Stimuli-responsive materials definition

Piezoelectric polymers have been known for more than 40 years, but in recent years they have gained repute as a valuable class of smart materials. There is no standard definition for smart materials, and terms such as intelligent materials, smart materials, adaptive materials, active devices, and smart systems are often used interchangeably. The term smart material generally designates a material that changes one or more of its properties in response to an external stimulus. 

By definition, ERMs are very well suited to bridge the gap between manmade materials and biological processes (see Table 6.1) (Ulijn, 2006 Zelzer et al., 2013). Responsiveness to enzymes provides not only a means of communication between the material and its biological environment, it also presents the possibility of designing materials that display reversible and dynamic responses to a stimulus. While reversibility is not an uncommon feature for smart polymers, a dynamic interaction wherein response of a material only persists in the presence of the stimulus or a cofactor is rare. Several reversible enzyme-responsive polymer systems have been prepared so far (Ku et al, 2011), but truly dynamic or fuelled polymer-based systems have yet to be developed. 

The notion of property deserves elaboration. While in service use, all materials are exposed to external stimuli that evoke some type of response. For example, a specimen subjected to forces experiences deformation, or a polished metal surface reflects light. A property is a material trait in terms of the kind and magnitude of response to a specific imposed stimulus. Generally, definitions of properties are made independent of material shape and size. 

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