The natural abilities of cuttlefish tissues and the ingenuity of chemists combine to take hydrogel research in new directions.
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 that contain large amounts of water, and are being explored for many uses, including medical prostheses, soft robotic components, and novel sensor systems.
The Hokkaido team reported in the journal their contribution to this fast-moving field of research NPG Asia Materials.
Normal biological tissues exhibit unique properties essential to their function, which researchers seek to replicate in hydrogels. Muscles, for example, in addition to strength and elasticity, 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 asymmetry.
In contrast to 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 squid-derived tissues with synthetic polymers, we demonstrated a hybrid strategy that serves as a general method for preparing hydrogels with beneficial hierarchical contrast as well as durability,” says polymer scientist Tasuku Nakajima of the Hokkaido University team.
The manufacturing process begins with a commercially available frozen squid shell – the main outer part of the squid. In living squid, the mantle expands to take water into the body, then contracts vigorously to shoot the water out in a jet. This ability depends on the anisotropic muscles within the squid connective tissue. The researchers took advantage of the molecular arrangements within this natural system to build a biomimetic gel.
Chemical and thermal treatment of thin slices of thawed squid tissue mixed with polyacrylamide polymer particles to form a cross-linked hybrid hydrogel was initiated. It has what is known as a double network structure, with a synthetic polymer network embedded and linked to a more natural muscle fiber network derived from the cuttlefish mantle.
“The DN gel we made is much stronger and more flexible than the mantle of natural cuttlefish,” explains Professor Jianping Gong, who led the team. “The unique composite structure makes the material impressively fracture-resistant, four times stronger than the original material.”
The current proof-of-concept work should be just the beginning of exploration of many other hybrid hydrogels that can exploit the unique properties of other natural systems. Jellyfish have already been used as a source material for the simplest single-lattice hydrogels, so they are the next obvious choice for exploring hybrid double-lattice options.
“Possible applications include weight-bearing artificial fibrous tissues, such as artificial ligaments and tendons, for medical use,” says Gong. Additional work by the team will explore the biocompatibility of the gels and investigate options for making a range of gels suitable for different uses.