Squid tissues and chemistry combine for versatile hydrogels

Research Press Release | January 20, 2023

The natural abilities of squid tissues and the creativity of chemists combine to take hydrogel research in new directions.

a neon flying squid. Photo by Gerald Robert Fischer under licence from shutterstock

The squid mantles used in this study were obtained from the neon flying squid (Gerald Robert Fischer/Shutterstock).

Researchers at Hokkaido University in Japan have combined natural squid tissues with synthetic polymers to develop a strong and versatile hydrogel that mimics many of the unique properties of biological tissues. Hydrogels are polymer networks containing large quantities of water, and are being explored for many uses, including medical prosthetics, soft robotic components and novel sensor systems.

The Hokkaido team report their contribution to this fast-moving research area in the journal NPG Asia Materials.

A photo of a purple-glved hand holding up a rectangular sample of the new squid/synthetic polymer DN gel. Photo by Tasuku Nakajima.

The new squid/synthetic polymer double-network gel developed in this study (Photo: Tasuku Nakajima).

Natural biological tissues exhibit unique properties essential for their functions, which researchers are seeking to replicate in hydrogels. Muscles, for example, in addition to strength and flexibility, have physical properties that vary in different directions and are built from a hierarchy of structures working together. Bones and blood vessels also display these features, known as hierarchical anisotropy.

Unlike the natural tissues that researchers wish to mimic, most synthetic hydrogels have uniform properties in all directions and are structurally weak.

“By combining the properties of tissues derived from squid with synthetic polymers, we have demonstrated a hybrid strategy that serves as a general method for preparing hydrogels with useful hierarchical anisotropy and also toughness,” says polymer scientist Tasuku Nakajima of the Hokkaido University team.

A schematic representation of the steps required for the preparation of the new composite material.

The squid mantle is cut into thin rectangles (left) and soaked in a polyacryamide (AAm) solution, which enters the mantle (center). Heating at 56°C for 12 hours resulted in the squid-synthetic DN gel (right). (Shou Ohmura, et al. NPG Asia Materials. January 20, 2023) .

The manufacturing process begins with commercially available frozen squid mantle – the main outer part of a squid. In live squid, the mantle expands to take water into the body, and then strongly contracts to shoot water outwards as a jet. This ability depends on the anisotropic muscles within squid connective tissue. The researchers took advantage of the molecular arrangements within this natural system to build their bio-mimicking gel.

Chemical and heat treatment of thin slices of the defrosted squid tissue mixed with polyacrylamide polymer molecules initiated formation of the cross-linked hybrid hydrogel. It has what is known as a double-network structure, with the synthetic polymer network embedded and linked within the more natural muscle fiber network derived from squid mantle.

“The DN gel we synthesized is much stronger and more elastic than the natural squid mantle,” explains Professor Jian Ping Gong, who led the team. “The unique composite structure also makes the material impressively resistant to fracture, four times tougher than the original material.”

When a notch is cut into the squid-synthetic double-network gel and it is gradually stretched, the break does not cut straight across the composite because the muscle fibers suppress the crack spread (Shou Ohmura, et al. NPG Asia Materials. January 20, 2023).

When a notch is cut into the squid-synthetic double-network gel and it is stretched with a weight of 500 grams, it does not fracture (Shou Ohmura, et al. NPG Asia Materials. January 20, 2023).

The current proof-of-concept work should be just the start for exploring many other hybrid hydrogels that could exploit the unique properties of other natural systems. Jellyfish have already been used as a source of material for simpler single-network hydrogels, so are an obvious next choice for exploring hybrid double-network options.

“Possible applications include load-bearing artificial fibrous tissues, such as artificial ligaments and tendons, for medical use,” says Gong. Further work by the team will explore the biocompatibility of the gels and investigate options for making a range of gels suitable for different uses.

Original Article:

Shou Ohmura, et al. Squid/Synthetic Polymer Double-Network Gel: Elaborated Anisotropy and Outstanding Fracture Toughness. NPG Asia Materials. January 20, 2023.

DOI: 10.1038/s41427-022-00454-9


This research was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI (17H06144, 22H04968).


Associate Professor Tasuku Nakajima

Faculty of Advanced Life Science; Institute for Chemical Reaction Design and Discovery (WPI-ICReDD)

Hokkaido University

Tel: +81-11-706-9016

Email: tasuku[at]sci.hokudai.ac.jp

Distinguished Professor Jian Ping Gong

Faculty of Advanced Life Science; Institute for Chemical Reaction Design and Discovery (WPI-ICReDD)

Hokkaido University

Tel: +81-11-706-9011

Email: gong[at]sci.hokudai.ac.jp

Sohail Keegan Pinto (International Public Relations Specialist)

Public Relations Division

Hokkaido University

Tel: +81-11-706-2186

Email: en-press[at]general.hokudai.ac.jp

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