Thesis Format
Integrated Article
Degree
Master of Engineering Science
Program
Mechanical and Materials Engineering
Supervisor
Shi, HaoTian
Abstract
Flexible strain sensors have seen significant research for applications in motion monitoring, soft robotics, and wearable electronics. However, issues like conformability, recyclability, and long-term stretchability remain. This thesis introduces a novel, sustainable composite strain sensor made from polyvinyl alcohol (PVA), silk fibroin (SF), and multi-walled carbon nanotubes (MWCNT) for wearable motion sensing. Inspired by viscoelastic silly putty, the addition of hygroscopic calcium chloride (CaCl2) allows the sensor to absorb ambient moisture and conform to various surfaces while maintaining stretchability and sensitivity. Using direct ink writing (DIW) for 3D printing, specific sensor geometries are created for easy application to three-dimensional substrates, such as human skin. This work covers material synthesis, sensor fabrication, mechanical and electrical performance testing, material characterization, and the sensor’s DIW printability. The sensor offers longevity, moldability, self-healability, and gauge factors from 0.1 to 0.8. This thesis also examines different PVA to SF ratios and ink viscoelastic properties at various temperatures, enhancing its usability in diverse environments.
Summary for Lay Audience
People from all walks of life are constantly on the move. Whether they are patients or athletes, there are a variety of biomechanical motions that can be made with different body parts, such as finger bending, knee bending, wrist bending, etc. These motions are often different in different types of situations, such as intense and repetitive movements during sports activities, uncontrolled movement due to illnesses like Parkinson's, or motion created in human-like robots designed for specific actions. To quantify these motions—how much and how fast they occur—flexible strain sensors are a viable solution.
Consider a rubber band tied to a finger; as the finger bends, the rubber band stretches and changes its shape. Similarly, a flexible strain sensor deforms with the body’s movement, allowing these movements to be monitored in real time. To track the movement, the sensor shall bend, stretch, and flex in the same way as the body part it is measuring; besides, the sensor needs to be conductive, in order to convert the extent of the movement into electrical resistance signals, hence monitor the motion quantitatively.
The resulting material, is referred to as “ink”, transforms into a stretchy, rubber band-like strain sensor upon drying. The drying process can be tailored to suit different fabrication needs—slow drying allows for moulding the material into specific shapes, while rapid drying through heating facilitates “direct ink writing” (DIW), a 3D printing technique that creates complex patterns by extruding the heated “ink” through a nozzle. This study delves into both the moulding and the DIW technique using a specially designed “ink”.
This study presents a novel design of flexible strain sensor and demonstrates the sensor’s ability to conform to the skin and absorb moisture from the air. The adaptability of the sensor is also explored, with sensing applications shown at different body parts. The performance and functionality of the sensors are aimed to be enhanced by exploring both molding and DIW techniques. Through this study, we aim to advance the field of flexible strain sensors by offering a comprehensive solution that is adaptable, reliable, and easy to fabricate.
Recommended Citation
Wu, Xiaohan, "Development of a Novel Direct Ink Writable, Skin-mounted, Wearable Strain Sensor for Human Motion Monitoring" (2024). Electronic Thesis and Dissertation Repository. 10220.
https://ir.lib.uwo.ca/etd/10220
Included in
Electrical and Electronics Commons, Manufacturing Commons, Polymer and Organic Materials Commons