(Invited) Additive Manufacturing: Sustainable Manufacturing of Flexible Sensors, Systems and Devices
Authors: Khosla Ajit , Arya Sandeep , Nagahara Larry A. , Thundat Thomas , Kawakami Masaru , Furukawa Hidemitsu 
Published: May 2020

Unlike subtractive manufacturing processes, additive manufacturing (AM), also called as 3D printing, can directly produce complex three‐dimensional parts. With near-complete design freedom, it is advantageous in markets that have a demand for customization, flexibility, design complexity, and high transportation costs. This process holds a great deal of potential for manufacturing novel designs and materials for sensors, electronics, energy conversion and storage devices, which were previously inaccessible due to the constraints of traditional manufacturing methods. Like any other manufacturing technology, AM suffers from certain limitations that hinder the use of AM in the field of sensor and energy research: 1) lack of materials available for AM; 2) multi-material AM; and 3) feature size and accuracy. In order to overcome these limitations, my team and I have developed a universal multi-material 3D printer that is capable of printing metals, thermoplastics, gels, pastes, elastomers, and nanocomposites. This newly developed 3D printer is unique in the sense that it employs a screw-based extrusion system. The different materials to be 3D printed (also known as feedstock) are fed into the hopper, the single screw extrusion system mixes and melts the materials, removes any air bubbles, and extrudes the nanocomposite material through a specially developed nozzle ensuring 3D printing without any defects. By using this universal multi-material 3D printer, my team and I have been able to 3D print steel, aluminum, silver, nickel, cobalt, copper, carbon fiber-based nanocomposites, ionic gels, semiconducting materials, titanium dioxide, various thermoplastics, wood, and epoxies. Work is ongoing to increase the resolution of this universal material 3D printer, but more research needs to be carried out to achieve sub 100-micron structures. With the success of this universal material 3D printer, we began to focus on developing 3D printed flexible sensors [1], electronics [2], solid state battries [3] and vanadium redox flow batteries by using recycled vanadium collected from ammonia slag [4]. We are also currently testing the mechanical properties of 3D printed materials against bulk materials in order to understand degradation mechanisms. Considering all of these factors, AM (3D printing) has great potential to become a sustainable manufacturing technology for flexible sensors, electronics and storage devices such as lithium ion batteries, redox flow batteries. This talk will discuss examples of ongoing research work on AM manufactured sensors, systems and devices.
Keeping in mind the interdisciplinary in nature of the work, his talk will focuses on the development of sustainable 3D and 4D printable hybrid nanocomposite materials, with applications in energy storage devices, energy harvesting, flexible/stretchable sensors for the Internet of Things (IoT), and soft robotics. Careful consideration is given to synthesis and designing of 3D and 4D printable hybrid materials, so that the processes involved do not compromise the natural environment, or the ability of future generations to maintain sustainable communities.
A key insight from our research over the last five years is that 3D and 4D printable hybrid nanocomposite materials for sensors, electronics, energy conversion and storage devices can only be implemented and improved when degradation mechanisms are clearly understood. With the goal of enhanced longevity, our research program aims to contribute to the fundamental understanding of degradation mechanisms, root causes, and failure modes in 3D and 4D hybrid nanocomposite materials. Specific research objectives are to:
1. Develop in-depth knowledge of key degradation mechanisms, from root cause to failure, in 3D and 4D hybrid nanocomposite materials;
2. Develop modeling tools for longevity predictions and demonstrate strategies for longevity enhancements in 3D and 4D hybrid nanocomposite materials;
3. Deploy and test 3D and 4D hybrid nanocomposite materials in real world scenarios.
4. Establish and promote research collaborations between scientists working in sustainable energy engineering, materials science and computer science (machine learning) fields; and
5. Establish collaborations with industrial and academic sectors, and all levels of government, to engage in dialogue on the societal implementation of developed technologies.
To realize a sustainable society, it is necessary to promote not only the circulation of resources, but also the efficient use of energy, the development of new technologies associated with the efficient use of energy and materials such as (machine learning and artificial intelligence), recycling of valuable resources, and the production of environmentally friendly materials and systems. My long-term goal is to be part of the solution to help build a sustainable world by training future generations of researchers, ensuring effective knowledge mobilization, and engaging communities to develop sustainable engineering solutions.
References:
1. Ajit Khosla, Shreyas Shah, MD Nahin Islam Shiblee, Sajjad Husain Mir, Larry Akio Nagahara, Thomas Thundat, Praveen Kumar Shekar, Masaru Kawakami and Hidemitsu Furukawa (2018). "Carbon fiber doped thermosetting elastomer for flexible sensors: physical properties and microfabrication." Nature Scientific Reports 8, no. 1 (2018):12313 https://doi.org/10.1038/s41598-018-30846-3
2. Sathish K Sukumaran, Takafumi Kobayashi, Shunsuke Takeda, Ajit Khosla, Hidemitsu Furukawa, and Masataka Sugimoto (2019). “Electrical Conductivity and Linear Rheology of Multiwalled Carbon Nanotube/Acrylonitrile Butadiene Styrene Polymer Nanocomposites Prepared by Melt Mixing and Solution Casting.” J. Electrochem. Soc. 2019 volume 166, issue 9, B3091-B3095. https://doi.org/10.1149/2.0171909jes
3. Kumkum Ahmed, Masaru Kawakami, Ajit Khosla and Hidemitsu Furukawa (2019). “Soft Conductive Nanocomposites Based on Ionic Liquid/Carbon Nanotube for 3D Printing of Flexible Electronic Device” Nature- Polymer. Vol 51, pages 511–521 (2019). https://doi.org/10.1038/s41428-018-0166-z
4. He Sun, Hirotaka Takahashi, Yuki Kamada, Kei Sato, Yuta Matsushima, Ajit Khosla, Masaru Kawakami, HidemitsuFurukawa, Philipp Stadler, and Tsukasa Yoshida (2019). “Vanadium Redox Flow Batteries Fabricated by 3D Printing and Employing Recycled Vanadium Collected from Ammonia Slag.” J. Electrochem. Soc. 2019 volume 166, issue 9, B3091-B3095. https://doi.org/10.1149/2.0251909jes