Imagine an automobile coating that changes its structure to adapt to a humid environment or a salt-covered road, better protecting the car from corrosion. Or consider a soldier’s uniform that could alter its own camouflage or more effectively protect against poison gas or shrapnel upon contact.
A trio of university researchers from Harvard School of Engineering and Applied Sciences (SEAS), the University of Illinois and the University of Pittsburgh Swanson School of Engineering is proposing to advance 3D printing one step—or rather, one dimension—further. Thanks to an $855,000 grant from the United States Army Research Office, the group proposes to develop 4D materials that can exhibit behavior that changes over time.
The research group includes principal investigator Anna C. Balazs, the Robert v. d. Luft Distinguished Professor of Chemical Engineering at the University of Pittsburgh Swanson School of Engineering, who studies the computational design of chemo-mechanically responsive gels and composites. Co-PIs are Jennifer A. Lewis, the Hansjörg Wyss Professor of Biologically Inspired Engineering at Harvard SEAS, who is an expert in the 3D printing of functional materials; and Ralph G. Nuzzo, the G. L. Clark Professor of Chemistry and Professor of Materials Science and Engineering at the University of Illinois, a synthetic chemist who has created novel stimuli-responsive materials.
The three will integrate their expertise to manipulate materials at nano and micro levels in order to produce, via 3D printing, materials that can modify their own structures over time at the macro level. 3D printing, also known as additive manufacturing, is the process of creating a three-dimensional solid object based upon a digital model by depositing successive layers of material.
“Rather than construct a static material or one that simply changes its shape, we’re proposing the development of adaptive, biomimetic composites that reprogram their shape, properties or functionality on demand, based upon external stimuli,” says Balazs. “By integrating our abilities to print precise, three-dimensional, hierarchically-structured materials, synthesize stimuli-responsive components, and predict the temporal behavior of the system, we expect to build the foundation for the new field of 4D printing.”
Lewis explains that current 3D printing technology allows the researchers to build in complicated functionality at the nano and micro levels not just throughout an entire structure, but also within specific areas of the structure. “If you use materials that possess the ability to change their properties or shape multiple times, you don’t have to build for a specific, one-time use,” she says. “Composites that can be reconfigured in the presence of different stimuli could dramatically extend the reach of 3D printing.”
As the research will utilize responsive fillers embedded within a stimuli-responsive hydrogel, Nuzzo says this opens new routes for producing the next generation of smart sensors, coatings, textiles and structural components. “The ability to create one fabric that responds to light by changing its color, and to temperature by altering its permeability, and even to an external force by hardening its structure, becomes possible through the creation of responsive materials that are simultaneously adaptive, flexible, lightweight and strong. It’s this ‘complicated functionality’ that makes true 4D printing a game changer.”