Dual-axis Cellular Force Microscope for mechanical characterization of living plant cells

Understanding the mechanisms of plant growth and morphogenesis is of importance, not only to the field of plant sciences but also in a broader agricultural and economical context, as plants provide important raw materials such as food, fiber, wood and fuel. Mathematical modeling and simulation can provide insights into intricate biomechanical growth mechanisms. Mechanical characterization at single cellular level is essential for providing quantitative model parameters. The dual-axis Cellular Force Microscope (CFM) provide many of these desired parameters by micro-indentation measurements. The dual-axis CFM integrates a MEMS force sensing technology with a piezoelectric nano-positioning system. The dual force feedback from the MEMS sensor allows the system to be used for arbitrary indentation angles and to accurately measure biological samples despite their curved surfaces. The accuracy of the dual-axis CFM is verified by measuring a force-standard with a certified stiffness of 15.15 N/m at indentation angles of 90° and 60°. The obtained stiffness measurements are 15.60 N/m and 14.63 N/m and differ from the calibrated value by 2.97% and 3.63%, respectively. Additionally, the dual-axis CFM offers topographic imaging which was used to visualize two hemispherical structures fabricated using two-photon photopolymerization with radii of 5 µm and 7.5 µm. The potential of the system to study plant cell mechanics at a single cell level is shown by indenting a Lilium longiflorum pollen tube along its axis at the tip. The topographical information combined with the recorded force feedback in axial and lateral directions show promising results for further mechanical characterization of plant cells using the dual-axis CFM.