Researchers from the University of Tokyo, the National Institute of Materials Science and the RIKEN Center for Emergent Matter Science and SPring-8 Center have come up with a new hydrogel featuring repulsive properties instead of the usual attractive interactions.

Published in the journal Nature, the study began through a secret discovery that titanate nanosheets suspended in aqueous colloidal dispersion will form an alignment, facing each other in a plane when a strong magnetic field is present. The magnetic field then maximizes electrostatic repulsion between the sheets, encouraging them to form a quasi-crystalline structure. In this form, the sheets are naturally oriented face to face, with electrostatic forces separating them.

To create a new material, Yasuhiro Ishida and colleagues used the method they discovered to arrange layers of nanosheets in a plane. Once the sheets were in place, they made the structure permanent by changing the dispersion into a hydrogel in a process known as light-triggered in-situ vinyl polymerization, a process that basically utilizes light pulses to congeal an aqueous solution and turn it into a hydrogel. Once in hydrogel form, the sheets will no longer be able to move, fixing in place the unique structural order they have.

Man-made materials have not been able to take advantage of the phenomenon until now but nature already has, such as cartilage moving without friction within joints even when high compression is present. Vehicles using non-contact bearings follow the same principle but differ in that attractive interactions, instead of repulsive ones, are utilized.

Thanks to light-triggered in-situ vinyl polymerization, a new material is produced, a hydrogel with interesting properties and the first example of a charged inorganic structure aligned face to face while influenced by a magnetic field. Should force be applied in a parallel manner, however, the nanosheets will easily be deformed. Apply force at right angles, though, and the sheets will stay in alignment, strongly resisting the external pressure.

Researchers are anticipating that the idea of embedding anisotropic repulsive electrostatics inside a composite material (taking inspiration from cartilage) will open up new possibilities in terms of developing soft materials imbued with unusual characteristics.

Yasuhiro added that the newly discovered material can be used for various applications, from machine engineering to regenerative medicine, as they can withstand vibrations, resist deformation and produce parts artificially.

Aside from Yasuhiro, other authors for the study include Takuzo Aida, Masaki Takata, Takaaki Hikima, Takayoshi Sasaki, Yasuo Ebina, Yasuhiro Ishida and Mingjie Liu.

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