4D printing of smart materials

Scientists have created a 4D printer for smart materials with magnetic and electromechanical properties.

These scientists, from the Carlos III University of Madrid (UC3M) in Spain, have created the software and hardware for said 4D printer, which will have applications in the biomedical field. In addition to 3D printing, this machine allows you to control an extra function: programming the response of the material so that it can change its shape when a magnetic field is applied or to change its electrical properties when it is deformed. This opens the door to the design of soft robots or smart sensors and substrates that transmit signals to different cellular systems, among other applications.

This line of research focuses on the development of soft multifunctional structures, made up of materials with mechanical properties that mimic biological tissues, including everything from the skin to the brain.

Until now, this team of researchers had made various advances in the design and manufacture of these materials, but they were very limited in terms of their shape and programming of intelligent responses. What they have achieved in their latest study has allowed them to open up new possibilities by developing a new 4D printing methodology. “This technology allows us not only to control the way in which we print the structures in three dimensions, but also allows us to provide it with the ability to change its properties or geometry in response to the action of external magnetic fields, or modifying its electrical properties by deform”, explains one of the researchers, Daniel García González, head of the ERC 4D-BIOMAP project (GA 947723) and professor in the Department of Mechanics of Continuums and Theory of Structures at UC3M.

This type of printing is complex since the material to be printed transitions from liquid to solid during the printing process. For this reason, it is necessary to understand the dynamics in order to be able to adapt the printing process, in such a way that a sufficiently liquid material is obtained when it flows through the nozzle of the printer, but, at the same time, solid enough so that it can maintain a specific way. To do this, they have developed an interdisciplinary methodology that combines theoretical and experimental techniques that has allowed them to build the printing device from scratch, both the physical part of the device (the hardware) and the computer programs that allow it to be controlled (the software).

The new 4D printer works with smart materials that have very useful magnetic and electromechanical properties. (Photo: UC3M)

A self-healing material

The researchers have also developed a new concept of material that is capable of repairing itself autonomously and without the need for external action. “This material consists of a soft polymeric matrix that includes magnetic particles with a remnant field. For practical purposes, it is as if we had small magnets distributed in the material, so that, if it breaks, when the resulting parts are brought closer together, they will come back together, recovering their structural integrity”, says Daniel García González.

Thanks to these advances, which have given rise to several registered patents, these scientists have been able to print three types of functional materials: some that change their shape and properties in the face of external magnetic fields; others with autonomous repair capacity; and others whose electrical properties (conductivity) vary according to their shape or deformation. With the first type of material, they have developed intelligent substrates to transmit forces and signals to cellular systems, so that they can influence biological processes such as cell proliferation or migration. These materials can also be used to design soft robots whose performance can be controlled by magnetic fields.

The combination of materials with self-healing capabilities and whose electrical conduction properties vary with deformation opens up enormous possibilities in sensor development. “We can think of sensors attached to our body that collect information about our movement from variations in electrical conductivity. In addition, the self-healing ability of the material allows the design of sensors with binary signals. For example, if we have had a knee injury and need to limit rotation to a maximum value, we can incorporate a small band of this material over our joint. In this way, when we exceed said maximum rotation, the material will break showing an abrupt change in its electrical properties, thus providing a warning signal. However, upon returning to a relaxed state of the knee, the repair ability of the material will result in recovery of the electrical signal. In this way we can monitor our movements and warn of risk conditions during postoperative periods or rehabilitation seasons”, says Daniel García González.

The most recent study in this line of research and development is entitled “Computationally Guided DIW Technology to Enable Robust Printing of Inks with Evolving Rheological Properties”. And it has been published in the academic journal Advanced Materials Technologies. (Source: UC3M)