Structure & Motion of Bat Wings Our lab integrates biological and physical studies of flight in living bats and the structures that facilitate bat flight. Our investigations of the material properties of bat wing tissues show that bat wing bones vary greatly in mineral content, ranging from highly mineralized and very stiff near the body to nearly cartilaginous and highly compliant at the wing tips. Bat wing skin is also unique, balancing the extreme mechanical demands of flight with the energetic benefits of reducing weight. We have found that the gross architecture of the wing skin’s collagen-elastin network allows a single wing to encompass an extraordinary range of mechanical characteristics, and the distribution of sensory structures on the wing likely allows for precise sensing of airflow over the wing. The wing muscles that actuate flight are uniquely susceptible to heat loss, and as such have developed adaptations to maintain fast function in the face of sometimes extreme temperature variation.

Biologists have long viewed the flapping wings of flying vertebrates as analogous to the stationary, rigid airfoils of fixed-wing aircraft. But small, slowly moving flying animals experience viscosity effects far greater than even the smallest of aircraft. At this scale, flow over foils becomes turbulent, unsteady, and unpredictable. Basic parameters such as wing aspect ratio, angle of attack, and camber can influence flow patterns and aerodynamic forces in dramatically different ways than in faster flows.





Experimental Fluid Dynamics Adapting techniques from experimental fluid dynamics, we can study wakes made by bats to better understand how these animals produce the forces employed in their distinctive flight. We carry out wind tunnel studies of bat wakes, coupled with detailed kinematics at high temporal and spatial resolution. We have found that the wing movements employed by bats generate characteristic wakes that have similarities with and differences from those of birds and insects. Wake structure can also differ almost as much among bat species as between a bird and a bat of comparable mass.

Our physical modeling experiments capture important aspects of the bat flight apparatus in simplified, abstracted form. Unlike the stiff wings of birds and insects, bats and gliding mammals employ airfoils made of stretchy or compliant material. Our pioneering work in compliant airfoils has demonstrated their remarkable capacity to generate lift at zero and very high angles of attack. We have found that the physical basis for this phenomenon lies in part in the self-cambering ability of compliant airfoils, which facilitates persistence of attached flow in conditions that would cause rigid airfoils to stall.

Our most sophisticated physical models are bat-like robots that capture many aspects of realistic bat flight with high fidelity, but allow us to independently modulate characteristics of the wingbeat in a manner that is impossible in living animals. These experiments help us study force production and flow dynamics, and give us controlled conditions under which we can tease apart the effect of motion and materials on aerodynamics and energetics.





A Preclinical Model for Human Shoulder Pathology Bat shoulders share important anatomical and functional similarities with humans. During flight, bats use large multiplanar ranges of motion while loading the shoulder primarily through muscular contraction. Anatomically, bats have blended rotator cuff tendons with broad attachments around the head of the humerus, similar to humans but different from other models commonly studied like rats, mice, sheep, and rabbits. We aim to characterize bats as a novel preclinical animal model for shoulder pathologies like rotator cuff disease and impingement. Investigating disease mechanisms, adaptations, and treatments in this functionally and anatomically relevant model will lead to improved interventions and outcomes for those suffering from shoulder pathology.