What Is 4D Printing?

4D printing is the process of creating 3D-printed objects that can transform over time based on specific stimuli, like exposure to air, water or heat.

4D printing is a process where 3D-printed objects are programmed to autonomously transform over time in response to environmental stimuli, such as heat or light.

Think autonomous, self-assembling furniture delivered in flat packs; buildings that build themselves; regenerative underground piping systems; functional, ready-to-print organs.

Or maybe, during a curious Google search, you’ve watched a curved, sine wave-shaped textile curl into something resembling a brutalist-era lounge chair or the Eiffel Tower miniature of a gelatine makeup gone flaccid, recovering shape when exposed to heat.

Whatever the case, these mighty morphing objects are the renderings of 4D printing, which introduces self-activation properties into the 3D printing process.

4D printing creates self-assembling, programmable matter designed to temporally transform, fabricating a kind of active origami. The 4D or fourth dimension term essentially stands for time, and details the effect of time on the printed object.

"With 4D printing, objects can be printed with extra features that allow them to change shape or function over time," said Xinyi Xiao, an assistant professor of mechanical and manufacturing engineering at Miami University. "This could be used to create objects that can adapt to their environment or even self-repair."

In 4D printing projects, 3D-printed renderings are basically made to be time-dependent. Once fully fabricated, these renderings can morph in response to environmental stimuli they interact with.

The shape-shifting, smart materials that make up 4D-printed items react to a catalyst — such as heat, water, light, wind or electricity — based on a set of instructions written into their geometric coding. They may elongate, bend, wrinkle, fold, twist or even disintegrate once activated. Anything from wood to rubber can be stratified with stimuli-responsive materials. The purpose of this practice is to discover new properties, and manipulate objects without human or mechanical intervention.

That's kind of the whole point. Skylar Tibbits, founder and research director of Massachusetts Institute of Technology's Self-Assembly Lab, described the objective of 4D printing — to create motorless, wireless, powerless tech — when he first coined the term during a Ted Talk in 2013.

"What we’re really trying to make is robots without robots," Tibbits told Fast Company. "We want to design materials that can transform themselves when exposed to energy, but which don't necessarily require circuit boards, electronics or other moving parts to operate."

"[Four-dimensional] printing has lots of potential influential application areas," Xiao said, listing medical, flexible electronics, soft robots and even furniture as use cases.

For example, conductive ink can be used to build electronic devices, she said. This process, however, is constrained on planar surfaces. By adapting the shape-shifting behavior available in 4D, more complicated electronic components can be developed.

Aerospace, automotive, clothing, construction, military, healthcare and manufacturing are the forefront industries exploring the 4D space, according to niche news outlet 3Dprint.com.

The true wonder of this tech lies in its distant horizon potential. Today's success of printing a simple, self-folding chair has researchers and 4D-enthusiasts dreaming up adaptive medical implants and self-constructed buildings.

"[Four-dimensional] printing is still in its early stages," noted Xiao, whose research efforts are currently fixed on quality control in additive manufacturing, based in both 3D and 4D, including the mastery of self-morphing structure and design. "But it is an exciting technology that has the potential to change the way we manufacture objects. Staying creative is imperative so that people can reimagine the digital-to-physical manufacturing line."

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Equipped with commercial 3D printers, researchers begin by inputting smart material, also known as metamaterial. These textiles, which hold the transformative properties unique to 4D objects, are commonly crafted out of hydrogel or shape memory polymers. Hydrogels are responsive to moisture, while shape memory polymers have the ability to bounce back to their original state after deformation.

"The simplest example of these would be a sponge — a material that changes shape when pressure is applied," said Vineeth Venugopal, a materials engineer at MIT.

A more complicated example, he said, would be a shape memory alloy such as NiTinol. Made out of titanium and nickel, it can spring back to its original shape after any sort of deformation.

"These ‘animate’ materials could totally change our world."

These animated traits can be credited to a geometric code preprogrammed into the material. According to its instructions, the printed object will activate once triggered by a set stimulus occurring naturally in its environment.

"These are called smart materials," said Venugopal, "And, if a recent report from the [United Kingdom's independent scientific academy] Royal Society is to be believed, these ‘animate’ materials could totally change our world."

Building with materials that have active, adaptive and autonomous properties would be a game changer across sectors, the Royal Society report notes, most noticeably in industries like construction and transport as well as medicine and textiles.

Four-dimensional printing "is the next step up from 3D printing," Xiao said, noting that you can't have one (4D) without the other (3D).

Differentiating between the two starts with establishing the base of both technologies. Three-dimensional printing is a rapid prototyping technique commonly referred to as additive manufacturing that deposits material layer by layer to fabricate three-dimensional objects.

This same mechanism is used in 4D printing to create parts. The bonus dimension that distinguishes one from the other, however, is determined in an object's geometric coding, as detailed above, which takes that extra step before pressing print. Here, researchers encode the object's desired functionality based on its angles, measurements and dimensions.

So, just as 3D printing is about adding depth to a 2D structure's limitations, 4D is about adding one more factor to the dimensional composition — time. More specifically, change over time. While 4D-printed objects will morph into some sort of action, 3D-printed renderings maintain their static, rigid form.

"[Four-dimensional printing] is able to create objects that can change shape and size after they have been printed whereas 3D printing is a more basic form that can only create objects with a fixed shape," Xiao said. "It is a creation other than the application."

More on 3D Printing3D Printing's Pros and Cons

Not yet commercialized, innovations in 4D printing are still restricted to research and laboratory experimentation. Any applications that are taking place, such as a breast implant that allows healthy tissue to grow in a cancer patient, are considered highly experimental anomalies that, before widespread usage, are pending substantive testing and government approval.

It's important to note, though, that the groundwork has already been laid. Real-world use cases of 3D-printing will foreshadow what's to come — at least in the near future — for 4D-printing. Immediate experimentation has researchers building on top of the decades of 3D-printed proof of concepts, but adding a self-activating twist.

Here's a look at some 4D-printing developments.

The example above, featuring a biodegradable, 4D breast implant, is an example of tissue engineering pioneered by researchers at Xi’an Jiaotong University's national lab. This particular application has developed since, using cellular adhesives known as scaffolds, or biomaterials engineered to promote cellular growth in the formation of new functional tissues. In this case, an additive structural shell is created out of the scaffolds that are photothermally triggered to move with the body and maintain shape as noncancerous tissues regenerate.

A group of researchers at the George Washington University are using tissue engineering to construct cardiac patches, made out of gelatine-based ink. These bio-bandaids can repair heart muscle damage, no glue necessary. The cross-linked structure is designed to stretch with expansion and contraction of the patient's beating heart.

Additionally, sourced from renewable soybean oil, another group based out of George Washington University developed a biocompatible resin that changes shape when interacting with a heat source, then returns to its default form when the temperature stabilizes. Down the line, researchers believe that the material may be used for stem cell growth using bone marrow.

Inspired by parasitic worms, theragrippers are metal, star-shaped, microdevices made out of shape-shifting film designed to carry any type of drug to a targeted part of the body and slow release it. They are coated in heat-sensitive paraffin wax that cling to a patient's intestinal tract. Once embedded, they begin administering the drug once it matches the host's body temperature. This technology, pioneered by researchers from the Johns Hopkins University, comes in the size of a dust speck and has the potential to carry one dose of any type of drug.

Another approach, pioneered by Michigan Technological University researchers, uses magnetic 3D-printed ink infused with microparticles. The magnetic properties of the microparticles can be remotely manipulated to clear blockages within the gastrointestinal tract, retrieve tissue samples and deliver treatment to a targeted location within a patient.

Two types of 4D-printed vascular stents (temporary tubular supports, often made out of metal mesh, stitched into vessels to promote blood flow) are being explored with the application of shape memory. A genetic algorithm is coded into the object, which then simulates a healthy blood vessel by rapidly expanding narrowed pathways, researchers from the Harbin Institute of Technology in China have found.

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Soft robots are biomimetic creations that trade in harsh hardware for compliant materials that better resemble living organisms. Their hydrogel makeup provides a flexible structure that changes in size and shape, making them more applicable to use cases requiring a softer touch, according to a study published in the scientific journal Polymer.

The gentleness and versatility offered by these 4D prototypes provides value to areas such as medical and bionic fields.

Two researchers at Rice University say that they’re not far off from 4D-printing shape-shifting, biomedical implants. With assistance from a liquid crystal polymer ink, their approach decouples the printing process from the object's autonomous transformation in order to optimize shaping control and print more complex structures, as reported by healthcare tech publication Tectales.

MIT's Self-Assembly Labs have developed a morphing jet engine air inlet prototype out of programmable carbon fiber. Unlike its mechanical counterparts, this model is lightweight, minimizes accident-prone mechanisms and operates independent of electronics, sensors or actuators, according to Air University researchers.

Self-assembling micro-drones are thought to be the next evolution of full-fledged, customizable 3D-printed quadcopters currently in use. Other applications include self-repairing bridges (in the event that cracks form) and self-assembling shelters.

One of MIT's Self Assembly Lab's ongoing projects — active textile tailoring — has dabbled in the experimentation of smart fibers that mend self-adjustable clothing. These wearables are able to adapt to a body's shape and movement in response to heat and moisture.

Specific to militant applications, testing in the works include chameleon-like camouflage that mirrors its color pattern to match its environment as it moves in real-time as well as uniforms armored in smart materials that protect soldiers against toxic gasses.

Imagine a warehouse full of boxes. Now, swap out the cardboard standard with a smart material imbued with shape-memory and light-activated polymers coded to self fold and self assemble. Hard to picture? Well, that's probably because it's an entirely new tier of automation in the making.

A 2015 feasibility study out of the Georgia Institute of Technology demonstrated this using thermally-responsive, shape-memory polymers. The technique enabled a manufacturing procedure with "promises to advance immediate engineering applications for low-cost, rapid, and mass production," according to the study.

Potential uses for this technology include milk cartons, shopping bags and car airbags.

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