LSU Engineering Professor Collaborates to Produce Smart, Healable Composites with Spider Silk-Inspired Polymer Threads

If you were asked to name the first thing that came to mind when you heard the word spider, you might conjure up images of Halloween, Charlotte’s Web or even Spiderman. If you asked LSU engineering researcher Guoqiang Li, his response would likely be “strong and self-healing.”

LSU Family WeekendNASA hopes Li and Meng’s research can be used to create techniques that quickly and effectively repair large-scale cracks on aircraft.

Jim Zietz/LSU University Relations

While it may seem hard to believe, Li, professor, LSU Department of Mechanical & Industrial Engineering, and Harper Meng, Southern University Department of Mechanical Engineering research associate, have discovered the healing power of spider-silk inspired polymer threads for macro cracks in moving structures in aerospace and transportation.

Li and Meng’s research is currently funded by NASA, in hopes of finding a way to quickly and effectively repair large-scale cracks on aircrafts. For example, an aircraft may be damaged by bird strike, causing a crack that needs repair.

Although researchers have already created composites that are able to heal microscopic cracks, the existing systems are not effective for repairing larger ones. When thinking of how to address this larger-scale problem, Li realized that healing large cracks in these materials should be similar to the healing of human injuries that required closure, or stitches, before the healing process could begin.

Meng connected Li with Jinlian Hu, a professor researching shape memory materials and textiles at the Hong Kong Polytechnic University, who provides the researchers with fibers. Using these fibers, Li is able to demonstrate the two-step healing process for macroscopic damages in conventional thermosetting polymer composite materials.

Mimicking spider dragline silk, the synthetic stimuli-responsive polymer thread features soft segments and hard segments at the molecular level. These hard and soft segments block the thread with both infrared light–responsive shape memory effect on demand and with remarkable toughness higher than Kevlar and steel. Cold drawing beyond yielding can further improve the mechanical strength of the stimuli-responsive thread. With the collaboration, the concept of healing macroscopic damages in regular structural materials has been tested and demonstrated.

Using their knowledge of the human body’s healing process, Li and Meng pre-embedded the spider-silk inspired stimuli-responsive thread as built-in sutures and dispersed thermoplastic particles as embedded new cells into conventional structural materials.

When a crack occurs in the structure, infrared light can be used to raise the temperature and trigger the shape memory effect of the spider silk-inspired synthetic thread. The shape recovery of the thread provides the mechanical power to pull the crack together as a stitch would do to a human wound.

In the second step, the embedded thermoplastic particles melt, and like blood, flow to the closed crack to promote healing. Not only are the threads “smart” in that they close cracks on demand by remembering their original shape, they also tremendously increase the toughness of the regular structure materials.

“We are currently working on a patent,” Li said. “We hope that this concept can be expanded to any engineering structure including cars, aircrafts, ships, pipes, buildings, bridges, etc.”

Li and Meng’s work is far from finished. The research pair plans to conduct more experimental testing and develop mathematical models providing guidance for further improvements.