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Boghdady CM, Kalashnikov N, Mok S, McCaffrey L, Moraes C. Revisiting tissue tensegrity: Biomaterial-based approaches to measure forces across length scales. APL Bioeng 2021; 5:041501. [PMID: 34632250 PMCID: PMC8487350 DOI: 10.1063/5.0046093] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2021] [Accepted: 09/08/2021] [Indexed: 12/18/2022] Open
Abstract
Cell-generated forces play a foundational role in tissue dynamics and homeostasis and are critically important in several biological processes, including cell migration, wound healing, morphogenesis, and cancer metastasis. Quantifying such forces in vivo is technically challenging and requires novel strategies that capture mechanical information across molecular, cellular, and tissue length scales, while allowing these studies to be performed in physiologically realistic biological models. Advanced biomaterials can be designed to non-destructively measure these stresses in vitro, and here, we review mechanical characterizations and force-sensing biomaterial-based technologies to provide insight into the mechanical nature of tissue processes. We specifically and uniquely focus on the use of these techniques to identify characteristics of cell and tissue "tensegrity:" the hierarchical and modular interplay between tension and compression that provide biological tissues with remarkable mechanical properties and behaviors. Based on these observed patterns, we highlight and discuss the emerging role of tensegrity at multiple length scales in tissue dynamics from homeostasis, to morphogenesis, to pathological dysfunction.
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Affiliation(s)
| | - Nikita Kalashnikov
- Department of Chemical Engineering, McGill University, Montréal, Québec H3A 0C5, Canada
| | - Stephanie Mok
- Department of Chemical Engineering, McGill University, Montréal, Québec H3A 0C5, Canada
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2
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Shellard A, Mayor R. Durotaxis: The Hard Path from In Vitro to In Vivo. Dev Cell 2020; 56:227-239. [PMID: 33290722 DOI: 10.1016/j.devcel.2020.11.019] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Revised: 09/21/2020] [Accepted: 11/17/2020] [Indexed: 01/21/2023]
Abstract
Durotaxis, the process by which cells follow gradients of extracellular mechanical stiffness, has been proposed as a mechanism driving directed migration. Despite the lack of evidence for its existence in vivo, durotaxis has become an active field of research, focusing on the mechanism by which cells respond to mechanical stimuli from the environment. In this review, we describe the technical and conceptual advances in the study of durotaxis in vitro, discuss to what extent the evidence suggests durotaxis may occur in vivo, and emphasize the urgent need for in vivo demonstration of durotaxis.
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Affiliation(s)
- Adam Shellard
- Department of Cell and Developmental Biology, University College London, Gower Street, London WC1E 6BT, UK
| | - Roberto Mayor
- Department of Cell and Developmental Biology, University College London, Gower Street, London WC1E 6BT, UK.
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3
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Salvador-Clavell R, Rodríguez-Fortún JM, López I, Martín de Llano JJ, Orús J, Sancho-Tello M, Carda C, Doweidar MH. Design and experimental validation of a magnetic device for stem cell culture. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2020; 91:124103. [PMID: 33379939 DOI: 10.1063/5.0016374] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Accepted: 11/23/2020] [Indexed: 06/12/2023]
Abstract
Cell culture of bone and tendon tissues requires mechanical stimulation of the cells in order to mimic their physiological state. In the present work, a device has been conceived and developed to generate a controlled magnetic field with a homogeneous gradient in the working space. The design requirement was to maximize the magnetic flux gradient, assuring a minimum magnetizing value in a 15 mm × 15 mm working area, which highly increases the normal operating range of this sort of devices. The objective is to use the machine for two types of biological tests: magnetic irradiation of biological samples and force generation on paramagnetic particles embedded in scaffolds for cell culture. The device has been manufactured and experimentally validated by evaluating the force exerted on magnetic particles in a viscous fluid. Apart from the magnetic validation, the device has been tested for irradiating biological samples. In this case, viability of human dental pulp stem cells has been studied in vitro after electromagnetic field exposition using the designed device. After three days of irradiation treatment, cellular microtissues showed a 59% increase in the viable cell number. Irradiated cells did not show morphological differences when compared with control cells.
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Affiliation(s)
- Rubén Salvador-Clavell
- Departamento de Patología, Facultad de Medicina y Odontología, Universitat de València, València 46010, Spain
| | | | - Irene López
- Instituto Tecnológico de Aragón (ITAINNOVA), Zaragoza 50018, Spain
| | - José Javier Martín de Llano
- Departamento de Patología, Facultad de Medicina y Odontología, Universitat de València, València 46010, Spain
| | - Javier Orús
- Instituto Tecnológico de Aragón (ITAINNOVA), Zaragoza 50018, Spain
| | - María Sancho-Tello
- Departamento de Patología, Facultad de Medicina y Odontología, Universitat de València, València 46010, Spain
| | - Carmen Carda
- Departamento de Patología, Facultad de Medicina y Odontología, Universitat de València, València 46010, Spain
| | - Mohamed H Doweidar
- Centro de Investigación Biomédica en Red en Bioingeniería, Biomateriales y Nanomedicina (CIBER-BBN), Madrid 28029, Spain
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4
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Spatial mapping of tissue properties in vivo reveals a 3D stiffness gradient in the mouse limb bud. Proc Natl Acad Sci U S A 2020; 117:4781-4791. [PMID: 32071242 DOI: 10.1073/pnas.1912656117] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Numerous hypotheses invoke tissue stiffness as a key parameter that regulates morphogenesis and disease progression. However, current methods are insufficient to test hypotheses that concern physical properties deep in living tissues. Here we introduce, validate, and apply a magnetic device that generates a uniform magnetic field gradient within a space that is sufficient to accommodate an organ-stage mouse embryo under live conditions. The method allows rapid, nontoxic measurement of the three-dimensional (3D) spatial distribution of viscoelastic properties within mesenchyme and epithelia. Using the device, we identify an anteriorly biased mesodermal stiffness gradient along which cells move to shape the early limb bud. The stiffness gradient corresponds to a Wnt5a-dependent domain of fibronectin expression, raising the possibility that durotaxis underlies cell movements. Three-dimensional stiffness mapping enables the generation of hypotheses and potentially the rigorous testing of mechanisms of development and disease.
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Fischer L, Menzel AM. Magnetostriction in magnetic gels and elastomers as a function of the internal structure and particle distribution. J Chem Phys 2019; 151:114906. [DOI: 10.1063/1.5118875] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Affiliation(s)
- Lukas Fischer
- Institut für Theoretische Physik II: Weiche Materie, Heinrich-Heine-Universität Düsseldorf, Universitätsstraße 1, D-40225 Düsseldorf, Germany
| | - Andreas M. Menzel
- Institut für Theoretische Physik II: Weiche Materie, Heinrich-Heine-Universität Düsseldorf, Universitätsstraße 1, D-40225 Düsseldorf, Germany
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Moerland CP, van IJzendoorn LJ, Prins MWJ. Rotating magnetic particles for lab-on-chip applications - a comprehensive review. LAB ON A CHIP 2019; 19:919-933. [PMID: 30785138 DOI: 10.1039/c8lc01323c] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Magnetic particles are widely used in lab-on-chip and biosensing applications, because they have a high surface-to-volume ratio, they can be actuated with magnetic fields and many biofunctionalization options are available. The most well-known actuation method is to apply a magnetic field gradient which generates a translational force on the particles and allows separation of the particles from a suspension. A more recently developed magnetic actuation method is to exert torque on magnetic particles by a rotating magnetic field. Rotational actuation can be achieved with a field that is uniform in space and it allows for a precise control of torque, orientation, and angular velocity of magnetic particles in lab-on-chip devices. A wide range of studies have been performed with rotating MPs, demonstrating fluid mixing, concentration determination of biological molecules in solution, and characterization of structure and function of biomolecules at the single-molecule level. In this paper we give a comprehensive review of the historical development of MP rotation studies, including configurations for field generation, physical model descriptions, and biological applications. We conclude by sketching the scientific and technological developments that can be expected in the future in the field of rotating magnetic particles for lab-on-chip applications.
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Affiliation(s)
- C P Moerland
- Department of Applied Physics, Department of Biomedical Engineering, Institute for Complex Molecular Systems, Eindhoven University of Technology, Eindhoven, The Netherlands.
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Khan FA, Akhtar S, Almohazey D, Alomari M, Almofty SA, Eliassari A. Fluorescent magnetic submicronic polymer (FMSP) nanoparticles induce cell death in human colorectal carcinoma cells. ARTIFICIAL CELLS NANOMEDICINE AND BIOTECHNOLOGY 2018; 46:S247-S253. [DOI: 10.1080/21691401.2018.1491476] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Firdos Alam Khan
- Department of Stem Cell Biology, Institute for Research and Medical Consultations, Imam Abdulrahman Bin Faisal University, Dammam, Saudi Arabia
| | - Sultan Akhtar
- Department of Biophysics, Institute for Research and Medical Consultations, Imam Abdulrahman Bin Faisal University, Dammam, Saudi Arabia
| | - Dana Almohazey
- Department of Stem Cell Biology, Institute for Research and Medical Consultations, Imam Abdulrahman Bin Faisal University, Dammam, Saudi Arabia
| | - Munthar Alomari
- Department of Stem Cell Biology, Institute for Research and Medical Consultations, Imam Abdulrahman Bin Faisal University, Dammam, Saudi Arabia
| | - Sarah Ameen Almofty
- Department of Stem Cell Biology, Institute for Research and Medical Consultations, Imam Abdulrahman Bin Faisal University, Dammam, Saudi Arabia
| | - Abdelhamid Eliassari
- University of Lyon, Lyon, France
- LAGEP-CPE, University Lyon 1, Villeurbanne, CNRS, UMR 5007, Villeurbanne, France
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Khan FA, Akhtar S, Almofty SA, Almohazey D, Alomari M. FMSP-Nanoparticles Induced Cell Death on Human Breast Adenocarcinoma Cell Line (MCF-7 Cells): Morphometric Analysis. Biomolecules 2018; 8:biom8020032. [PMID: 29882888 PMCID: PMC6022976 DOI: 10.3390/biom8020032] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2018] [Revised: 05/13/2018] [Accepted: 05/15/2018] [Indexed: 12/15/2022] Open
Abstract
Currently, breast cancer treatment mostly revolves around radiation therapy and surgical interventions, but often these treatments do not provide satisfactory relief to the patients and cause unmanageable side-effects. Nanomaterials show promising results in treating cancer cells and have many advantages such as high biocompatibility, bioavailability and effective therapeutic capabilities. Interestingly, fluorescent magnetic nanoparticles have been used in many biological and diagnostic applications, but there is no report of use of fluorescent magnetic submicronic polymer nanoparticles (FMSP-nanoparticles) in the treatment of human breast cancer cells. In the present study, we tested the effect of FMSP-nanoparticles on human breast cancer cells (MCF-7). We tested different concentrations (1.25, 12.5 and 50 µg/mL) of FMSP-nanoparticles in MCF-7 cells and evaluated the nanoparticles response morphometrically. Our results revealed that FMSP-nanoparticles produced a concentration dependent effect on the cancer cells, a dose of 1.25 µg/mL produced no significant effect on the cancer cell morphology and cell death, whereas dosages of 12.5 and 50 µg/mL resulted in significant nuclear augmentation, disintegration, chromatic condensation followed by dose dependent cell death. Our results demonstrate that FMSP-nanoparticles induce cell death in MCF-7 cells and may be a potential anti-cancer agent for breast cancer treatment.
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Affiliation(s)
- Firdos Alam Khan
- Department of Stem Cell Biology, Institute for Research and Medical Consultations, Imam Abdulrahman Bin Faisal University, Post Box No. 1982, Dammam 31441, Saudi Arabia.
| | - Sultan Akhtar
- Department of Biophysics, Institute for Research and Medical Consultations, Imam Abdulrahman Bin Faisal University, Post Box No. 1982, Dammam 31441, Saudi Arabia.
| | - Sarah Ameen Almofty
- Department of Stem Cell Biology, Institute for Research and Medical Consultations, Imam Abdulrahman Bin Faisal University, Post Box No. 1982, Dammam 31441, Saudi Arabia.
| | - Dana Almohazey
- Department of Stem Cell Biology, Institute for Research and Medical Consultations, Imam Abdulrahman Bin Faisal University, Post Box No. 1982, Dammam 31441, Saudi Arabia.
| | - Munthar Alomari
- Department of Stem Cell Biology, Institute for Research and Medical Consultations, Imam Abdulrahman Bin Faisal University, Post Box No. 1982, Dammam 31441, Saudi Arabia.
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Miller H, Zhou Z, Shepherd J, Wollman AJM, Leake MC. Single-molecule techniques in biophysics: a review of the progress in methods and applications. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2018; 81:024601. [PMID: 28869217 DOI: 10.1088/1361-6633/aa8a02] [Citation(s) in RCA: 70] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Single-molecule biophysics has transformed our understanding of biology, but also of the physics of life. More exotic than simple soft matter, biomatter lives far from thermal equilibrium, covering multiple lengths from the nanoscale of single molecules to up to several orders of magnitude higher in cells, tissues and organisms. Biomolecules are often characterized by underlying instability: multiple metastable free energy states exist, separated by levels of just a few multiples of the thermal energy scale k B T, where k B is the Boltzmann constant and T absolute temperature, implying complex inter-conversion kinetics in the relatively hot, wet environment of active biological matter. A key benefit of single-molecule biophysics techniques is their ability to probe heterogeneity of free energy states across a molecular population, too challenging in general for conventional ensemble average approaches. Parallel developments in experimental and computational techniques have catalysed the birth of multiplexed, correlative techniques to tackle previously intractable biological questions. Experimentally, progress has been driven by improvements in sensitivity and speed of detectors, and the stability and efficiency of light sources, probes and microfluidics. We discuss the motivation and requirements for these recent experiments, including the underpinning mathematics. These methods are broadly divided into tools which detect molecules and those which manipulate them. For the former we discuss the progress of super-resolution microscopy, transformative for addressing many longstanding questions in the life sciences, and for the latter we include progress in 'force spectroscopy' techniques that mechanically perturb molecules. We also consider in silico progress of single-molecule computational physics, and how simulation and experimentation may be drawn together to give a more complete understanding. Increasingly, combinatorial techniques are now used, including correlative atomic force microscopy and fluorescence imaging, to probe questions closer to native physiological behaviour. We identify the trade-offs, limitations and applications of these techniques, and discuss exciting new directions.
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Affiliation(s)
- Helen Miller
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, OX1 3PU, United Kingdom
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10
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Waigh TA. Advances in the microrheology of complex fluids. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2016. [PMID: 27245584 DOI: 10.1088/0034-4885/68/3/r04] [Citation(s) in RCA: 351] [Impact Index Per Article: 43.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
New developments in the microrheology of complex fluids are considered. Firstly the requirements for a simple modern particle tracking microrheology experiment are introduced, the error analysis methods associated with it and the mathematical techniques required to calculate the linear viscoelasticity. Progress in microrheology instrumentation is then described with respect to detectors, light sources, colloidal probes, magnetic tweezers, optical tweezers, diffusing wave spectroscopy, optical coherence tomography, fluorescence correlation spectroscopy, elastic- and quasi-elastic scattering techniques, 3D tracking, single molecule methods, modern microscopy methods and microfluidics. New theoretical techniques are also reviewed such as Bayesian analysis, oversampling, inversion techniques, alternative statistical tools for tracks (angular correlations, first passage probabilities, the kurtosis, motor protein step segmentation etc), issues in micro/macro rheological agreement and two particle methodologies. Applications where microrheology has begun to make some impact are also considered including semi-flexible polymers, gels, microorganism biofilms, intracellular methods, high frequency viscoelasticity, comb polymers, active motile fluids, blood clots, colloids, granular materials, polymers, liquid crystals and foods. Two large emergent areas of microrheology, non-linear microrheology and surface microrheology are also discussed.
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Affiliation(s)
- Thomas Andrew Waigh
- Biological Physics Group, School of Physics and Astronomy, University of Manchester, Oxford Rd., Manchester, M13 9PL, UK. Photon Science Institute, University of Manchester, Oxford Rd., Manchester, M13 9PL, UK
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11
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Lee JH, Dustin ML, Kam LC. A microfluidic platform reveals differential response of regulatory T cells to micropatterned costimulation arrays. Integr Biol (Camb) 2015; 7:1442-53. [PMID: 26400012 PMCID: PMC4630128 DOI: 10.1039/c5ib00215j] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2015] [Accepted: 09/10/2015] [Indexed: 12/28/2022]
Abstract
T cells are key mediators of adaptive immunity. However, the overall immune response is often directed by minor subpopulations of this heterogeneous family of cells, owing to specificity of activation and amplification of functional response. Knowledge of differences in signaling and function between T cell subtypes is far from complete, but is clearly needed for understanding and ultimately leveraging this branch of the adaptive immune response. This report investigates differences in cell response to micropatterned surfaces by conventional and regulatory T cells. Specifically, the ability of cells to respond to the microscale geometry of TCR/CD3 and CD28 engagement is made possible using a magnetic-microfluidic device that overcomes limitations in imaging efficiency associated with conventional microscopy equipment. This device can be readily assembled onto micropatterned surfaces while maintaining the activity of proteins and other biomolecules necessary for such studies. In operation, a target population of cells is tagged using paramagnetic beads, and then trapped in a divergent magnetic field within the chamber. Following washing, the target cells are released to interact with a designated surface. Characterization of this system with mouse CD4(+) T cells demonstrated a 50-fold increase in target-to-background cell purity, with an 80% collection efficiency. Applying this approach to CD4(+)CD25(+) regulatory T cells, it is then demonstrated that these rare cells respond less selectively to micro-scale features of anti-CD3 antibodies than CD4(+)CD25(-) conventional T cells, revealing a difference in balance between TCR/CD3 and LFA-1-based adhesion. PKC-θ localized to the distal pole of regulatory T cells, away from the cell-substrate interface, suggests a mechanism for differential regulation of TCR/LFA-1-based adhesion. Moreover, specificity of cell adhesion to anti-CD3 features was dependent on the relative position of anti-CD28 signaling within the cell-substrate interface, revealing an important role for coincidence of TCR and costimulatory pathway in triggering regulatory T cell function.
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Affiliation(s)
- Joung-Hyun Lee
- Department of Biomedical Engineering, Columbia University in the City of New York, New York, USA.
| | - Michael L Dustin
- Kennedy Institute of Rheumatology, Nuffield Department of Orthopaedics, Rheumatology, and Musculoskeletal Sciences, University of Oxford, Oxford, UK
| | - Lance C Kam
- Department of Biomedical Engineering, Columbia University in the City of New York, New York, USA.
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12
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Sun J, Xiao Y, Wang S, Slepian MJ, Wong PK. Advances in Techniques for Probing Mechanoregulation of Tissue Morphogenesis. ACTA ACUST UNITED AC 2015; 20:127-37. [DOI: 10.1177/2211068214554802] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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Chen L, Offenhäusser A, Krause HJ. Magnetic tweezers with high permeability electromagnets for fast actuation of magnetic beads. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2015; 86:044701. [PMID: 25933874 DOI: 10.1063/1.4916255] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
As a powerful and versatile scientific instrument, magnetic tweezers have been widely used in biophysical research areas, such as mechanical cell properties and single molecule manipulation. If one wants to steer bead position, the nonlinearity of magnetic properties and the strong position dependence of the magnetic field in most magnetic tweezers lead to quite a challenge in their control. In this article, we report multi-pole electromagnetic tweezers with high permeability cores yielding high force output, good maneuverability, and flexible design. For modeling, we adopted a piece-wise linear dependence of magnetization on field to characterize the magnetic beads. We implemented a bi-linear interpolation of magnetic field in the work space, based on a lookup table obtained from finite element simulation. The electronics and software were custom-made to achieve high performance. In addition, the effects of dimension and defect on structure of magnetic tips also were inspected. In a workspace with size of 0.1 × 0.1 mm(2), a force of up to 400 pN can be applied on a 2.8 μm superparamagnetic bead in any direction within the plane. Because the magnetic particle is always pulled towards a tip, the pulling forces from the pole tips have to be well balanced in order to achieve control of the particle's position. Active video tracking based feedback control is implemented, which is able to work at a speed of up to 1 kHz, yielding good maneuverability of the magnetic beads.
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Affiliation(s)
- La Chen
- Institute of Bioelectronics (ICS-8/PGI-8), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
| | - Andreas Offenhäusser
- Institute of Bioelectronics (ICS-8/PGI-8), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
| | - Hans-Joachim Krause
- Institute of Bioelectronics (ICS-8/PGI-8), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
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Sirbuly DJ, Friddle RW, Villanueva J, Huang Q. Nanomechanical force transducers for biomolecular and intracellular measurements: is there room to shrink and why do it? REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2015; 78:024101. [PMID: 25629797 DOI: 10.1088/0034-4885/78/2/024101] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Over the past couple of decades there has been a tremendous amount of progress on the development of ultrasensitive nanomechanical instruments, which has enabled scientists to peer for the first time into the mechanical world of biomolecular systems. Currently, work-horse instruments such as the atomic force microscope and optical/magnetic tweezers have provided the resolution necessary to extract quantitative force data from various molecular systems down to the femtonewton range, but it remains difficult to access the intracellular environment with these analytical tools as they have fairly large sizes and complicated feedback systems. This review is focused on highlighting some of the major milestones and discoveries in the field of biomolecular mechanics that have been made possible by the development of advanced atomic force microscope and tweezer techniques as well as on introducing emerging state-of-the-art nanomechanical force transducers that are addressing the size limitations presented by these standard tools. We will first briefly cover the basic setup and operation of these instruments, and then focus heavily on summarizing advances in in vitro force studies at both the molecular and cellular level. The last part of this review will include strategies for shrinking down the size of force transducers and provide insight into why this may be important for gaining a more complete understanding of cellular activity and function.
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Affiliation(s)
- Donald J Sirbuly
- Department of NanoEngineering, University of California, San Diego, La Jolla, CA 92093, USA. Materials Science and Engineering, University of California, San Diego, La Jolla, CA, 92093, USA
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15
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Cheng P, Jhiang SM, Menq CH. Real-time visual sensing system achieving high-speed 3D particle tracking with nanometer resolution. APPLIED OPTICS 2013; 52:7530-7539. [PMID: 24216655 DOI: 10.1364/ao.52.007530] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2013] [Accepted: 10/04/2013] [Indexed: 06/02/2023]
Abstract
This paper presents a real-time visual sensing system, which is created to achieve high-speed three-dimensional (3D) motion tracking of microscopic spherical particles in aqueous solutions with nanometer resolution. The system comprises a complementary metal-oxide-semiconductor (CMOS) camera, a field programmable gate array (FPGA), and real-time image processing programs. The CMOS camera has high photosensitivity and superior SNR. It acquires images of 128×120 pixels at a frame rate of up to 10,000 frames per second (fps) under the white light illumination from a standard 100 W halogen lamp. The real-time image stream is downloaded from the camera directly to the FPGA, wherein a 3D particle-tracking algorithm is implemented to calculate the 3D positions of the target particle in real time. Two important objectives, i.e., real-time estimation of the 3D position matches the maximum frame rate of the camera and the timing of the output data stream of the system is precisely controlled, are achieved. Two sets of experiments were conducted to demonstrate the performance of the system. First, the visual sensing system was used to track the motion of a 2 μm polystyrene bead, whose motion was controlled by a three-axis piezo motion stage. The ability to track long-range motion with nanometer resolution in all three axes is demonstrated. Second, it was used to measure the Brownian motion of the 2 μm polystyrene bead, which was stabilized in aqueous solution by a laser trapping system.
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Zhang Z, Long F, Menq CH. Three-Dimensional Visual Servo Control of a Magnetically Propelled Microscopic Bead. IEEE T ROBOT 2013. [DOI: 10.1109/tro.2012.2229671] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Cell mechanosensitivity: mechanical properties and interaction with gravitational field. BIOMED RESEARCH INTERNATIONAL 2012; 2013:598461. [PMID: 23509748 PMCID: PMC3591207 DOI: 10.1155/2013/598461] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/07/2012] [Revised: 11/17/2012] [Accepted: 11/27/2012] [Indexed: 02/08/2023]
Abstract
This paper addressed the possible mechanisms of primary reception of a mechanical stimulus by different cells. Data concerning the stiffness of muscle and nonmuscle cells as measured by atomic force microscopy are provided. The changes in the mechanical properties of cells that occur under changed external mechanical tension are presented, and the initial stages of mechanical signal transduction are considered. The possible mechanism of perception of different external mechanical signals by cells is suggested.
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Snook JH, Guilford WH. A High-Throughput Technique Reveals the Load- and Site Density-Dependent Kinetics of E-Selectin. Cell Mol Bioeng 2012; 5:493-503. [PMID: 24511329 PMCID: PMC3915287 DOI: 10.1007/s12195-012-0247-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
The kinetics of bond rupture between receptors and ligand are critically dependent on applied mechanical force. Force spectroscopy of single receptor-ligand pairs to measure kinetics is a laborious and time-consuming process that is generally performed using individual force probes and making one measurement at a time when typically hundreds of measurements are needed. A high-throughput approach is thus desirable. We report here a magnetic bond puller that provides high-throughput measurements of single receptor-ligand bond kinetics. Electromagnets are used to apply pN tensile and compressive forces to receptor-coated magnetic microspheres while monitoring their contact with a ligand-coated surface. Bond lifetimes and the probability of forming a bond are measured via videomicroscopy, and the data are used to determine the load dependent rates of bond rupture and bond formation. The approach is simple, customizable, relatively inexpensive, and can make dozens of kinetic measurements simultaneously. We used the device to investigate how compressive and tensile forces affect the rates of formation and rupture, respectively, of bonds between E-selectin and sialyl Lewisa (sLea), a sugar on P-selectin glycoprotein ligand-1 to which selectins bind. We confirmed earlier findings of a load-dependent rate of bond formation between these two molecules, and that they form a catch-slip bond like other selectin family members. We also make the novel observation of an "ideal" bond in a highly multivalent system of this receptor-ligand pair.
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Affiliation(s)
- Jeremy H Snook
- Department of Biomedical Engineering, University of Virginia, Box 800759, Charlottesville, VA 22908, USA
| | - William H Guilford
- Department of Biomedical Engineering, University of Virginia, Box 800759, Charlottesville, VA 22908, USA
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Tseng P, Judy JW, Di Carlo D. Magnetic nanoparticle-mediated massively parallel mechanical modulation of single-cell behavior. Nat Methods 2012; 9:1113-9. [PMID: 23064517 PMCID: PMC3501759 DOI: 10.1038/nmeth.2210] [Citation(s) in RCA: 127] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2012] [Accepted: 09/06/2012] [Indexed: 12/31/2022]
Abstract
We report a technique for generating controllable, time-varying and localizable forces on arrays of cells in a massively parallel fashion. To achieve this, we grow magnetic nanoparticle-dosed cells in defined patterns on micromagnetic substrates. By manipulating and coalescing nanoparticles within cells, we apply localized nanoparticle-mediated forces approaching cellular yield tensions on the cortex of HeLa cells. We observed highly coordinated responses in cellular behavior, including the p21-activated kinase-dependent generation of active, leading edge-type filopodia and biasing of the metaphase plate during mitosis. The large sample size and rapid sample generation inherent to this approach allow the analysis of cells at an unprecedented rate: in a single experiment, potentially tens of thousands of cells can be stimulated for high statistical accuracy in measurements. This technique shows promise as a tool for both cell analysis and control.
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Affiliation(s)
- Peter Tseng
- Department of Bioengineering, University of California, Los Angeles, Los Angeles, California
- Department of Electrical Engineering, University of California, Los Angeles, Los Angeles, California
| | - Jack W. Judy
- Department of Bioengineering, University of California, Los Angeles, Los Angeles, California
- Department of Electrical Engineering, University of California, Los Angeles, Los Angeles, California
- California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California
| | - Dino Di Carlo
- Department of Bioengineering, University of California, Los Angeles, Los Angeles, California
- California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California
- Jonsson Comprehensive Cancer Center, University of California, Los Angeles, Los Angeles, California
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20
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Mann JM, Lam RHW, Weng S, Sun Y, Fu J. A silicone-based stretchable micropost array membrane for monitoring live-cell subcellular cytoskeletal response. LAB ON A CHIP 2012; 12:731-40. [PMID: 22193351 PMCID: PMC4120061 DOI: 10.1039/c2lc20896b] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
External forces are increasingly recognized as major regulators of cellular structure and function, yet the underlying mechanism by which cells sense forces and transduce them into intracellular biochemical signals and behavioral responses ('mechanotransduction') is largely undetermined. To aid in the mechanistic study of mechanotransduction, herein we devised a cell stretching device that allowed for quantitative control and real-time measurement of mechanical stimuli and cellular biomechanical responses. Our strategy involved a microfabricated array of silicone elastomeric microposts integrated onto a stretchable elastomeric membrane. Using a computer-controlled vacuum, this micropost array membrane (mPAM) was activated to apply equibiaxial cell stretching forces to adherent cells attached to the microposts. Using the mPAM, we studied the live-cell subcellular dynamic responses of contractile forces in vascular smooth muscle cells (VSMCs) to a sustained static equibiaxial cell stretch. Our data showed that in response to a sustained cell stretch, VSMCs regulated their cytoskeletal (CSK) contractility in a biphasic manner: they first acutely enhanced their contraction to resist rapid cell deformation ('stiffening') before they allowed slow adaptive inelastic CSK reorganization to release their contractility ('softening'). The contractile response across entire single VSMCs was spatially inhomogeneous and force-dependent. Our mPAM device and live-cell subcellular contractile measurements will help elucidate the mechanotransductive system in VSMCs and thus contribute to our understanding of pressure-induced vascular disease processes.
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Affiliation(s)
- Jennifer M. Mann
- Integrated Biosystems and Biomechanics Laboratory, University of Michigan, Ann Arbor, MI, 48105, USA
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, 48105, USA
| | - Raymond H. W. Lam
- Integrated Biosystems and Biomechanics Laboratory, University of Michigan, Ann Arbor, MI, 48105, USA
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, 48105, USA
| | - Shinuo Weng
- Integrated Biosystems and Biomechanics Laboratory, University of Michigan, Ann Arbor, MI, 48105, USA
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, 48105, USA
| | - Yubing Sun
- Integrated Biosystems and Biomechanics Laboratory, University of Michigan, Ann Arbor, MI, 48105, USA
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, 48105, USA
| | - Jianping Fu
- Integrated Biosystems and Biomechanics Laboratory, University of Michigan, Ann Arbor, MI, 48105, USA
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, 48105, USA
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, 48105, USA
- Correspondence should be addressed to J. Fu [J. Fu (, Tel: 01-734-615-7363, Fax: 01-734-647-7303)]
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21
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Sadr N, Zhu M, Osaki T, Kakegawa T, Yang Y, Moretti M, Fukuda J, Khademhosseini A. SAM-based cell transfer to photopatterned hydrogels for microengineering vascular-like structures. Biomaterials 2011; 32:7479-90. [PMID: 21802723 DOI: 10.1016/j.biomaterials.2011.06.034] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2011] [Accepted: 06/14/2011] [Indexed: 12/27/2022]
Abstract
A major challenge in tissue engineering is to reproduce the native 3D microvascular architecture fundamental for in vivo functions. Current approaches still lack a network of perfusable vessels with native 3D structural organization. Here we present a new method combining self-assembled monolayer (SAM)-based cell transfer and gelatin methacrylate hydrogel photopatterning techniques for microengineering vascular structures. Human umbilical vein cell (HUVEC) transfer from oligopeptide SAM-coated surfaces to the hydrogel revealed two SAM desorption mechanisms: photoinduced and electrochemically triggered. The former, occurs concomitantly to hydrogel photocrosslinking, and resulted in efficient (>97%) monolayer transfer. The latter, prompted by additional potential application, preserved cell morphology and maintained high transfer efficiency of VE-cadherin positive monolayers over longer culture periods. This approach was also applied to transfer HUVECs to 3D geometrically defined vascular-like structures in hydrogels, which were then maintained in perfusion culture for 15 days. As a step toward more complex constructs, a cell-laden hydrogel layer was photopatterned around the endothelialized channel to mimic the vascular smooth muscle structure of distal arterioles. This study shows that the coupling of the SAM-based cell transfer and hydrogel photocrosslinking could potentially open up new avenues in engineering more complex, vascularized tissue constructs for regenerative medicine and tissue engineering applications.
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Affiliation(s)
- Nasser Sadr
- Center for Biomedical Engineering, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Cambridge, MA 02139, USA
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22
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Zhang Z, Menq CH. Design and Modeling of a 3-D Magnetic Actuator for Magnetic Microbead Manipulation. IEEE/ASME TRANSACTIONS ON MECHATRONICS : A JOINT PUBLICATION OF THE IEEE INDUSTRIAL ELECTRONICS SOCIETY AND THE ASME DYNAMIC SYSTEMS AND CONTROL DIVISION 2011; 16:10.1109/TMECH.2011.2105500. [PMID: 24382943 PMCID: PMC3875236 DOI: 10.1109/tmech.2011.2105500] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
This paper presents the design, implementation, modeling, and analyses of a hexapole magnetic actuator that is capable of 3-D manipulation of a magnetic microbead. The magnetic actuator employs six sharp-tipped magnetic poles placed in hexapole configuration, six actuating coils, and a magnetic yoke. The magnetic poles concentrate the magnetic flux generated by the coils to the workspace, resulting in a high magnetic field with a large field gradient for magnetic force generation on the magnetic microbead. A lumped-parameter magnetic force model is then established to characterize nonlinearity of the magnetic force exerting on the magnetic microbead with respect to the applied currents to the coils and the position dependence of the magnetic force in the workspace. The force generation capability of the designed system is then explored using the force model. Moreover, an inverse force model is derived and its effect on the magnetic actuation capability is investigated. The inverse force model facilitates the implementation of a feedback control law to stabilize and control the motion of a magnetic microbead. Experimental results in terms of the magnetic force in relation to stable motion control of a magnetic microbead are used to validate the force model.
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Affiliation(s)
- Zhipeng Zhang
- Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, OH 43210 USA. He is now with the GE Global Research Center, Niskayuna, NY 12309 USA ( )
| | - Chia-Hsiang Menq
- Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, OH 43210 USA ( )
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23
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Bamrungsap S, Phillips JA, Xiong X, Kim Y, Wang H, Liu H, Hebard A, Tan W. Magnetically driven single DNA nanomotor. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2011; 7:601-605. [PMID: 21370463 DOI: 10.1002/smll.201001559] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2010] [Indexed: 05/30/2023]
Affiliation(s)
- Suwussa Bamrungsap
- Center for Research at the Bio/nano Interface, Department of Chemistry, Shands Cancer Center, University of Florida, Gainesville, FL 32611-7200, USA
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24
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Teo KY, Dutton JC, Han B. Spatiotemporal measurement of freezing-induced deformation of engineered tissues. J Biomech Eng 2010; 132:031003. [PMID: 20459191 DOI: 10.1115/1.4000875] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
In order to cryopreserve functional engineered tissues (ETs), the microstructure of the extracellular matrix (ECM) should be maintained, as well as the cellular viability since the functionality is closely related to the ECM microstructure. Since the post-thaw ECM microstructure is determined by the deformation of ETs during cryopreservation, freezing-induced deformation of ETs was measured with a newly developed quantum dot (QD)-mediated cell image deformetry system using dermal equivalents as a model tissue. The dermal equivalents were constructed by seeding QD-labeled fibroblasts in type I collagen matrices. After 24 h incubation, the ETs were directionally frozen by exposing them to a spatial temperature gradient (from 4 degrees C to -20 degrees C over a distance of 6 mm). While being frozen, the ETs were consecutively imaged, and consecutive pairs of these images were two-dimensionally cross-correlated to determine the local deformation during freezing. The results showed that freezing induced the deformation of ET, and its magnitude varied with both time and location. The maximum local dilatation was 0.006 s(-1) and was always observed at the phase change interface. Due to this local expansion, the unfrozen region in front of the freezing interface experienced compression. This expansion-compression pattern was observed throughout the freezing process. In the unfrozen region, the deformation rate gradually decreased away from the freezing interface. After freezing/thawing, the ET experienced an approximately 28% decrease in thickness and 8% loss in weight. These results indicate that freezing-induced deformation caused the transport of interstitial fluid, and the interstitial fluid was extruded. In summary, the results suggest that complex cell-fluid-matrix interactions occur within ETs during freezing, and these interactions determine the post-thaw ECM microstructure and eventual post-thaw tissue functionality.
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Affiliation(s)
- Ka Yaw Teo
- Department of Mechanical and Aerospace Engineering, University of Texas at Arlington, Arlington, TX 76019, USA
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25
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Fallesen T, Hill DB, Steen M, Macosko JC, Bonin K, Holzwarth G. Magnet polepiece design for uniform magnetic force on superparamagnetic beads. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2010; 81:074303. [PMID: 20687745 PMCID: PMC2924904 DOI: 10.1063/1.3469792] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2010] [Accepted: 07/02/2010] [Indexed: 05/29/2023]
Abstract
Here we report construction of a simple electromagnet with novel polepieces which apply a spatially uniform force to superparamagnetic beads in an optical microscope. The wedge-shaped gap was designed to keep partial differential B(x)/ partial differential y constant and B large enough to saturate the bead. We achieved fields of 300-600 mT and constant gradients of 67 T/m over a sample space of 0.5x4 mm(2) in the focal plane of the microscope and 0.05 mm along the microscope optic axis. Within this space the maximum force on a 2.8 microm diameter Dynabead was 12 pN with a spatial variation of approximately 10%. Use of the magnet in a biophysical experiment is illustrated by showing that gliding microtubules propelled by the molecular motor kinesin can be stopped by the force of an attached magnetic bead.
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Affiliation(s)
- Todd Fallesen
- Department of Physics, Wake Forest University, Winston-Salem, North Carolina 27109, USA
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26
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Zhipeng Zhang, Yanan Huang, Chia-Hsiang Menq. Actively Controlled Manipulation of a Magnetic Microbead Using Quadrupole Magnetic Tweezers. IEEE T ROBOT 2010. [DOI: 10.1109/tro.2010.2047526] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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27
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Abou-Saleh RH, Connell SD, Harrand R, Ajjan RA, Mosesson MW, Smith DAM, Grant PJ, Ariëns RAS. Nanoscale probing reveals that reduced stiffness of clots from fibrinogen lacking 42 N-terminal Bbeta-chain residues is due to the formation of abnormal oligomers. Biophys J 2009; 96:2415-27. [PMID: 19289066 DOI: 10.1016/j.bpj.2008.12.3913] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2008] [Revised: 12/12/2008] [Accepted: 12/15/2008] [Indexed: 10/21/2022] Open
Abstract
Removal of Bbetal-42 from fibrinogen by Crotalus atrox venom results in a molecule lacking fibrinopeptide B and part of a thrombin binding site. We investigated the mechanism of polymerization of desBbeta1-42 fibrin. Fibrinogen trinodular structure was clearly observed using high resolution noncontact atomic force microscopy. E-regions were smaller in desBbeta1-42 than normal fibrinogen (1.2 nm +/- 0.3 vs. 1.5 nm +/- 0.2), whereas there were no differences between the D-regions (1.7 nm +/- 0.4 vs. 1.7 nm +/- 0.3). Polymerization rate for desBbeta1-42 was slower than normal, resulting in clots with thinner fibers. Differences in oligomers were found, with predominantly lateral associations for desBbeta1-42 and longitudinal associations for normal fibrin. Clot elasticity as measured by magnetic tweezers showed a G' of approximately 1 Pa for desBbeta1-42 compared with approximately 8 Pa for normal fibrin. Spring constants of early stage desBbeta1-42 single fibers determined by atomic force microscopy were approximately 3 times less than normal fibers of comparable dimensions and development. We conclude that Bbeta1-42 plays an important role in fibrin oligomer formation. Absence of Bbeta1-42 influences oligomer structure, affects the structure and properties of the final clot, and markedly reduces stiffness of the whole clot as well as individual fibrin fibers.
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Affiliation(s)
- Radwa H Abou-Saleh
- Molecular and Nanoscale Physics Group, Department of Physics and Astronomy, University of Leeds, Leeds, United Kingdom
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28
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Abstract
The response of cells to mechanical stresses is a field of growing inquiry. It is well known that both the morphologic and molecular expression of cells depend, in part, on the local mechanical environment, especially for cells such as endothelial cells that experience shear stress, stretch, and pressures. To systematically study the large variety of responses of cells to physical forces (e.g., signaling, adhesion, or stiffness changes), a number of techniques have been developed and used. Here we present methods for three types of cell mechanical studies, from the multicellular to the subcellular scales, and describe the basic principle and main use of each technique along with some design and setup considerations.
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29
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Desai KV, Bishop TG, Vicci L, O'Brien ET, Taylor RM, Superfine R. Agnostic particle tracking for three-dimensional motion of cellular granules and membrane-tethered bead dynamics. Biophys J 2008; 94:2374-84. [PMID: 18055538 PMCID: PMC2257905 DOI: 10.1529/biophysj.107.114140] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2007] [Accepted: 10/05/2007] [Indexed: 11/18/2022] Open
Abstract
The ability to detect biological events at the single-molecule level provides unique biophysical insights. Back-focal-plane laser interferometry is a promising technique for nanoscale three-dimensional position measurements at rates far beyond the capability of standard video. We report an in situ calibration technique for back-focal-plane, low-power (nontrapping) laser interferometry. The technique does not rely on any a priori model or calibration knowledge, hence the name "agnostic". We apply the technique to track long-range (up to 100 microm) motion of a variety of particles, including magnetic beads, in three-dimensions with high spatiotemporal resolution ( approximately 2 nm, 100 micros). Our tracking of individual unlabeled vesicles revealed a previously unreported grouping of mean-squared displacement curves at short timescales (<10 ms). Also, tracking functionalized magnetic beads attached to a live cell membrane revealed an anchorage-dependent nonlinear response of the membrane. The software-based technique involves injecting small perturbations into the probe position by driving a precalibrated specimen-mounting stage while recording the quadrant photodetector signals. The perturbations and corresponding quadrant photodetector signals are analyzed to extract the calibration parameters. The technique is sufficiently fast and noninvasive that the calibration can be performed on-the-fly without interrupting or compromising high-bandwidth, long-range tracking of a particle.
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Affiliation(s)
- Kalpit V Desai
- Department of Biomedical Engineering, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
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30
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Dyachenko V, Christ A, Gubanov R, Isenberg G. Bending of z-lines by mechanical stimuli: an input signal for integrin dependent modulation of ion channels? PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2008; 97:196-216. [PMID: 18367237 DOI: 10.1016/j.pbiomolbio.2008.02.007] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
We studied which components of mechanical cell deformation are involved in "stretch modulated ion currents" (SMIC). Murine ventricular myocytes were attached to glass coverslips and deformed in x, y and z with a 16 microm thin glass stylus (S) of calibrated stiffness. Three-dimensional confocal microscopy characterized cell deformation (T-tubular membranes, mitochondria) and bending of S (indicative of the applied force). Axial (x-) displacement of S sheared the upper cell part versus the attached bottom, close to S, it changed sarcomere length and bent z-lines ("z-line displacement"). Vertical (z-press) or transversal (y-shear) displacement of S bulged cytoplasm and mitochondria transversally without detectable z-line displacement. Axial stiffness increased with the extent of stress ("stress stiffening"). Depolymerization of F-actin or block of integrin receptors reduced stiffness. SMIC served as a proxy readout of deformation-induced signaling. Axial deformation activated a non-selective cation conductance (Gns) and deactivated an inwardly rectifying K+ conductance (GK1), z-press or y-shear did not induce SMIC. Depolymerization of F-actin or block of integrin receptors reduced SMIC. SMIC did not depend on changes in sarcomere length but correlated with the extent of z-line bending. We discuss that both shear stress at the attached cell bottom and z-line bending could activate mechanosensors. Since SMIC was absent during deformations without z-line bending we postulate that z-line bending is a necessary component for SMIC signaling.
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Affiliation(s)
- V Dyachenko
- Department of Physiology, Martin-Luther-University Halle, Halle, Germany
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31
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Common variation in the C-terminal region of the fibrinogen beta-chain: effects on fibrin structure, fibrinolysis and clot rigidity. Blood 2007; 111:643-50. [PMID: 17925485 DOI: 10.1182/blood-2007-05-091231] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Fibrinogen BbetaArg448Lys is a common polymorphism, positioned within the carboxyl terminus of the Bbeta-chain of the molecule. Studies suggest that it is associated with severity of coronary artery disease and development of stroke. The effects of the amino acid substitution on clot structure remains controversial, and the aim of this study was to investigate the effect(s) of this polymorphism on fibrin clot structure using recombinant techniques. Permeation, turbidity, and scanning electron microscopy showed that recombinant Lys448 fibrin had a significantly more compact structure, with thin fibers and small pores, compared with Arg448. Clot stiffness, measured by means of a novel method using magnetic tweezers, was significantly higher for the Lys448 compared with the Arg448 variant. Clots made from recombinant protein variants had similar lysis rates outside the plasma environment, but when added to fibrinogen-depleted plasma, the fibrinolysis rates for Lys448 were significantly slower compared with Arg448. This study demonstrates for the first time that clots made from recombinant BbetaLys448 fibrinogen are characterized by thin fibers and small pores, show increased stiffness, and appear more resistant to fibrinolysis. Fibrinogen BbetaArg448Lys is a primary example of common genetic variation with a significant phenotypic effect at the molecular level.
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Abstract
We discuss herein the theory as well as some design considerations of magnetic tweezers. This method of generating force on magnetic particles bound to biological entities is shown to have a number of advantages over other techniques: forces are exerted in noncontact mode, they can be large in magnitude (order of 10 nanonewtons), and adjustable in direction, static or oscillatory. One apparatus built in our laboratory is described in detail, along with examples of experimental applications and results.
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Affiliation(s)
- Monica Tanase
- Department of Biological Sciences, Columbia University, New York, New York 10027, USA
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33
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Gullapalli RR, Tabouillot T, Mathura R, Dangaria JH, Butler PJ. Integrated multimodal microscopy, time-resolved fluorescence, and optical-trap rheometry: toward single molecule mechanobiology. JOURNAL OF BIOMEDICAL OPTICS 2007; 12:014012. [PMID: 17343487 PMCID: PMC3251961 DOI: 10.1117/1.2673245] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Cells respond to forces through coordinated biochemical signaling cascades that originate from changes in single-molecule structure and dynamics and proceed to large-scale changes in cellular morphology and protein expression. To enable experiments that determine the molecular basis of mechanotransduction over these large time and length scales, we construct a confocal molecular dynamics microscope (CMDM). This system integrates total-internal-reflection fluorescence (TIRF), epifluorescence, differential interference contrast (DIC), and 3-D deconvolution imaging modalities with time-correlated single-photon counting (TCSPC) instrumentation and an optical trap. Some of the structures hypothesized to be involved in mechanotransduction are the glycocalyx, plasma membrane, actin cytoskeleton, focal adhesions, and cell-cell junctions. Through analysis of fluorescence fluctuations, single-molecule spectroscopic measurements [e.g., fluorescence correlation spectroscopy (FCS) and time-resolved fluorescence] can be correlated with these subcellular structures in adherent endothelial cells subjected to well-defined forces. We describe the construction of our multimodal microscope in detail and the calibrations necessary to define molecular dynamics in cell and model membranes. Finally, we discuss the potential applications of the system and its implications for the field of mechanotransduction.
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Affiliation(s)
- Ramachandra R Gullapalli
- The Pennsylvania State University, Department of Bioengineering, 205 Hallowell Building, University Park, Pennsylvania 16802, USA
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34
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Ragan T, Huang H, So P, Gratton E. 3D Particle Tracking on a Two-Photon Microscope. J Fluoresc 2006; 16:325-36. [PMID: 16544202 DOI: 10.1007/s10895-005-0040-1] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2005] [Accepted: 11/21/2005] [Indexed: 11/29/2022]
Abstract
A 3D single-particle-tracking (SPT) system was developed based on two-photon excitation fluorescence microscopy that can track the motion of particles in three dimensions over a range of 100 mum and with a bandwidth up to 30 Hz. We have implemented two different techniques employing feedback control. The first technique scans a small volume around a particle to build up a volumetric image that is then used to determine the particle's position. The second technique scans only a single plane but utilizes optical aberrations that have been introduced into the optical system that break the axial symmetry of the point spread function and serve as an indicator of the particle's axial position. We verified the performance of the instrument by tracking particles in well-characterized models systems. We then studied the 3D viscoelastic mechanical response of 293 kidney cells using the techniques. Force was applied to the cells, by using a magnetic manipulator, onto the paramagnetic spheres attached to the cell via cellular integrin receptors. The deformation of the cytoskeleton was monitored by following the motion of nearby attached fluorescent polystyrene spheres. We showed that planar stress produces strain in all three dimensions, demonstrating that the 3D motion of the cell is required to fully model cellular mechanical responses.
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Affiliation(s)
- Timothy Ragan
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
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35
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Fisher JK, Cribb J, Desai KV, Vicci L, Wilde B, Keller K, Taylor RM, Haase J, Bloom K, O'Brien ET, Superfine R. Thin-foil magnetic force system for high-numerical-aperture microscopy. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2006; 77:nihms8302. [PMID: 16858495 PMCID: PMC1513178 DOI: 10.1063/1.2166509] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
Forces play a key role in a wide range of biological phenomena from single-protein conformational dynamics to transcription and cell division, to name a few. The majority of existing microbiological force application methods can be divided into two categories: those that can apply relatively high forces through the use of a physical connection to a probe and those that apply smaller forces with a detached probe. Existing magnetic manipulators utilizing high fields and high field gradients have been able to reduce this gap in maximum applicable force, but the size of such devices has limited their use in applications where high force and high-numerical-aperture (NA) microscopy must be combined. We have developed a magnetic manipulation system that is capable of applying forces in excess of 700 pN on a 1 mum paramagnetic particle and 13 nN on a 4.5 mum paramagnetic particle, forces over the full 4pi sr, and a bandwidth in excess of 3 kHz while remaining compatible with a commercially available high-NA microscope objective. Our system design separates the pole tips from the flux coils so that the magnetic-field geometry at the sample is determined by removable thin-foil pole plates, allowing easy change from experiment to experiment. In addition, we have combined the magnetic manipulator with a feedback-enhanced, high-resolution (2.4 nm), high-bandwidth (10 kHz), long-range (100 mum xyz range) laser tracking system. We demonstrate the usefulness of this system in a study of the role of forces in higher-order chromosome structure and function.
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Affiliation(s)
- J K Fisher
- Department of Biomedical Engineering, University of North Carolina, Chapel Hill, North Carolina 27599-7575
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36
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Huang H, Cruz F, Bazzoni G. Junctional adhesion molecule-A regulates cell migration and resistance to shear stress. J Cell Physiol 2006; 209:122-30. [PMID: 16783819 DOI: 10.1002/jcp.20712] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Junctional adhesion molecule-A (JAM-A) is an adhesive protein expressed in endothelial cells, epithelial cells, platelets, and some leukocytes. JAM-A localizes to the tight junctions between contacting endothelial and epithelial cells, where it contributes to cell-cell adhesion and to the control of paracellular permeability. JAM-A also regulates cell motility, even though the quantitative biophysical features have not been characterized. In this study, we evaluated the role of JAM-A in the regulation of cell motility using JAM-A-expressing and JAM-A-deficient murine endothelial cells. We report that, in the absence of shear stress, JAM-A absence increases cell motility by increasing directional persistence but not cell speed. In addition, in the presence of shear stress, JAM-A absence increases protrusion extension in the direction of flow and increased downstream cellular displacement (while, conversely, decreasing upstream displacement). All these effects of JAM-A absence are mitigated by the microtubule-stabilizing compound taxol. A motility- and microtubule-related function, integrin-mediated adhesiveness, was only slightly reduced in JAM-A-deficient cells compared with JAM-A-expressing cells. However, overexpression of JAM-A in the JAM-A-deficient cells increased integrin adhesiveness to the same levels as those observed in taxol-treated JAM-A-deficient cells. Taken together, these data indicate that JAM-A regulates cell motility by cooperating with microtubule-stabilizing pathways.
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Affiliation(s)
- Hayden Huang
- Cardiovascular Division, Brigham and Women's Hospital, Cambridge, Massachusetts 02139, USA.
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37
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Overby DR, Matthews BD, Alsberg E, Ingber DE. Novel dynamic rheological behavior of individual focal adhesions measured within single cells using electromagnetic pulling cytometry. Acta Biomater 2005; 1:295-303. [PMID: 16701808 DOI: 10.1016/j.actbio.2005.02.003] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2004] [Revised: 02/02/2005] [Accepted: 02/03/2005] [Indexed: 01/13/2023]
Abstract
The rheology of cells and sub-cellular structures, such as focal adhesions, are important for cell form and function. Here we describe electromagnetic pulling cytometry (EPC), a technique to analyze cell rheology by applying dynamic tensional forces to ligand-coated magnetic microbeads bound to cell surface integrin receptors. EPC utilizes an electromagnetic microneedle that is integrated with a computerized control and image acquisition system and an inverted microscope and CCD camera to monitor bead displacement. Arbitrary force regimens may be defined over a wide range of frequency (DC to 10 Hz) and force (100 pN to 10 nN). With EPC, the viscoelastic creep response of individual focal adhesions was measured over three decades in time using RGD-coated magnetic microbeads bound to integrins that induce local focal adhesion assembly and coupling to the internal cytoskeleton. These data were compared to the power-law-like predictions from the soft glassy model of cell rheology proposed by Fabry et al. Although power-law-like behavior was observed in some focal adhesions, 52% of these structures did not exhibit power-law-like behavior, but instead exhibited either a multi-phase response characterized by abrupt changes in slope or experienced a retraction in the opposite direction to the applied force, especially in response to prolonged force application. These data suggest that while the soft glassy model may provide reasonable estimates for aggregate mechanical behavior of living cells, the rheological behavior of individual focal adhesions may be more heterogeneous and complex than suggested by the soft glassy model. These results are considered in context with the hierarchical nature of cytoskeletal architecture.
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Affiliation(s)
- Darryl R Overby
- Vascular Biology Program, Departments of Pathology and Surgery, Children's Hospital, Harvard Medical School, Boston, MA 02115, USA
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38
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Kaazempur Mofrad MR, Abdul-Rahim NA, Karcher H, Mack PJ, Yap B, Kamm RD. Exploring the molecular basis for mechanosensation, signal transduction, and cytoskeletal remodeling. Acta Biomater 2005; 1:281-93. [PMID: 16701807 DOI: 10.1016/j.actbio.2005.02.008] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2004] [Revised: 02/14/2005] [Accepted: 02/15/2005] [Indexed: 11/17/2022]
Abstract
Living cells respond to mechanical stimulation in a variety of ways that affect nearly every aspect of their function. Such responses can range from changes in cell morphology to activation of signaling cascades and changes in cell phenotype. Although the biochemical signaling pathways activated by mechanical stimulus have been extensively studied, little is known of the basic mechanisms by which mechanical force is transduced into a biochemical signal, or how the cell changes its behavior or properties in response to external or internal stresses. One hypothesis is that forces transmitted via individual proteins either at the site of cell adhesion to its surroundings or within the stress-bearing members of the cytoskeleton cause conformational changes that alter their binding affinity to other intracellular molecules. This altered equilibrium state can subsequently either initiate a biochemical signaling cascade or produce more immediate and local structural changes. To understand the phenomena related to mechanotransduction, the mechanics and chemistry of single molecules that form the signal transduction pathways must be examined. This paper presents a range of case studies that seek to explore the molecular basis of mechanical signal sensation and transduction, with particular attention to their macroscopic manifestation in the cell properties, e.g. in focal adhesion remodeling due to local application of force or changes in cytoskeletal rheology and remodeling due to cellular deformation.
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Affiliation(s)
- M R Kaazempur Mofrad
- Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Mass. Ave, NE47-321, Cambridge, MA 02139, USA.
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39
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de Vries AHB, Krenn BE, van Driel R, Kanger JS. Micro magnetic tweezers for nanomanipulation inside live cells. Biophys J 2004; 88:2137-44. [PMID: 15556976 PMCID: PMC1305265 DOI: 10.1529/biophysj.104.052035] [Citation(s) in RCA: 176] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
This study reports the design, realization, and characterization of a multi-pole magnetic tweezers that enables us to maneuver small magnetic probes inside living cells. So far, magnetic tweezers can be divided into two categories: I), tweezers that allow the exertion of high forces but consist of only one or two poles and therefore are capable of only exerting forces in one direction; and II), tweezers that consist of multiple poles and allow exertion of forces in multiple directions but at very low forces. The magnetic tweezers described here combines both aspects in a single apparatus: high forces in a controllable direction. To this end, micron scale magnetic structures are fabricated using cleanroom technologies. With these tweezers, magnetic flux gradients of nablaB = 8 x 10(3) T m(-1) can be achieved over the dimensions of a single cell. This allows exertion of forces up to 12 pN on paramagnetic probes with a diameter of 350 nm, enabling us to maneuver them through the cytoplasm of a living cell. It is expected that with the current tweezers, picoNewton forces can be exerted on beads as small as 100 nm.
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Affiliation(s)
- Anthony H B de Vries
- Biophysical Engineering, Faculty of Science and Technology, Institute for Biomedical Technology, University of Twente, 7500 AE Enschede, The Netherlands
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Mack PJ, Kaazempur-Mofrad MR, Karcher H, Lee RT, Kamm RD. Force-induced focal adhesion translocation: effects of force amplitude and frequency. Am J Physiol Cell Physiol 2004; 287:C954-62. [PMID: 15189816 DOI: 10.1152/ajpcell.00567.2003] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Vascular endothelial cells rapidly transduce local mechanical forces into biological signals through numerous processes including the activation of focal adhesion sites. To examine the mechanosensing capabilities of these adhesion sites, focal adhesion translocation was monitored over the course of 5 min with GFP-paxillin while applying nN-level magnetic trap shear forces to the cell apex via integrin-linked magnetic beads. A nongraded steady-load threshold for mechanotransduction was established between 0.90 and 1.45 nN. Activation was greatest near the point of forcing (<7.5 μm), indicating that shear forces imposed on the apical cell membrane transmit nonuniformly to the basal cell surface and that focal adhesion sites may function as individual mechanosensors responding to local levels of force. Results from a continuum, viscoelastic finite element model of magnetocytometry that represented experimental focal adhesion attachments provided support for a nonuniform force transmission to basal surface focal adhesion sites. To further understand the role of force transmission on focal adhesion activation and dynamics, sinusoidally varying forces were applied at 0.1, 1.0, 10, and 50 Hz with a 1.45 nN offset and a 2.25 nN maximum. At 10 and 50 Hz, focal adhesion activation did not vary with spatial location, as observed for steady loading, whereas the response was minimized at 1.0 Hz. Furthermore, applying the tyrosine kinase inhibitors genistein and PP2, a specific Src family kinase inhibitor, showed tyrosine kinase signaling has a role in force-induced translocation. These results highlight the mutual importance of force transmission and biochemical signaling in focal adhesion mechanotransduction.
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Affiliation(s)
- P J Mack
- Department of Mechanical Enginnering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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41
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Karcher H, Lammerding J, Huang H, Lee RT, Kamm RD, Kaazempur-Mofrad MR. A three-dimensional viscoelastic model for cell deformation with experimental verification. Biophys J 2004; 85:3336-49. [PMID: 14581235 PMCID: PMC1303611 DOI: 10.1016/s0006-3495(03)74753-5] [Citation(s) in RCA: 161] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
A three-dimensional viscoelastic finite element model is developed for cell micromanipulation by magnetocytometry. The model provides a robust tool for analysis of detailed strain/stress fields induced in the cell monolayer produced by forcing one microbead attached atop a single cell or cell monolayer on a basal substrate. Both the membrane/cortex and the cytoskeleton are modeled as Maxwell viscoelastic materials, but the structural effect of the membrane/cortex was found to be negligible on the timescales corresponding to magnetocytometry. Numerical predictions are validated against experiments performed on NIH 3T3 fibroblasts and previous experimental work. The system proved to be linear with respect to cytoskeleton mechanical properties and bead forcing. Stress and strain patterns were highly localized, suggesting that the effects of magnetocytometry are confined to a region extending <10 microm from the bead. Modulation of cell height has little effect on the results, provided the monolayer is >5 micro m thick. NIH 3T3 fibroblasts exhibited a viscoelastic timescale of approximately 1 s and a shear modulus of approximately 1000 Pa.
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Affiliation(s)
- Hélène Karcher
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
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42
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Huang H, Kamm RD, Lee RT. Cell mechanics and mechanotransduction: pathways, probes, and physiology. Am J Physiol Cell Physiol 2004; 287:C1-11. [PMID: 15189819 DOI: 10.1152/ajpcell.00559.2003] [Citation(s) in RCA: 340] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cells face not only a complex biochemical environment but also a diverse biomechanical environment. How cells respond to variations in mechanical forces is critical in homeostasis and many diseases. The mechanisms by which mechanical forces lead to eventual biochemical and molecular responses remain undefined, and unraveling this mystery will undoubtedly provide new insight into strengthening bone, growing cartilage, improving cardiac contractility, and constructing tissues for artificial organs. In this article we review the physical bases underlying the mechanotransduction process, techniques used to apply controlled mechanical stresses on living cells and tissues to probe mechanotransduction, and some of the important lessons that we are learning from mechanical stimulation of cells with precisely controlled forces.
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Affiliation(s)
- Hayden Huang
- Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02139, USA.
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43
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Fass JN, Odde DJ. Tensile force-dependent neurite elicitation via anti-beta1 integrin antibody-coated magnetic beads. Biophys J 2003; 85:623-36. [PMID: 12829516 PMCID: PMC1303117 DOI: 10.1016/s0006-3495(03)74506-8] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
Abstract
Previous work using glass microneedles to apply calibrated, localized force to neurons showed that tensile force is a sufficient signal for neurite initiation and elongation. However, previous studies did not examine the kinetics or probability of neurite initiation as a function of force or the rate of force application. Here we report the use of a new technique-magnetic bead force application-to systematically investigate the role of force in these phenomena with better ease of use and control over force than glass microneedles. Force-induced neurite initiation from embryonic chick forebrain neurons appeared to be a first-order random process whose rate increased with increasing force, and required the presence of peripheral microtubules. In addition, the probability of initiation was more than twofold lower for neurons exposed to rapid initial force ramps (450 pN/s) than for neurons exposed to slower ramps (1.5 and 11 pN/s). We observed a low force threshold for elongation (15-100 pN), which was not previously detected in chick forebrain neurites elongated by glass microneedles. Finally, neurites subjected to constant force elongated at variable instantaneous rates, and switched abruptly between elongation and retraction, similar to spontaneous, growth-cone-mediated outgrowth and microtubule dynamic instability.
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Affiliation(s)
- Joseph N Fass
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, USA
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