Spiders' sturdy silk fibers can be replicated in the lab

The answer lies in how the insects control the water content of the silk protein.

"This finding could lead to the development of processing methods resulting in new high-strength and high-performance materials used for biomedical applications and protective apparel for military and police forces," said David Kaplan, professor and chair of biomedical engineering and director of Tufts' Bioengineering Center.

"We identified key aspects of the process that should provide a road map to optimize the artificial spinning of silks as well as improved production of silks in genetically engineered host systems such as bacteria and transgenic animals," Kaplan said.

Kaplan and former postdoctoral fellow Hyoung-Joon Jin, now a faculty member at the University of Bristol in England, published their findings in the August 28 issue of the international science journal Nature. The research was funded with $1 million from the National Institutes of Health and $200,000 from the U.S. Air Force Office of Scientific Research. Kaplan collaborated with Tufts colleagues in engineering, veterinary medicine and dental medicine.

Silk proteins are organized into pseudo-micelle or soap-like structures that form globular and gel states during processing in the insects' glands, Kaplan said. This semi-stable state prevents the proteins from crystallizing until the spinning process is under way.

The control of water content is essential because premature crystallization of the protein could cause a permanent block in the spinning mechanism, leading to the insects' death.

This process, when combined with the novel polymer design features in silk proteins, retains sufficient water to keep the protein soluble, while allowing the protein to self-organize and reach spinnable concentrations. Achieving a sufficient concentration of protein is key to the proper spinning of fibers and to spider and silkworm survival.

Other potential applications of laboratory-made silk, Kaplan said, include high-performance materials for sports equipment, hiking gear and protective clothing; cell growth in tissue engineering, tissue and organ repair and an environmentally sound method to make fibers and films because the entire process occurs in water.

Last year, Kaplan and a team of researchers from Tufts' schools of Engineering and Medicine developed a process to repair one of the world's most common knee injuries—ruptured anterior cruciate ligament (ACL)—by bioengineering an artificial ACL using silk scaffolding for cell growth.