The viscoelastic conduct of soppy supplies, particularly cells and tissues, has been extensively investigated on account of its significance in lots of organic and physiological processes that happen throughout growth and even illness.*
Many strategies are used to quantify the mechanical properties of cells, amongst them micropipette aspiration, optical stretching, deformability cytometry and atomic pressure microscopy (AFM).*
The AFM, particularly, remains to be these days one of the vital common strategies on account of its conformity with numerous materials varieties and geometries and the fairly easy evaluation strategy of the fabric properties.*
For a typical AFM indentation measurement, an AFM cantilever, with a definite AFM tip form, strikes towards the pattern with a predefined velocity and indents it till a prescribed pressure is reached. The AFM cantilever then strikes upwards whereas detaching from the pattern. The deflection and displacement indicators of the AFM cantilever are processed additional to extract the mechanical properties of the pattern. Usually, a Hertzian mannequin is fitted to the strategy a part of the force-indentation curves to quantify the obvious Younger’s modulus.*
When making use of the Hertzian mannequin, few assumptions must be thought-about, similar to the fabric being homogeneous, isotropic, and linearly elastic. *
Cells and tissues, nonetheless, present not solely elastic but in addition viscous conduct that’s evident from the hysteresis between the strategy and retraction segments of the force-indentation curve. Consequently, assessing this viscoelastic conduct is crucial for understanding the advanced nature of organic matter.*
A variety of research utilized AFM to measure the viscoelastic properties of cells in each time and frequency domains.*
Ideally, to analyze the entire vary of the viscoelastic conduct one must probe the fabric for a very long time and observe its response or apply oscillatory indicators and consider its section lag. These approaches require the consumer to change the probing methodology and add a number of steps to account for the time-dependent drift or the impact of the hydrodynamic drag of the encircling medium. On prime of that, in a lot of research, the organic supplies had been probed with a linear strategy adopted by rapid retraction. The force-indentation curves from these research had been used to guage the obvious elastic modulus of the probed materials utilizing the usual Hertzian mannequin. Nevertheless, extra info regarding power dissipation can nonetheless be extracted from the identical curves to guage the viscoelasticity of the fabric.*
Within the article “An express mannequin to extract viscoelastic properties of cells from AFM force-indentation curves”, Shada Abuhattum, Dominic Mokbel, Paul Müller, Despina Soteriou, Jochen Guck and Sebastian Aland suggest a brand new becoming mannequin to extract the viscoelastic properties of soppy supplies from AFM force-indentation curves. *
To assemble the specific relation of pressure and indentation, the authors first use a generalization of Maxwell and Kelvin-Voigt fashions to explain tender supplies, and numerically simulate the indentation of such materials with a spherical indenter. *
Shada Abuhattum et al. present that the proposed Kelvin-Voigt-Maxwell (KVM) mannequin adequately captures the force-indentation curves of supplies having totally different mechanical traits. *
Based mostly on the simulation outcomes, Shada Abuhattum et al. additional suggest an express force-indentation relation to be fitted to the force-indentation curves. This express relation simplifies the affiliation of the mechanical properties with bodily significant elements and processes.
Lastly, the authors apply the becoming mannequin to plenty of samples, together with poroelastic and viscoelastic hydrogels in addition to HeLa cells in two totally different cell cycle phases, interphase and mitotic. *
Shada Abuhattum et al. reveal that the distinct nature of the hydrogels, arising from the totally different crosslinking mechanisms, will be described with the becoming mannequin. For the HeLa cells, the mitotic cells had a better obvious elasticity and a decrease obvious viscosity, implying a stiffer actin cortex and a diluted cytoplasm protein focus, when put next with interphase cells.*
Their findings reveal that the proposed mannequin can reliably extract viscoelastic properties from standard force-indentation curves. Furthermore, the mannequin is ready to assess the contribution of the totally different elastic and viscous parts, and thus permits a direct comparability between the viscoelastic nature of various supplies.*
AFM measurements had been preformed utilizing a commercially accessible Atomic Drive Microscope. To indent the samples, NanoWorld Pyrex-Nitride tipless AFM cantilevers PNP-TR-TL with a nominal spring fixed of 0.08 mN/m had been modified by gluing 5 μm diameter polystyrene beads to the underside of the AFM cantilevers utilizing two element glue.*
The AFM cantilevers had been calibrated prior to every experiment utilizing the thermal noise methodology and their correct spring fixed ranged between 0.047-0.059 mN/m. For PAAm and agarose hydrogels, the AFM cantilever was lowered with a continuing velocity (5, 10, or 15 μm/s) towards the floor of the pattern till a pressure of two nN for agarose and 4 nN for PAAm was reached. These pressure set factors accounted for an indentation within the vary of 0.5–1 μm. For HeLa cells, the AFM cantilever was lowered with a continuing velocity of two μm/s and the cells had been indented till a pressure of two nN was reached, which accounted for an indentation depth within the vary of 0.5–1.5 μm.*
*Shada Abuhattum, Dominic Mokbel, Paul Müller, Despina Soteriou, Jochen Guck and Sebastian Aland
An express mannequin to extract viscoelastic properties of cells from AFM force-indentation curves
iScience, Quantity 25, ISSUE 4, 104016, April 15, 2022
DOI: https://doi.org/10.1016/j.isci.2022.104016
The article “An express mannequin to extract viscoelastic properties of cells from AFM force-indentation curves” by Shada Abuhattum, Dominic Mokbel, Paul Müller, Despina Soteriou, Jochen Guck and Sebastian Aland is licensed beneath a Inventive Commons Attribution 4.0 Worldwide License, which allows use, sharing, adaptation, distribution and replica in any medium or format, so long as you give acceptable credit score to the unique creator(s) and the supply, present a hyperlink to the Inventive Commons license, and point out if adjustments had been made. The photographs or different third-party materials on this article are included within the article’s Inventive Commons license, until indicated in any other case in a credit score line to the fabric. If materials is just not included within the article’s Inventive Commons license and your supposed use is just not permitted by statutory regulation or exceeds the permitted use, you’ll need to acquire permission immediately from the copyright holder. To view a duplicate of this license, go to https://creativecommons.org/licenses/by/4.0/.