Bioengineers at Tufts University in the US have ascertained how spiders and silkworms spin webs made of incredibly strong fibres. The answer lies in how they control the silk protein solubility and structural organisation in their glands.
‘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 roadmap for others to optimise artificial spinning of silks as well as in improved production of silks in genetically engineered host systems such as bacteria and transgenic animals,’ said Kaplan, also a professor of chemical and biological engineering.
He and former postdoctoral fellow Hyoung-Joon Jin have published their findings, ‘Mechanism of Processing of Silks in Insects and Spiders,’ in the August 28 issue of Nature.
Silk is the strongest natural fibre known, but its strength has yet to be replicated in a laboratory. One reason may be the previous lack of understanding how spiders and silkworm process the silk. The Tufts team has identified the way that spiders and silkworms control the solubility, concentration and structure of the proteins in their glands that spin the silk.
According to Kaplan, silk proteins are organised into pseudo-micelle or soap-like structures that form globular and gel states during processing in the glands. This semi-stable state, with sufficiently entrapped water and liquid crystalline structures, prevents the proteins from crystallising too early, until the spinning process.
The structures formed in the process can be easily converted artificially into fibres with physical shear (moving the silk gel between two plates of glass) or during fibre spinning in the native process. The control of water content and structure development are essential because premature crystallisation of the protein could cause a permanent blockage of the spinning system, leading to catastrophic consequences for the spider or silkworm.
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-organise and reach spinnable concentrations. Achieving sufficient concentration of protein is key to the proper spinning of fibres and to the spider’s and silkworm’s survival.
Kaplan said this new insight into silk processing could result in new high-strength and high-performance materials; new biomaterial applications for cell growth in tissue engineering; and environmentally sound processes to generate fibres and films from these types of polymers, since the entire process occurs in water.
‘Kaplan’s research is distinctive because it addresses a fundamental problem common to all prior research in this field,’ said Jamshed Bharucha, Tufts provost and senior vice president.