Researchers at the Fraunhofer Institute have taken a page from sports physiology and developed a low-cost optical sensor to measure the force with which tiny, migrating somatic cells push themselves away from an underlying surface. Force analysis devices like these could help to identify specific cell types more reliably than using a microscope or other conventional methods.

The sensor consists of a smooth surface that is studded with 250,000 tiny plastic columns measuring only five microns in diameter, rather like a fakir’s bed of nails. These columns are made of elastic polyurethane plastic. When a cell glides across them, it bends them very slightly sideways. This deflection is registered by a digital camera and analyzed by a special software program.

The researchers working with project manager Dr. Norbert Danz of the Fraunhofer Institute for Applied Optics and Precision Engineering IOF in Jena have already shown that their ‘Cellforce’ sensor works. It will be the task of initial biological tests to show how different cell types behave.

The optical sensor has 250,000 tiny plastic columns five microns in diameter. When a cell creeps across the tips of the columns, it makes each column deflect. © Fraunhofer IFAM © 6/2008 Fraunhofer-Gesellschaft

“Analysis of cell locomotion is important for numerous applications,” says Danz. “It could be used to check whether bone cells are successfully populating an implant, or how well a wound is healing.”

The sensor is a real accomplishment because the columns have to be coated in such a way that living cells will move across their tips and not journey down between the columns, resulting in no deflection at all.

Building the delicate column structure developed by researchers at the Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research IFAM in Bremen required researchers to press liquid plastic at a pressure of 2000 bar into a negative mold and allow it to harden. It was a challenge even to manufacture the required mold, with its 250,000 micron-sized holes.

To allow cost-effective production of the ‘Cellforce’ sensor in future, the researchers utilize commercially available plastics and well-established techniques from chip manufacture. The first ‘Cellforce’ prototype is expected to be ready in a year’s time.