Is 4D printing the final frontier?

4D printing machine

What is 4D printing? Andy Pye looks at how a 3D printer can create objects that change shape when removed from the printer, the fourth dimension being time.

4D printing means different things to different people. Printing machinery specialist Heidelberg takes it to mean printing onto 3D objects. The company’s Jetmaster Dimension is one prong of the German offset printing giant’s latest drive into digital inkjets, geared at printing onto three-dimensional objects.

According to Gerold Linzbach, Heidelberg CEO, the company’s foray into digital “4D” is anticipated to unlock millions of Euros in new business. “As part of our expansion in the digital sector, we are exploring printing on three-dimensional objects and thus breaking into market segments that are entirely new to Heidelberg. Overall we estimate that the digital sector offers us sales potential of more than €200 million per year in the medium term,” said Linzbach.

The first of its Jetmaster Dimensions has already been picked up by leading German online print shop, FlyerAlarm, principally for embellishing standard sports balls with personalised print. Heidelberg plans to take its 4D system into industrial applications in the automotive or aerospace industries, where it could be used to print custom full-colour motifs on cars, trucks or aeroplanes.

But 4D printing has an even more exciting interpretation: a 4D printing technique first invented at MIT in 2013 consists of smart materials that adapt and re-programme their properties, functionality or shape on demand, based upon external stimuli (such as submersion in water, or exposure to heat, pressure, current, ultraviolet light or some other source of energy). Researchers are combining different types of plastics and fibres to create smart materials that self-assemble or change shape after 3D printing. Here, the fourth dimension relates to the time taken for the self-transformation. With the addition of time (a stimulus) to additive manufacturing, objects can become adaptable: self-evolving structures, as some researchers call them.

4D printing is unfolding as a technology that takes 3D printing to an entirely new level; an exciting emerging technology for creating dynamic devices that can change their shape and/or function on-demand and over time. The technique combines smart actuating and sensing materials with additive manufacturing techniques to offer an innovative, versatile, and convenient method for crafting custom-designed sensors, robotics and self-assembling structures.

Future potential of 4D printing

But while it has potential for the future, it also faces challenges: firstly, the printing process is relatively slow compared to other methods – printing large objects can take days; secondly, there is a limitation with respect to the materials that can be used (the materials currently available are nowhere near as strong or effective as those used in other modern manufacturing processes); and thirdly, 4-D printing faces the limitation of size. But the technology is very young and is likely to take big steps forward as 3D printing becomes more accessible.

According to early reports, 4D printing technology is expected to be commercialised in 2019. After that, the global 4D printing market is expected to grow at a CAGR of 42.98% between 2019 and 2025. The market is segmented on the basis of material segments into programmable carbon fibre, programmable wood grain, and programmable textiles. The programmable carbon fibre segment is expected to be the largest contributor to the overall market, with a share of around 62% of the market, in 2019.

Some of the early key players in this market include 3D Systems, Autodesk, Hewlett Packard, Stratasys, ExOne, Organovo Holdings (all US), plus Materialise (Belgium) and Dassault Systèmes SA (France). The end-user industries for which the 4D printing technology is expected to be used include aerospace, automotive, clothing, construction, military and defence, healthcare and the utilities. As 3D printing technology matures with more printable materials and higher resolution at larger scales, the researchers believe the technology will help provide a new approach to creating reversible or tuneable 3D surfaces and solids in engineering, like the composite shells of complex shapes used in automobiles, aircraft and antennas.

Early applications

Dress printed from on single piece of materialSo far, examples of 4D printing have included simple self-assembling bodies that fold together when baked, polymers that bend into shape in response to water, heat or pressure, and smart strands inspired by self-assembling nanostructures. A recently produced example is a fully wearable dress printed in one single piece, in a collaboration between Shapeways and the Nervous System design studio.

Early 4D printing applications utilise water absorption or thermal shape memory to demonstrate impressive shape change, but they are slow to respond, and are restricted to bending type motions of flexible structures that generate little force. They often take a long time to respond, the materials lose mechanical strength as they bend, and the shape-shifting is only reversible only up to a point.

One early example developed at the University of Colorado works by incorporating shape memory polymer fibres into composite materials. In this way, the researchers produce an object fixed in one shape that can later be changed to take on a new shape.

“The initial configuration is created by 3D printing, and then the programmed action of the shape memory fibres creates time dependence of the configuration – the 4D aspect,” explained co-researcher Martin Dunn, from the Singapore University of Technology and Design.

The team advanced the concept by creating composite materials that can morph into several different, complicated shapes based on a different physical mechanism. The orientation and location of the fibres within the composite determines the degree of shape memory effects like folding, curling, stretching or twisting. The ability to control those effects is dependent on heating or cooling the composite material. “The secret of using shape memory polymer fibres to generate desired shape changes of the composite material is how the architecture of the fibres is designed, including their location, orientation and other factors,” Dunn explained.

In December 2014, led by mathematician Dr Dan Raviv, a report providing a deep examination of 4D printing was published, called “Active Printed Materials for Complex Self-Evolving Deformations”. The team comprises members from MIT, Stratasys, and Autodesk. Raviv is a postdoctoral fellow in the MIT Media Lab, where he works in the Camera Culture Group providing new tools for geometric data analysis.

“Researchers are printing biocompatible parts to be implanted in our body,” says Raviv. “We can now generate structures that will change shape and functionality without external intervention. We want to print parts that can survive a lifetime inside the body if necessary. While progress is promising, for things that go inside the body, we want to go 10 to 100 times smaller. For home appliances, we want to go 10 times larger.”

The water-absorbent material they are using — with a secret formula developed by Stratasys —can double in volume when immersed in water. Currently, the test materials eventually wear out after several dozen wet-dry cycles involving shape changes, and lose their shape changing abilities. While  water is the primary stimulus being studied so far, materials that respond to other stimuli — such as light and heat — will be a goal of development.

Nanoscale 4D printing

In June of this year, Northwestern University’s International Institute for Nanotechnology was awarded $8.5 million in funding by the US Department of Defense for a project that will last over the next five years as part of the Multidisciplinary University Research Initiative (MURI) program.

The project will deal with developing 4D printing technology at the nanoscale, serving to further materials sciences, chemistry, and defence-related fields with numerous smart materials that are sensitive also to other materials, signals, and environment. Milan Mrksich is co-principal investigator on the grant, and is also the Henry Wade Rogers Professor of Biomedical Engineering, Chemistry and Cell and Molecular Biology. “Ultimately, the 4-D printer will provide a foundation for a new generation of tools to develop novel architectures, wherein the hard materials that form the functional components of electronics can be merged with biological or soft materials,” he says.

Heat sensitive medical gel

Scientists at the Australian University of Wollongong have developed a special hydrogel that goes in a very different direction, generating quick, reversible and mechanically reliable changes of shape in response to changes in water temperature. The hydrogel material is compatible with a 3D printer. The team sees applications for them in medical soft robotics.

An ionic covalent entanglement (ICE) hydrogel can be 3D printed and demonstrate high toughness. This is important, since thin sections are needed that can respond quickly to external stimuli but also need to be mechanically robust to support the internal and external mechanical loads.

ICE gels are a type of an interpenetrating polymer network that is made up of an entanglement of one polymer network crosslinked with metal cations and a second polymer network crosslinked with covalent bonds. The gels shows reversible length changes of 41%–49% when heated and cooled between 20 and 60C. Blocked stresses generated in tension were in the range of 10–21kPa.

The unique structure of the 4D printing hydrogel toughens the material and prevents microscopic cracks from forming, thus avoiding mechanical failures. Beyond a temperature of about 35C, the gel quickly loses its water content and shrinks down in volume by nearly 50%.

The researchers have used this phenomenon to 3D-print a valve that closes when exposed to hot water and opens once water temperature drops. Unlike a standard 3D-printed material, the gel morphs without human intervention and can repeatedly open and close without straining. “The cool thing about it is, it’s a working, functioning device that you just pick up from the printer,” says the four-dimensionally-named ACES Professor Marc in het Panhuis. “There’s no other assembly required.”

The smart valve controls the flow of water by printing a gel ink alongside other static materials. The valve, a 3D printed structure, includes the actuators, which are activated solely by the introduction of water. The valve automatically closes upon exposure to hot water, reducing the flow rate by 99%, and opens in cold water. With CAD modelling, this 4D printing technique can be easily extended to make other types of moving structures.

As the ACES Chief Investigator, Panhuis says his group was the first to combine the printing a 4D device with four different cartridges at once. The process uses the tough hydrogels – fibre reinforced in a single-step process – and these composite materials were fabricated using a combination of a alginate-acrylamide gel precursor solution and an epoxy based UV-curable adhesive known as Emax 904 Gel-SC.

Panhuis believes that the ability to 4D print robust, actuating hydrogel materials opens a new avenue for fabricating hydrogel-based sensors and self-assembling structures for water treatment, soft robotics, bionics and tissue engineering applications. The main research focus is to combine bio and synthetic polymers with carbon nanostructures, and or conducting polymers via processing techniques such as additive fabrication into soft (wet and tough) materials.

References

4D Printing Market by Material (Programmable Carbon Fiber, Programmable Wood – Custom Printed Wood Grain, Programmable Textiles), End User (Aerospace, Automotive, Clothing, Construction, Defense, Healthcare & Utility) & Geography – Global Trends & Forecasts to 2019 – 2025
By: Marketsandmarkets.com, June 2015. Report Code: SE 3552.

Advances in 4D Printing (Technical Insights) Nine Pronged Technology Evaluation — Next Paradigm in Manufacturing Report D545-TI, Frost & Sullivan, June 2014

Shannon E Bakarich, Robert Gorkin III, Marc in het Panhuis, Geoffrey M Spinks
4D Printing with Mechanically Robust, Thermally Actuating Hydrogels
Macromol. Rapid Commun. 2015, 36, 1211−1217

Andy Pye

Andy Pye

Andy Pye is a graduate of Cambridge University and has had a high profile career in the technical press as well as being a pioneer in web publishing.
Andy Pye

Latest posts by Andy Pye (see all)

About Andy Pye

Andy Pye is a graduate of Cambridge University and has had a high profile career in the technical press as well as being a pioneer in web publishing.

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