P3.176 Friday, Jan. 6 Pre-stressed compliant fibers within the wing membrane of Glossophaga soricina, Pallas’ long tongued bat CHENEY, J. A.*; BEARNOT, A.; BREUER, K. S.; SWARTZ, S. M.; Brown University; Brown University; Brown University; Brown University Jorn_Cheney@Brown.edu
The wing membrane of bats is composed of a double-layer of skin, with macroscopic bundles of elastin fibrils located within the dermis. These fibers run primarily along the proximo-distal, or spanwise, axis of the wing. In typical human-engineered fiber-reinforced composites, fibers have a higher elastic modulus than the surrounding material or matrix, and their functional roles include increasing toughness and strength. Bat wing membranes therefore comprise an unusual fiber composite, in that the embedded elastin fibers are more compliant than the surrounding tissue.
To better understand the role of compliant fibers in a more rigid matrix, we conducted quasi-static tensile mechanical tests of fresh wing membrane tissue from Glossophaga soricina, Pallas’ long-tongued bat. As expected from previous studies, the wing membrane displayed anisotropic behavior. We found that specimens oriented with elastin fibers parallel to the sample axis were more compliant than those with elastin fibers oriented transversely.
To explain the greater compliance parallel to the fibers, we propose a simple model of wing membrane mechanics based on key aspects of wing histology and mechanical behavior of wing tissue. We hypothesize that like most mammalian skin, the dermis and epidermis are isotropic; therefore, the anisotropic behavior is due specifically to the elastin fibers, even though they are more compliant than the matrix. Our model proposes that the elastin fibers are pre-stressed and modify tissue mechanical behavior by causing the thin surrounding matrix to buckle. Therefore in tensile tests, at low strain the measured stress is due to the elastin fibers, and at high strain the matrix is unfolded and engaged and the measured stress is due to both fiber and matrix.