Microrobotics and Microfluidics for Quantifying the Growth Mechanics of 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. In our lab, we are developing microrobotic and microfluidic systems to characterize the biomechanics of plant cells and to investigate the effect of external mechanical stress and force on the plant growth and development.
An ideal model system to study the impact of biomechanics and mechanical cues at a single-cell level is the pollen tube (PT), a cellular protrusion which transports sperm cells from the grain to the ovules. The PT is one of the fastest, if not the fastest, growing cell with in vivo growth rates reaching around 2.7 µm/s in maize. Despite its small diameter in the range of 5-15 µm, the PT can grow up to 30 cm in length while precisely navigating towards the ovule using various guidance cues.
Micromechanical characterization of plant cells
Our group developed the cellular force microscope (CFM), a microrobotic platform for mechanical stimulation and characterization of living cells at different scales ranging from individual cell, tissue of cells to organs [1,2]. The CFM combines a three-axis positioning system offering a micrometer travel range and a nanometer resolution with a microelectromechanical systems (MEMS)-based capacitive force sensor (Femtotools AG, Buchs ZH, Switzerland) with adjustable force ranges from ±100 µN to ±100’000 µN with nN resolution (Fig. 1). The system produces accurate quantitative data which is given as input parameters to mathematical models and simulations in order to provide insights into intricate biomechanical growth mechanisms.
How pollen tubes perceive and overcome obstacles
Physical forces are involved in the regulation of plant development and morphogenesis by translating mechanical stress into the modification of physiological processes, which, in turn, can affect cellular growth. We combined a lab-on-a-chip device with a MEMS-based capacitive force sensor to mimic and quantify the forces that are involved in pollen tube navigation upon confronting mechanical obstacles (Fig. 2). We were able to show, that Pollen tubes literally feel their way through their environment to avoid obstacles as they deliver sperm cells to the ovule [3].
Microfluidic and acoustic three-dimensional manipulation of plant cells
The ability to precisely control the three-dimensional (3D) orientation of micrometer-sized biological samples is critical for its phenotypic investigation. We are developing acoustic wave-based microfluidic devices that can be used for the trapping and rotational manipulation of single plant cells [4]. Resonant acoustic excitation of air-filled microbubbles generates localized vortices that can be used for the controlled three-dimensional rotation of single cells (Fig. 3).
