The following article was part of a Star-Ledger and NJ.com op-ed series on engineering fields that will change the world by Rutgers School of Engineering faculty.
By Howon Lee
When first developed in the 1980s, 3D printing seemed like something out of science fiction. Yet in recent years, 3D printing, or additive manufacturing, has jumped in popularity. Makers of everything from jewelry to biomedical devices have embraced its ability to print three-dimensional objects quickly and economically from all variety of materials ranging from metals and rubber to chocolate and living cells.
Today, industry and academic researchers continue to explore ways to enhance and exploit this sophisticated technology. In the near future, breakthroughs such as 3D-printed houses, plant-based meats and lightweight 3D-printed car and airplane parts are likely to become commonplace.
The 3D printing process itself is fairly straightforward. Working from a digital file, the 3D printer layers materials ranging from metals to plastics to build three-dimensional objects.
Hydrogels, which remain solid despite having 70 percent water content like our body, are among the 3D-printed objects being produced by my laboratory at Rutgers University School of Engineering. These smart materials can deform themselves–swell or shrink–in response to external stimuli such as temperature or electric fields.
While hydrogels have long been part of our everyday life–present in everything from disposable diapers and Jell-O to contact lenses and breast implants–these smart gels clearly point to the future when they meet 3D printing.
Imagine a human-like, 1-inch tall, 3D printed hydrogel that can walk underwater and grab and move objects when activated by electricity. It may sound implausible, but it’s not. We have created a hydrogel that does just that–and that offers tremendous potential for medical innovation because it closely resembles soft tissues in the human body that contain lots of water and pass through small molecules such as drugs. This means that moving smart gel could lead to the development of artificial hearts, stomachs and other muscles as well as soft robotic devices for diagnosing diseases and delivering drugs.
Time is the fourth dimension in 4D printing that lets us create smart, flexible, lightweight–and previously unimaginable–materials that are able to change shape and morph from being as stiff as wood to being soft as a sponge. It is thanks to the innovative marriage of 3D printing and smart materials that 4D-printed objects are able to change shape and property when they are triggered by temperature or other environmental factors. Now 4D printing enables printed objects to sense the environment and react to it, just like we always do.
For example, “metamaterials”–from the Greek word “meta,” which means higher or beyond–are artificial materials engineered to have counterintuitive properties not found in nature. However, despite the limitless potential, the shape and properties of metamaterials are inalterably set once they are manufactured. But with 4D printing, we can change them with heat, so that they can readily morph from being rigid to flexible and back again.
When exposed to heat, these metamaterials’ rigidity can be adjusted more than 100-fold to control shock absorption. They can be endlessly shaped and reshaped–and returned on demand to their original shapes when heated.
4D printing’s unprecedented interplay of materials science, mechanics and 3D printing is sure to create a new pathway to a range of exciting applications that will improve technology, health, safety and quality of life.
In the future, shape-shifting airplane or drone wings could help improve aerodynamic performance, while soft robots composed of flexible, rubber-like materials could be tailored to function in challenging environments. 4D printing can also help to create small, supple biomedical devices which could eventually be less painfully inserted or implanted in people for diagnostic or drug delivery purposes. Furthermore, 4D printing may also help us respond to future epidemics more quickly by providing a new tool to accelerate the pace of innovations in pharmaceutical labs.
Yet 4D printing presents its own set of challenges. To date, we have been able to create small features with precise dimensional control afforded by our 3D printing technology. In order to maintain this precision while making larger objects, the issue of scalability must be addressed.
Additionally, we need to consider these objects’ mechanical properties. We can create all the flexible–even futuristic–interesting devices and applications we want, but if they are ultimately to make it to the marketplace, we must resolve concerns about mechanical properties of reliability, fatigue resistance and durability. In short, we need to answer the question of how to improve them while enhancing their performance.
Finally, we need to continue to bring our imaginations into play. When engineers design things, we often tend to limit ourselves to existing materials and manufacturing methods. With these emerging classes of materials characterized by unprecedented functionalities and rapidly advancing 3D and 4D manufacturing technologies, we now are only limited by the scope of our imaginations.
Howon Lee is an assistant professor in the Department of Mechanical and Aerospace Engineering at Rutgers University School of Engineering.