Engineered multifunctionality and environmental sustainability

Continual transformation is a characteristic of the biological world. Most random mutations in sexual reproduction are either infertile or fail to reproduce beyond a few generations, but some are better suited to altering circumstances and therefore thrive. A progression of successful mutations may eventually lead to a new species, and then possibly to a new genus, a new family, and so on. Conversely, when circumstances become unfavorable, a species can go extinct (Coyne 2009). Whether speciation occurs slowly or quickly and whether extinctions are gradual or cataclysmic, biological organs are remarkably versatile. Large swaths of the biological world are assemblages of the same organs, not of many different types but each type displaying a diversity of shape and size. Some organs have even emerged independently in species whose common ancestor lacked those organs, a splendid example being the appearance of wings in bats and birds that evolved over eons from flightless dinosaurs (McGhee 2013). One factor responsible for the persistence of a biological organ is its multifunctionality (Lakhtakia 2015). Limbs are used for moving, signaling, gathering and preparing food, wielding weapons, and initiating as well as warding off physical assaults, among other things. Similarly, teeth are used to bite, cut, and chew food as well as a tool to prise, incise, tear, or stab materials or beings. While adaptation to altered circumstances does bring about minor changes, biological organs are unlikely to undergo a complete overhaul except over very long periods of time. It is this multi-functionality that is central to the emergence of engineered biomimicry as a technological paradigm (McDowell et al. 2010; Lakhtakia 2015). The economy of multifunctionality is obviously attractive because structures that can perform several distinct functions can be incorporated in a variety of mechanisms and products. Inventory costs are reduced because fewer types of structures need to be manufactured, stored, transported, tracked, and eventually disposed off in landfills. Furthermore, the standardization of such structures promotes reusability in a wide range of mechanisms and products, not unlike intra-species or inter-species transplants of biological organs. Standardization also promotes easy repairability. The resultant extension of the lifetime of a product or mechanism slows down the depletion of raw materials, restricts manufacturing energy consumption, and reduces waste disposal. One way to engineer a multifunctional structure is to use multifunctional materials with numerous attributes. An example is that of lithium niobate, a perovskite material (bearing characteristics of a calcium titanium oxide mineral) which is piezoelectric (generating electricity from pressure), pyroelectric (creating voltage when heated or cooled), ferroelectric (reversing electric polarization), and displays electrically controllable optical properties. Many other perovskites display similar features (Bhalla et al. 2000), and organic perovskites are being extensively researched for harvesting solar energy (Chilvery et al. 2015). However, multifunctional materials are rare in nature. Another way to create a multifunctional structure is to exploit the commonalities in diverse products by housing them in a single unit with shared modules. A very common contemporary example of such a structure is a smartphone whose functionalities will continue to be revised and extended for several years to come. This second approach to multifunctionality is easier to implement but * Akhlesh Lakhtakia akhlesh@psu.edu