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Understanding Pollen Tube Growth Inspires the Design of Autonomous Soft Robots

Lay summary

Pollenschläuche folgen biochemischen Signalen, um schnell und über grosse Distanzen durch Gewebe hindurch zu ihrem Ziel zu gelangen und dort die Spermien freizusetzen. Damit haben sie Eigenschaften, die in der Medizin von grosser Bedeutung sein könnten, wie z.B.  das gerichtete Wachstum zu einer Signalquelle hin und die gezielte Freisetzung von Substanzen am Zielort. Wir untersuchen hier die mechanischen und biochemischen Grundlagen des Pollenschlauchwachstums, um zu verstehen, wie Pollenschläuche durch biochemische und mechanische Stimuli gesteuert werden und deren «Entladung» am Zielort ausgelöst wird. Dies erfordert neue Methoden zur präzisen, lokalen Manipulation von wachsenden Pollenschläuchen sowie neue Geräte zur Messung von lokalen Veränderungen der Zellwandelastizität, die das Wachstum von Pollenschläuchen steuern. Aus den Resultaten des Projekts erwarten wir neue Impulse und Konzepte für den Bau von sogenannten «Soft Robots», die autonom ihr Umfeld wahrnehmen, zu einem bestimmten Ziel im Gewebe wachsen und dort Interventionen vornehmen.

Wir bearbeiten damit eine biologische Grundlagenfrage aus den Blickwinkeln der Ingenieurwissenschaften und der Molekular- und Zellbiologie. Die Kombination dieser Disziplinen führt nicht nur zu neuen Erkenntnissen in der pflanzlichen Reproduktionsbiologie, sondern auch zur Entwicklung neuer Messtechniken und mikromechanischer Methoden. Schliesslich liefert das Projekt eine Vision, wie «Soft Robots» für Anwendungen in der Medizin konstruiert werden könnten.   

Abstract

Biology has long been a source of inspiration for robotic engineers to obtain new insights to fabricate ever-more capable micromachines. In this project, we will investigate the mechanical and biochemical basis of pollen tube (PT) growth to inspire the design of soft microrobots. PTs are the most rapidly growing cells on our planet and grow exclusively at their tips, similar to fungal hyphae or neuronal axons. Their navigation involves the perception, transduction, and reaction of various biochemical and physical stimuli. Although many biochemical factors required for PT growth have been identified, their exact function, timing, and interplay in controlling tip growth is not well understood. In particular, it is unclear how information on the mechanical properties of the rigid cell wall, which has to be loosened locally to allow growth at the tip, is integrated with intracellular, biochemical events controlling tip growth. A better understanding of these processes requires novel methods for the precise, local manipulation of rapidly growing PTs in real time.

To shed light onto the mechanical and biochemical principles underlying PT growth and navigation, new microrobots for precise measurement and manipulation will be engineered based on micro-electro-mechanical systems (MEMS) and microfluidics (Lab-on-a-Chip, LoC) devices. These will be used to characterize mechanical properties of the cell wall of Arabidopsis PTs and the external application of bioactive compounds. Intracellularly, biochemical properties will be locally manipulated using light-inducible switches, allowing for rapid changes in activity. The gained knowledge will help the design of soft, self-growing microrobots that can autonomously sense the environment, reach distant targets, and perform targeted interventions.

Specifically, we will
· integrate MEMS-based force sensors into a laser scanning confocal microscope (confocal Cellular Force Microscope, cCFM) for precise measurements of mechanical and biochemical parameters during Arabidopsis PT growth in real time;
· develop novel optogenetic and LoC-based methods for the precise and highly localized manipulation of intra- and extracellular determinants during PT growth, such as calcium (Ca2+) and other signaling molecules, to develop an integrated mechanical-biochemical model for tip growth;
· build and characterize bioinspired soft robots, which autonomously grow and navigate along a Ca2+ gradient, based on the unraveled principles underlying PT growth.

In this interdisciplinary SINERGIA project, we will develop novel tools to manipulate PTs and follow their responses using live-imaging. The project relies on the complementary expertise of the two applicants, Ueli Grossniklaus (molecular and cellular plant biology) and Bradley Nelson (mechanical engineering, micro- and nanorobotics) and will have three main outputs:
(1) It will provide a detailed understanding of the interplay between extra- and intracellular processes that allow rapid tip growth without rupture of the PT, which is highly relevant to plant growth and development in general, and plant productivity in particular.
(2) It will offer interdisciplinary training opportunities for young researchers at the interface of biology and engineering.
(3) It will lead to the development of novel microrobotic tools for the characterization and manipulation of cellular properties that can be applied to a wide variety of experimental systems and approaches.

In particular, autonomously growing and navigating soft robots have the potential to revolutionize biotechnology and medicine in the long-term, for instance in areas as diverse as diagnostics, labroscopic surgery, and targeted drug delivery.

  Dr.Ueli Grossniklaus
Hannes Vogler
Bradley Nelson