title: Nonlinear viscoelastic characterization of the porcine spinal cord.
abstract: Although quasi-static and quasi-linear viscoelastic properties of the spinal cord have been reported previously, there are no published studies that have investigated the fully (strain-dependent) nonlinear viscoelastic properties of the spinal cord. In this study, stress relaxation experiments and dynamic cycling were performed on six fresh porcine lumbar cord specimens to examine their viscoelastic mechanical properties. The stress relaxation data were fitted to a modified superposition formulation and a novel finite ramp time correction technique was applied. The parameters obtained from this fitting methodology were used to predict the average dynamic cyclic viscoelastic behavior of the porcine cord. The data indicate that the porcine spinal cord exhibited fully nonlinear viscoelastic behavior. The average weighted root mean squared error for a Heaviside ramp fit was 2.8 kPa, which was significantly greater (p<0.001) than that of the nonlinear (comprehensive viscoelastic characterization method) fit (0.365 kPa). Further, the nonlinear mechanical parameters obtained were able to accurately predict the dynamic behavior, thus exemplifying the reliability of the obtained nonlinear parameters. These parameters will be important for future studies investigating various damage mechanisms of the spinal cord and studies developing high-resolution finite elements models of the spine.
authors.affiliation: Department of Mechanical Engineering, Colorado State University, Fort Collins, CO, USA.
authors.forename: Snehal S
authors.initials: SS
authors.lastname: Shetye
authors.affiliation: Department of Mechanical Engineering, Colorado State University, Fort Collins, CO, USA.
authors.forename: Kevin L
authors.initials: KL
authors.lastname: Troyer
authors.affiliation: International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, Canada.
authors.forename: Femke
authors.initials: F
authors.lastname: Streijger
authors.affiliation: International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, Canada.
authors.forename: Jae H T
authors.initials: JH
authors.lastname: Lee
authors.affiliation: Department of Orthopaedic Surgery, University of British Columbia, Vancouver, BC, Canada.
authors.forename: Brian K
authors.initials: BK
authors.lastname: Kwon
authors.affiliation: Department of Orthopaedic Surgery, University of British Columbia, Vancouver, BC, Canada; Department of Mechanical Engineering, University of British Columbia, Vancouver, BC, Canada.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Cripton
authors.affiliation: Department of Mechanical Engineering, Colorado State University, Fort Collins, CO, USA; School of Biomedical Engineering, Colorado State University, Fort Collins, CO, USA; Department of Clinical Sciences, Colorado State University, Fort Collins, CO, USA. Electronic address: puttlitz@engr.colostate.edu.
authors.forename: Christian M
authors.initials: CM
authors.lastname: Puttlitz
mesh_terms: D000818:Animals; D004548:Elasticity; D005260:Female; D017711:Nonlinear Dynamics; D013116:Spinal Cord / Q000502:physiology*; D013314:Stress, Mechanical; D034421:Sus scrofa; D013997:Time Factors; D014159:Transducers; D014783:Viscosity
keywords: Biomechanics; Constitutive modeling; Spinal cord; Spinal cord injury; Viscoelasticity