Squid Beak Hardness Guided By Gradients

How squid control the hardness of their beaks be used to guide the development of greener biomimetic materials.

AsianScientist (Jun. 11, 2015) – Squid have found a unique way to tackle the problem of mismatch between their extremely hard beaks and surrounding soft tissue—biomechanical gradients. In a paper published in Nature Chemical Biology, researchers describe the processes squid use to create these gradients, a finding which could inform the design of biomimetic materials.

In previous research, Professor Ali Miserez and colleagues from the Nanyang Technological University investigated squid suckerin proteins, extraordinarily strong structures made entirely out of proteins. In the present study, they turned their attention to another non-mineralized structure that is similarly strong: squid beaks.

“Furthermore, the beak exhibits a mechanical gradient from a soft, gel-like base to the very hard tip (rostrum). Thus it serves as a great model system for artificial joint implants, because making implant with mechanical gradients remains a major challenge,” Miserez told Asian Scientist Magazine.

Taking an interdisciplinary approach, the research team used sequencing, proteomics, biotechnology and biophysical characterization to probe the chemical mechanisms behind beak formation. They found that the beak was made of two major families of beak proteins: chitin-binding proteins and histidine-rich beak proteins (DgHBPs).

Under beak micro-environmental conditions, the DgHBPs formed structures known as protein coacervates which were key to the formation of hard beak structures.

“Coacervates are an intriguing state of matter, which are formed by phase separation from an initial protein solution. Upon coacervation, the proteins phase-separate into a very concentrated protein droplets and into a much more dilute phase,” Miserez explained.

“These coacervates have three physico-chemical properties that make them ideal for the processing of a hard composite structure: firstly, although they are very concentrated, they are still liquid, thus they can still flow. Secondly, they have a very low surface tension, which is key in order to spread and ‘infiltrate’ the chitin-fiber network. Lastly, they also exhibit the so-called ‘shear-tinning’ behavior: when they are sheared under confinement, they viscosity decreases if the shear rate increases.”

The research team was also able to identify the peptide domains of DgHBPs where covalent cross-linking occurs. They showed that histidine is often flanked by glycine, providing the right environment for covalent cross-linking.

These results could be used to develop biomimetic materials such as tough hydrogels or new types of self-assembled proteins.

“What we find particularly exciting, now that we understand how natural chitin/protein composites are processed, is that we could use the beak protein coacervates as a new polymer matrix in green composite processing,” Miserez said.

“High-performance composite materials are used in many applications and the binder used to link carbon fibers are petro-chemical derived. Now, we can envision producing high-performance composites from aqueous solutions and at ambient temperature and pressures. That’s very exciting from a sustainability perspective.”

The article can be found at: Tan et al. (2015) Infiltration of Chitin by Protein Coacervates Defines the Squid Beak Mechanical Gradient.

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Copyright: Asian Scientist Magazine; Photo: Ali Miserez/NTU.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

Rebecca did her PhD at the National University of Singapore where she studied how macrophages integrate multiple signals from the toll-like receptor system. She was formerly the editor-in-chief of Asian Scientist Magazine.

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