© 2017 HCII Institute, Carnegie Mellon University

Living Cell Nanoactuators

2015

Nature has engineered its own actuators, as well as the efficient material composition, geometry and structure needed to utilize its actuators and achieve functional transformation. Based on the natural phenomenon of cells’ hygromorphic transformation, we introduce the living Bacillus Subtilis natto cell as a humidity-sensitive nanoactuator.

  • Lining Yao, Wen Wang, Guanyun Wang, Helene Steiner, Chin-Yi Cheng, Jifei Ou, Oksana Anilionyte, Hiroshi Ishii

  • Tangible Media Group, MIT Media Lab

  • Paper - CHI 2015, ACM
     Interface - Second Skin
    Interface - Breathing Shade
    Interface - Living Being
    Interface - Living Tea

We introduce Bacillus subtilis natto cells as nanoactuators for designing transformable thin sheet materials, which respond to humidity change. The hygromorphic phenomenon of cells has been well studied, especially with regard to some plants, such as pine cones and wheat awns. We observed similar hygromorphic behavior in the B. Subtilis natto cell. By varying the relative humidity around the cells, the size of the cells can reversibly change.

In order to quantify the transformation, we equipped an atomic force microscope (AFM) with a customized humidifier. An air stream with controllable relative humidity addressed the cells to be measured directly. We observed a volume change of up to 40 % when we ad- justed the relative humidity from 15 % to 95 %.

Beyond natto cells, we also tested a variety of other cells, e.g., Escherichia coli and yeasts. Natto cells were eventually chosen based on a few criteria: biosafety level, expertise level to handle, syn- thesis complexity and actuator performance. For example, E. coli has a higher requirement on its biosafety level; moreover, while yeast is safe to use, the actuating performance is inadequate compared to the natto cell.

Our hypothesis regarding the natto cells’ working principle at the molecular level is as follows: cell expansion behavior is due to water absorption by intracellular components, including nucleic acids, proteins and polysaccharides. We further strengthened our hypothesis by testing whether pure proteins, cellulose and DNA also display hygromorphic behaviors.

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In order to translate the expansion and contraction of cells at a micron-scale into visible transfor- mation at the macroscale, we developed a biohybrid composite film. The composite film contains two layers: the cell layer and the substrate layer. The film can vary the bending curvature trig- gered by the relative humidity changes.

With biofilm providing the basic building blocks, we designed responsive structures and transformations, which can be referenced when we try to achieve a certain shape change in the design of final applications.

Structural primitives with latex-cell hybrid films are further implemented.

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