A simulation scheme to investigate the role of stiffness gradient along the body column of Hydra

Abstract

Animals have evolved a variety of features that help them to move in different media, like air, water or land. Such features usually develop such that the finite amount of energy available to the animals is utilized more efficiently. Hydra is one such animal, which has a diverse set of mechanisms for loco- motion, including looping, swaying and somersault. It has a small (about 5 mm) tubular shaped body with tentacles at one end. Hydra belongs to the phylum of Cnidaria, which were the earliest phylum to evolve differentiated neuronal/muscular tissues and extracellular matrix (ECM) properties. The motivation for the thesis comes from the experiment conducted in Dr. Shivprasad Patil’s lab, by Suyash Naik, Manu Unni and Shatruhan Singh Rajput. In this experiment, an AFM (Atomic Force Microscope) was used to produce a spatially resolved map of tissue elasticity along the Hydra’s body column. It was observed that Hydra polyps have a three times higher stiffness in first 25% of their body column than the rest (the stiffness ratio of 3 : 1). A careful examination of Hydra’s motion led to the hypothesis by Dr. Shivprasad Patil that the stiffness gradient of 3 : 1 may help Hydra utilise its stored energy more efficiently during its somersault motion, compared to a Hydra with no stiffness variation. In this thesis, we propose a coarse grained computer simulation model, to investigate the link between Hydra’s somersault and the observed stiffness gradient. We explore the energetics the somersault motion by analysing the dynamics of action-reaction forces like viscous drag, gravity, buoyancy in our simulations. We also compare and contrast other stiffness ratios and attempt to understand if there is a special significance of the ratio 3 : 1. The last chapter of the thesis is dedicated to some additional work done on the topic of Shear banding in wormlike Micelles. In this chapter, we report preliminary results of first time observation of the phenomena of shear banding in a wormlike micellar system, using molecular dynamics simulations.