Conception et caractérisation d'un substitut physique de moelle épinière instrumenté

Abstract

The interaction between the spinal column and the spinal cord when an injury occurs is complex. The biomechanics of spinal cord injuries is poorly understood. In vitro replication of the injury is often used to better understand the fracture biomechanics. The aim is to link the spinal compression to the loading of the spine. However, recording the spinal cord compression is difficult and often neglected. Indeed, current techniques to assess the spinal canal occlusion are indirect, too slow or incomplete. They do not measure the spinal cord strain, nor mimic the mechanical properties of the spinal cord. In this study, a physical spinal cord surrogate was designed, fabricated, and validated under different testing scenarios. A literature analysis allowed identifying weaknesses of the existing spinal cord surrogates. The required specifications for the spinal cord surrogate were established based on this this literature analysis. A design process has been followed to identify a material matching the mechanical properties of the porcine spinal cord and a measuring technique. The mechanical characterization of the instrumented surrogate was performed to compare the results to those obtained with fresh porcine spinal cords. The spinal cord surrogate was also submitted to various transverse compression magnitudes (up to 90 %) and speeds (up to 500 mm/s) to reproduce typical contusions associated to vertebral burst fractures. The aim was to assess its compression sensing capability by identifying its metrological characteristics. The spinal cord surrogate was made of silicone foam. Spinal cord compression magnitude was evaluated using a resistive polymer filament embedded within the silicone foam. Sensing was based on the longitudinal strain experienced by the resistive filament during the spinal cord compression. The results shows that the spinal cord surrogate has similar viscoelastic properties to the porcine spinal cord (ICC > 0,95) under transverse compression. The polymer filament resistivity increases by 37% when the surrogate is compressed from 0 to 75%. The filament resistivity varies by 4,7% between the 1st and the 10th calibration test. The spinal cord surrogate measures the transverse compression with a maximum deviation of less than 4%. The filament response time is less than 5 ms. To conclude, this surrogate replicates the spinal cord biomechanics and allows accurate, precise and dynamic in situ recording of the spinal cord compression. These results demonstrate the feasibility of using this new tool to improve our understanding of spinal cord injury mechanisms.

Date	9 Aug 2017
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Éric Wagnac (Supervisor) & Yvan Petit (Co-supervisor)