The wings of all flying animals are composed in part of an outer surface -- the skin, feathers, and/or cuticle -- but this key component of wing structure is much less well studied than the internal skeletal, muscular, and nervous systems. Because skin can make up the majority of the wing surface, understanding the mechanical nature of skin in flying animals is critically important to understanding both how animals fly, and the evolutionary origins and diversification of animal flight. One way in which bats differ from all other flying animals and from the flying vehicles that humans build is that their wings deform and stretch tremendously during flight. This research program will focus on the unique structure and function of bat skin, and how it contributes to the flight capacity of bats. This project proposes to understand how the skin of the wing helps to control the dynamic changes in 3D wing shape that are integral to bat flight performance. To achieve this goal, this collaborative project will integrate biology and engineering research to gain an in-depth understanding of the nature of bat wing skin, a remarkable and complex biological material. First, high-speed videography of natural flight in bats will be used to document how wing skin stretches and deforms during normal wing movements. Second, a comparative analysis of the diversity of structure of connective tissues and muscles underlying wing skin will be undertaken in a group of 87 of the more than 1200 living bat species, selected to represent bat diversity and evolutionary relationships. Third, unique mechanical tests of wing skin will be made by applying forces in a manner that mimics, for the first time, what skin experiences during flight. Using a special technique that employs polarized light, it will be possible to quantify microscopic deformations over entire skin samples for the first time. This new method will make it possible to gain fundamental insights into wing skin as a material and into wings as airfoils. Finally, data from all of these studies will be incorporated into engineering models of structure-property relationships for bat skin. These models will not only provide deeper insights into the mechanics of the skin, but will also make predictions about skin function and dynamics that go beyond what can be observed under laboratory test conditions. Engineering sciences increasingly look to the biological world for design ideas and studies of bat wing architecture and materials can uncover a menu of distinctive traits that can inspire novel aerospace materials, airfoil designs, and other cutting-edge technologies. In addition, theory and modeling tools developed here for highly deforming wing skin will be applicable to tissue mechanics in a variety of biological and biomedical applications. Public fascination with bats and the beauty of bat form and motion provide natural starting points for communication; the principal investigators and their students will conduct outreach at local public schools and museums, create web-based content for many audiences, and participate in film and television programming. The investigators will make special efforts to identify, recruit, and retain undergraduate and graduate students from underrepresented groups, and to involve them as team members at every level. A biology component will be added to the NSF-GEMS (Girls in Engineering, Math & Science) program in Kingston, Jamaica, which will incorporate animal flight and natural history of Jamaica. This enhancement will broaden the range of science in the program, offer outreach training to graduate students, and give girls hands-on experience of science in their own environment.
