- •Contents
- •Contributors
- •Preface
- •1 Introduction, with the biological basis for cell mechanics
- •Introduction
- •The role of cell mechanics in biological function
- •Maintenance of cell shape
- •Cell migration
- •Mechanosensing
- •Stress responses and the role of mechanical forces in disease
- •Active cell contraction
- •Structural anatomy of a cell
- •The extracellular matrix and its attachment to cells
- •Transmission of force to the cytoskeleton and the role of the lipid bilayer
- •Intracellular structures
- •Overview
- •References
- •2 Experimental measurements of intracellular mechanics
- •Introduction
- •Forces to which cells are exposed in a biological context
- •Methods to measure intracellular rheology by macrorheology, diffusion, and sedimentation
- •Whole cell aggregates
- •Sedimentation of particles
- •Diffusion
- •Mechanical indentation of the cell surface
- •Glass microneedles
- •Cell poker
- •Atomic force microscopy
- •Mechanical tension applied to the cell membrane
- •Shearing and compression between microplates
- •Optical traps
- •Magnetic methods
- •Twisting of magnetized particles on the cell surface and interior
- •Passive microrheology
- •Optically detected individual probes
- •One-particle method
- •Two-particle methods
- •Dynamic light scattering and diffusing wave spectroscopy
- •Fluorescence correlation spectroscopy
- •Optical stretcher
- •Acoustic microscopy
- •Outstanding issues and future directions
- •References
- •3 The cytoskeleton as a soft glassy material
- •Introduction
- •Magnetic Twisting Cytometry (MTC)
- •Measurements of cell mechanics
- •The structural damping equation
- •Reduction of variables
- •Universality
- •Scaling the data
- •Collapse onto master curves
- •Theory of soft glassy rheology
- •What are soft glassy materials
- •Sollich’s theory of SGMs
- •Soft glassy rheology and structural damping
- •Open questions
- •Biological insights from SGR theory
- •Malleability of airway smooth muscle
- •Conclusion
- •References
- •4 Continuum elastic or viscoelastic models for the cell
- •Introduction
- •Purpose of continuum models
- •Principles of continuum models
- •Boundary conditions
- •Mechanical and material characteristics
- •Example of studied cell types
- •Blood cells: leukocytes and erythrocytes
- •Limitations of continuum model
- •Conclusion
- •References
- •5 Multiphasic models of cell mechanics
- •Introduction
- •Biphasic poroviscoelastic models of cell mechanics
- •Analysis of cell mechanical tests
- •Micropipette aspiration
- •Cells
- •Biphasic properties of the pericellular matrix
- •Indentation studies of cell multiphasic properties
- •Analysis of cell–matrix interactions using multiphasic models
- •Summary
- •References
- •6 Models of cytoskeletal mechanics based on tensegrity
- •Introduction
- •The cellular tensegrity model
- •The cellular tensegrity model
- •Do living cells behave as predicted by the tensegrity model?
- •Circumstantial evidence
- •Prestress-induced stiffening
- •Action at a distance
- •Do microtubules carry compression?
- •Summary
- •Examples of mathematical models of the cytoskeleton based on tensegrity
- •The cortical membrane model
- •Tensed cable nets
- •Cable-and-strut model
- •Summary
- •Tensegrity and cellular dynamics
- •Conclusion
- •Acknowledgement
- •References
- •7 Cells, gels, and mechanics
- •Introduction
- •Problems with the aqueous-solution-based paradigm
- •Cells as gels
- •Cell dynamics
- •Gels and motion
- •Secretion
- •Muscle contraction
- •Conclusion
- •Acknowledgement
- •References
- •8 Polymer-based models of cytoskeletal networks
- •Introduction
- •The worm-like chain model
- •Force-extension of single chains
- •Dynamics of single chains
- •Network elasticity
- •Nonlinear response
- •Discussion
- •References
- •9 Cell dynamics and the actin cytoskeleton
- •Introduction: The role of actin in the cell
- •Interaction of the cell cytoskeleton with the outside environment
- •The role of cytoskeletal structure
- •Actin mechanics
- •Actin dynamics
- •The emergence of actin dynamics
- •The intrinsic dynamics of actin
- •Regulation of dynamics by actin-binding proteins
- •Capping protein: ‘decommissioning’ the old
- •Gelsolin: rapid remodeling in one or two steps
- •β4-thymosin: accounting (sometimes) for the other half
- •Dynamic actin in crawling cells
- •Actin in the leading edge
- •Monomer recycling: the other ‘actin dynamics’
- •The biophysics of actin-based pushing
- •Conclusion
- •Acknowledgements
- •References
- •10 Active cellular protrusion: continuum theories and models
- •Cellular protrusion: the standard cartoon
- •The RIF formalism
- •Mass conservation
- •Momentum conservation
- •Boundary conditions
- •Cytoskeletal theories of cellular protrusion
- •Network–membrane interactions
- •Network dynamics near the membrane
- •Special cases of network–membrane interaction: polymerization force, brownian and motor ratchets
- •Network–network interactions
- •Network dynamics with swelling
- •Other theories of protrusion
- •Numerical implementation of the RIF formalism
- •An example of cellular protrusion
- •Protrusion driven by membrane–cytoskeleton repulsion
- •Protrusion driven by cytoskeletal swelling
- •Discussion
- •Conclusions
- •References
- •11 Summary
- •References
- •Index
Introduction, with the biological basis for cell mechanics |
15 |
state can exert a force on their surroundings. Forces have been measured in resting fibroblasts, for example, where intracellular tension gives rise to stresses in the focal adhesions of the cell adherent to a flexible two-dimensional substrate of about 5 nN/µm2, or 5 kPa (Balaban, Schwarz et al., 2001). In experiments with various cell types grown in a three-dimensional gel such as collagen, the cells actively contract the matrix by more than 50 percent (Sieminski, Hebbel et al., 2004). These contractile forces are associated with intracellular molecular motors such as those in the myosin family.
Overview
This book presents a full spectrum of views on current approaches to modeling cell mechanics. In part, this diversity of opinion stems from the different backgrounds of contributors to the field. Indeed, the authors of this book come from the biophysics, bioengineering, and physical chemistry communities, and each joins the discussion with a unique perspective on biological systems. Consequently, the approaches range from finite element methods commonly used in continuum mechanics to models of the cytoskeleton as a cross-linked polymer network to models of soft glassy materials and gels. Studies reflect both the static, instantaneous nature of the structure as well as its dynamic nature due to polymerization and the full array of biological processes. It is unlikely that a single unifying approach will evolve from this diversity, in part because of the complexity of the phenomena underlying the mechanical properties of the cell. It is our hope, however, that a better appreciation of the various perspectives will lead to a more highly coordinated approach to the essential problems and might facilitate discussions among investigators with differing views.
Perhaps the most important purpose of this monograph is to stimulate new ideas and approaches. Because no single method has emerged as clearly superior, this might reflect the need for approaches not yet envisaged. That much of the work presented here derives from publications over the past several years reinforces the notion that cell mechanics is a rapidly evolving field. The next decade will likely yield further advances not yet foreseen.
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