24 September 2014

Hagfish slime

First, this incredible information about the technology of the threads of slime:
In self-defense the hagfish produces from its glands a slime that is composed of nanometer width threads and what is likely sugar or glyco-modifications.  The slime is thought to impede capture by making the hagfish slippery, and possibly by clogging the gills of a predator.  The nanothreads are remarkable: comparable to spider silk in tensile strength (800 megapascals or near 1 gigapascal) and lightness, and 5 times stronger than steel on a weight basis. Moreover, each thread is only 12 nanometers wide but 15 centimeters long.  Amazingly, a full thread is wrapped up in so that it fits within a single cell, highly specialized and called a gland thread cell (GTC).

Scientists have uncovered, using electron microscopy, the organization of a single hagfish nano-sized thread, helping resolve the mystery of why extrusion of such a long (compared to its width) thread from the cell does not cause tangling.  The thread is coiled up in a conical “skein” in 15-20 layers.  As a GTC matures, its nucleus migrates to an extreme pole, leaving most of the cell volume packed with a single coil of thread.

For a quantitative comparison, spider drag line silk has a tensile strength of up to 1100 megapascals, whereas hagfish thread goes up to 800 megapascals.  Steel has higher tensile strength up to 5000 megapascals but it is also much denser.  Two rather unusual materials more recently discovered, graphene and carbon nanotubes, have stratospheric tensile strengths of 63 and 130 gigapascals.

The research was carried out by PhD student Timothy Winegard, a team of scientists, and led by senior author Professor Douglas Fudge at the University of Guelph.
Here's a scanning EM of a disrupted thread cell (from the Journal of Cellular Biology):

And finally a video of a hagfish defending itself with slime:

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