The Singapore University of Technology and Design (SUTD) and Massachusets Institute of Technology (MIT) have been working on a material to produce three-dimensional structures that can “remember” their original shapes after a deformation process. The object can be twisted or bent to irregular forms but due to the use of light in the making process, the material will be able to regain their original shape when heat is applied.
This technology was developed by a multidisciplinary team that published their results in the Scientific Reports journal this month. This heat-responsive material can bring considerable advances to solar panel installations and other structures. Heat-response technology may be useful for other applications, such as medical and aerospace appliances.
The printing process
The team found out that adding light to the printing process could mean integrating the fourth dimension to the process, which translates into a 4D printing that allows the material to change over time.
This formula allows stretching shape-memory polymers, the base material, ten times larger than the polymers used by commercial 3D printers. This 4D print can be done at a micro-scale, as small as the diameter of human hair, a size that has not been achieved with other printable materials. The restriction on the dimension limits as well how fast the material can turn back to the original shape.
The same team built the artifact used for this advanced printing, and it’s called Microsterolithography. The machine uses light from a projector to create particular patterns in the layers of resin and the polymer solution, that then solidifies. The first structure was designed in the Computer-Aided Design (CAD) first.
“We’re printing with light, layer by layer. It’s almost like how dentists form replicas of teeth and fill cavities, except that we’re doing it with high-resolution lenses that come from the semiconductor industry, which give us intricate parts, with dimensions comparable to the diameter of a human hair,” said Nicholas Fang, member of the research team and associate professor of mechanical engineering at MIT.
Material that can remember and be responsive
The polymer used in this research is a mix of polymers instead of a single component material; this composition allows the machine to print the light patterns in its layers. The two most important polymers composing this material are long-chain polymers and materials that resemble rigid scaffolds. This mix creates the incredibly flexible polymer in the final “memory” structures.
The shape-memory polymers utilized in this research can switch between two primary states according to the temperature the material is exposed to. When keeping a low temperature the material will stay hard, but when put under high temperature the material will be rubbery and soft. The idea is to maintain the stretched shapes at room temperature with the possibility to go back to the original sturdy form, because when the material is heated it will “remember” their shape.
The idea is to maintain the stretched forms at room temperature with the possibility to go back to the original sturdy form, because when the material is heated it will “remember” their shape.
However, the team is exploring several materials to expand the capacity of deformation and response to environmental stimuli, which could be not only temperature but also light itself or electricity. The goal is to achieve a material that can be a response to body temperature since this result could be translated into relevant medical appliances such as creating fever-response drugs, artificial muscles or soft robotics as a biomedical device.
From flowers and Eiffel towers to possible biomedical parts
Among structures printed by the team, there are flowers, coils and a miniature version of the Eiffel tower that can remember their original shape when bent or twisted in any way. The objects can be stretched up to three times their original length and the artifacts respond quickly and without breaking.
In seconds, the objects can go back to their original shape without harming their composition. This, however, is linked to the size of the object and the pixels printed in the layers. The speed of the response is related to small dimensions, the smaller the object, the faster the response.
But larger objects (such as biomedical parts or artifacts for solar panels) may take more than a few seconds to get the back its original shape, so further investigation is needed to determine the possibilities to make big objects transform or recover fast.