26 research outputs found
Colloquium: Mechanical formalisms for tissue dynamics
The understanding of morphogenesis in living organisms has been renewed by
tremendous progressin experimental techniques that provide access to
cell-scale, quantitative information both on theshapes of cells within tissues
and on the genes being expressed. This information suggests that
ourunderstanding of the respective contributions of gene expression and
mechanics, and of their crucialentanglement, will soon leap forward.
Biomechanics increasingly benefits from models, which assistthe design and
interpretation of experiments, point out the main ingredients and assumptions,
andultimately lead to predictions. The newly accessible local information thus
calls for a reflectionon how to select suitable classes of mechanical models.
We review both mechanical ingredientssuggested by the current knowledge of
tissue behaviour, and modelling methods that can helpgenerate a rheological
diagram or a constitutive equation. We distinguish cell scale ("intra-cell")and
tissue scale ("inter-cell") contributions. We recall the mathematical framework
developpedfor continuum materials and explain how to transform a constitutive
equation into a set of partialdifferential equations amenable to numerical
resolution. We show that when plastic behaviour isrelevant, the dissipation
function formalism appears appropriate to generate constitutive equations;its
variational nature facilitates numerical implementation, and we discuss
adaptations needed in thecase of large deformations. The present article
gathers theoretical methods that can readily enhancethe significance of the
data to be extracted from recent or future high throughput
biomechanicalexperiments.Comment: 33 pages, 20 figures. This version (26 Sept. 2015) contains a few
corrections to the published version, all in Appendix D.2 devoted to large
deformation
Monocytic cells become less compressible but more deformable upon activation
Aims
Monocytes play a significant role in the development of atherosclerosis. During the process of inflammation, circulating monocytes become activated in the blood stream. The consequent interactions of the activated monocytes with the blood flow and endothelial cells result in reorganization of cytoskeletal proteins, in particular of the microfilament structure, and concomitant changes in cell shape and mechanical behavior. Here we investigate the full elastic behavior of activated monocytes in relation to their cytoskeletal structure to obtain a better understanding of cell behavior during the progression of inflammatory diseases such as atherosclerosis.
Methods and Results
The recently developed Capillary Micromechanics technique, based on exposing a cell to a pressure difference in a tapered glass microcapillary, was used to measure the deformation of activated and non-activated monocytic cells. Monitoring the elastic response of individual cells up to large deformations allowed us to obtain both the compressive and the shear modulus of a cell from a single experiment. Activation by inflammatory chemokines affected the cytoskeletal organization and increased the elastic compressive modulus of monocytes with 73–340%, while their resistance to shape deformation decreased, as indicated by a 25–88% drop in the cell’s shear modulus. This decrease in deformability is particularly pronounced at high strains, such as those that occur during diapedesis through the vascular wall.
Conclusion
Overall, monocytic cells become less compressible but more deformable upon activation. This change in mechanical response under different modes of deformation could be important in understanding the interplay between the mechanics and function of these cells. In addition, our data are of direct relevance for computational modeling and analysis of the distinct monocytic behavior in the circulation and the extravascular space. Lastly, an understanding of the changes of monocyte mechanical properties will be important in the development of diagnostic tools and therapies concentrating on circulating cells