Session: Rising Stars of Mechanical Engineering Celebration & Showcase

Paper Number: 148634

148634 - Designing Materials and Processes for Ink-Based 3d Printing of Multiscale Multimaterial Multifunctional Systems 

The ability to precisely assemble multiple materials in three-dimensional (3D) space over multiple length scales could revolutionize a wide range of emerging fields, from single multifunctional materials and devices for optoelectronics, sensors, actuators, and living materials, to the creation of fully integrated systems such as adaptive and autonomous architectures, wearables, implantables, and robotics. Ink-based 3D printing processes, such as extrusion and droplet-based printing, are well-suited manufacturing techniques for these types of applications because they can pattern an unlimited number of materials sets across a broad range of length scales, can be incorporated readily with a multitude of other ink-based printheads for multi-material printing, and can be combined directly with pick and place techniques to realize fully integrated systems. Central to ink-based 3D printing is the requirement to simultaneously satisfy compatibility with the printing process while achieving targeted multifunctional properties with high part fidelity. This work seeks to address this challenge through two young investigator award projects.

For the AFOSR YIP, we investigated two separate materials systems. The first system is a set of heterogeneous multiscale epoxy composites (HMECs) and synthetic fascia for 4D printed electrically controllable multifuntional structures with high stiffness and toughness, both compatible with direct ink writing (DIW). The HMECs exhibit an elastic modulus range four orders of magnitude greater than that of existing 4D printed materials and offers tunable electrical conductivities for simultaneous Joule heating actuation and self-sensing. Utilizing electrically controllable bilayers as building blocks, we design and print flat geometries that change shape into 3D self-standing lifting robots, displaying record actuation stress and specific force when compared to other 3D printed actuators, and culminating in a 4D printed crawling robotic lattice. We then integrated our HMECs with a 3D printable PDMS adhesive that serves as synthetic fascia to hold our synthetic muscle together. Through this approach, we achieved a three order of magnitude increase in toughness, all while maintaining the high stiffness and responsiveness. Utilizing this fabrication method, we printed electrically controllable actuators and sensing surfaces that exhibit damage detection and tolerance. Ultimately, we present a 4D printed lattice showcasing a sensitive electrically responsive surface that can endure external compressive damage equivalent to 10⁵ times its own weight. The second materials systems we investigated were new multifunctional liquid metal emulsions for multifunctional soft and stretchable electronics. We introduced a dense liquid metal emulsion that is compatible with DIW and can achieve high electrical conductivity under mechanical sintering, requiring an order of magnitude lower activation stress compared to current approaches. We then introduced chemically coalescing liquid metal emulsion that obviates the need for mechanical sintering or any other extreme sintering methods. Both of these emulsions are then integrated with pick and place techniques to realize custom soft electronic systems. Finally, we develop a liquid metal in ionic liquid emulsion to demonstrate a first mechanically activated liquid metal air battery, which is used as a simple power source for LEDs, and as a self-powered soft keypad.

For the NSF CAREER award, we are developing a combined theoretical, experimental, and computational framework for the rapid determination of both the multi-component dispersion composition and the subsequent print routine needed to manufacture films of a desired multi-layer morphology. In particular, we are utilizing a combination of modeling, computational, and characterization techniques to develop an understanding of 1) the solvent, particle, and polymer thermodynamic relationships necessary to form multi-layer multi-material deposits, 2) the effects of solvent/particle/polymer chemistry and concentration on layer thickness, deposit formation dynamics, and multi-layer deposit morphology of drying droplets, and 3) the effects of drop spacing and deposition sequence on migration of ink between deposited droplets and the resulting morphology of the 2D film. To realize this, we have characterized contact angles between a multitude of solvents and ligands and have explored an ethanol-water systems more in depth as an initial model system. The multifunctional inks from the AFOSR YIP could be tailored for this approach.

Presenting Author: John (William) Boley Boston University

Presenting Author Biography: Will Boley is an Assistant Professor in the Department of Mechanical Engineering and the Division of Materials Science and Engineering at Boston University, and is the founding director of the Additive Assembly Laboratory (AAL) at Boston University. Professor Boley’s research group focuses on understanding and harnessing the relationships between materials synthesis, assembly process, and multi-scale architecture in additive manufacturing to create new functional materials and devices. To accomplish this, his research combines aspects of materials science, thermal fluid science, design, and optimization. Target application areas include electronics, optics, sensors, and soft robotics. He is the recipient of the 2020 AFOSR YIP and the 2021 NSF CAREER.

Authors:

John (William) Boley Boston University