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Ma J, Wang J, Yang Y, Wu J, Liu Z, Miao J, Yan X. Biomechanical study of spinal cord and nerve root in idiopathic scoliosis: based on finite element analysis. BMC Musculoskelet Disord 2024; 25:717. [PMID: 39243084 PMCID: PMC11378384 DOI: 10.1186/s12891-024-07832-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/24/2024] [Accepted: 08/29/2024] [Indexed: 09/09/2024] Open
Abstract
BACKGROUND Current research lacks comprehensive investigation into the biomechanical changes in the spinal cord and nerve roots during scoliosis correction. This study employs finite element analysis to extensively explore these biomechanical variations across different Cobb angles, providing valuable insights for clinical treatment. METHODS A personalized finite element model, incorporating vertebrae, ligaments, spinal cord, and nerve roots, was constructed using engineering software. Forces and displacements were applied to achieve Cobb angle improvements, designating T1/2-T4/5 as the upper segment, T5/6-T8/9 as the middle segment, and T9/10-L1/2 as the lower segment. Simulations under traction, pushing, and traction + torsion conditions were conducted, and biomechanical changes in each spinal cord segment and nerve roots were analyzed. RESULTS Throughout the scoliosis correction process, the middle spinal cord segment consistently exhibited a risk of injury under various conditions and displacements. The lower spinal cord segment showed no significant injury changes under traction + torsion conditions. In the early correction phase, the upper spinal cord segment demonstrated a risk of injury under all conditions, and the lower spinal cord segment presented a risk of injury under pushing conditions. Traction conditions posed a risk of nerve injury on both sides in the middle and lower segments. Under pushing conditions, there was a risk of nerve injury on both sides in all segments. Traction + torsion conditions implicated a risk of injury to the right nerves in the upper segment, both sides in the middle segment, and the left side in the lower segment. In the later correction stage, there was a risk of injury to the upper spinal cord segment under traction + torsion conditions, the left nerves in the middle segment under traction conditions, and the right nerves in the upper segment under pushing conditions. CONCLUSION When the correction rate reaches 61-68%, particular attention should be given to the upper-mid spinal cord. Pushing conditions also warrant attention to the lower spinal cord and the nerve roots on both sides of the main thoracic curve. Traction conditions require attention to nerve roots bilaterally in the middle and lower segments, while traction combined with torsion conditions necessitate focus on the right-side nerve roots in the upper segment, both sides in the middle segment, and the left-side nerve roots in the lower segment.
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Affiliation(s)
- Jibin Ma
- Clinical School/Colledge of Orthopedics, Tianjin Medical University, No. 22 Qixiangtai Road, Heping District, Tianjin, China
- Department of Orthopedics, The Second People's Hospital of Changzhi, No. 83 Peace West Street, Luzhou District, Changzhi, Shanxi Province, China
| | - Jian Wang
- Clinical School/Colledge of Orthopedics, Tianjin Medical University, No. 22 Qixiangtai Road, Heping District, Tianjin, China
| | - Yuming Yang
- Clinical School/Colledge of Orthopedics, Tianjin Medical University, No. 22 Qixiangtai Road, Heping District, Tianjin, China
| | - Jincheng Wu
- Department of Orthopedics, Hainan Medical University Second Affiliated Hospital, No. 48 Baishuitang Road, Longhua District, Haikou, Hainan Province, China
| | - Ziwen Liu
- Clinical School/Colledge of Orthopedics, Tianjin Medical University, No. 22 Qixiangtai Road, Heping District, Tianjin, China
| | - Jun Miao
- Department of Spine Surgery, Tianjin Hospital, Tianjin University, Jiefangnanlu 406, Hexi District, Tianjin, China.
| | - Xu Yan
- Department of Hand Surgery, Tianjin Hospital, Tianjin University, Jiefangnanlu 406, Hexi District, Tianjin, China.
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Harinathan B, Jebaseelan D, Yoganandan N, Vedantam A. Effect of Cervical Stenosis and Rate of Impact on Risk of Spinal Cord Injury During Whiplash Injury. Spine (Phila Pa 1976) 2023; 48:1208-1215. [PMID: 37341525 DOI: 10.1097/brs.0000000000004759] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/26/2023] [Accepted: 06/09/2023] [Indexed: 06/22/2023]
Abstract
STUDY DESIGN Finite Element Study. OBJECTIVE To determine the risk of spinal cord injury with pre-existing cervical stenosis during a whiplash injury. SUMMARY OF BACKGROUND DATA Patients with cervical spinal stenosis are often cautioned on the potential increased risk of spinal cord injury (SCI) from minor trauma such as rear impact whiplash injuries. However, there is no consensus on the degree of canal stenosis or the rate of impact that predisposes cervical SCI from minor trauma. METHODS A previously validated three-dimensional finite element model of the human head-neck complex with the spinal cord and activated cervical musculature was used. Rear impact acceleration was applied at 1.8 m/s and 2.6 m/s. Progressive spinal stenosis was simulated at the C5 to C6 segment, from 14 mm to 6 mm, at 2 mm intervals of ventral disk protrusion. Spinal cord von Mises stress and maximum principal strain were extracted and normalized with respect to the 14 mm spine at each cervical spine level from C2 to C7. RESULTS The mean segmental range of motion was 7.3 degrees at 1.8 m/s and 9.3 degrees at 2.6 m/s. Spinal cord stress above the threshold for SCI was noted at C5 to C6 for 6 mm stenosis at 1.8 m/s and 2.6 m/s. The segment (C6-C7) inferior to the level of maximum stenosis also showed increasing stress and strain with a higher rate of impact. For 8 mm stenosis, spinal cord stress exceeded SCI thresholds only at 2.6 m/s. Spinal cord strain above SCI thresholds were only noted in the 6 mm stenosis model at 2.6 m/s. CONCLUSION Increased spinal stenosis and rate of impact are associated with greater magnitude and spatial distribution of spinal cord stress and strain during a whiplash injury. Spinal canal stenosis of 6 mm was associated with consistent elevation of spinal cord stress and strain above SCI thresholds at 2.6 m/s.
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Affiliation(s)
- Balaji Harinathan
- Department of Neurosurgery, Medical College of Wisconsin, Milwaukee, WI
- School of Mechanical Engineering, Vellore Institute of Technology, Chennai, India
| | - Davidson Jebaseelan
- School of Mechanical Engineering, Vellore Institute of Technology, Chennai, India
| | | | - Aditya Vedantam
- Department of Neurosurgery, Medical College of Wisconsin, Milwaukee, WI
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Jiang F, Sakuramoto I, Nishida N, Onomoto Y, Ohgi J, Chen X. The mechanical behavior of bovine spinal cord white matter under various strain rate conditions: tensile testing and visco-hyperelastic constitutive modeling. Med Biol Eng Comput 2023; 61:1381-1394. [PMID: 36708501 DOI: 10.1007/s11517-023-02787-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2020] [Accepted: 01/17/2023] [Indexed: 01/29/2023]
Abstract
The mechanical behavior of the white matter is important for estimating the damage of the spinal cord during accidents. In this study, we conducted uniaxial tension testing in vitro of bovine spinal cord white matter under extremely high strain rate conditions (up to 100 s-1). A visco-hyperelastic constitutive law for modeling the strain rate-dependent behavior of the bovine spinal cord white matter was developed. A set of material constants was obtained using a Levenberg-Marquardt fitting algorithm to match the uniaxial tension experimental data with various strain rates. Our experimental data confirmed that the modulus and tensile strength increased when the strain rate is higher. For the extremely high strain rate condition (100 s-1), we found that both the modulus and failure stress significantly increased compared with the low strain rate case. These new data in terms of mechanical response at high strain rate provide insight into the spine injury mechanism caused by high-speed impact. Moreover, the developed constitutive model will allow researchers to perform more realistic finite element modeling and simulation of spinal cord injury damage under various complicated conditions.
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Affiliation(s)
- Fei Jiang
- Department of Mechanical Engineering, Graduate School of Sciences and Technology for Innovation, Yamaguchi University, 2-16-1 Tokiwadai, Ube, Yamaguchi, 755-8611, Japan.
| | - Itsuo Sakuramoto
- Department of Mechanical and Electrical Engineering, National Institute of Technology, Tokuyama College, Gakuendai, Shunan, Yamaguchi, 745-8585, Japan
| | - Norihiro Nishida
- Department of Orthopedic Surgery, Yamaguchi University Graduate School of Medicine, 1-1-1, MinamiKogushi, Yamaguchi, 755-8505, Ube City, Japan
| | - Yoshikatsu Onomoto
- Department of Mechanical Engineering, Graduate School of Sciences and Technology for Innovation, Yamaguchi University, 2-16-1 Tokiwadai, Ube, Yamaguchi, 755-8611, Japan
| | - Junji Ohgi
- Department of Mechanical Engineering, Graduate School of Sciences and Technology for Innovation, Yamaguchi University, 2-16-1 Tokiwadai, Ube, Yamaguchi, 755-8611, Japan
| | - Xian Chen
- Department of Mechanical Engineering, Graduate School of Sciences and Technology for Innovation, Yamaguchi University, 2-16-1 Tokiwadai, Ube, Yamaguchi, 755-8611, Japan
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Talebi A, Labbaf S, Rahmati S. Biofabrication of a flexible and conductive 3D polymeric scaffold for neural tissue engineering applications; physical, chemical, mechanical, and biological evaluations. POLYM ADVAN TECHNOL 2022. [DOI: 10.1002/pat.5872] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Alireza Talebi
- Biomaterials Research Group, Department of Materials Engineering Isfahan University of Technology Isfahan Iran
| | - Sheyda Labbaf
- Biomaterials Research Group, Department of Materials Engineering Isfahan University of Technology Isfahan Iran
| | - Saba Rahmati
- Biomaterials Research Group, Department of Materials Engineering Isfahan University of Technology Isfahan Iran
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Talebi A, Labbaf S, Atari M, Parhizkar M. Polymeric Nanocomposite Structures Based on Functionalized Graphene with Tunable Properties for Nervous Tissue Replacement. ACS Biomater Sci Eng 2021; 7:4591-4601. [PMID: 34461017 DOI: 10.1021/acsbiomaterials.1c00744] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Electroconductive scaffolds can be a promising approach to repair conductive tissues when natural healing fails. Recently, nerve tissue engineering constructs have been widely investigated due to the challenges in creating a structure with optimized physiochemical and mechanical properties close to the native tissue. The goal of the current study was to fabricate graphene-containing polycaprolactone/gelatin/polypyrrole (PCL/gelatin/PPy) and polycaprolactone/polyglycerol-sebacate/polypyrrole (PCL/PGS/PPy) with intrinsic electrical properties through an electrospinning process. The effect of graphene on the properties of PCL/gelatin/PPy and PCL/PGS/PPy were investigated. Results demonstrated that graphene incorporation remarkably modulated the physical and mechanical properties of the scaffolds such that the electrical conductivity increased from 0.1 to 3.9 ± 0.3 S m-1 (from 0 to 3 wt % graphene) and toughness was found to be 76 MPa (PCL/gelatin/PPy 3 wt % graphene) and 143.4 MPa (PCL/PGS/PPy 3 wt % graphene). Also, the elastic moduli of the scaffolds with 0, 1, and 2 wt % graphene were reported as 210, 300, and 340 kPa in the PCL/gelatin/PPy system and 72, 85, and 92 kPa for the PCL/PGS/PPy system. A cell viability study demonstrated the noncytotoxic nature of the resultant scaffolds. The sum of the results presented in this study suggests that both PCL/gelatin/PPy/graphene and PCL/PGS/PPy/graphene compositions could be promising biomaterials for a range of conductive tissue replacement or regeneration applications.
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Affiliation(s)
- Alireza Talebi
- Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran
| | - Sheyda Labbaf
- Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran
| | - Mehdi Atari
- Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran
| | - Maryam Parhizkar
- School of Pharmacy, University College London, Torrington Place, London WC1E 7JE, U.K
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Prager J, Adams CF, Delaney AM, Chanoit G, Tarlton JF, Wong LF, Chari DM, Granger N. Stiffness-matched biomaterial implants for cell delivery: clinical, intraoperative ultrasound elastography provides a 'target' stiffness for hydrogel synthesis in spinal cord injury. J Tissue Eng 2020; 11:2041731420934806. [PMID: 32670538 PMCID: PMC7336822 DOI: 10.1177/2041731420934806] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2020] [Accepted: 05/21/2020] [Indexed: 12/14/2022] Open
Abstract
Safe hydrogel delivery requires stiffness-matching with host tissues to avoid
iatrogenic damage and reduce inflammatory reactions. Hydrogel-encapsulated cell
delivery is a promising combinatorial approach to spinal cord injury therapy,
but a lack of in vivo clinical spinal cord injury stiffness
measurements is a barrier to their use in clinics. We demonstrate that
ultrasound elastography – a non-invasive, clinically established tool – can be
used to measure spinal cord stiffness intraoperatively in canines with
spontaneous spinal cord injury. In line with recent experimental reports, our
data show that injured spinal cord has lower stiffness than uninjured cord. We
show that the stiffness of hydrogels encapsulating a clinically relevant
transplant population (olfactory ensheathing cells) can also be measured by
ultrasound elastography, enabling synthesis of hydrogels with comparable
stiffness to canine spinal cord injury. We therefore demonstrate
proof-of-principle of a novel approach to stiffness-matching hydrogel-olfactory
ensheathing cell implants to ‘real-life’ spinal cord injury values; an approach
applicable to multiple biomaterial implants for regenerative therapies.
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Affiliation(s)
- Jon Prager
- Bristol Veterinary School, University of Bristol, Bristol, UK.,The Royal Veterinary College, University of London, Hatfield, UK
| | - Christopher F Adams
- Cellular and Neural Engineering Group, Institute for Science and Technology in Medicine, Keele University, Keele, UK
| | - Alexander M Delaney
- Cellular and Neural Engineering Group, Institute for Science and Technology in Medicine, Keele University, Keele, UK
| | | | - John F Tarlton
- Bristol Veterinary School, University of Bristol, Bristol, UK
| | | | - Divya M Chari
- Cellular and Neural Engineering Group, Institute for Science and Technology in Medicine, Keele University, Keele, UK
| | - Nicolas Granger
- The Royal Veterinary College, University of London, Hatfield, UK
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Diotalevi L, Bailly N, Wagnac É, Mac-Thiong JM, Goulet J, Petit Y. Dynamics of spinal cord compression with different patterns of thoracolumbar burst fractures: Numerical simulations using finite element modelling. Clin Biomech (Bristol, Avon) 2020; 72:186-194. [PMID: 31901589 DOI: 10.1016/j.clinbiomech.2019.12.023] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Revised: 12/15/2019] [Accepted: 12/23/2019] [Indexed: 02/07/2023]
Abstract
BACKGROUND In thoracolumbar burst fractures, spinal cord primary injury involves a direct impact and energy transfer from bone fragments to the spinal cord. Unfortunately, imaging studies performed after the injury only depict the residual bone fragments position and pattern of spinal cord compression, with little insight on the dynamics involved during traumas. Knowledge of underlying mechanisms could be helpful in determining the severity of the primary injury, hence the extent of spinal cord damage and associated potential for recovery. Finite element models are often used to study dynamic processes, but have never been used specifically to simulate different severities of thoracolumbar burst fractures. METHODS Previously developed thoracolumbar spine and spinal cord finite element models were used and further validated, and representative vertebral fragments were modelled. A full factorial design was used to investigate the effects of comminution of the superior fragment, presence of an inferior fragment, fragments rotation and velocity, on maximum Von Mises stress and strain, maximum major strain, and pressure in the spinal cord. FINDINGS Fragment velocity clearly was the most influential factor. Fragments rotation and presence of an inferior fragment increased pressure, but rotation decreased both strains outputs. Although significant for both strains outputs, comminution of the superior fragment isn't estimated to influence outputs. INTERPRETATION This study is the first, to the authors' knowledge, to examine a detailed spinal cord model impacted in situ by fragments from burst fractures. This numeric model could be used in the future to comprehensively link traumatic events or imaging study characteristics to known spinal cord injuries severity and potential for recovery.
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Affiliation(s)
- Lucien Diotalevi
- Department of Mechanical Engineering, École de Technologie Supérieure, 1100 Notre-Dame Street West, Montréal, Québec H3C 1K3, Canada; Research Center, Hôpital du Sacré-Cœur de Montréal, 5400 Gouin blvd, Montréal H4J 1C5, Québec, Canada; International Laboratory on Spine Imaging and Biomechanics (iLab-Spine), Canada
| | - Nicolas Bailly
- Department of Mechanical Engineering, École de Technologie Supérieure, 1100 Notre-Dame Street West, Montréal, Québec H3C 1K3, Canada; Research Center, Hôpital du Sacré-Cœur de Montréal, 5400 Gouin blvd, Montréal H4J 1C5, Québec, Canada; International Laboratory on Spine Imaging and Biomechanics (iLab-Spine), Canada
| | - Éric Wagnac
- Department of Mechanical Engineering, École de Technologie Supérieure, 1100 Notre-Dame Street West, Montréal, Québec H3C 1K3, Canada; Research Center, Hôpital du Sacré-Cœur de Montréal, 5400 Gouin blvd, Montréal H4J 1C5, Québec, Canada; International Laboratory on Spine Imaging and Biomechanics (iLab-Spine), Canada.
| | - Jean-Marc Mac-Thiong
- Research Center, Hôpital du Sacré-Cœur de Montréal, 5400 Gouin blvd, Montréal H4J 1C5, Québec, Canada; Department of Orthopaedic Surgery, Université de Montréal, P.O. box 6128, Station Centre-Ville, Montréal, Québec H3C 3J7, Canada
| | - Julien Goulet
- Research Center, Hôpital du Sacré-Cœur de Montréal, 5400 Gouin blvd, Montréal H4J 1C5, Québec, Canada; Department of Orthopaedic Surgery, Université de Montréal, P.O. box 6128, Station Centre-Ville, Montréal, Québec H3C 3J7, Canada.
| | - Yvan Petit
- Department of Mechanical Engineering, École de Technologie Supérieure, 1100 Notre-Dame Street West, Montréal, Québec H3C 1K3, Canada; Research Center, Hôpital du Sacré-Cœur de Montréal, 5400 Gouin blvd, Montréal H4J 1C5, Québec, Canada; International Laboratory on Spine Imaging and Biomechanics (iLab-Spine), Canada.
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Technique and preliminary findings for in vivo quantification of brain motion during injurious head impacts. J Biomech 2019; 95:109279. [DOI: 10.1016/j.jbiomech.2019.07.023] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2019] [Revised: 06/25/2019] [Accepted: 07/18/2019] [Indexed: 11/18/2022]
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Ramo NL, Troyer K, Puttlitz C. Comparing Predictive Accuracy and Computational Costs for Viscoelastic Modeling of Spinal Cord Tissues. J Biomech Eng 2019; 141:2727822. [PMID: 30835287 DOI: 10.1115/1.4043033] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2018] [Indexed: 11/08/2022]
Abstract
The constitutive equation used to characterize and model spinal tissues can significantly influence the conclusions from experimental and computational studies. Therefore, researchers must make critical judgements regarding the balance of computational efficiency and predictive accuracy necessary for their purposes. The objective of this study is to quantitatively compare the fitting and prediction accuracy of linear viscoelastic (LV), quasi-linear viscoelastic (QLV), and (fully) non-linear viscoelastic (NLV) modeling of spinal-cord-pia-arachnoid-construct (SCPC), isolated cord parenchyma, and isolated pia-arachnoid-complex (PAC) mechanics in order to better inform these judgements. Experimental data collected during dynamic cyclic testing of each tissue condition were used to fit each viscoelastic formulation. These fitted models were then used to predict independent experimental data from stress-relaxation testing. Relative fitting accuracy was found not to directly reflect relative predictive accuracy, emphasizing the need for material model validation through predictions of independent data. For the SCPC and isolated cord, the NLV formulation best predicted the mechanical response to arbitrary loading conditions, but required significantly greater computational run time. The mechanical response of the PAC under arbitrary loading conditions was best predicted by the QLV formulation.
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Affiliation(s)
- Nicole L Ramo
- School of Biomedical Engineering, Colorado State University, 1376 Campus Delivery, Fort Collins, CO 80523
| | - Kevin Troyer
- Department of Mechanical Engineering, Colorado State University, 1374 Campus Delivery, Fort Collins, CO 80523
| | - Christian Puttlitz
- School of Biomedical Engineering, Colorado State University, Department of Mechanical Engineering, Colorado State University, Department of Clinical Sciences, Colorado State University, 1374 Campus Delivery, Fort Collins, CO 80523
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Lucas E, Whyte T, Liu J, Russell C, Tetzlaff W, Cripton PA. High-Speed Fluoroscopy to Measure Dynamic Spinal Cord Deformation in an In Vivo Rat Model. J Neurotrauma 2018; 35:2572-2580. [PMID: 29786472 DOI: 10.1089/neu.2017.5478] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Although spinal cord deformation is thought to be a predictor of injury severity, few researchers have investigated dynamic cord deformation, in vivo, during impact. This is needed to establish correlations among impact parameters, internal cord deformation, and histological and functional outcomes. Relying on surface deformations alone may not sufficiently represent spinal cord deformation. The objective of this study was to develop a high-speed fluoroscopic method of tracking the surface and internal cord deformations of rat spinal cord during experimental cord injury. Two radio-opaque beads were injected into the cord at C5/6 in the dorsal and ventral white matter. Four additional beads were glued to the surface of the cord. Dynamic bead displacement was tracked during a dorsal impact (130 mm/sec, 1 mm depth) by high-speed radiographic imaging at 3000 FPS, laterally. The internal spinal cord beads displaced significantly more than the surface beads in the ventral direction (1.1-1.9 times) and more than most surface beads in the cranial direction (1.2-1.5 times). The dorsal beads (internal and surface) displaced more than the ventral beads during all impacts. The bead displacement pattern implies that the spinal cord undergoes complex internal and surface deformations during impact. Residual displacement of the internal beads was significantly greater than that of the surface beads in the cranial-caudal direction but not the dorsoventral direction. Finite element simulation confirmed that the additional bead mass likely had little effect on the internal cord deformations. These results support the merit of this technique for measuring in vivo spinal cord deformation.
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Affiliation(s)
- Erin Lucas
- 1 Orthopaedic Injury Biomechanics Group, Departments of Mechanical Engineering and Orthopaedics and the School of Biomedical Engineering, The University of British Columbia , Vancouver, British Columbia, Canada .,2 International Collaboration on Repair Discoveries (ICORD), The University of British Columbia , Vancouver, British Columbia, Canada
| | - Thomas Whyte
- 1 Orthopaedic Injury Biomechanics Group, Departments of Mechanical Engineering and Orthopaedics and the School of Biomedical Engineering, The University of British Columbia , Vancouver, British Columbia, Canada .,2 International Collaboration on Repair Discoveries (ICORD), The University of British Columbia , Vancouver, British Columbia, Canada
| | - Jie Liu
- 2 International Collaboration on Repair Discoveries (ICORD), The University of British Columbia , Vancouver, British Columbia, Canada
| | - Colin Russell
- 1 Orthopaedic Injury Biomechanics Group, Departments of Mechanical Engineering and Orthopaedics and the School of Biomedical Engineering, The University of British Columbia , Vancouver, British Columbia, Canada .,2 International Collaboration on Repair Discoveries (ICORD), The University of British Columbia , Vancouver, British Columbia, Canada
| | - Wolfram Tetzlaff
- 2 International Collaboration on Repair Discoveries (ICORD), The University of British Columbia , Vancouver, British Columbia, Canada
| | - Peter Alec Cripton
- 1 Orthopaedic Injury Biomechanics Group, Departments of Mechanical Engineering and Orthopaedics and the School of Biomedical Engineering, The University of British Columbia , Vancouver, British Columbia, Canada .,2 International Collaboration on Repair Discoveries (ICORD), The University of British Columbia , Vancouver, British Columbia, Canada
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Ramo NL, Troyer KL, Puttlitz CM. Viscoelasticity of spinal cord and meningeal tissues. Acta Biomater 2018; 75:253-262. [PMID: 29852238 DOI: 10.1016/j.actbio.2018.05.045] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2018] [Revised: 05/02/2018] [Accepted: 05/25/2018] [Indexed: 01/08/2023]
Abstract
Compared to the outer dura mater, the mechanical behavior of spinal pia and arachnoid meningeal layers has received very little attention in the literature. This is despite experimental evidence of their importance with respect to the overall spinal cord stiffness and recovery following compression. Accordingly, inclusion of the mechanical contribution of the pia and arachnoid maters would improve the predictive accuracy of finite element models of the spine, especially in the distribution of stresses and strain through the cord's cross-section. However, to-date, only linearly elastic moduli for what has been previously identified as spinal pia mater is available in the literature. This study is the first to quantitatively compare the viscoelastic behavior of isolated spinal pia-arachnoid-complex, neural tissue of the spinal cord parenchyma, and intact construct of the two. The results show that while it only makes up 5.5% of the overall cross-sectional area, the thin membranes of the innermost meninges significantly affect both the elastic and viscous response of the intact construct. Without the contribution of the pia and arachnoid maters, the spinal cord has very little inherent stiffness and experiences significant relaxation when strained. The ability of the fitted non-linear viscoelastic material models of each condition to predict independent data within experimental variability supports their implementation into future finite element computational studies of the spine. STATEMENT OF SIGNIFICANCE The neural tissue of the spinal cord is surrounded by three fibrous layers called meninges which are important in the behavior of the overall spinal-cord-meningeal construct. While the mechanical properties of the outermost layer have been reported, the pia mater and arachnoid mater have received considerably less attention. This study is the first to directly compare the behavior of the isolated neural tissue of the cord, the isolated pia-arachnoid complex, and the construct of these individual components. The results show that, despite being very thin, the inner meninges significantly affect the elastic and time-dependent response of the spinal cord, which may have important implications for studies of spinal cord injury.
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Affiliation(s)
- Nicole L Ramo
- School of Biomedical Engineering, Colorado State University, Fort Collins, CO, USA
| | - Kevin L Troyer
- Department of Mechanical Engineering, Colorado State University, Fort Collins, CO, USA
| | - Christian M Puttlitz
- School of Biomedical Engineering, Colorado State University, Fort Collins, CO, USA; Department of Mechanical Engineering, Colorado State University, Fort Collins, CO, USA; Department of Clinical Sciences, Colorado State University, Fort Collins, CO, USA.
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Radiography used to measure internal spinal cord deformation in an in vivo rat model. J Biomech 2018; 71:286-290. [PMID: 29477261 DOI: 10.1016/j.jbiomech.2018.01.036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2017] [Revised: 12/01/2017] [Accepted: 01/29/2018] [Indexed: 11/21/2022]
Abstract
Little is known about the internal mechanics of the in vivo spinal cord during injury. The objective of this study was to develop a method of tracking internal and surface deformation of in vivo rat spinal cord during compression using radiography. Since neural tissue is radio-translucent, radio-opaque markers were injected into the spinal cord. Two tantalum beads (260 µm) were injected into the cord (dorsal and ventral) at C5 of nine anesthetized rats. Four beads were glued to the lateral surface of the cord, caudal and cranial to the injection site. A compression plate was displaced 0.5 mm, 2 mm, and 3 mm into the spinal cord and lateral X-ray images were taken before, during, and after each compression for measuring bead displacements. Potential bead migration was monitored for by comparing displacements of the internal and glued surface beads. Dorsal beads moved significantly more than ventral beads with a range in averages of 0.57-0.71 mm and 0.31-0.35 mm respectively. Bead displacements during 0.5 mm compressions were significantly lower than 2 mm and 3 mm compressions. There was no statistically significant migration of the internal beads. The results indicate the merit of this technique for measuring in vivo spinal cord deformation. The pattern of bead displacements illustrates the complex internal and surface deformations of the spinal cord during transverse compression. This information is needed for validating physical and finite element spinal cord surrogates and to define relationships between loading parameters, internal cord deformation, and biological and functional outcomes.
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Ramo NL, Shetye SS, Streijger F, Lee JHT, Troyer KL, Kwon BK, Cripton P, Puttlitz CM. Comparison of in vivo and ex vivo viscoelastic behavior of the spinal cord. Acta Biomater 2018; 68:78-89. [PMID: 29288084 PMCID: PMC5803400 DOI: 10.1016/j.actbio.2017.12.024] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2017] [Revised: 11/28/2017] [Accepted: 12/18/2017] [Indexed: 11/22/2022]
Abstract
Despite efforts to simulate the in vivo environment, post-mortem degradation and lack of blood perfusion complicate the use of ex vivo derived material models in computational studies of spinal cord injury. In order to quantify the mechanical changes that manifest ex vivo, the viscoelastic behavior of in vivo and ex vivo porcine spinal cord samples were compared. Stress-relaxation data from each condition were fit to a non-linear viscoelastic model using a novel characterization technique called the direct fit method. To validate the presented material models, the parameters obtained for each condition were used to predict the respective dynamic cyclic response. Both ex vivo and in vivo samples displayed non-linear viscoelastic behavior with a significant increase in relaxation with applied strain. However, at all three strain magnitudes compared, ex vivo samples experienced a higher stress and greater relaxation than in vivo samples. Significant differences between model parameters also showed distinct relaxation behaviors, especially in non-linear relaxation modulus components associated with the short-term response (0.1-1 s). The results of this study underscore the necessity of utilizing material models developed from in vivo experimental data for studies of spinal cord injury, where the time-dependent properties are critical. The ability of each material model to accurately predict the dynamic cyclic response validates the presented methodology and supports the use of the in vivo model in future high-resolution finite element modeling efforts. STATEMENT OF SIGNIFICANCE Neural tissues (such as the brain and spinal cord) display time-dependent, or viscoelastic, mechanical behavior making it difficult to model how they respond to various loading conditions, including injury. Methods that aim to characterize the behavior of the spinal cord almost exclusively use ex vivo cadaveric or animal samples, despite evidence that time after death affects the behavior compared to that in a living animal (in vivo response). Therefore, this study directly compared the mechanical response of ex vivo and in vivo samples to quantify these differences for the first time. This will allow researchers to draw more accurate conclusions about spinal cord injuries based on ex vivo data (which are easier to obtain) and emphasizes the importance of future in vivo experimental animal work.
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Affiliation(s)
- Nicole L Ramo
- School of Biomedical Engineering, Colorado State University, Fort Collins, CO, USA
| | - Snehal S Shetye
- McKay Orthopaedic Research Laboratory, University of Pennsylvania, Philadelphia, PA, USA
| | - Femke Streijger
- International Collaboration on Repair Discoveries (ICORD), University of British Columbia, Vancouver, BC, Canada
| | - Jae H T Lee
- Department of Orthopaedics, University of British Columbia, Vancouver, BC, Canada
| | - Kevin L Troyer
- Department of Mechanical Engineering, Colorado State University, Fort Collins, CO, USA
| | - Brian K Kwon
- Department of Orthopaedics, University of British Columbia, Vancouver, BC, Canada; International Collaboration on Repair Discoveries (ICORD), University of British Columbia, Vancouver, BC, Canada
| | - Peter Cripton
- Department of Orthopaedics, University of British Columbia, Vancouver, BC, Canada; Department of Mechanical Engineering, University of British Columbia, Vancouver, BC, Canada; International Collaboration on Repair Discoveries (ICORD), University of British Columbia, Vancouver, BC, Canada
| | - Christian M Puttlitz
- School of Biomedical Engineering, Colorado State University, Fort Collins, CO, USA; Department of Mechanical Engineering, Colorado State University, Fort Collins, CO, USA; Department of Clinical Sciences, Colorado State University, Fort Collins, CO, USA.
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Fradet L, Cliche F, Petit Y, Mac-Thiong JM, Arnoux PJ. Strain rate dependent behavior of the porcine spinal cord under transverse dynamic compression. Proc Inst Mech Eng H 2016; 230:858-866. [DOI: 10.1177/0954411916655373] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The accurate description of the mechanical properties of spinal cord tissue benefits to clinical evaluation of spinal cord injuries and is a required input for analysis tools such as finite element models. Unfortunately, available data in the literature generally relate mechanical properties of the spinal cord under quasi-static loading conditions, which is not adapted to the study of traumatic behavior, as neurological tissue adopts a viscoelastic behavior. Thus, the objective of this study is to describe mechanical properties of the spinal cord up to mechanical damage, under dynamic loading conditions. A total of 192 porcine cervical to lumbar spinal cord samples were compressed in a transverse direction. Loading conditions included ramp tests at 0.5, 5 or 50 s−1 and cyclic loading at 1, 10 or 20 Hz. Results showed that spinal cord behavior was significantly influenced by strain rate. Mechanical damage occurred at 0.64, 0.68 and 0.73 strains for 0.5, 5 or 50 s−1 loadings, respectively. Variations of behavior between the tested strain rates were explained by cyclic loading results, which revealed behavior more or less viscous depending on strain rate. Also, a parameter (stress multiplication factor) was introduced to allow transcription of a stress–strain behavior curve to different strain rates. This factor was described and was significantly different for cervical, thoracic and lumbar vertebral heights, and for the strain rates evaluated in this study.
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Affiliation(s)
- Léo Fradet
- Département de Génie Mécanique, École Polytechnique de Montréal, Montréal, QC, Canada
- iLab-Spine (International Laboratory - Spine Imaging and Biomechanics), Montreal, Canada and Marseille, France
| | - Francis Cliche
- iLab-Spine (International Laboratory - Spine Imaging and Biomechanics), Montreal, Canada and Marseille, France
- Département de Génie Mécanique, École de technologie supérieure, Montréal, QC, Canada
- Research Center, Hôpital du Sacré-Coeur de Montréal, Montréal, QC, Canada
| | - Yvan Petit
- iLab-Spine (International Laboratory - Spine Imaging and Biomechanics), Montreal, Canada and Marseille, France
- Département de Génie Mécanique, École de technologie supérieure, Montréal, QC, Canada
- Research Center, Hôpital du Sacré-Coeur de Montréal, Montréal, QC, Canada
- Laboratoire de Biomécanique Appliquée, UMRT24 IFSTTAR, Université de la Méditerranée Aix-Marseille II, Marseille, France
| | - Jean-Marc Mac-Thiong
- iLab-Spine (International Laboratory - Spine Imaging and Biomechanics), Montreal, Canada and Marseille, France
- Research Center, Hôpital du Sacré-Coeur de Montréal, Montréal, QC, Canada
- Department of Surgery, Université de Montréal, Montréal, QC, Canada
| | - Pierre-Jean Arnoux
- iLab-Spine (International Laboratory - Spine Imaging and Biomechanics), Montreal, Canada and Marseille, France
- Laboratoire de Biomécanique Appliquée, UMRT24 IFSTTAR, Université de la Méditerranée Aix-Marseille II, Marseille, France
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15
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Jannesar S, Nadler B, Sparrey CJ. The Transverse Isotropy of Spinal Cord White Matter Under Dynamic Load. J Biomech Eng 2016; 138:2536524. [DOI: 10.1115/1.4034171] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2016] [Indexed: 01/31/2023]
Abstract
The rostral-caudally aligned fiber-reinforced structure of spinal cord white matter (WM) gives rise to transverse isotropy in the material. Stress and strain patterns generated in the spinal cord parenchyma following spinal cord injury (SCI) are multidirectional and dependent on the mechanism of the injury. Our objective was to develop a WM constitutive model that captures the material transverse isotropy under dynamic loading. The WM mechanical behavior was extracted from the published tensile and compressive experiments. Combinations of isotropic and fiber-reinforcing models were examined in a conditional quasi-linear viscoelastic (QLV) formulation to capture the WM mechanical behavior. The effect of WM transverse isotropy on SCI model outcomes was evaluated by simulating a nonhuman primate (NHP) contusion injury experiment. A second-order reduced polynomial hyperelastic energy potential conditionally combined with a quadratic reinforcing function in a four-term Prony series QLV model best captured the WM mechanical behavior (0.89 < R2 < 0.99). WM isotropic and transversely isotropic material models combined with discrete modeling of the pia mater resulted in peak impact forces that matched the experimental outcomes. The transversely isotropic WM with discrete pia mater resulted in maximum principal strain (MPS) distributions which effectively captured the combination of ipsilateral peripheral WM sparing, ipsilateral injury and contralateral sparing, and the rostral/caudal spread of damage observed in in vivo injuries. The results suggest that the WM transverse isotropy could have an important role in correlating tissue damage with mechanical measures and explaining the directional sensitivity of the spinal cord to injury.
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Affiliation(s)
- Shervin Jannesar
- Department of Mechatronic Systems Engineering, Simon Fraser University, 250-13450 102 Avenue, Surrey, BC V3T 0A3, Canada e-mail:
| | - Ben Nadler
- Department of Mechanical Engineering, University of Victoria, Victoria, BC, Canada e-mail:
| | - Carolyn J. Sparrey
- Department of Mechatronic Systems Engineering, Simon Fraser University, 250-13450 102 Avenue, Surrey, BC V3T 0A3, Canada
- International Collaboration on Repair Discoveries (ICORD), Vancouver, BC V5Z 1M9, Canada e-mail:
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Khuyagbaatar B, Kim K, Man Park W, Hyuk Kim Y. Biomechanical Behaviors in Three Types of Spinal Cord Injury Mechanisms. J Biomech Eng 2016; 138:2528303. [DOI: 10.1115/1.4033794] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2015] [Indexed: 01/08/2023]
Abstract
Clinically, spinal cord injuries (SCIs) are radiographically evaluated and diagnosed from plain radiographs, computed tomography (CT), and magnetic resonance imaging. However, it is difficult to conclude that radiographic evaluation of SCI can directly explain the fundamental mechanism of spinal cord damage. The von-Mises stress and maximum principal strain are directly associated with neurological damage in the spinal cord from a biomechanical viewpoint. In this study, the von-Mises stress and maximum principal strain in the spinal cord as well as the cord cross-sectional area (CSA) were analyzed under various magnitudes for contusion, dislocation, and distraction SCI mechanisms, using a finite-element (FE) model of the cervical spine with spinal cord including white matter, gray matter, dura mater with nerve roots, and cerebrospinal fluid (CSF). A regression analysis was performed to find correlation between peak von-Mises stress/peak maximum principal strain at the cross section of the highest reduction in CSA and corresponding reduction in CSA of the cord. Dislocation and contusion showed greater peak stress and strain values in the cord than distraction. The substantial increases in von-Mises stress as well as CSA reduction similar to or more than 30% were produced at a 60% contusion and a 60% dislocation, while the maximum principal strain was gradually increased as injury severity elevated. In addition, the CSA reduction had a strong correlation with peak von-Mises stress/peak maximum principal strain for the three injury mechanisms, which might be fundamental information in elucidating the relationship between radiographic and mechanical parameters related to SCI.
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Affiliation(s)
- Batbayar Khuyagbaatar
- Department of Mechanical Engineering, Kyung Hee University, 1 Seocheon-dong, Giheung-gu, Yongin-si, Gyeonggi-do 446-701, Korea e-mail:
| | - Kyungsoo Kim
- Department of Applied Mathematics, Kyung Hee University, 1 Seocheon-dong, Giheung-gu, Yongin-si, Gyeonggi-do 446-701, Korea e-mail:
| | - Won Man Park
- Department of Mechanical Engineering, Kyung Hee University, 1 Seocheon-dong, Giheung-gu, Yongin-si, Gyeonggi-do 446-701, Korea e-mail:
| | - Yoon Hyuk Kim
- Department of Mechanical Engineering, Kyung Hee University, 1 Seocheon-dong, Giheung-gu, Yongin-si, Gyeonggi-do 446-701, Korea e-mail:
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17
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Mechanical properties of the lamprey spinal cord: uniaxial loading and physiological strain. J Biomech 2013; 46:2194-200. [PMID: 23886481 DOI: 10.1016/j.jbiomech.2013.06.028] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Revised: 06/26/2013] [Accepted: 06/28/2013] [Indexed: 11/22/2022]
Abstract
During spinal cord injury, nerves suffer a strain beyond their physiological limits which damages and disrupts their structure. Research has been done to measure the modulus of the spinal cord and surrounding tissue; however the relationship between strain and spinal cord fibers is still unclear. In this work, our objective is to measure the stress-strain response of the spinal cord in vivo and in vitro and model this response as a function of the number of fibers. We used the larvae lamprey (Petromyzon Marinus), a model for spinal cord regeneration and animal locomotion. We found that physiologically the spinal cord is pre-stressed to a longitudinal strain of 10% and this strain increases to 15% during swimming. Tensile measurements show that uniaxial, longitudinal loading is independent of the meninges. Stress values for uniaxial strains below 18%, are homogeneous through the length of the body. However, for higher uniaxial strains the Head section shows more resistance to longitudinal loading than the Tail. These data, together with the number of fibers obtained from histological sections were used in a composite-material model to obtain the properties of the spinal cord fibers (2.4 MPa) and matrix (0.017 MPa) to uniaxial longitudinal loading. This model allowed us to approximate the percentage of fibers in the spinal cord, establishing a relationship between uniaxial longitudinal strains and spinal cord composition. We showed that there is a proportional relationship between the number of fibers and the properties of the spinal cord at large uniaxial strains.
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18
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Kroeker SG, Ching RP. Coupling between the spinal cord and cervical vertebral column under tensile loading. J Biomech 2013; 46:773-9. [DOI: 10.1016/j.jbiomech.2012.11.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2012] [Revised: 11/03/2012] [Accepted: 11/09/2012] [Indexed: 11/26/2022]
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19
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Building biocompatible hydrogels for tissue engineering of the brain and spinal cord. J Funct Biomater 2012; 3:839-63. [PMID: 24955749 PMCID: PMC4030922 DOI: 10.3390/jfb3040839] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2012] [Accepted: 10/24/2012] [Indexed: 01/07/2023] Open
Abstract
Tissue engineering strategies employing biomaterials have made great progress in the last few decades. However, the tissues of the brain and spinal cord pose unique challenges due to a separate immune system and their nature as soft tissue. Because of this, neural tissue engineering for the brain and spinal cord may require re-establishing biocompatibility and functionality of biomaterials that have previously been successful for tissue engineering in the body. The goal of this review is to briefly describe the distinctive properties of the central nervous system, specifically the neuroimmune response, and to describe the factors which contribute to building polymer hydrogels compatible with this tissue. These factors include polymer chemistry, polymerization and degradation, and the physical and mechanical properties of the hydrogel. By understanding the necessities in making hydrogels biocompatible with tissue of the brain and spinal cord, tissue engineers can then functionalize these materials for repairing and replacing tissue in the central nervous system.
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20
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Galle B, Ouyang H, Shi R, Nauman E. A transversely isotropic constitutive model of excised guinea pig spinal cord white matter. J Biomech 2010; 43:2839-43. [PMID: 20832804 DOI: 10.1016/j.jbiomech.2010.06.014] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2010] [Revised: 04/15/2010] [Accepted: 06/12/2010] [Indexed: 10/19/2022]
Abstract
Narrowing of the spinal canal generates an amalgamation of stresses within the spinal cord parenchyma. The tissue's stress state cannot be quantified experimentally; it must be described using computational methods, such as finite element analysis. The objective of this research was to propose a compressible, transversely isotropic constitutive model, an augmentation of the isotropic Mooney-Rivlin hyperelastic strain energy function, to describe the guinea pig spinal cord white matter. Model parameters were derived from a combination of inverse finite element analysis on transverse compression experiments and least squared error analysis applied to quasi-static longitudinal tensile tests. A comparison of the residual errors between the predicted response and the experimental measurements indicated that the transversely isotropic constitutive law that incorporates an offset stretch reduced the error by a factor of four when compared to other commonly used models.
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Affiliation(s)
- Beth Galle
- School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907, USA
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21
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Sparrey CJ, Manley GT, Keaveny TM. Effects of white, grey, and pia mater properties on tissue level stresses and strains in the compressed spinal cord. J Neurotrauma 2009; 26:585-95. [PMID: 19292657 DOI: 10.1089/neu.2008.0654] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Recent demographics demonstrate an increase in the number of elderly spinal cord injury patients, motivating the desire for a better understanding of age effects on injury susceptibility. Knowing that age and disease affect neurological tissue, there is a need to better understand the sensitivity of spinal cord injury mechanics to variations in tissue behavior. To address this issue, a plane-strain, geometrically nonlinear, finite element model of a section of a generic human thoracic spinal cord was constructed to model the response to dorsal compression. The material models and stiffness responses for the grey and white matter and pia mater were varied across a range of reported values to observe the sensitivity of model outcomes to the assigned properties. Outcome measures were evaluated for percent change in magnitude and alterations in spatial distribution. In general, principal stresses (114-244% change) and pressure (75-119% change) were the outcomes most sensitive to material variation. Strain outcome measures were less sensitive (7-27% change) than stresses (74-244% change) to variations in material tangent modulus. The pia mater characteristics had limited (<4% change) effects on outcomes. Using linear elastic models to represent non-linear behavior had variable effects on outcome measures, and resulted in highly concentrated areas of elevated stresses and strains. Pressure measurements in both the grey and white matter were particularly sensitive to white matter properties, suggesting that degenerative changes in white matter may influence perfusion in a compressed spinal cord. Our results suggest that the mechanics of spinal cord compression are likely to be affected by changes in tissue resulting from aging and disease, indicating a need to study the biomechanical aspects of spinal cord injury in these specific populations.
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Affiliation(s)
- Carolyn J Sparrey
- Department of Mechanical Engineering, University of California-Berkeley, Berkeley, California 94720-1740, USA
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22
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Clarke EC, Cheng S, Bilston LE. The mechanical properties of neonatal rat spinal cord in vitro, and comparisons with adult. J Biomech 2009; 42:1397-1402. [PMID: 19442976 DOI: 10.1016/j.jbiomech.2009.04.008] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2008] [Revised: 04/06/2009] [Accepted: 04/07/2009] [Indexed: 11/25/2022]
Abstract
A number of studies have investigated the mechanical properties of adult spinal cord under tension, however it is not known whether age has an effect on these properties. This is of interest to those aiming to understand the clinical differences between adults and children with spinal cord injury (e.g. severity and recovery), and those developing experimental or computational models for paediatric spinal cord injury. Entire spinal cords were freshly harvested from neonatal rats (14 days) and tested in vitro under uniaxial tension at a range of strain rates (0.2, 0.02, 0.002/s) to a range of strains (2%, 3.5%, 5%), with relaxation responses being recorded for 15 min. These mechanical properties were compared to previously reported data from similar experiments on adult rat spinal cords, and the peak stress and the stress after 15 min of relaxation were found to be significantly higher for spinal cords from adults than neonates (p<0.001). A non-linear viscoelastic model was developed and was observed to adequately predict the mechanical behaviour of this tissue. The model developed in this study may be of use in computational models of paediatric spinal cord. The significant differences between adult and neonatal spinal cord properties may explain the higher initial severity of spinal cord injury in children and may have implications for the development of experimental animal models for paediatric spinal cord injury, specifically for those aiming to match the injury severity with adult experimental models.
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Affiliation(s)
- Elizabeth C Clarke
- Prince of Wales Medical Research Institute, University of New South Wales, Randwick, NSW 2031, Sydney, Australia.
| | - Shaokoon Cheng
- Prince of Wales Medical Research Institute, University of New South Wales, Randwick, NSW 2031, Sydney, Australia
| | - Lynne E Bilston
- Prince of Wales Medical Research Institute, University of New South Wales, Randwick, NSW 2031, Sydney, Australia.
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Gene expression profiles of neurotrophic factors in rat cultured spinal cord cells under cyclic tensile stress. Spine (Phila Pa 1976) 2008; 33:2596-604. [PMID: 18981959 DOI: 10.1097/brs.0b013e31818917af] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
STUDY DESIGN An experimental study to investigate the in vitro gene expression of neurotrophic factors and receptors in cultured rat spinal cord cells subjected to cyclic mechanical stretch forces. OBJECTIVE We evaluated in vitro expression of neurotrophic factors and receptors in cultured rat spinal cord cells under cyclic tensile stress. SUMMARY OF BACKGROUND DATA Application of compressive mechanical stress to the spinal cord results in multiple changes making it difficult to examine the expression of neurotrophic factors and their receptors. There are no in vitro studies that investigated the biologic responses of cultured spinal cord cells to tensile stress. METHODS Spinal cord cells were isolated for culture from 15-day Sprague-Dawley rat embryos. We used the FX3000 Flexercell Strain Unit to induce mechanical stress. We analyzed the effects of mechanical stress on cell morphology, mRNA expression levels of various neurotrophic factors, and their immunoreactivities at 0, 2, 6, 12, 24, and 36 hours. RESULTS Tensile stress for 6 hours resulted in reduction of spinal cord cells and loss of neurites. Cells that survived 24-hours stress showed swollen irregular-shaped soma, bleb formation, and fragmented neurites. The cell survival rate decreased, whereas lactate dehydrogenase release increased significantly at 6 hours. There were significant increases in mRNA expression levels of nerve growth factor, brain-derived neurotrophic factor, trkB, p75 neurotrophin receptor (p75), glial cell line-derived neurotrophic factor, and caspase-9 during the early period after application of tensile stress. CONCLUSION Our results suggest survival of spinal cord neuronal cells under injurious tensile stress with increased synthesis and utilization of several neurotrophic factors, receptors, and expression of proteins related to cell apoptosis.
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Bueno FR, Shah SB. Implications of Tensile Loading for the Tissue Engineering of Nerves. TISSUE ENGINEERING PART B-REVIEWS 2008; 14:219-33. [DOI: 10.1089/ten.teb.2008.0020] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- Franklin Rivera Bueno
- Fischell Department of Bioengineering, University of Maryland, College Park, Maryland
| | - Sameer B. Shah
- Fischell Department of Bioengineering, University of Maryland, College Park, Maryland
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The effect of cerebrospinal fluid on the biomechanics of spinal cord: an ex vivo bovine model using bovine and physical surrogate spinal cord. Spine (Phila Pa 1976) 2008; 33:E580-8. [PMID: 18670325 DOI: 10.1097/brs.0b013e31817ecc57] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
STUDY DESIGN A biomechanical study using ex vivo bovine spinal cord and dura, and a synthetic surrogate spinal cord with bovine dura. OBJECTIVE To investigate the effect of cerebrospinal fluid (CSF) on spinal cord deformation characteristics and to evaluate the biofidelity of a new surrogate spinal cord using an ex vivo bovine model of the burst fracture process. SUMMARY OF BACKGROUND DATA Spinal cord injury is associated with significant personal, economic and social costs. The role of CSF during the injury event and its effect on the spinal cord deformation and neurologic injury is not well understood. Such knowledge could inform preventative strategies and clinical interventions and aid the development and validation of experimental and computational models. METHODS The transverse impact of a propelled bone fragment analogue with bovine and surrogate cord models was recorded with high speed video and the images analyzed to determine deformation trajectories. Each cord specimen was tested in 3 states: with dura and CSF, with dura only, and without dura. The effect of these states on deformation magnitude, duration, and energy loss parameters was assessed. RESULTS.: The estimated spinal cord deformation was significantly reduced, although not eliminated, in the presence of CSF when compared to the bare state. The duration of deformation was generally increased in the presence of CSF, though this difference was not statistically significant. This may indicate a reduction in the cord-fragment interaction force for a given impulse. The dura was found to have no significant effect on deformation parameters for the bovine spinal cord. The deformation of the surrogate cord gave similar trends for the different states in comparison to the bovine cord, but was significantly less than the bovine spinal cord for all conditions. CONCLUSION The results indicate that the protective mechanism of CSF may not eliminate cord deformationunder the high energy transverse impact characteristic of a burst fracture. However, CSF may contribute to a lessening of cord deformation and applied force.
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Cheng S, Clarke EC, Bilston LE. Rheological properties of the tissues of the central nervous system: a review. Med Eng Phys 2008; 30:1318-37. [PMID: 18614386 DOI: 10.1016/j.medengphy.2008.06.003] [Citation(s) in RCA: 144] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2008] [Revised: 05/23/2008] [Accepted: 06/01/2008] [Indexed: 10/21/2022]
Abstract
Knowledge of the biomechanical properties of central nervous system (CNS) tissues is important for understanding mechanisms and thresholds for injury, and aiding development of computer or surrogate models of these tissues. Many investigations have been conducted to estimate the properties of CNS tissues including under shear, compressive and tensile loading, however there is much variability in this body of literature, making it difficult to separate the material properties from effects that result from a given experimental protocol. This review summarises previous studies of brain and spinal cord properties; discussing their main findings and points of difference, and displays the reported data on comparable scales. Additionally, based on the observed effects of methodological choices on reported tissue properties, recommendations for future studies of brain and spinal cord properties are made.
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Affiliation(s)
- Shaokoon Cheng
- Prince of Wales Medical Research Institute, University of New South Wales, Barker Street, Randwick, Sydney, NSW, 2031, Australia
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Chu WCW, Lam WMW, Ng BKW, Tze-ping L, Lee KM, Guo X, Cheng JCY, Burwell RG, Dangerfield PH, Jaspan T. Relative shortening and functional tethering of spinal cord in adolescent scoliosis - Result of asynchronous neuro-osseous growth, summary of an electronic focus group debate of the IBSE. SCOLIOSIS 2008; 3:8. [PMID: 18588673 PMCID: PMC2474583 DOI: 10.1186/1748-7161-3-8] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/25/2008] [Accepted: 06/27/2008] [Indexed: 12/17/2022]
Abstract
There is no generally accepted scientific theory for the causes of adolescent idiopathic scoliosis (AIS). As part of its mission to widen understanding of scoliosis etiology, the International Federated Body on Scoliosis Etiology (IBSE) introduced the electronic focus group (EFG) as a means of increasing debate on knowledge of important topics. This has been designated as an on-line Delphi discussion. The Statement for this debate was written by Dr WCW Chu and colleagues who examine the spinal cord to vertebral growth interaction during adolescence in scoliosis. Using the multi-planar reconstruction technique of magnetic resonance imaging they investigated the relative length of spinal cord to vertebral column including ratios in 28 girls with AIS (mainly thoracic or double major curves) and 14 age-matched normal girls. Also evaluated were cerebellar tonsillar position, somatosensory evoked potentials (SSEPs), and clinical neurological examination. In severe AIS compared with normal controls, the vertebral column is significantly longer without detectable spinal cord lengthening. They speculate that anterior spinal column overgrowth relative to a normal length spinal cord exerts a stretching tethering force between the two ends, cranially and caudally leading to the initiation and progression of thoracic AIS. They support and develop the Roth-Porter concept of uncoupled neuro-osseous growth in the pathogenesis of AIS which now they prefer to term 'asynchronous neuro-osseous growth'. Morphological evidence about the curve apex suggests that the spinal cord is also affected, and a 'double pathology' is suggested. AIS is viewed as a disorder with a wide spectrum and a common neuroanatomical abnormality namely, a spinal cord of normal length but short relative to an abnormally lengthened anterior vertebral column. Neuroanatomical changes and/or abnormal neural function may be expressed only in severe cases. This asynchronous neuro-osseous growth concept is regarded as one component of a larger concept. The other component relates to the brain and cranium of AIS subjects because abnormalities have been found in brain (infratentorial and supratentorial) and skull (vault and base). The possible relevance of systemic melatonin-signaling pathway dysfunction, platelet calmodulin levels and putative vertebral vascular biology to the asynchronous neuro-osseous growth concept is discussed. A biomechanical model to test the spinal component of the concept is in hand. There is no published research on the biomechanical properties of the spinal cord for scoliosis specimens. Such research on normal spinal cords includes movements (kinematics), stress-strain responses to uniaxial loading, and anterior forces created by the stretched cord in forward flexion that may alter sagittal spinal shape during adolescent growth. The asynchronous neuro-osseous growth concept for the spine evokes controversy. Dr Chu and colleagues respond to five other concepts of pathogenesis for AIS and suggest that relative anterior spinal overgrowth and biomechanical growth modulation may also contribute to AIS pathogenesis.
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Affiliation(s)
- Winnie CW Chu
- Department of Diagnostic Radiology and Organ Imaging, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong, PR China
| | - Wynnie MW Lam
- Department of Diagnostic Radiology and Organ Imaging, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong, PR China
| | - Bobby KW Ng
- Orthopaedics and Traumatology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong, PR China
| | - Lam Tze-ping
- Orthopaedics and Traumatology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong, PR China
| | - Kwong-man Lee
- Orthopaedics and Traumatology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong, PR China
| | - Xia Guo
- Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hong Kong, PR China
| | - Jack CY Cheng
- Orthopaedics and Traumatology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong, PR China
| | - R Geoffrey Burwell
- The Centre for Spinal Studies & Surgery, Nottingham University Hospitals Trust, Queen's Medical Centre Campus, Nottingham NG7 2UH, UK
| | | | - Tim Jaspan
- Department of Radiology, Nottingham University Hospitals Trust, Queen's Medical Centre Campus, Nottingham NG7 2UH, UK
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Greaves CY, Gadala MS, Oxland TR. A three-dimensional finite element model of the cervical spine with spinal cord: an investigation of three injury mechanisms. Ann Biomed Eng 2008; 36:396-405. [PMID: 18228144 DOI: 10.1007/s10439-008-9440-0] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2006] [Accepted: 01/10/2008] [Indexed: 10/22/2022]
Abstract
The spinal cord may be injured through various spinal column injury patterns (e.g., burst fracture, fracture dislocation); however, the relationship between column injury pattern and cord damage is not well understood. A three-dimensional finite element model of a human cervical spine and spinal cord segment was developed, verified using published experimental data, and used to investigate differences in cord strain distributions during various column injury patterns. For a transverse contusion injury, as would occur in a burst fracture, a 33% canal occlusion resulted in two peaks of strain between the indentor and opposing vertebral body and intermediate peak strain values. For a distraction injury, relevant to column distortion injuries, a 2.6 mm axial displacement to the cord resulted in more uniform strains throughout the cord and low peak strain values. For a dislocation injury, as would occur in a fracture dislocation, an anterior displacement of C5 corresponding to 30% of the sagittal dimension of the vertebral body resulted in high peak strain values adjacent to the shearing vertebrae and increased strains in the lateral columns compared to contusion. This model includes more anatomical details compared to previous studies and provides a baseline for mechanical comparisons in spinal cord injury.
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Affiliation(s)
- Carolyn Y Greaves
- Division of Orthopaedic Engineering Research, Departments of Mechanical Engineering and Orthopaedics, University of British Columbia, #566-828 West 10th Ave, Vancouver, BC, Canada
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Oakland RJ, Hall RM, Wilcox RK, Barton DC. The biomechanical response of spinal cord tissue to uniaxial loading. Proc Inst Mech Eng H 2006; 220:489-92. [PMID: 16808065 DOI: 10.1243/09544119jeim135] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The spinal cord is an integral component of the spinal column and is prone to physical injury during trauma or more long-term pathological insults. The development of computational models to simulate the cord-column interaction during trauma is important in developing a proper understanding of the injury mechanism. Such models would be invaluable in seeking both preventive strategies that reduce the propensity for injury and identifying specific treatment regimes. However, these developments are hampered by the limited information available on the structural and mechanical properties of this soft tissue owing to the difficulty in handling this material in a cadaveric situation. The purpose of the present paper is to report the rapid deterioration in the quality of the tissues once excised, which provides a further challenge to the successful elucidation of the structural properties of the tissue. In particular, the tangent modulus of the tissue is seen to increase sharply over a period of 72 h.
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Affiliation(s)
- R J Oakland
- School of Mechanical Engineering, University of Leeds, Leeds, UK
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Fiford RJ, Bilston LE. The mechanical properties of rat spinal cord in vitro. J Biomech 2005; 38:1509-15. [PMID: 15922762 DOI: 10.1016/j.jbiomech.2004.07.009] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2003] [Accepted: 07/19/2004] [Indexed: 11/29/2022]
Abstract
Freshly excised rat spinal cords were tested in uniaxial tension, in vitro, at strain rates ranging from 0.002 to 0.2 s-1. Stress relaxation tests were performed for a range of strains from 2% to 5%, with the relaxation behaviour being recorded for a period of at least 30 min. Samples exhibited a characteristic "J" shaped non-linear stress-strain response, with stiffness increasing with applied strain. The cords were labelled with rows of small markers and the uniaxial tension tests were recorded via video. Subsequent image analysis enabled the distribution of strain on the cord surface to be determined. Viscoelastic models were developed to model the mechanical behaviour of the specimens and were found to adequately describe the material behaviour.
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Affiliation(s)
- Rodney J Fiford
- School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney, New South Wales, 2006, Australia.
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Bilston LE. The effect of perfusion on soft tissue mechanical properties: a computational model. Comput Methods Biomech Biomed Engin 2002; 5:283-90. [PMID: 12186707 DOI: 10.1080/10255840290032658] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
Some simple finite element models were constructed to investigate the magnitude and character of changes in mechanical properties of very soft tissues due to the loss of perfusion. Changes in the apparent stress-strain curve were used to characterise the effect of simulated blood perfusion pressure on the engineering stress-strain curve. The results indicated that the blood to tissue volume ratio and the perfusion pressure have the strongest effect on the effective stress-strain response of a representative tissue cell. Tissue viscoelasticity increased the sensitivity of the system to perfusion pressure changes.
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Affiliation(s)
- Lynne E Bilston
- School of Aerospace, Mechanical and Mechatronic Engineering, Building J07, University of Sydney, NSW 2006, Sydney, Australia.
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Bilston LE, Thibault LE. The mechanical properties of the human cervical spinal cord in vitro. Ann Biomed Eng 1996; 24:67-74. [PMID: 8669719 DOI: 10.1007/bf02770996] [Citation(s) in RCA: 142] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The response of spinal cord tissue to mechanical loadings is not well understood. In this study, isolated fresh cervical spinal cord samples were obtained from cadavers at autopsy and tested in uniaxial tension at moderate strain rates. Stress relaxation experiments were performed with an applied strain rate and peak strain in the physiological range, similar to those seen in the spinal cord during voluntary motion. The spinal cord samples exhibited a nonlinear stress-strain response with increasing strain increasing the tangent modulus. In addition, significant relaxation was observed over 1 min. A quasilinear viscoelastic model was developed to describe the behavior of the spinal cord tissue and was found to describe the material behavior adequately. The data also were fitted to both hyperelastic and viscoelastic fluid models for comparison with other data in the literature.
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Affiliation(s)
- L E Bilston
- Department of Mechanical and Mechatronic Engineering, University of Sydney, Australia
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Hung TK, Chang GL, Lin HS, Walter FR, Bunegin L. Stress-strain relationship of the spinal cord of anesthetized cats. J Biomech 1981; 14:269-76. [PMID: 7240289 DOI: 10.1016/0021-9290(81)90072-5] [Citation(s) in RCA: 33] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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