Modeling neural injury in organotypic cultures by application of inertia-driven shear strain

In vitro models of traumatic brain injury (TBI) are indispensable to explore the effects of mechanotrauma on neurological injury cascades and injury thresholds. This study characterizes a novel in vitro model of neural shear injury, which for the first time subjects organotypic cultures to inertia-driven shear strain. In this model, organotypic cultures preserved a high level of biological heterogeneity and spatial cytoarchitecture, while inertia-driven shear strain represented a tissue-level insult typical for closed head TBI in vivo. For neural injury simulation, organotypic hippocampal cultures derived from rats were inserted in an inertial loading module, which was subjected to impacts at five graded impact velocities ranging from 2 to 10 m/sec. The mechanical insult was quantified by measuring the transient shear deformation of the culture surface during impact with a high-speed camera. The resultant cell death was quantified with propidium iodide (PI) staining 24 hours following shear injury. Increasing impact velocities of 2, 4.6, 6.6, 8.1, and 10.4 m/sec caused graded peak shear elongation of 2.0 +/- 0.9%, 5.4 +/- 3.8%, 15.1 +/- 14.6%, 25.4 +/- 14.7%, and 56.3 +/- 51.3%, respectively. Cell death in response to impact velocities of 6.6 m/sec or less was not significantly higher than baseline cell death in sham cultures (4.4 +/- 1.5%). Higher impact velocities of 8.1 and 10.4 m/sec resulted in a significant increase in cell death to 19.9 +/- 12.9% and 36.7 +/- 14.2%, respectively (p < 0.001). The neural shear injury model delivered a gradable, defined mechanotrauma and thereby provides a novel tool for investigation of biological injury cascades in organotypic cultures.