The conversion of external stimuli into mechanical motion capable of performing work is at the foundation of fields centered around the fabrication of microrobotics, artificial muscles, and advanced smart actuator systems for diverse applications. Stimuli-responsive materials, such as shape memory alloys, dielectric polymers, electro-active polymers, and polymer hydrogels are examples of material frameworks that appeal to these emerging applications. Our group is working on developing materials, structures and devices that can reversibly change their shape, color, and functionalities on command by applying external stimuli.  The applied stimulus could include light, temperature or pH change. As an example, we have shown that by properly patterning and engineering hydrogels on plastic substrates, self-folding cubes and “flowers” can be made that reversibly respond to a small change of temperature (Nano Letters,11, 3239-3244, 2011). 

 
   More recently, we have demonstrated motors that can self-propel toward or away from incident light, and we have developed smart curtains that can spontaneously close or open upon light exposure (submitted, 2013).  Moving forward, we envision developing new types of electronic systems, where not only stimuli can be detected but the system can also respond by changing its shape and/or physical properties. This presents a new class of user-interactive substrates.