3D printing technology has transformed the potential of many industrial and manufacturing processes for almost three decades, but creeping up behind it is a new technology that takes the concept of additive manufacturing even further – 4D printing.

4D printing is the process of enabling a 3D printed object to transforms itself into another structure. The difference between 3D printing and this next generation approach is that 4D printing technology uses programmable and advanced materials to create a new form and potential functionality by adding hot water, light or heat. 4D printing could transform the fields of health and manufacturing, overhauling entire production processes and product composition. For example, compact cardiac stents – tubes for placing in blood vessels to keep them open – could open up in an artery in response to body temperature, or drug capsules could be designed to bend and break open when body temperature rises with infection, whilst flat-pack furniture or construction materials could assemble itself when heated. For example, a research project by the MIT Self-assembly Lab developed programmable material technologies that have resulted in a 4D Printed ‘Self-Folding Surface Cube’. Once placed in hot water, the flat-printed structure slowly folds itself into a cube. All of these elements mean that the expected growth of the 4D printing market is huge. For instance, research predicts that the global 4D printing market will grow by more than 33% between 2019 to 2027, starting from $55.5mn in 2018, driven by an increasing demand for advanced technologies that help to deliver quality products, at a low cost. One of the companies leading the 4D printing market is Organovo Holdings Inc working on 4D bioprinting of living cells that grow and change as children age, eliminating the need for future surgeries. 

 

They are also working on developing specially designed tissues that could revolutionise drugs screening, toxicity studies and disease modelling. Materialise NV are also working on 4D printing applications in the medical sector, helping develop rapid prototypes, low volume manufacture of medical devices relating to cardiac disease. 4D bioprinting technology has the potential to change how we look at the manufacturing process. It allows the product to evolve and extend in life cycle, moving away from the single-use model of consumption that was created by the industrial revolution. Its potential is far-reaching yet there are challenges to overcome. For example, 4D printing may rely on simple properties delivering many potential applications, but it is currently a laborious process. The most common materials used in 4D printing, shape-memory polymers, require at least five steps to make them into adaptable objects. As an alternative, Hydrogels are simpler to use, but too soft to fashion into rigid structures. To solve these issues, work is being done to improve and speed up the process. For instance, Zhen Ding at the Singapore University of Technology and Design and his colleagues have found a way to rapidly print rigid 4D objects with just a commercial 3D printer and a heat source. 

 

The technique uses flat 3D-printed strips made from layers of a polymer with elastic properties that can be printed in less than a minute. As the strip cools, the shape-memory polymer stiffens again to lock the object into its new, curved configuration. Using this technique, the team developed a flower that closes its petals, a flat star shape that morphs into a dome, and lattices that contract and elongate. One of the other critical challenges impacting the field is the lack of advanced 4D-printable bioinks – material used to produce live tissue using printing technology. These materials are currently struggling to meet the requirements of 3D bioprinting whilst also demonstrating the dynamic capabilities required to respond to changes in the environment. However, a solution is likely to be around the corner and when it emerges, the next generation of printing could change how we design, manufacture and view products all over the world.