Synthetic hydrogel like cartilage, but with a simpler structure -Potential as artificial cartilage and anti-vibration materials-
Mingjie Liu, Yasuhiro Ishida, Yasuo Ebina, Takayoshi Sasaki, Takaaki Hikima, Masaki Takata, and Takuzo Aida
T. Aida the University of Tokyo, Y. Ishida at RIKEN, and T. Sasaki at National Institute for Materials Science et al. have developed a novel hydrogel with highly anisotropic mechanical properties, which contains negatively charged inorganic nanosheets that are oriented cofacially by magneto-induced ordering.
Electrostatic and magnetic repulsive forces are used in various places, such as maglev trains etc. However, design of polymer materials, such as rubbers and plastics, has focused overwhelmingly on attractive interactions for their reinforcement, while little attention has been given to the utility of internal repulsive forces. Nevertheless, in nature, articular cartilage in animal joints utilizes an electrostatically repulsive force for insulating interfacial mechanical friction even under high compression.
The researchers discovered that when nanosheets of unilamellar titanate, colloidally dispersed in an aqueous medium, are subjected to a strong magnetic field, they align cofacial to one another, where large and anisotropic electrostatic repulsion emerges between the nanosheets. This magneto-induced temporal structural ordering can be fixed by transforming the dispersion into a hydrogel. The anisotropic electrostatics thus embedded allows the hydrogel to show unprecedented mechanical properties, where the hydrogel easy deforms along a shear force applied parallel to the nanosheet plane but is highly resistive against a compressive force applied orthogonally.
The concept of embedding repulsive electrostatics in a composite material, inspired from articular cartilage, will open new possibilities for developing soft materials with unusual functions.
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