Researchers Turn to Multi-Material 3D Printing to Develop Responsive, Versatile Smart Composites

3D printing technology has been used multiple times to help create drug delivery and release systems, from programmable release capsules and cancer drug-emitting implants to micro-rockets that deliver drugs inside the body and even a biomaterial sleeve that can reduce the risk of infection after a body piercing. Some researchers are working to develop 3D printed pills and vaccines that will combine multiple medications into one, and an Israeli drug delivery company will soon seek FDA approval for its 3D printed medical marijuana inhaler, which can control the doses a person inhales. But I would bet you $20 that none of these innovative systems and products have their roots in cephalopods…except for the sequential cell-opening mechanism with drug delivery applications that researchers at the University of New Hampshire (UNH) are currently developing.

Actually, the UNH research team was inspired by the color-changing mechanism in marine animals like squid, octopus, and cuttlefish; an organ called a chromatophore. Their design concept also has applications, not surprisingly, in color-altering camouflage materials. The work – using design and 3D printing to explore the mechanics of auxetic chiral metamaterials – is supported by a National Science Foundation (NSF) Career award that assistant professor of mechanical engineering Yaning Li received in 2016.

Last year, Li told UNH Today, “3D printing has given me the opportunity to do this research, so I’m really in the right place at the right time.”

Auxetics are materials that become perpendicular to the applied force when they’re stretched; they promote growth and flexibility, and the unique phenomena has been used before to make 3D printed clothes. Chiral is an odd form of asymmetry, where the structure and its mirror image are not superimposable.

To develop the concept, the researchers modified the chiral geometry of a large cell and a small one that were designed to mimic the chromatophores. The cells, which possess different attributes, opened sequentially – one after the other – when they were loaded in only one direction.

Yaning Li

“We used two different types of cells, one would open right away and the other would rotate first before opening in the sequence. What makes this unique is that if each cell is assigned a different color, you could alter the sequential opening mechanism to create a material that might be dark green when the first cell opened and then change to bright yellow when the second one opened after it,” explained Li. “This concept could also be used for particle release, such as two different medicines being released sequentially through a bandage to help address medical issues like wound swelling.”

The team recently published the study as a cover story, titled “Novel 3D-Printed Hybrid Auxetic Mechanical Metamaterial with Chirality-Induced Sequential Cell Opening Mechanisms,” in Advanced Engineering Materials; co-authors include UNH mechanical engineering doctoral candidate Yunyao Jiang and Li.

The abstract explains, “New hybrid auxetic chiral mechanical metamaterial are designed and fabricated via multi-material 3D printing. Due to the chirality-induced rotation, the material have unique sequential cell-opening mechanisms. Mechanical experiments on the 3D printed prototypes and systematic FE simulations show that the effective stiffness, the Poisson’s ratio and the cell-opening mechanisms of the new design can be tuned in a very wide range by tailoring two non-dimensional parameters: the cell size ratio and stiffness ratio of component materials. As example applications, sequential particle release mechanisms and color changing mechanisms of the new designs are also systematically explored. The present new design concepts can be used to develop new multi-functional smart composites, sensors and/or actuators which are responsive to external load and/or environmental conditions for applications in drug delivery and color changing for camouflage.”

The researchers used a multi-material 3D printer to quickly fabricate a design prototype, so they could use it to prove their concept. This was easier said than done, as the concept relied on complicated geometry and materials, so Li and Jiang turned to a previous study they had completed on auxetic chiral metamaterials to create a soft meta-material.

They customized the chiral geometry of the large and small cells at two different levels, which enabled the cells to open sequentially when they were loaded in just one direction.

Jiang, who was the lead author of this study, said, “The order of the cell opening can also be altered via geometry and material combination to alter the behavior of the cells and increase the number of potential applications.”

The team’s concept of a sequential cell-opening mechanism could potentially be used to design smart materials that are responsive to different types of external stimuli, such as humidity, light, and temperature; they could even be developed into sensors and materials for drug delivery, camouflage that changes color, and particle release. Applications include foldable device, biomedical scaffolds, stretchable soft electronic materials, drug-release bandages, and smart responsive composites; UNHInnovation, which manages, and promotes the university’s intellectual property, filed a patent for the concept, which is currently pending.

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[Source/Images: UNH]