Liquid-crystal & Bacterial Living Materials Self-organize & Move Together

Liquid crystals, when combined with bacteria, can create living materials and move together. There are materials that live, and they might be self-healing as well as shape-changing. They can transform energy into mechanical motion.

Igor S. Aronson, holder of the Huck Chair and Professor of Biomedical Engineering, Chemistry and Mathematics, is exploring living materials, with predictive computational models and experiments. The living materials he is examining is composed of a bacterium called Bacillus subtilis, which can move quickly with its long flagella and nematic liquid crystals called disodium cromoglycate.

These liquid crystals are in a state between a liquid and a solid. In disodium cromoglycate, the liquid crystals are lined up in long, parallel rows. But they are not fixed. They move in a single direction unless they are disrupted, according to Science Daily.

Aronson said that these liquid crystals are like a straight-ploughed field with the ridges. The molecules and the furrows are the areas in between. "An emergent property of the combination of a liquid crystal and bacteria is that at about a 0.1 percent-by-volume bacterial concentration we start to see a collective response from the bacteria," he explained.

The living material isn't only a combination of two components, but two parts making something that has extraordinary, optical, physical or electrical properties. Still, the bacteria and the liquid do not have any direct links. The experts' computer models displayed collective behavior like that observed in liquid crystal and bacteria combinations, according to Physical Review.

Scientists' predictive computational models for the liquid crystals and bacteria systems show a change from straight parallel channels when only a small bacteria population exists, to a more complex, and organized configuration with higher populations. Even if the patterns are changing, they form pointer defects or arrow shapes serving as traps, concentrating the bacteria in areas. The triangle defects deflect the bacteria away from the area.

When there is dense bacterial concentration in some areas, there is greater bacterial velocity. Configurations in those areas that have more bacterial population tend to change faster than other areas with less bacteria. Aronson and his team tried to make the liquid crystals thin film independent, without touching surfaces. Hence, they used a device to create the film and suspended it so that it was away from surface contact. Their approach showed defect patterns in the structure of the material. The researchers said that experimenting with thin films of liquid crystals and bacteria brought them results just as in computational models.