February 1, 2016 (Vol. 36, No. 3)
Skylar Tibbits Shares His Insights on the Biotechnology and Medical Applications of 4D Printing
One of the most rapidly developing technologies that is already affecting a wide range of research and industrial applications is 4D printing. Skylar Tibbits, a pioneer in the field, is the director of the Self-Assembly Lab at MIT (www.selfassemblylab.net). Tibbits has a professional degree in Architecture and a minor in experimental computation from Philadelphia University. Continuing his education at MIT, he received a Masters of Science in Design Computation and a Masters of Science in Computer Science. He is also the editor-in-chief of 3D Printing and Additive Manufacturing, published by Mary Ann Liebert, Inc. GEN recently spoke to Tibbits about specific biotech and medical applications of 4D printing.
GEN: There’s been a lot of talk about 4D printing over the last year. Just what is it and how does it differ from its 3D predecessors?
Skylar Tibbits: We introduced 4D printing about three years ago during a collaboration with Stratasys and Autodesk. We wanted to go beyond simple 3D printing static things and print highly active structures. The four in 4D refers to chronology, so these products can transform, change shape, and reconfigure over time.
It’s much like printing smart materials with the main goal to fully customize those materials. We can print them in any shape or quantity and then design how they’re going to transform. We can now make these materials easily and print them to do whatever we want them to do.
Fundamentally, we’re still using 3D printers. In the beginning we printed with multiple material properties at the same time. One of the materials was usually a rigid polymer. The other material in the original 4D printing work was a hydrogel, which can expand as much as 150% when it receives moisture, and that gives it the energy to transform. More recently, we’ve shown we can do 4D with a whole series of different polymers and material compositions.
GEN: I often hear the term self assembly associated with 4D printing. What are we talking about here?
Skylar Tibbits: There are two different notions of self-assembly. Our lab is called the Self-Assembly Lab at MIT, so when we say self-assembly, we usually mean the pure definition of self-assembly, that is, independent components coming together on their own without human or machine intervention and without guided energy. For example, at the macro scale, when someone thinks of Ikea furniture, it usually involves a person who physically assembles things.
With 4D printing the way we’re doing it, we’re proposing the creation of printed furniture that would be able to assemble itself, or that the components of the products would be able to transform themselves into one particular state or another.
At the small or nano scale, self-assembly is everywhere. It’s a fundamental principle of biology, chemistry, and materials science. That’s how precision, functionality, and every higher-order structure emerge. They come from local interactions with components and from their relationship to the surrounding environment. There are no sledgehammers, no screwdrivers, and no industrial robots doing the assembling. Biology has to put itself together.
Now, this is an obvious fundamental principle to any biologist or chemist. More recently though there have been a lot of advances in materials science, like DNA origami and self-assembly in bacteria and cellular structures. This is being looked at as a new method for manufacturing or constructing at those nanoscales. You can hijack these phenomena to build things that wouldn’t normally be possible.
GEN: Can you expand on the connection between synthetic biology and self assembly?
Skylar Tibbits: The biological world probably has the best examples things that have been highly active, self-reconfiguring, and self-assembling forever. These things transform themselves based on their environment. They build themselves.
Synthetic biology is allowing this notion of self assembly to catalyze in a way that relates to printing different things in terms of bioprinting or programming biological materials to have shape-change or functionality-change over time.
The medical industry was one of the first to adopt smart materials, as was the case with stents, for example, which all use nitinol or shape-memory alloys. There are shape-memory polymers. There are self-dissolving materials. So synthetic medical applications, especially those involving surgeons, have been using smart materials for a long time.
GEN: What are some current and future medical applications for 4D printing?
Skylar Tibbits: Biology and chemistry are related to one another, and they offer the best examples of smart materials and self-assembling systems. The medical space fits well with 4D printing.
Earlier this year researchers from the University of Wollongong in Australia reported in Macromolecular Rapid Communications that they had 4D printed a valve that automatically opens and contracts in the presence of water and temperature. The team used a 4D printer with four different types of hydrogel. One of the applications the scientists foresee is for medical implants that change their shape inside the body. The valve itself is mechanical and autonomous; no power or programming is needed.
Also, in May, investigators at the CS Mott Children’s Hospital at the University of Michigan published an article in Science Translational Medicine about a new way to treat three boys with tracheobronchomalacia, which causes the windpipe to collapse when they breathe. The team 4D printed a splint made of polycaprolactone, a biodegradable plastic that could be sewn around the trachea and bronchi to keep them open. The splints eventually dissolve as the children’s tracheas grow stronger.
We already had a surgeon come to us to talk about applications where a specific 4D design emerges. So you print a structure, you deposit it in the body—whether it’s a stent or some other device—and then it resolves to local forces and responds to the local environment to shape and change into whatever it needs to be. It eliminates sculpting or customizing of those materials and eliminates having standard sets and sizes. Each device can be unique, and they could be easily produced in the hospital or in the operating room. Some of the other applications are orthodontics and audiology
So there’s already a lot of medically related printing happening. The next obvious step is to keep creating smarter materials and better shape-changing structures. Hearing and audiology are obviously interesting applications. Externally, there are applications like braces, support structures and compression garments that can morph and help increase the performance or the effectiveness of treatment.