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Development of a Multi-material Extruder System to 3D Print Hard Thermoplastics, Soft Elastomers and Liquid Metals
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- Author / Creator
- Khondoker, Mohammad Abu Hasan
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Functional sensors often consist of rigid parts, soft rubber-like parts, and mechanically tunable electronic components. As part of a larger project to 3D print tunable antennas, it was tasked to develop a printer that could directly produce 3D stretchable electronics with soft and hard components. First, an extruder system which can directly print from raw pellets was developed to widen the input material choice as well as to lower the raw material cost. The new feeding system, fused pellets printing (FPP), permits printing of almost any thermoplastic materials by converting a screw extruder into a direct source for feed material of fused deposition modeling (FDM) style 3D printers. This innovation decouples the high-quality filament or large mass extruder from an FDM print head that can move with high speed and precision. The utility of the technique was demonstrated through direct printing of pneumatic driven soft robots which could in future be used to control antenna shapes. A tri-extruder system with three input channels was also developed to print functional devices in a single step which consists of a hard-rigid thermoplastic, a soft, stretchable elastomer, and a liquid metal. This extruder introduces mechanical interlocking in their extrudates when printing chemically immiscible polymers with nearly three orders of magnitude of difference in their elastic moduli. This intermixed printing was found to improve adhesion between adjacent printed layers by more than 12 times compared to simple side-by-side extrusion. To demonstrate the printing capability of intermixed soft and hard plastics, a tendon-driven soft robotic gripper composed of high impact polystyrene (HIPS) and styrene-ethylene-butylene-styrene (SEBS) was printed and characterized. The functionally gradient material (FGM) gripper printed with this technology did not show any noticeable interface failure after 10,000 cycles of operation whereas other samples printed without intermixing experienced layer delamination. Additionally, the extruder is also capable to co-axially extrude liquid metal alloy within an encapsulating polymer shell, in this case, SEBS. Hence, an extremely stretchable and flexible conductive wire can be produced which does not require any post-processing and an extra sealing step. 2D spiral pressure sensors and 3D inductors for sensing circumferential strain were successfully printed and characterized. An immediate drawing process was also found to be useful to produce liquid metal based micro-wires having only ~25 μm of liquid metal core with ~12 μm thick SEBS shell. These micro-wires are stretchable up to 400% without any noticeable mechanical failure and electrical loss. That opens up new possibilities to utilize the smart extruder system in neural interfaces and functional electrical stimulation (FES) therapeutical applications.
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- Graduation date
- Spring 2019
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
- Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.