from tens of Pa to several kPa and at probing frequencies up to the kHz regime. The built-in active microrheology routine works in an easy and intuitive fashion for non-expert users. Just introduce the amplitude and frequency range of the oscillatory perturbation and get the results!
Application example 1. Active micro-rheology of water:glycerol mixtures and polyacrylamide gels.
Application example 2. Intracellular active micro-rheology inside living mouse embryos and oocytes.
Application Note. Micro-rheology of soft biological samples using SENSOCELL optical tweezers.
Active micro-rheology of water:glycerol mixtures and polyacrylamide gels
In collaboration with BIOPT lab from the University of Barcelona.
In this experiment, 3-micron latex beads were added to different water:glycerol mixtures (0%, 20%, 40%, 60% and 80% glycerol in water). For each single experiment, a bead was trapped using our SENSOCELL optical tweezers and forced to oscillate sinusoidally with 200 nm amplitude at increasing frequencies (3Hz to 100 Hz) launching the active microrheology built-in routine. The calculated viscosity values were then obtained by fitting the frequency dependence of the measured loss modulus (G”).
Fig. 1 Left: example of measured loss moduli at increasing frequencies for a 40% glycerol mixture. Right: predicted versus measured viscosity values of the different mixtures (increasing viscosity values correspond to increasing glycerol percentages). Symbols indicate mean of 9 different beads probed, error bars indicate S.D.
Viscoelastic properties of soft gels
In a similar fashion, active micro-rheology experiments can be carried out inside polyacrylamide gels with embedded micrometer beads to get their complex shear moduli.
Fig 2. Example of the frequency-dependent behavior of the complex shear moduli of soft polyacrylamide gels. Blue symbols indicate storage modulus (G’) and red symbols indicate loss modulus (G”). Symbols are median values and error bars indicate Q1 and Q3 ranges. N = 13 beads probed for this experiment.
Intracellular active micro-rheology inside living mouse embryos and oocytes
Here we present some preliminary data of micro-rheology tests carried out inside mouse oocytes and mouse early embryos Samples were kindly provided by Dr. Maria Almonacid from College de France and Dr. Jean Leon Maitre from Institute Curie. For these tests, no beads were internalized. Instead, endogenous vesicles located inside the cells’ cytoplasm were optically trapped and used as probes. The vesicles were forced to oscillate sinusoidally with 200 nm amplitude at increasing frequencies (10 Hz to 100 Hz) . Below we show the frequency-dependent behavior of the complex shear moduli obtained for some of these tests.
Fig 1. Example of the frequency-dependent behavior of the complex shear moduli data obtained for tests carried out inside the cytoplasm of mouse oocytes (left) and early mouse embryo cells (right).
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Micro-rheology of soft biological samples using optical tweezers
Publications related with intracellular active microrheology using our technology:
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