The viscoelastic habits of sentimental supplies, particularly cells and tissues, has been extensively investigated because of its significance in lots of organic and physiological processes that happen throughout improvement and even illness.*
Many methods 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 in style strategies because of its conformity with varied materials sorts and geometries and the slightly easy evaluation means 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 alerts 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 of, corresponding to the fabric being homogeneous, isotropic, and linearly elastic. *
Cells and tissues, nevertheless, present not solely elastic but additionally viscous habits that’s evident from the hysteresis between the strategy and retraction segments of the force-indentation curve. Consequently, assessing this viscoelastic habits is crucial for understanding the advanced nature of organic matter.*
Quite a few 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 alerts and consider its section lag. These approaches require the person to change the probing technique 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 high of that, in lots of research, the organic supplies had been probed with a linear strategy adopted by speedy 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. Nonetheless, further info regarding vitality 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 sentimental supplies from AFM force-indentation curves. *
To assemble the express relation of pressure and indentation, the authors first use a generalization of Maxwell and Kelvin-Voigt fashions to explain gentle 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. *
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 parts and processes.
Lastly, the authors apply the becoming mannequin to quite a few 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 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 show 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 completely 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 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 had been modified by gluing 5 μm diameter polystyrene beads to the underside of the AFM cantilevers utilizing two part glue.*
The AFM cantilevers had been calibrated prior to every experiment utilizing the thermal noise technique 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 Artistic Commons Attribution 4.0 Worldwide License, which allows use, sharing, adaptation, distribution and copy 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 Artistic Commons license, and point out if adjustments had been made. The pictures or different third-party materials on this article are included within the article’s Artistic 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 Artistic Commons license and your meant use is just not permitted by statutory regulation or exceeds the permitted use, you will want to acquire permission instantly from the copyright holder. To view a duplicate of this license, go to https://creativecommons.org/licenses/by/4.0/.