An ex vivo injury model perfused with whole blood reveals rapid mechanical and transcriptional changes within the spinal cord

Secondary spinal cord injury (SCI), which includes a cascade of both biophysical and biochemical processes that mitigate neurological recovery, is thought to initiate within minutes of the direct, primary injury. However, previous in vitro and in vivo-based approaches are incapable of determining how quickly and to what extent these processes occur following injury. In contrast, the perfused bovine ex vivo indentation injury model described here represents a new platform to investigate the short-term effects of observed phenomena like altered blood flow and blood-spinal cord barrier disruption following traumatic SCI. The model can assess tissue changes on the scale of minutes to determine how rapidly the spinal cord responds to injury. Indentation tests simultaneously simulate a crush injury and measure the mechanical properties of the tissue using Hertz contact theory. Our results indicate that injured cords exhibit changes to bulk perfusion, as evidenced by laser speckle contrast imaging, in addition to decreased barrier function minutes after injury. Mechanical testing of the cord reveals that the tissue softening observed previously in the days following injury initiates as early as 30 minutes. Moreover, perfusing red blood cells resuspended in saline instead of whole blood mitigates the drop in elastic modulus, highlighting the importance of leukocytes and plasma proteins in mediating the extracellular matrix mechanical response after SCI. Transcriptomic analysis reveals key differences in gene expression within 15 minutes of injury, including those related to inflammation and the immune response. Identifying the timeframe and extent to which biomechanical and biochemical changes occur after injury provides a more complete understanding of secondary injury.