A research team at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) has developed a transformative workflow for 3D printing Liquid Crystal Elastomers (LCEs) with predictable and controllable properties. This breakthrough research, conducted in collaboration with Princeton University, Lawrence Livermore National Laboratory, and Brookhaven National Laboratory, establishes a fundamental framework for designing and fabricating these advanced materials across multiple scales.
The development marks a significant advancement in the field of synthetic soft materials, offering new possibilities for applications ranging from soft robotics and prosthetics to compression textiles. The research findings have been published in the Proceedings of the National Academy of Sciences.
Scientific Innovation in Material Design
The research team, under the leadership of Jennifer Lewis, the Hansjörg Wyss Professor of Biologically Inspired Engineering at Harvard SEAS, has successfully addressed the longstanding challenge of controlling molecular alignment during the 3D printing process of liquid crystal elastomers.
Through extensive research and experimentation, the team discovered that nozzle geometry plays a crucial role in molecular alignment. Their findings demonstrate that hyperbolic nozzles achieve superior and more uniform alignment compared to conventional tapered designs, marking a significant advancement in printing technology.
The researchers employed sophisticated X-ray characterisation techniques during the printing process, enabling real-time measurement of molecular alignment within the printer nozzles. This breakthrough allows for unprecedented control over the material's shape-morphing capabilities and mechanical properties.
Technical Advancement and Practical Applications
The research team developed a comprehensive understanding of how various printing parameters influence molecular alignment. By consolidating multiple factors into a single parameter called the Weissenberg number, they created a predictable method for controlling molecular organisation during the printing process.
"When this project began, we simply did not have a good understanding of how to precisely control liquid crystal alignment during extrusion-based 3D printing. Yet it is their degree of alignment that gives rise to varying amounts of actuation and contraction when heated."
- Rodrigo Telles, SEAS graduate student and first author of the study
Former Harvard postdoctoral researcher Emily Davidson, now at Princeton University, emphasises the significance of nozzle design: "In the 3D printing community, most of us use a relatively small number of commercially available printheads. This study showed us that it is important to pay attention to the details of both nozzle geometry and flow – and that we can exploit them to control material properties."
The research received substantial support from the National Science Foundation through the Harvard Materials Research Science and Engineering Center and the U.S. Army Research Office Multidisciplinary University Research Initiatives Program.
Understanding Liquid Crystal Elastomers
Liquid crystal elastomers represent an advanced class of synthetic materials that exhibit unique shape-changing properties in response to heat, similar to muscle contractions. These materials contain mesogens, which are rigid molecular building blocks that must be precisely aligned during the printing process to achieve optimal performance. When properly configured, LCEs can function as artificial muscles or adaptive structures, responding to environmental stimuli with controlled shape changes. This characteristic makes them particularly valuable for applications in soft robotics, medical devices, and advanced manufacturing processes.
