Probing cell behavior: Combining MEMS (microelectromechanical systems) technology with high resolution live cell imaging

Abstract

Cell biological experimentation has benefitted from the development of microdevices based on microfluidics and MEMS (microelectromechanical systems) technology. These devices exploit the possibility to create microscopic 3D structures that can be used to manipulate single cells. Furthermore, microdevices can be used to miniaturize laboratory functions (Lab‐on‐a‐Chip). We developed an experimental platform with the specific aim to study tip growing cells, the TipChip [1]. The device allows positioning of single cells such as pollen grains or fungal spores at the entrances of serially arranged microchannels harboring microscopic experimental setups. The transport of the cells is mediated by fluid‐flow. Once positioned in the device, the tip growing cells, pollen tubes, filamentous yeast or fungal hyphae, can be exposed to chemical gradients, microstructural features, integrated biosensors or directional triggers. The device is compatible with Nomarski optics and fluorescence microscopy and can thus be used for live cell imaging. Using the TipChip platform we investigated the growth mechanism in pollen tubes. The pollen tube is a cellular transport system that is generated to connect the male gametophyte with its female counterpart. Through this catheter‐like protuberance the sperm cells are delivered from the pollen grain to the ovule nestled deep within the pistillar tissues. To be competitive, the pollen tube elongates extremely rapidly and it has to do so against the impedance of the apoplast of the transmitting tissue and through the maze of pistillar cells that separate the pollen grain from the ovule. Using calibrated micro‐cantilevers we quantified the invasive force of the pollen tube and we found that sperm cell discharge can be triggered by mechanical constriction [2]. Further applications include exposure of cells to precisely calibrated electric fields and micron‐sharp, tunable chemical gradients. The TipChip is therefore a highly versatile tool for the combined quantitative biophysical and optical investigation of polar growth in plant cells.