Nature has engineered its own actuators, as well as the efficient material composition, geometry and structure 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. In this paper, we unfold the process of exploring and comparing cell types that are proper for HCI use, the development of the composite biofilm, the development of the responsive structures, the control setup for actuating biofilms, and a simulation and fabrication platform. Finally, we provide a variety of application designs, with and without computer control to demonstrate the potential of our bio actuators. Through this paper, we intend to enable the use of natto cells and our platform technologies for HCI researchers, designers and bio-hackers. More generally, we try to encourage the research and use of biological responsive materials and interdisciplinary research in HCI.