The viscoelastic habits of soppy supplies, particularly cells and tissues, has been extensively investigated as a result of its significance in lots of organic and physiological processes that happen throughout growth and even illness.*
Many methods are used to quantify the mechanical properties of cells, amongst them micropipette aspiration, optical stretching, deformability cytometry and atomic drive microscopy (AFM).*
The AFM, particularly, remains to be these days one of the vital widespread strategies as a result of its conformity with numerous materials varieties and geometries and the reasonably 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 drive 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 method 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, reminiscent of the fabric being homogeneous, isotropic, and linearly elastic. *
Cells and tissues, nonetheless, present not solely elastic but in addition viscous habits that’s evident from the hysteresis between the method and retraction segments of the force-indentation curve. Consequently, assessing this viscoelastic habits is crucial for understanding the advanced nature of organic matter.*
Numerous research utilized AFM to measure the viscoelastic properties of cells in each time and frequency domains.*
Ideally, to research the entire vary of the viscoelastic habits 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 person 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 encompassing medium. On high of that, in a lot of research, the organic supplies have been probed with a linear method adopted by speedy retraction. The force-indentation curves from these research have been used to judge the obvious elastic modulus of the probed materials utilizing the usual Hertzian mannequin. Nonetheless, further data regarding power dissipation can nonetheless be extracted from the identical curves to judge the viscoelasticity of the fabric.*
Within the article “An specific 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 express relation of drive and indentation, the authors first use a generalization of Maxwell and Kelvin-Voigt fashions to explain smooth 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 completely different mechanical traits. *
Primarily based on the simulation outcomes, Shada Abuhattum et al. additional suggest an specific force-indentation relation to be fitted to the force-indentation curves. This specific relation simplifies the affiliation of the mechanical properties with bodily significant parts and processes.
Lastly, the authors apply the becoming mannequin to a variety of samples, together with poroelastic and viscoelastic hydrogels in addition to HeLa cells in two completely different cell cycle phases, interphase and mitotic. *
Shada Abuhattum et al. show that the distinct nature of the hydrogels, arising from the completely different crosslinking mechanisms, will be described with the becoming mannequin. For the HeLa cells, the mitotic cells had the next obvious elasticity and a decrease obvious viscosity, implying a stiffer actin cortex and a diluted cytoplasm protein focus, compared with interphase cells.*
Their findings show that the proposed mannequin can reliably extract viscoelastic properties from typical force-indentation curves. Furthermore, the mannequin is ready to assess the contribution of the completely different elastic and viscous components, and thus permits a direct comparability between the viscoelastic nature of various supplies.*
AFM measurements have been preformed utilizing a commercially out there Atomic Power Microscope. To indent the samples, NanoWorld Pyrex-Nitride tipless AFM cantilevers PNP-TR-TL with a nominal spring fixed of 0.08 mN/m have been modified by gluing 5 μm diameter polystyrene beads to the underside of the AFM cantilevers utilizing two element glue.*
The AFM cantilevers have 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 relentless velocity (5, 10, or 15 μm/s) towards the floor of the pattern till a drive of two nN for agarose and 4 nN for PAAm was reached. These drive set factors accounted for an indentation within the vary of 0.5–1 μm. For HeLa cells, the AFM cantilever was lowered with a relentless velocity of two μm/s and the cells have been indented till a drive 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 specific 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 specific 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 underneath 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 modifications have been made. The photographs or different third-party materials on this article are included within the article’s Inventive Commons license, except indicated in any other case in a credit score line to the fabric. If materials will not be included within the article’s Inventive Commons license and your supposed use will not be 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/.