Researchers at Rice University, Houston, Texas, developed a new 3D-printing process with focused microwaves that overcomes a fundamental constraint of electronics 3D printing that has limited the field’s potential for more than a decade: the inability to heat printed ink — a crucial processing step — without damaging the materials underneath.
The ability to integrate functional materials and spatially program their properties governs both device performance and the limits of what can be built. Existing manufacturing approaches are fundamentally limited in both aspects. Electronic components, for instance, are fabricated in massive, centralized foundries, often decoupled from the final device. Integrating them requires complex, labor-intensive assembly that constrains both the form and the function of what can ultimately be created.
Multimaterial 3D printing should, in principle, allow fabrication of free-form architectures in which electronic and mechanical properties are programmed directly into the structure. However, the thermal processing required to render printed electronic inks functional destroys the very materials these devices require.
In a recently published paper in Science Advances, the team demonstrates that by concentrating microwave energy into a confined heating zone as small as the diameter of a human hair, the researchers can selectively heat the electronic ink during the 3D-printing process while keeping the surrounding material relatively cool and thereby reducing potential damage.
“The ability to selectively heat the printed materials enables us to spatially program the ink’s functional properties, even when surrounded by temperature-sensitive material,” said Yong Lin Kong, assistant professor of mechanical engineering at Rice’s George R. Brown School of Engineering and Computing. “This allows us to integrate freeform electronics onto a broad range of substrates, including biopolymers and living biological tissue, all within a desktop-size printer without the needs of complex facilities or labor-intensive manual processes.”
A collaboration with the National University of Singapore resulted in the development of the “Meta-NFS” (metamaterial-inspired near-field electromagnetic structure), a device that confines microwave energy in the near field to achieve the high energy density required to post-process printed inks while maintaining the integrity of the surrounding structure.
When integrated with a micro-extrusion 3D-printing process, the ability to control heating with focused microwaves enables a capability that previous electronics manufacturing approaches cannot achieve: spatially programming functional properties continuously, even within a single printing process. By adjusting microwave parameters, for example, the researchers can precisely modulate the degree of heating to control the microstructure of the printed particles. This allows the creation of multifunctional circuitry with orders-of-magnitude differences in mechanical and electronic properties in a single printing process without the need for material switching.
The researchers also demonstrated that the approach extends to a broad range of functional materials from metals and ceramics to thermoset polymers, showing that near-field microwave printing can process and program diverse material classes in situ. Further, the selective nature of microwaves allows the energy to penetrate deeply to heat target materials even when fully encapsulated.
Together, these unique attributes allow multimaterial devices to be built seamlessly from a broad material palette in a continuous manufacturing process, all within a desktop-size platform — a stark contrast to conventional approaches that require complex equipment, labor-intensive processing and manual assembly.
Functional electronics can also be directly printed into temperature-sensitive biopolymers and biological constructs, something that was previously challenging to achieve. As proof of concept, the researchers printed wireless strain sensors onto ultrahigh-molecular-weight polyethylene, a biopolymer commonly used in joint replacements, creating electronics-enhanced implants that could potentially monitor stress or wear without altering their structure. They also printed wireless sensors directly onto a bovine femur bone and a living leaf, opening new possibilities for understanding and controlling biological processes.
Image – Photographs showing the printing of freestanding silver microarchitecture with a 30-μm trace diameter on (A) a leaf, demonstrating the ability to print on a temperature-sensitive substrate and (B) on silicone, demonstrating the ability to achieve high-resolution features.
For more information:
Rice University
https://www.rice.edu/
