Morphing 3D-Printed Architectures into 4D

The latest advances in additive manufacturing technology require engineers and manufacturers to view design, development and production processes in a completely new way. These transformational changes push design boundaries beyond traditional parameters. No longer will designers focus solely on dimensions like height, width and depth.

What’s behind this paradigm shift? The introduction of a new element to the equation: the fourth dimension—time.

This metamorphosis is triggered by the development of 4D (four-dimensional) printing technology, which creates objects that change their physical form over time. After the printing process, the objects, responding to trigger events, reshape or self-assemble themselves in pre-defined ways, which introduces novel levels of design and production flexibility.

Printing in 4D

Much like various forms of 3D printing, the new process converts design specifications into physical structures using stereolithography. The 4D-printing technique also relies on photopolymerization to bind substrates, layer by layer, before the curing process.

Unlike 3D printing, however, where the printer builds a shape according to the specifications defined in a digital blueprint, a 4D printer follows a geometric code based on the angles and dimensions of the desired shape. This “genetic code” tells the printed object how it should respond to certain environmental conditions.

The primary difference between the 3D and 4D printing technologies lies in the use of materials that can be programmed to alter an object’s physical properties in a pre-defined way when exposed to a specific stimulus, such as water, heat, mechanical force, a magnetic field or electricity. These “smart” materials are often hydrogels, shape-memory polymers or cellulose composites.

Some research teams have begun investigating ways of programming the object’s desired shape into the microstructure of standard materials. If successful, this technology will help engineers create solids with engineered molecular spatial distribution using 3D printers and materials already on the market.

Ramifications and Applications

Although 4D printing is still in the research and development stage, a number of promising applications would benefit fields like computer science, aerospace and mechanical engineering.

Engineers from the University of Pennsylvania have printed active polydimethylsiloxane-hydrogel-based structures that maintain elastic energy. A gate embedded in the structure is controlled by the interaction between the structural material’s “genetic code” and weight, water and oil-based solvent triggers. Combined, these elements activate the gate’s kinetic movement. (See the video here).

Structures like these could prove useful in microfluidics applications. For example, instead of using solid-state sensors, microprocessors and actuators, engineers could harness 4D technology to design organic gates that shut automatically when they detect contaminants.

In another project, a research team at City University of Hong Kong has developed a method of 4D printing ceramics. Ceramics have a high melting point and are prone to deformation, which makes the material difficult to use with some laser printing processes. To overcome these challenges, the research team created “ceramic ink” by combining polymers and ceramic nanoparticles, producing soft ceramic precursors that can be stretched three times their original length. The elastic energy enables the morphing of the object’s shape. Heat treatment then turns the precursors into ceramics that have a great compressive strength-to-density ratio and can be used to create large objects.

One potential application might be electronic devices. Ceramic materials transmit electromagnetic signals better than metallic materials. Other uses of the technology may benefit the aerospace industry. Because ceramic tolerates high temperatures, the 4D-printed material could be used in propulsion systems. Combined, the new features of the technology could mark a major turning point in the structural application of ceramics.

The market has yet to determine 4D printing’s full potential. A key benefit that promises to bring fundamental change to design, however, lies in the technology’s ability to provide actuation, programmability and sensing without the use of electromechanical devices and systems.