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      In situ determination of exerted forces in magnetic pulling cytometry

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      AIP Advances
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          Abstract

          Localized application of exogenous forces on soft biomaterials and cells is often essential for the study of their response to external mechanical stimuli. Magnetic means of applying forces, particularly those based on permanent magnets and magnetic beads coupled to substrates or cells provide an accessible means of exerting forces of appropriate magnitude. The amount of force exerted, however, is often inferred from calibration performed ex situ, with typically similar but different magnetic beads. Here, we construct a simple magnetic tweezer by coupling a pencil-shaped stainless-steel probe to permanent neodymium magnets using a 3D printed adapter. We then demonstrate the in situ determination of magnetic bead pulling forces on a super-paramagnetic micro-bead coupled to a soft substrate using traction force microscopy. We determine the force exerted on the magnetic bead by the magnet probe – and thus exerted by the magnetic bead on the soft polyacrylamide substrate – as a function of the distance between the probe tip and the magnetic bead. We also show that we can determine the force exerted on a magnetic bead coupled to a cell by the changes in the traction force exerted by the cell on the soft substrate beneath. We thus demonstrate that forces of nanonewton magnitude can be locally exerted on soft substrates or cells and simultaneously determined using traction force microscopy. Application of this method for the in situ measurement of localized exogenous forces exerted on cells can also enable dissection of cellular force transmission pathways.

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          Most cited references25

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          Mechanotransduction at cell-matrix and cell-cell contacts.

          Mechanical forces play an important role in the organization, growth, maturation, and function of living tissues. At the cellular level, many of the biological responses to external forces originate at two types of specialized microscale structures: focal adhesions that link cells to their surrounding extracellular matrix and adherens junctions that link adjacent cells. Transmission of forces from outside the cell through cell-matrix and cell-cell contacts appears to control the maturation or disassembly of these adhesions and initiates intracellular signaling cascades that ultimately alter many cellular behaviors. In response to externally applied forces, cells actively rearrange the organization and contractile activity of the cytoskeleton and redistribute their intracellular forces. Recent studies suggest that the localized concentration of these cytoskeletal tensions at adhesions is also a major mediator of mechanical signaling. This review summarizes the role of mechanical forces in the formation, stabilization, and dissociation of focal adhesions and adherens junctions and outlines how integration of signals from these adhesions over the entire cell body affects how a cell responds to its mechanical environment. This review also describes advanced optical, lithographic, and computational techniques for the study of mechanotransduction.
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            Mechanotransduction: use the force(s)

            Mechanotransduction - how cells sense physical forces and translate them into biochemical and biological responses - is a vibrant and rapidly-progressing field, and is important for a broad range of biological phenomena. This forum explores the role of mechanotransduction in a variety of cellular activities and highlights intriguing questions that deserve further attention.
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              Calculation of forces at focal adhesions from elastic substrate data: the effect of localized force and the need for regularization.

              Forces exerted by stationary cells have been investigated on the level of single focal adhesions by combining elastic substrates, fluorescence labeling of focal adhesions, and the assumption of localized force when solving the inverse problem of linear elasticity theory. Data simulation confirms that the inverse problem is ill-posed in the presence of noise and shows that in general a regularization scheme is needed to arrive at a reliable force estimate. Spatial and force resolution are restricted by the smoothing action of the elastic kernel, depend on the details of the force and displacement patterns, and are estimated by data simulation. Corrections arising from the spatial distribution of force and from finite substrate size are treated in the framework of a force multipolar expansion. Our method is computationally cheap and could be used to study mechanical activity of cells in real time.
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                Author and article information

                Contributors
                Journal
                AIP Adv
                AIP Adv
                AAIDBI
                AIP Advances
                AIP Publishing LLC
                2158-3226
                14 March 2019
                March 2019
                14 March 2019
                : 9
                : 3
                : 035221
                Affiliations
                Mechanical & Aerospace Engineering, Old Dominion University , Kaufman 238e, 1 Old Dominion University, Norfolk, Virginia 23529, USA
                Author notes
                [a) ]Corresponding author’s address: Venkat Maruthamuthu. phone: 1-757-683-4978. fax: 1-757-683-5344 e-mail: vmarutha@ 123456odu.edu
                Article
                045903ADV 1.5084261 ADV18-AR-03984-TR1
                10.1063/1.5084261
                6417906
                30915259
                f9077124-1e94-4e10-89f2-30dd62fd0201
                © 2019 Author(s).

                2158-3226/2019/9(3)/035221/6/ $0.00

                All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 05 December 2018
                : 05 March 2019
                Page count
                Pages: 6
                Funding
                Funded by: National Institute of General Medical Sciences http://dx.doi.org/10.13039/100000057
                Award ID: 1R15GM116082
                Categories
                Regular Articles
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