The cellular force microscope (CFM): A microrobotic system for quantitating the growth mechanics of living, growing plant cells in situ

As the field of biology becomes a more quantitative and predictive natural science, an increasing need for investigation and quantification of the mechanics of growth at individual cellular levels arises. This paper describes a microrobotic force-feedback based system and its application to the mechanical characterization of living, growing plant cells. The Cellular Force Microscope (CFM) is capable of performing the automated mechanical characterization of living plant cells in situ as these cells proliferate and grow. The microrobotic measurement system employs a single-axis capacitive MEMS microforce sensor capable of resolving forces down to 20 nN (1σ, at 10Hz). A multi-axis positioning system with 5 nm resolution position feedback is integrated into a complete system with a high-resolution optical microscope and a custom user interface for guiding an automated force-based measurement process. The CFM has been applied to characterize the mechanical properties of 20µm wide Lilium pollen tubes while they grow at a rate of about 10 µm/min in growth medium. For the mechanical characterization of pollen tubes, loads up to 400 nN are applied that cause indentations up to 300 nm. The force-deformation data acquired show an increase in the observed stiffness from the tip to the apex demonstrating that CFM is a promising tool for better understanding the changing mechanics of living plant cell growth.