New Technique for Determining Cell Adhesive Force

Biophysicists at Heidelberg University have developed a new technique for the determination of cell adhesion strength. This is the force generated by cells when they are in contact withsurfaces. To reliably quantify this force, the scientists of the Physical Chemistry of Biosystems research group headed by Prof. Dr. Motomu Tanaka have combined a picosecond laser with an optical microscope. The research team at Heidelberg University’s Institute of Physical Chemistry were also able to demonstrate that the micromechanical environment of cells can be dynamically regulated by certain polymers. Their research findings have been published in the "Journal of the American Chemical Society“.

The  cell adhesion strength  is evaluated by determining the critical pressure required to detach  the target cell from the surface . For this purpose, a strong laser pulse is focused on the surface through the objective of a microscope. This sets off a pressure wave moving at supersonic speed and strong enough to detach cells from their substrate. The critical pressure required for cell detachment and hence the cell adhesion strength can be quantitatively determined via the distance between the focal point of the laser and the target. “The combination of a picosecond laser with an optical microscope is a probe-free technique with which reliable, statistically evaluable numbers can be obtained for a large variety of cells,” says Dr. Hiroshi Yoshikawa who developed this technique in the Heidelberg research group and now an assistant professor at Saitama University in Japan. This technique is now being used to determine the adhesion strength of different types of cell, including blood stem cells.

In the course of their work, the Heidelberg researchers have also examined the potential of so-called smart hydrogels for regulating the micromechanical environment of cells. Careful adjustment of the pH value can reversibly modulate the surface stiffness of these polymers by a factor of 40 without any adverse effects on cell viability, says Prof. Tanaka. Cells can react to changes in the elasticity of their substrate caused by hydrogels. Microscope experiments carried out at the Nikon Imaging Center in Heidelberg have demonstrated the prove of principlee . “With this new method for determining cell adhesion force and the use of smart hydrogels, we can study how contractile cells adapt their morphology to mechanical stimuli from their environment,” explains Prof. Tanaka. “That means we can study the different ways in which the development of stem cells is affected by dynamic mechanical stimuli..”

Cooperating partners for the Heidelberg scientists were Prof. Steven P. Armes of the University of Sheffield (UK) and the British company Biocompatibles Inc., which synthesised the hydrogels.

Original publication
Hiroshi Y. Yoshikawa, Fernanda F. Rossetti, Stefan Kaufmann, Thomas Kaindl, Jeppe Madsen, Ulrike Engel, Andrew L. Lewis, Steven P. Armes, Motomu Tanaka: “Quantitative Evaluation of Mechanosensing of Cells on Dynamically Tunable Hydrogels”, Journal of the American Chemical Society, 133, 1367 (2011), doi: 10.1021/ja1060615

Contact
Prof. Dr. Motomu Tanaka
Institute of Physical Chemistry
phone: +49 6221 544916
tanaka@uni-heidelberg.de

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