Artificial Muscles and Tactile Sensor Array Made of Plant Epidermal Cells

In this dissertation, an onion actuator and tactile sensor was proposed. Actuators functionalize dynamics of mechanisms or systems via an energy conversion, such as the transformation of electricity into mechanical deformation. Most motor-driven actuators and engineered artificial muscles are very capable at either bending or contraction/elongation. However, there are currently no actuators that can accomplish these actions simultaneously. Here we show the successful development of such a device. We found that the simple latticed microstructure of onion epidermal cells allowed itself to simultaneously stretch and bend. By modulating the magnitude of the voltage, the actuator made of onion epidermal cells would deflect in opposing directions while either contracting or elongating. At voltages of 0 - 50 V, the actuator elongated and had a maximum deflection of -30 μm at voltages of 50 - 1000 V, the actuator contracted and deflected 1.0 mm. The strain rate ranges from 10-5 s-1 to 10-3 s-1 and underwent up to 200 actuation cycles at 50 V/s without any strain degradation. The strain changes were observed in our onion artificial muscle after acid pretreatment at different sweep rates, even much greater than 1 V/s. The artificial muscle has also been statically driven at 1000 V for continuous 6 hours, and the displacement shift was negligible. The maximum force response is 20 μN at 1000 V. We demonstrated the combination of two onion cell actuators to act as tweezers and gripping a small cotton ball of around 0.1 mg in weight. The results show how an artificial muscle can be produced from never used materials. And in this dissertation we also presents and demonstrates the development of flexible tactile sensor utilizing the microstructures of onion epidermal cells, which replace the intermediate dielectric layer in a typical parallel-plate capacitive sensor. The onion epidermal cells can effectively reduce the complexity of the sensor structure and thus simplifies the device fabrication process. The single layer of the onion epidermal cells is robust for high tactile sensitivity, mechanical flexibility and optical transmittance with potentially low-cost sensor manufacturing in a large area. The 5 × 5 tactile sensor array with the total area of 22 × 22 mm2 is demonstrated. A single tactile sensor has the initial capacitance of 3 pF without applying external pressure. The force ranging from 0 N-1.8 N (200 kPa) is applied for sensor characterization. The sensitivity of the sensor is 0.02 kPa-1. The fabricated sensor shows high sensitivity and linearity. We show how a new type of actuator and tactile sensor can be produced from a never used material―onion epidermal cell, in the hope of initiating a new field of fusing plant and mechatronics for the benefits of inducing large deflection measurements in both transverse and longitudinal directions in a ubiquitous and low-cost manner. And the proposed sensor array will be applied in robotic electronic skin and biomedical devices in the future.