Euglenoid Movement and Novel Mechanisms for Soft Robots

  • Krishna Manaswi Digumarti

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


Organisms in nature utilise giant changes in body shape to perform everyday functions such as locomotion, object manipulation and feeding. These changes are observed across diverse scales and enable organisms to overcome challenges in their environment. This thesis focuses on the Euglena family of micro-organisms that display a unique manner of locomotion called euglenoid movement in which the cell undergoes a large change in shape. Novel mechanisms for highly deformable soft robots, inspired by this interesting behaviour are presented.

To numerically describe the shapes observed in euglenoids and the key features that change during locomotion, a mathematical method based on elliptic Fourier transforms is presented. This is a boundary-based, model free approach to quantify dynamic shapes of soft-bodied organisms and robots. In addition, it allows the comparison of shapes between two entities by providing a measure of similarity.

Two approaches to replicating the shape changing behaviour of the euglenoids were explored and are presented in this thesis. In the first approach, a novel soft pneumatic actuator called the hyper-elastic bellows (HEB) actuator is presented, which achieves 450% axial expansion, 80% radial expansion and up to 300 times change in volume. This actuator is then used in the design of soft robots capable of swimming autonomously in a manner that is hydrodynamically similar to that of the euglenoids. A similarity in shape of 85% is demonstrated.

In the second approach, the microscopic mechanism of pellicular sliding seen in euglenoids was replicated at a macro scale. The surface of the cell is covered in strips of protein, the relative sliding of which enables the organism to drastically alter its shape. Mimicking this structure, the design, fabrication and characterisation of morphing surfaces is presented which consist of flexible polymeric strips. These are used in the construction of a soft robotic module with an actively deforming surface.

This thesis demonstrates that behaviours seen in microscopic organisms can be replicated at larger scales in a robotic system to achieve functional advantages.
Date of Award25 Jun 2019
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorJonathan M Rossiter (Supervisor), Andrew T Conn (Supervisor) & Arthur G Richards (Supervisor)

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