New discovery: Spider silk reinforcement related to protein arrangement

A recent study has found that the motion of spider silk spinning plays a crucial role in the toughness and strength of the thread. During the stretching process, the alignment of protein chains inside the thread increases stability, thereby strengthening its resilience and strength. Scientists suggest that this discovery opens up possibilities for developing stronger special fibers in the future.

For a long time, scientists have been interested in spider silk because it is stronger than steel, comparable in toughness to nylon and Kevlar fibers (commonly used in bulletproof vests), and possesses a rubber-like elasticity. However, obtaining natural silk by farming spiders is costly, energy-intensive, and challenging. As a result, scientists aim to develop materials similar to spider silk in the laboratory to create high-functioning biomimetic materials.

The research revealed that during the stretching of spider silk, the protein chains within the fibers exhibit an “alignment” phenomenon, resulting in the rearrangement of the entire protein chain, thereby increasing the number of hydrogen bonds inside the protein. These hydrogen bonds act as bridges between protein chains, forming fibers and simultaneously enhancing the overall strength, toughness, and elasticity of the fibers.

Northwestern University (NU) and Washington University in St. Louis (WashU) collaborated to simulate the molecular motion inside artificial spider silk using computational models to observe how the stretching action impacts the strength of the silk and the arrangement of proteins within the fiber. Subsequently, they validated this simulation through experimentation. The results showed that the simulation findings were reliable. The research findings were published in the journal “Science” on March 7.

To validate their simulation results, the research team used Raman spectroscopy to examine how protein chains in artificial fibers, developed by the Washington University team, reassembled after being stretched. The results indicated that the experimental and simulated tests yielded consistent outcomes.

Furthermore, they conducted stretching tests on artificial spider silk measuring five centimeters in length to examine how much tension and deformation the fiber could withstand before breaking, and to determine how much toughness the artificial silk could add. The results showed that the artificial silk could be stretched up to six times its original length, with its elasticity coefficient continuously increasing during stretching. However, a significant increase in overall toughness occurred only when stretched beyond three times its original length.

The senior author of the study, Sinan Keten, from Northwestern University, commented to the university newsroom, saying, “Until we conducted the computational simulations, researchers could not understand the internal changes that occur in fibers after stretching. This new discovery will help us grasp the mechanical performance relationship between stretching and fibers.”

The first author of the study, Jacob Graham from Northwestern University, explained, “When spiders spin silk, they use their hind legs to grasp and pull the fibers, leading to the fibers being stretched as they form, making them very strong and elastic. We found that by simply changing the amount of stretching, the mechanical properties of the fibers could be altered.”

He further elaborated, “These silk protein fibers are initially weak when extruded, but if stretched to six times their original length, they become very strong. This material, in its unstretched state, is a spherical cluster of protein, and only through stretching does the cluster transform into a thread, enabling effective stacking of protein chains inside.”

He also stated, “Spider silk can be considered the strongest organic fiber currently, with the advantage of being biodegradable, suitable for use as surgical sutures and wound closure adhesives as it can naturally and harmlessly degrade within the human body.”

Compared to other synthetic materials, mainly petroleum-derived plastics, engineering spider silk offers a stronger, biodegradable alternative. This understanding can assist researchers in designing improved engineering proteins to enhance the performance of this special fiber for use in other spun items (such as bulletproof vests).

This research was supported by the National Science Foundation (NSF) with funding reference numbers OIA-2219142 and DMR-2207879.