Abstract

This thesis presents design, modeling, fabrication, and testing of different Lab-on-chip (LOC) devices to study static and dynamic behavior of pollen tubes in bio-mechanical-chemical environments. The main components of microfluidic platform include microfluidic network for manipulation, trapping and growing of a series of pollen tubes in a controlled environment, actuating channels in order to introduce chemicals and drugs toward the pollen tube, microstructural elements such as microgaps and microcantilevers to provide Ex-Vivo environment for characterizing static and dynamic responses of pollen tubes.

A Lab-On-Chip (LOC), called, TipChip was developed as a flexible platform that can simplify sophisticated functions such as chemical reactions, drug development, by integrating them within a single micro-device. The configuration of the microfluidic network was developed in such a way that it allows observation under chemical or mechanical manipulation of multiple pollen tubes. The growth of pollen tubes under different flow rates and geometrical dimensions of microfluidic network has been studied and the challenges have been identified. The microfluidic platform design was enhanced to deal with the challenges by adapting the dimensions of the microfluidic network and the inlet flow. It provides identical growth environments for growing pollen tubes along each microchannel and improves the performance of microfluidic device, through varying the dimensions and geometries of the microfluidic network.

The thesis identifies the static response of pollen tube to chemical stimulation which was used to determine the role of a few of the growth regulators such as sucrose and calcium ions as they regulate tube turgor pressure and cell wall mechanical properties of pollen tube. New experimental platforms were fabricated to treat locally the pollen tube at the tip in order to characterize its static response to local treatment in reorienting the growth direction. The device is also used to locally stimulate the cylindrical region of pollen tube. Using these LOC devices we attempted to answer some questions regarding the role of regulators in pollen tube growth.

The thesis explores in detail the dynamic growth of pollen tube in normal condition and also under chemical stimulation. Waveform analysis is employed in order to extract primary and secondary oscillation frequencies of pollen tube as significant indicators of dynamic growth of pollen tube. The dynamic response of pollen tubes is implemented as a whole-plant cell sensor for toxicity detection in order to detect toxic materials in concentration-based manner. Aluminum ions were tested as the toxic substance. The degree of toxicity was defined by measuring the reduction in growth rate as well as peak oscillation frequencies in the case of static and dynamic response of pollen tube, respectively.

The thesis addresses the quantification of mechanical properties of pollen tube cell wall using the Bending LOC (BLOC) platform. The flexural rigidity of the pollen tube and the Young’s modulus of the cell wall are estimated through finite element modeling of the observed fluid-structure interaction.

The thesis also explores the feasibility of studying the pollen tube response to the mechanical stimulation. The microfluidic device also enables integrating mechanical force obstructing pollen tube growth in order to characterize the interaction of pollen tube and mechanical structures which are similar to the in-vivo interaction between a pollen tube and the growth matrix during the course of growth toward the ovule. The behavior of the pollen tube while passing through microgap was also explored in detail. The deflection of microgap under growth force and the changes in diameter of the pollen tube under reaction force from microgap were evaluated. This part explores the role of mechanical forces in bursting the pollen tube tip which could explain the contribution of mechanical signal in the bursting of tube near the vicinity of the ovule. In addition, the configuration of microgap enabled the estimation of the maximum invasive force exerted by pollen tube.

Thus, the proposed microfluidic platform is highly suitable for cellular analysis, pollen tube biology and detection of toxicity.