News from Nanotechjapan


Stimuli-responsive hydroxyapatite liquid crystal with macroscopically controllable ordering and magneto-optical functions

 The University of Tokyo announced on 9th February, 2018, that the research group led by Takashi Kato (Professor at the Department of Chemistry and Biotechnology, School of Engineering) successfully induced liquid-crystal properties into aqueous dispersions of rod-shaped hydroxyapatite (HAp) nanocrystallites. The results were published in Nature Communications*.

 HAp is a major component of human bones and teeth, and their properties such as morphology, crystallinity and orientation are biologically well controlled under mild condition in the human body by self-assembly mechanism. If the self-asssemble of HAp could be artificially reproduced, HAp will be more utilized as functional and bio-friendly materials. To provide the liquid crystal properties is thought to be a way to control the self-assembly of HAp.

 The research group used a bio-inspired self-organization approach to prepare HAp colloidal liquid crystals. In the biomineralization process, acidic proteins play an important role in the formation of self-organized structures to stabilize the biomineral amorphous precursors. In this research, acidic macromolecules (polyacrylicacid ; PAA) were used instead of the acidic protein and mesogenic HAp nanorods were synthesized which can form colloidal liquid crystals.

 By mixing aqueous solutions of CaCl2 and K3PO4 in the presence of PAA, nanorod-shaped HAp crystals were formed and a colloidal dispersion of HAp was obtained. The nanorods had polycrystalline structures comprising rod-shaped nanocrystallites. The average length and width of the nanorods were about 100nm and 21nm, respectively. The alignment of the nanorods can be controlled using external magnetic fields and mechanical forces to functionalize the HAp liquid crystals. These effects were demonstrated by magnet-optical responses.

 It is expected that the method developed by the study will expand the range of compounds available as liquid crystal.

*Masanari Nakayama, Satoshi Kajiyama, Akihito Kumamoto, Tatsuya Nishimura, Yuichi Ikuhara, Masafumi Yamato, and Takashi Kato, "Stimuli-responsive hydroxyapatite liquid crystal with macroscopically controllable ordering and magneto-optical functions", Nature Communications, Vol. 9, Article number: 568 (2018), doi: 10.1038/s41467-018-02932-7; Published online: 08 February 2018