The use of embedded optical fibers to assess the transient compression distribution at key locations of an instrumented spinal cord surrogate
1Facchinello Y, 2Wagnac E, 2Ung B, 2Petit Y, 2Pradhan P, 1Mac-Thiong J
1Research Center, Hôpital du Sacré-Coeur de Montréal, Montréal, QC, Canada; 2École de technologie supérieure, Montreal, QC, Canada
Traumatic spinal cord injury (TSCI) occurs at an annual incidence of 10 to 60 cases per millions of inhabitants depending on the country . TSCI are often due to bone fragment compromising the spinal canal at high velocity. The neurological injury can be severe, lead to a loss of autonomy and a poor quality of life. The long-term neurological outcome is positively correlated with the spinal cord compression magnitude, distribution and speed occurring transiently during the trauma according to in vivo animal study. However, the biomechanics of the injury is not known in clinical cases as the residual compression of the spinal cord assessed using conventional imaging techniques is not necessarily related to the acute compression. A better understanding of the injury biomechanics could lead to better prediction of the recovery, advances in treatments and help developing innovative safety devices. In vitro replication of the injury is often proposed to study the biomechanics of injury. However, there is no existing technology allowing for an accurate recording of the acute spinal cord compression. The objective of this project is to develop an innovative technology capable to dynamically record the compression distribution within soft materials.
In a recent communication, we proposed the use of optical fibers to assess the global compression magnitude of an instrumented spinal cord surrogate . Based on this knowledge, an instrumented spinal cord surrogate capable of recording the transient compression at 4 key locations within the spinal cord transverse section was produced. The spinal cord physical surrogate was made of silicone rubber (FlexFoam-iT! III, Smooth-on, USA). Four 250 µm diameter bare optical fibers (SMF28, Corning, USA) were used as sensing elements. The sensing technology was based on the optical power loss recorded when an optical fiber is bent to a given curvature radius, with smaller radii leading to more power losses . As the surrogate is being compressed, the optical fiber bends to adapt to the deformed shape, leading to a decreasing optical power transmitted by the fiber as its curvature radius decreases. Mechanical characterization was performed using a Bose 3200 (TA Electroforce, USA) tensile and compression testing apparatus.
The instrumented surrogate was found capable of recording transverse compression greater than 35 %. Excellent sensing capabilities were observed for both static and dynamic loading with a maximum error of 5%. Localized compressions were also detected by the instrumented surrogate. The 4 embedded optical fibers had no significant effect on the mechanical properties of the material with an increase lower than 7% of the force-displacement curve.
This communication describes a technology capable of an accurate, localized and dynamic recording of the internal strain occurring within soft material. Due to the small size and biocompatibility of the optical fibers, this technology could also be used during in vitro or ex vivo compression of biological spinal cord.
This work was funded by the Medtronic Chair in Spinal Trauma at Universite de Montreal.
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