Magnetic microposts as an approach to apply forces to living cells
- Nathan J. Sniadecki*,
- Alexandre Anguelouch†,
- Michael T. Yang*,
- Corinne M. Lamb†,
- Zhijun Liu*,
- Stuart B. Kirschner†,
- Yaohua Liu†,
- Daniel H. Reich†, and
- Christopher S. Chen*,‡
- *Department of Bioengineering, University of Pennsylvania, 510 Skirkanich Hall, 210 South 33rd Street, Philadelphia, PA 19104; and
- †Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218
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Edited by David Mooney, Harvard University, Cambridge, MA, and accepted by the Editorial Board July 14, 2007 (received for review January 3, 2007)
Abstract
Cells respond to mechanical forces whether applied externally or generated internally via the cytoskeleton. To study the cellular response to forces separately, we applied external forces to cells via microfabricated magnetic posts containing cobalt nanowires interspersed among an array of elastomeric posts, which acted as independent sensors to cellular traction forces. A magnetic field induced torque in the nanowires, which deflected the magnetic posts and imparted force to individual adhesions of cells attached to the array. Using this system, we examined the cellular reaction to applied forces and found that applying a step force led to an increase in local focal adhesion size at the site of application but not at nearby nonmagnetic posts. Focal adhesion recruitment was enhanced further when cells were subjected to multiple force actuations within the same time interval. Recording the traction forces in response to such force stimulation revealed two responses: a sudden loss in contractility that occurred within the first minute of stimulation or a gradual decay in contractility over several minutes. For both types of responses, the subcellular distribution of loss in traction forces was not confined to locations near the actuated micropost, nor uniformly across the whole cell, but instead occurred at discrete locations along the cell periphery. Together, these data reveal an important dynamic biological relationship between external and internal forces and demonstrate the utility of this microfabricated system to explore this interaction.
Footnotes
- ‡To whom correspondence should be addressed. E-mail: chrischen{at}seas.upenn.edu
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Author contributions: N.J.S., D.H.R., and C.S.C. designed research; N.J.S., A.A., M.T.Y., C.M.L., Z.L., S.B.K., Y.L., and D.H.R. performed research; and N.J.S., D.H.R., and C.S.C. wrote the paper.
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The authors declare no conflict of interest.
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This article is a PNAS Direct Submission. D.M. is a guest editor invited by the Editorial Board.
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This article contains supporting information online at www.pnas.org/cgi/content/full/0611613104/DC1.
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↵ § The average strain energy u as calculated does not account for the applied force at the magnetic posts. An upper bound to the missing strain energy, provided by observed deflections in the absence of cells, contributes only an additional 0.04 fJ to u at t = 0.
- Abbreviations:
- FA,
- focal adhesion;
- PDMS,
- poly(dimethylsiloxane).
- © 2007 by The National Academy of Sciences of the USA
