University of Wollongong Research Online University of Wollongong Thesis Collection 2017+ University of Wollongong Thesis Collections 2020 Hydrogel Based Braided Artificial Muscles Bidita Binte Salahuddin University of Wollongong Follow this and additional works at: https://ro.uow.edu.au/theses1 University of Wollongong Copyright Warning You may print or download ONE copy of this document for the purpose of your own research or study. The University does not authorise you to copy, communicate or otherwise make available electronically to any other person any copyright material contained on this site. You are reminded of the following: This work is copyright. Apart from any use permitted under the Copyright Act 1968, no part of this work may be reproduced by any process, nor may any other exclusive right be exercised, without the permission of the author. Copyright owners are entitled to take legal action against persons who infringe their copyright. 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For further information contact the UOW Library: [email protected] Hydrogel Based Braided Artificial Muscles By Bidita Binte Salahuddin School of Mechanical, Materials, Mechatronic and Biomedical Engineering Intelligent Polymer Research Institute Wollongong, Australia This thesis is presented as part of the requirements for the award of the degree of Doctor of Philosophy from the University of Wollongong Australia February 2020 I DECLARATION I, Bidita Binte Salahuddin, declare that this thesis, submitted in fulfilment of the requirements for awarding the degree of Doctor of Philosophy at the School of Mechanical, Materials, Mechatronic and Biomedical Engineering at the University of Wollongong, is entirely my own, unless otherwise stated, referenced or acknowledged. This Document has not been submitted for qualifications at any other academic institution. Bidita Binte Salahuddin February 2020 II ACKNOWLEDGEMENTS I would like to express my gratitude to my supervisors Prof. Geoffrey M. Spinks and Dr Holly Warren who gave me the support throughout my PhD studies and their concerns in my education. A special thanks to my principal supervisor Prof. Spinks for giving me the golden opportunity to join his research group, and I am so grateful for the guidance, idea, support, and encouragement through the PhD program. He always steered me in the right direction by his expertise whenever he thought I required it. His proficiency and extraordinary knowledge in artificial muscle technology will undoubtedly prove to be precious all the way through research career. I am also thankful to Dr Sina Naficy for his support as my former supervisor with his valuable scientific knowledge on the synthesis of hydrogels. I am gratefully indebted to all of them for their support and guidance during a distinct and productive research project. I am also grateful of all my friends at the Intelligent Polymer Research Institute (IPRI) because it was excellent sharing the laboratory with all of you during the last four years. Very special gratitude goes out to all at the workshop of the Australian Institute of Innovative Materials (AIIM) for their technical support during the construction of custom-built mechanical and electrical apparatuses/devices. Finally, I express my very profound gratitude to my parents, Salahuddin Zangi Chowdhury and Sufia Aktar and to my beloved husband, Shazed Md Aziz for giving me constant support and incessant inspiration all over my years of study and throughout the progression of researching and writing this thesis. I am also grateful to my siblings, Chowdhury Tanveer Salahuddin and Farah Binte Salahuddin who have provided me III with moral and emotional support in my life. This accomplishment would not have been possible without them. Thanks for all your encouragement! IV ABSTRACT Artificial muscles are devices or materials which can contract, expand, or rotate when acted upon by an external stimulus (such as electricity, pH, pressure, magnetic field, or temperature). The applications of artificial muscles are versatile because they can exhibit linear actuation as in hydraulic rams, torsional actuation like electric motors, and bending actuation as seen in nature. Artificial muscles have also exhibited great potential in robot fabrication and in surgery tools due to their resemblance to biological muscles along with high actuation force per unit mass. One successful type of artificial muscle uses a braided bladder that generates muscle-like contractions when the bladder is pressurised with gas or liquid. These systems are used commercially in industry, but are not useful in portable applications, such as robotics, because of the need for an external pump or compressor. This thesis investigated the use of a volume-changing hydrogel material as a means for pressurizing and depressurizing a braid. The hydrogel has the potential to replace the pump/compressor and make possible a smaller, lighter artificial muscle. For further investigation of these artificial muscles as linear actuators and for the practical application of linear actuators, it was imperative to standardize methods for characterizing their performance. This thesis introduces such an integrated characterisation method and demonstrates its use in the determination of the free stroke of a hydraulic artificial muscle (HAM); the stroke while operating against an externally applied force (isotonic); the blocked force of these muscles upon applying constant length (isometric); force and displacement change at constant pressure (isobaric); and actuation against a return spring (variable force, pressure). The linear mechanics approach has been verified and allows the prediction of V fundamental characteristics of the actuator: free stroke, blocked force and stiffness while varying the preload condition. This thesis further demonstrates the method of fabricating temperature-sensitive, hydrogel filled, novel braided muscles with different hydrogel compositions and investigates the characteristics of these hydrogel filled muscles by employing a spring-test method. The experimental investigation of the gel-filled muscles is carried out by heating and cooling the muscle at different temperatures. The results show that the blocked force and free stroke depend on the monomer concentration used to prepare the hydrogels and the spring stiffness against which the muscle actuates. The force and displacement are more significant in the muscle with higher monomer concentration. The hydrogel muscles are then further developed into a new type of thermally-actuated braided hydrogel muscle made by systematically integrating cotton fibre and hydrogel. The performance of these actuators is also studied experimentally based on the integrated test method. The actuation mechanism is examined by varying the monomer composition and braid angle. The degree of actuation is found to be greater for higher monomer concentration and higher braid angle due to the relationship of volume change to the applied temperature change. Hysteresis is shown to be affected by temperature change. The generated blocked force and displacement are examined at varied pre-load conditions when combined with the measured muscle stiffness. It has been found that the greater the stiffness and pre-load, the higher the blocked force and displacement. The effect of hydrogel fill on the linear actuation is also investigated, and it is observed that solid hydrogel filled braided hydrogel muscle is capable of generating almost double the force compared with a braided hydrogel muscle without hydrogel filling (shell-gel). This was VI the first time these porous braided hydrogel muscles are fabricated. These novel actuators are experimentally investigated using the integrated method to determine the influence of hydrogel thickness on the actuation mechanism. Finally, to show the applicability of braided hydrogel muscles in a closed system, a novel enclosed shell-gel braided hydrogel muscle is introduced in which the linear actuation of a shell-gel muscle occurs within an encapsulating rubber bladder. A hot air gun is used for heating while cooling occurred naturally to room temperature. There is no significant difference in actuation acquired for encapsulated shell-gel compared to the shell-gel muscle operated in an open water bath and this suggests the compatibility of these braided hydrogel muscles for both open and closed system. Overall, this thesis establishes fabrication strategies for hydrogel based novel braided artificial muscles, determines their actuating response using a new efficient, integrated characterisation method and validates the experimental results by using graphical modelling approaches.