Engineers and chemists from Lawrence Livermore National Laboratory (LLNL) and Meta created a new type of 3D printed material for realistic wearables applications. The new materials can mimic the properties of biological tissue, which could have an impact on the future of “augmented humanity.”
LLNL and Meta researchers describe a framework for creating a “one-pot” 3D-printable resin in which light is used to pattern smooth gradients in stiffness to approximate gradients found in biology, such as where bone meets muscle, in a paper recently published in the journal Matter. The framework addresses a key issue in developing more realistic wearables: “mechanical mismatch.” Whereas natural tissues are soft, electronic devices are typically made of rigid materials, making traditional assembly difficult and time-consuming.
The material was demonstrated by the team by creating a 3D-printed wearable braille device that can “translate” text messages to braille on the fly by filling the device with air at strategic points.
3D Printed Material for Realistic Wearables
Lead author and LLNL engineer Sijia Huang explains that for engineers, the challenge lies in combining softer and stiffer materials, a common occurrence in nature. Traditionally, engineers have manufactured a stiff component and a separate soft component, manually assembling them, resulting in a sharp interface that can undermine mechanical performance. This research, led by Huang, focuses on the exploration of the feasibility of designing continuous mechanical gradients within a single resin system. In this approach, the entire structure is 3D printed, with light dosage serving as the means to control the modulus throughout the material.
Huang explained that the technique modulates the deposited plastic material by varying the intensity of light applied to a photopolymer resin during the Digital Light Processing 3D printing process — a layer-by-layer technique that can rapidly produce parts by projecting light into a liquid resin. A softer material results from a lower light intensity, while a stiffer material results from a higher light intensity.
Engineers at Meta used the material to 3D-print an inexpensive braille display that could be worn on a single finger and connected to a smartphone and an air pump to demonstrate its potential. When text is sent via phone, sections of the wearable fill with air, causing it to deform and form braille letters, allowing a blind person to “read” the text through the device. To make the device work, researchers needed to vary the stiffness of a single device so that it deformed differently when air was pumped into it, according to Huang.
Huang, a Lawrence Postdoctoral Fellow in LLNL’s Materials Engineering Division, started the project as an intern at Meta’s Reality Labs in 2019, with the goal of creating wearable devices out of a material that could vary in modulus but could be made in a single part. She worked on it before going to graduate school, and when she got a job at LLNL through the Lawrence fellowship, she discovered that her old manager at Meta, paper co-author Thomas Wallin, had begun a collaboration with LLNL. Fortunately, Huang was able to complete the project at the Lab.
“A beautiful feature of additive manufacturing is that we can create these impossible structures, but also we are somewhat limited in terms of the material properties — we only have a certain amount of material that we can pick from. One of the initial motivations was, ‘what if we could have the same resin system and replicate the engineered plastic systems effortlessly by merely adjusting the light intensity?’ That would save a significant amount of time and effort for engineers, particularly when incorporating new properties of materials.”
– Huang, a Lawrence Postdoctoral Fellow in LLNL’s Materials Engineering Division
The material can be stretched to around 200 times its original properties, and its toughness increases by 10 times as the gradient transitions from soft to stiffer material. The material, according to Huang, could be tailored for energy-absorbing materials, soft robotics, and wearable electronic devices.
Huang added, “One of the requirements that we want to look at for wearable devices is the necessity for a consistently stable material over the long term. What sets this work apart is our demonstration of the material’s stability under light and ambient conditions; we actually expose our materials under the ultraviolet (UV) light to observe their behaviour over extended exposure periods. Using UV curing techniques tends to decrease the mechanical gradients over time, so this shows how stable our material is.”
“This development is important because plastics generally struggle to maintain performance over long periods of years to decades, compared to some other materials like metals. For 3D-printed plastics, this is even more of a challenge, even when impossible exquisite geometries can be printed. This paper describes a significant advance for variable-stiffness polymer materials with long-term stability. These results advance LLNL’s mission focus of discovering and developing new paths forward in both manufacturing methods and their associated materials.”
– Maxim Shusteff, Co-Author and a group leader in the Materials Engineering Division
Johanna Schwartz of LLNL, Steven Adelmund and Pradip Pichumani of Meta’s Reality Labs, and Yiit Mengüç of the Collaborative Robotics and Intelligent Systems Institute are also co-authors on the paper.
