Dynamic mechanical response and functional mechanisms in rabbit pulmonary tissue

Lung tissue plays a crucial role in biological functions and exhibits significant sensitivity to mechanical loading. Its mechanical properties have garnered increased attention for their potential to guide human protection strategies against collisions and explosions. However, the behavior and underlying mechanisms remain largely undefined, particularly under dynamic loading conditions. In the present study, rabbit lung tissues were subjected to directional compression loadings, both parallel and perpendicular to the trachea. For accurate dynamic measurements, a modified Hopkinson pressure bar was employed. To minimize spike-like stress characteristics, annular specimens were utilized, and a polymethyl methacrylate bar served as the transmission tube, in conjunction with semiconductor strain gauges, to enhance the amplification of transmission signals. Experiments were meticulously conducted using the modified split Hopkinson pressure bar and an Instron machine, covering a strain rate range of 0.0005–3000 s⁻¹. The results revealed a pronounced rate-dependence in the stress–strain curves of lung tissue, characterized by an initial linear elastic regime, a deformation plateau, and ultimate densification. A significant dependency on strain rate was observed, with the strength of tissue increasing a thousandfold from quasi-static to dynamic loading. Anisotropic behavior was evident under both loading directions. Furthermore, both strain rate dependency and anisotropic behavior became more pronounced beyond 0.3 strain under dynamic loading and 0.45 under quasi-static loading. Finally, potential mechanisms involving tissue fluid discharge and the mechanical characteristics of orientated collagen were proposed. These mechanisms were corroborated by staining techniques that demonstrated the predominant orientation of collagen in a specific direction within rabbit lung tissue.