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Single-Molecule Kinetics
Published in Clive R. Bagshaw, Biomolecular Kinetics, 2017
Magnetic tweezers require the attachment of a micrometer-diameter magnetic bead to the molecule of interest [669–671]. Strong permanent magnets or electromagnets are positioned within a few millimeters from the sample and exert a force on the magnetic bead. The force can be changed by changing the distance between the sample and magnet or the current applied to an electromagnet. Torque can be applied by rotating the magnet. The latter is of particular interest in studying DNA, where super-coiling and unwinding are mechanical properties central to its function. Magnetic tweezers are simpler to set up than optical traps but are less versatile in their ability to rapidly change the force. Higher forces can be achieved by coupling the molecule of interest between the substrate and a cantilever of an atomic force microscope [672,673]. Glass microneedles have also been used to monitor force, where bending is followed directly by imaging [674].
Mechanical properties of human glioma
Published in Neurological Research, 2020
Abraham Tsitlakidis, Elias C. Aifantis, Aristeidis Kritis, Anastasia S. Tsingotjidou, Angeliki Cheva, Panagiotis Selviaridis, Nicolas Foroglou
A disadvantage of AFM nanoindentation, due to its versatility, is that the estimated elastic modulus may differ between experimental setups. Therefore, the conditions imposed on every study have produced an assortment of conflicting results. As an example, very thin samples or large indentation depth may result in overestimation of the elastic modulus, due to the substrate effect, i.e. the influence of the typically hard substrate [50]. Additionally, very low indentation speeds (<1 μm/s) may lead to viscous dissipation, while indenting at very high speed (>10 μm/s) may lead to increased forces due to hydrodynamic drag. Moreover, tip shape plays a pivotal role in the determination of elastic modulus. Spherical probes tend to apply forces in a uniform way and they are less prone to cause sample damage, strain hardening, or substrate effect [51]. As a consequence, results of AFM nanoindentation using spherical tips agree with other sensitive at low applied forces techniques, like optical and magnetic tweezers [52]. Conversely, sharp tips, although better for mapping surfaces, may cause nonlinear elastic or inelastic behavior [53] with more prominent viscous effects [54]. In addition, because of the higher pressures involved, strain hardening and substrate effects cannot be excluded. As a result, the elastic modulus tends to be overestimated [52]. Furthermore, buffer composition [55], osmolarity, and pH [56] also affect the measurements, often leading to an overestimation of the elastic modulus [57].
Auxeticity in biosystems: an exemplification of its effects on the mechanobiology of heterogeneous living cells
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2022
Sundeep Singh, Roderick Melnik
Biological cells are constantly exposed and must respond to a variety of extracellular and intracellular mechanical loads in vivo (Haase and Pelling 2015). This continual process of sensing, transmission and responding to the external mechanical stimuli is known as mechanotransduction. It is critical for maintenance of normal cell functioning and development, such as in growth, motility, differentiation, proliferation and apoptosis, and the application of this process has attracted widespread attention in modern medical therapies such as in the fields of tissue engineering, regenerative medicine and some disease treatments (Haase and Pelling 2015; Basoli et al. 2018; Liu et al. 2019; Singh et al. 2020). In recent years, tremendous focus has been given to understanding how the mechanical properties influence the cellular dynamics with respect to its surrounding microenvironment. A better understanding of mechanotransduction mechanisms would pave the way for further improvements and inventions in the areas of early disease diagnoses and treatments, as well as drug development. Furthermore, advances in the mechanics of biological cells have fueled the development of several biophysical techniques to measure the mechanical properties of the cell, viz., optical stretcher, atomic force microscopy (AFM), magnetic tweezer, micropipette aspiration and traction force microscopy (Addae-Mensah and Wikswo 2008; Ding et al. 2017; Basoli et al. 2018). Among these experimental techniques, AFM has become the most popular and powerful tool for mechanical characterization of both healthy and diseased cells at different stages of the cell-cycle, due to its enhanced capabilities in precise force and location control (Melnik et al. 2009; Basoli et al. 2018; Krieg et al. 2019; Liu et al. 2019; Garcia et al. 2020). The experimental sample preparation of the AFM requires the deposition, absorption or culture of the cell specimen on the rigid support (e.g. mica, glass or silicon) (Garcia and Garcia 2018b). Once prepared, the sample is indented with a tip-cantilever system and the force-distance (or indentation) curve is recorded at the AFM tip that reflects the deformation of the cantilever against a prescribed force into the sample, which is utilized to quantify the mechanical properties of cells (Basoli et al. 2018).