Whilst 3D printing continues to grow in popularity, some scientists are already looking at the next step – how to make their objects transform from one shape to another using 4D printing.
Essentially, 4D printing uses the same process as 3D printing – the computer-programmed deposition of materials in successive layers – but adds the exciting dimension of witnessing a transformation over time. The process is based in stereolithography and uses photopolymerization to bind substrates positioned layer by layers to create a polymeric network before curing with ultraviolet light once printing is complete.
It utilizes programmable matter i.e. matter that has the ability to change its physical properties in a programmable way based either on user input or autonomous sensing. During 3D printing, a machine is programmed to construct a shape layer by layer; in 4D printing a precise geometric code is also added that is based on the angles and dimensions of the desired shape. This gives the shape a memory and directions on how to move or adapt in certain environmental conditions.
To transform after its creation, a 4D printed object must have a trigger or stimulus; this might be water, heat, wind or other parameters in the environment. For some processes, special material that reacts to the trigger are necessary, but some research teams are investigating programming the object’s desired shape into the microstructure of standard materials, meaning current 3D printers and materials can be utilized. The capacity to transform arises from the near unlimited configurations at a micrometer resolution thus creating solids with engineered molecular spatial distribution and an extraordinary level of multifunctional performance.
4D printing is a relatively new advancement in biofabrication technology and is still in the research and development stage, although some laboratories and prototyping facilities might use the technology, perhaps as part of an art installation or architectural exhibition. 4D printed objects could find uses in bioengineering, material science, chemistry and even computer science, and it’s likely that you may come across the technology in the future in the form of medical implants or mechanical systems that transform with a change in environmental conditions.
Biomedicine is one area in particular in which 4D printed object might find the most uses. A 4D printed water valve that closes when exposed to hot water and re-opens when it is cooler has been demonstrated by researchers at the University of Wollongong in Australia. It utilizes a hydrogel ink that responds rapidly when exposed to heat. Whilst the research is still in its infancy, the team hope it might have application in biotechnology and medical fields in the near future.
A team from The George Washington University in America have demonstrated a new type of 4D printable, photo-curable liquid resin – a renewable soybean-oil epoxidized acrylate compound - that could be used as a scaffold for bone marrow stem cell growth. Meanwhile a team from the University of Georgia have developed a means to fabricate hollow self-folding tubes and control their diameters and architectures at high resolution using a technique based on printing of shape‐morphing biopolymer hydrogels.
4D printed objects may also find use in:
- Architecture – in adaptive facades and opening roofs. It would offer simple installation and direct activation caused by weather conditions, thus removing the need for large control systems or input energy.
- Transportation and shipping – 4D materials can be tailored to specific environments and respond to factors like humidity, temperature and pressure. They may also find use in packing as they could be packaged flat and have their designed shape activated on site by a simple stimulus.
- Fashion – imagine shoes that change how they fit depending on the activity or clothes that change their composition depending on the weather.
But these are just a few examples - 4D printing could be used to create a number of smart objects that can bend, flex, expand or contract, fold up or out or even disappear…the possibilities are endless!
References and further reading
4D printing: all you need to know in 2018
What is 4D printing?
4D printing smart biomedical scaffolds with novel soybean oil epoxidized acrylate
4D Biofabrication Using Shape‐Morphing Hydrogels