(2p) 3D Printing across Length Scales and Material Classes for Energy, Environmental, and Health Applications

In recent years, additive manufacturing (AM), also known as 3D printing, has emerged as a uniquely powerful tool for creating complex, individualized structures. Vat photopolymerization (VP) is an AM technique which forms parts through light-initiated polymerization, capable of achieving both high resolution and high throughput. While VP has been utilized to fabricate a wide variety of polymeric materials, fabricating functional materials such as ceramics, metals, and inorganic composites, and translating these materials into the real world has remained a challenge. My lab will develop VP printing technologies that combine functional materials development and optimized designs to enable creative solutions to societal challenges that span energy, environment, and health applications.

Previous and current research

During my graduate work with Prof. Greer, I developed VP techniques that rely on in-situ chemical reactions within an AM part to produce a range of functional materials, from battery active materials to metals and ceramics. For example, aqueous photoresins that contained dissolved aqueous precursors enabled fabrication of LiCoO₂ cathodes for Li-ion batteries (Yee, ..., Saccone, et al., Adv. Mat. Tech. 2021) and water-in-oil emulsion resins enabled targeted delivery of aqueous precursors with tailorable pore formation for Li-S batteries (Saccone & Greer, J. Mat. Res. 2021). My research focused both on printing strategies and electrochemical testing of 3D printed battery systems, leading to a perspective on 3D printing for battery applications (Narita*, Saccone*, et al., J. Mat. Res. 2022).

At that point, forming functional materials via VP relied heavily on the incorporation of precursors into resins. A limitation of this approach was that new material development required burdensome resin re-optimization. The remainder of my graduate work focused on developing a general method for fabricating functional materials via an infusion-reaction framework coined hydrogel infusion additive manufacturing (HIAM) that enabled AM of a wide variety of metals and alloys with microscale resolution (Saccone*, Gallivan*, et al. Nature 2022). HIAM enabled fabrication micro-architected metals such as copper, nickel, silver, cobalt, cupronickel alloys, high entropy alloys, and tungsten with critical dimensions of ~50 µm, showing how a single architected gel can respond to a variety of chemical and thermal stimuli to transform into a vast array of metals.

For my postdoctoral work with Prof. DeSimone, I have focused on advancing manufacturing science to translate advanced additively manufactured materials into useful real-world applications. I am leading projects on the fabrication of microneedle array patches for transdermal vaccination, electrodes for redox flow batteries (in collaboration with Prof. Tarpeh), and conductive susceptors for inductively heated thermochemical reaction engineering (in collaboration with Prof. Fan). I aim to show how the combination of optimized VP printing processes such as continuous liquid interface production (CLIP), functional materials such as refractory carbides, and creative 3D designs work together to enable previously impossible performance from processes which have potential for real-world scaleup.

Future research

To create custom-made materials with specified material properties for a variety of applications, we need (1) comprehensive materials synthesis strategies that combine top-down (deterministic) and bottom-up (self-assembled) design principles to create all classes of materials, (2) fundamental characterization of printing processes and printed materials to ensure repeatability and reliability, and (3) optimized designs to demonstrate scalable applications in energy, environment, and health.

Area 1: Materials synthesis strategies for AM of all classes of materials at all length scales

Enabling the design flexibility advantages of AM to be applied across disparate problems will require a comprehensive palette of materials by design that can span length scales from nanometer to meter. VP printing is a deterministic “top-down” process that inherently trades off resolution and throughput due to the balance between voxel size and voxel patterning rate. This process can create structures with features at the 10-100 µm scale with high throughput, but self-assembled “bottom-up” structure is needed to provide control at the sub-10 µm scale while maintaining high throughput. For instance, block copolymers are known to self-assemble into a variety of phases and morphologies; taking advantage of this geometric control as well as the chemical properties of distinct blocks will enable targeted deposition of precursors within a polymer, and selective removal through thermal processing to create order on the nm-µm scale.

Furthermore, despite the proliferation of materials compatible with VP techniques, there are still conspicuous gaps for some types of materials. For instance, VP printing of metals that are not able to be reduced by hydrogen or carbon remains a challenge. Industrially, these metals are often reduced with alkali or alkaline earth metals, such as in the Kroll process, which forms titanium metal after reduction with molten magnesium. Exploration of stronger reducing agents as well as electrochemical reduction, and development of specialized equipment to facilitate these processes will start to fill in the remaining gaps in the palette of VP materials.

Area 2: Advance manufacturing science through material and process characterization

Understanding and engineering chemical interactions between polymeric materials and precursors of functional materials is imperative for controlling phase composition. For instance, HIAM enables fabrication of high entropy alloys, formed from 4 or more metals. However, understanding the affinity of metal cation precursors for the polymer backbone (via methods such as isothermal titration calorimetry) is needed to control composition in these systems. Furthermore, engineering domains of higher or lower affinity for certain precursors (e.g. through block-copolymer integration) would enable tailorable precursor distribution within a 3D printed part. To characterize the resulting materials, both in situand ex situ characterization is needed. Advanced characterization techniques such as neutron and X-ray scattering would enable measurement of never-before-observed photopolymerization dynamics in the VP process such as the polymerization gradient during a single layer of curing, and the distribution of precursors and fillers at the nm-µm scale. These techniques would further permit investigation of process-induced anisotropy resulting from both the gradient of UV intensity throughout a layer of curing resin, as well as shear-induced polymer alignment associated with resin reflow.

Area 3: Process scale-up for energy, environmental, and health applications

One of the great advantages of additive manufacturing is the ability to design and fabricate complex structures that can address multiple performance objectives in coupled systems. For example, AM can enable synergistic properties to be optimized in multifunctional batteries, where energy storage materials also bear load, leading to overall weight reduction in applications including satellites, spacecraft, and electric vehicles. AM can also enable energy and environmental applications such as 3D-designed micro-flow reactors that can be optimized for heat and mass transfer, gas diffusion electrodes, micro-filtration systems, and refractory components for nuclear energy applications. In the realm of health, AM can enable point-of-care and personalized medical device fabrication. In these applications, structural complexity is required to simultaneously optimize multiple performance objectives, and this complexity is only realistically achievable through additive manufacturing. To accomplish these goals, focus will be given to collaboration with subject matter experts who can help shape problem definitions and provide real-world use feedback across this diverse set of applications.

Teaching Interests

I aim to provide students with fundamental knowledge that they can use to understand a variety of problems, and the practical skill of applying that knowledge to solve problems for the benefit of society. I have experience teaching undergraduate level chemical engineering thermodynamics and engineering design courses; I am also interested in teaching and/or developing a graduate level class in polymer science and materials characterization for 3D printing. I use evidence-based best practices for teaching; I learned and refined pedagogical skills through a Certificate of Practice in University Teaching program at Caltech, which involved 150+ hours of formal education, feedback, and classroom observations. I carried forward from the course a respect for students’ prior knowledge, experiences and learning styles, and the ways that they impact current learning. I also learned to focus on trying to teach a way of thinking by prioritizing the process of problem solving rather than memorization of facts or procedures.

Past teaching experience

As a graduate student, I served as a teaching assistant for undergraduate Chemical Engineering Thermodynamics(ChemE 63A). In this role, my top priority as a teacher was to create a comfortable, supportive, and inclusive space for learning. I stressed the importance of self-care and getting enough sleep; I communicated that I was there for the students, and that I would be flexible and accommodating of their needs. This classroom culture is a necessary foundation for teaching technical skills and knowledge. In end-of-term feedback, my students reflected that I “displayed a deep interest in helping students succeed,” was “helpful and approachable,” and a “top-notch TA who really cared about the students.” As an undergraduate, I was a four-time teaching assistant for Introduction to Engineering (ENGS 21). In this role, I served as the primary mentor for student teams as they delved into the iterative design process and learned about engineering design through long-term projects that focused on solving real-world problems. This was a hands-on class in which students prototyped designs in the lab, fabricated parts in the machine shop, and went out into the world to meet and consult potential product users.