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ABSTRACT: Planar biaxial tension remains a critical loading modality for fibrous soft tissue and is widely used to characterize tissue mechanical response, evaluate treatments, develop constitutive formulas, and obtain material properties for use in finite element studies. Although the application of tension on all edges of the test specimen represents the in situ environment, there remains a need to address the interpretation of experimental results. Unlike uniaxial tension, in biaxial tension the applied forces at the loading clamps do not transmit fully to the region of interest (ROI), which may lead to improper material characterization if not accounted for. In this study, we reviewed the tensile biaxial literature over the last ten years, noting experimental and analysis challenges. In response to these challenges, we used finite element simulations to quantify load transmission from the clamps to the ROI in biaxial tension and to formulate a correction factor that can be used to determine ROI stresses. Additionally, the impact of sample geometry, material anisotropy, and tissue orientation on the correction factor were determined. Large stress concentrations were evident in both square and cruciform geometries and for all levels of anisotropy. In general, stress concentrations were greater for the square geometry than the cruciform geometry. For both square and cruciform geometries, materials with fibers aligned parallel to the loading axes reduced stress concentrations compared to the isotropic tissue, resulting in more of the applied load being transferred to the ROI. In contrast, fiber-reinforced specimens oriented such that the fibers aligned at an angle to the loading axes produced very large stress concentrations across the clamps and shielding in the ROI. A correction factor technique was introduced that can be used to calculate the stresses in the ROI from the measured experimental loads at the clamps. Application of a correction factor to experimental biaxial results may lead to more accurate representation of the mechanical response of fibrous soft tissue.
Journal of Biomechanical Engineering 02/2013; 135(2):021004. · 1.90 Impact Factor
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ABSTRACT: Experimental measurement and normalization of in vitro disc torsion mechanics and collagen content for several animal species used in intervertebral disc research and comparing these with the human disc.
To aid in the selection of appropriate animal models for disc research by measuring torsional mechanical properties and collagen content.
There is lack of data and variability in testing protocols for comparing animal and human disc torsion mechanics and collagen content.
Intervertebral disc torsion mechanics were measured and normalized by disc height and polar moment of inertia for 11 disc types in 8 mammalian species: the calf, pig, baboon, goat, sheep, rabbit, rat, and mouse lumbar discs, and cow, rat, and mouse caudal discs. Collagen content was measured and normalized by dry weight for the same discs except the rat and the mouse. Collagen fiber stretch in torsion was calculated using an analytical model.
Measured torsion parameters varied by several orders of magnitude across the different species. After geometric normalization, only the sheep and pig discs were statistically different from human discs. Fiber stretch was found to be highly dependent on the assumed initial fiber angle. The collagen content of the discs was similar, especially in the outer annulus where only the calf and goat discs were statistically different from human. Disc collagen content did not correlate with torsion mechanics.
Disc torsion mechanics are comparable with human lumbar discs in 9 of 11 disc types after normalization by geometry. The normalized torsion mechanics and collagen content of the multiple animal discs presented are useful for selecting and interpreting results for animal disc models. Structural organization of the fiber angle may explain the differences that were noted between species after geometric normalization.
Spine 02/2012; 37(15):E900-7. · 2.08 Impact Factor
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ABSTRACT: This review challenges an earlier view that the intervertebral joint could not be classified as a diarthrodial joint and should remain as an amphiarthrosis. However, a careful analysis of the relevant literature and in light of more recent studies, it is clear that while some differences exist between the spinal articulation and the generic synovial joint, there are clear structural, functional and developmental similarities between the joints that in sum outweigh the differences. Further, since the intervertebral motion segment displays movement in three dimensions and the whole spine itself provides integrated rotatory movements, it is proposed that it should be classified not as an amphiarthrose, "a slightly moveable joint" but as a complex polyaxial joint. Hopefully, reclassification will encourage further analysis of the structure and function of the two types of overlapping joints and provide common new insights into diseases that afflict the many joints of the human skeleton.
Bone 12/2011; 50(3):771-6. · 4.02 Impact Factor
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ABSTRACT: The intervertebral disc maintains a balance between externally applied loads and internal osmotic pressure. Fluid flow plays a key role in this process, causing fluctuations in disc hydration and height. The objectives of this study were to quantify and model the axial creep and recovery responses of nondegenerate and degenerate human lumbar discs. Two experiments were performed. First, a slow compressive ramp was applied to 2000 N, unloaded to allow recovery for up to 24 h, and re-applied. The linear-region stiffness and disc height were within 5% of the initial condition for recovery times greater than 8 h. In the second experiment, a 1000 N creep load was applied for four hours, unloaded recovery monitored for 24 h, and the creep load repeated. A viscoelastic model comprised of a "fast" and "slow" exponential response was used to describe the creep and recovery, where the fast response is associated with flow in the nucleus pulposus (NP) and endplate, while the slow response is associated with the annulus fibrosus (AF). The study demonstrated that recovery is 3-4X slower than loading. The fast response was correlated with degeneration, suggesting larger changes in the NP with degeneration compared to the AF. However, the fast response comprised only 10%-15% of the total equilibrium displacement, with the AF-dominated slow response comprising 40%-70%. Finally, the physiological loads and deformations and their associated long equilibrium times confirm that diurnal loading does not represent "equilibrium" in the disc, but that over time the disc is in steady-state.
Journal of the mechanical behavior of biomedical materials. 10/2011; 4(7):933-42.
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ABSTRACT: The primary function of the disc is mechanical; therefore, degenerative changes in disc mechanics and the interactions between the annulus fibrosus (AF) and nucleus pulposus (NP) in nondegenerate and degenerate discs are important to functional evaluation. The disc experiences complex loading conditions, including mechanical interactions between the pressurized NP and the surrounding fiber-reinforced AF. Our objective was to noninvasively evaluate the internal deformations of nondegenerate and degenerate human discs under axial compression with flexion, neutral, and extension positions using magnetic resonance imaging and image correlation. The side of applied bending (e.g., anterior AF in flexion) had higher tensile radial and compressive axial strains, and the opposite side of bending exhibited tensile axial strains even though the disc was loaded under axial compression. Degenerated discs exhibited higher compressive axial and tensile radial strains, which suggest that load distribution through the disc subcomponents are altered with degeneration, likely due to the depressurized NP placing more of the applied load directly on the AF. The posterior AF exhibited higher compressive axial and higher tensile radial strains than the other AF regions, and the strains were not correlated with degeneration, suggesting this region undergoes high strains throughout life, which may predispose it to failure and tears. In addition to understanding internal disc mechanics, this study provides important new data into the changes in internal strain with degeneration, data for validation of finite element models, and provides a technique and baseline data for evaluating surgical treatments.
Journal of Orthopaedic Research 04/2011; 29(4):547-55. · 2.81 Impact Factor
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ABSTRACT: Biomechanics of human intervertebral discs before and after nucleotomy.
To noninvasively quantify the effect of nucleotomy on internal strains under axial compression in flexion, neutral, and extension positions, and to determine whether the change in strains depended on degeneration.
Herniation and nucleotomy may accelerate the progression of disc degeneration. Removal of nucleus pulposus (NP) tissue has resulted in altered disc mechanics in vitro, including a decrease in internal pressure and an increase in the deformations at physiologically relevant strains. We recently presented a technique to quantify internal disc strains using magnetic resonance imaging (MRI).
Degeneration was quantitatively assessed by the T1ρ relaxation time in the NP. Samples were prepared from human levels L3-L4 and/or L4-L5. A 1000-N compressive load was applied while in the magnetic resonance scanner. Nucleotomy was performed by removing 2 g of NP through the posterior-lateral annulus fibrosus (AF). The discs were rehydrated, reimaged, and retested. The analyzed parameters include axial deformation, AF radial bulge, and strains. RESULTS.: The axial deformation was more compressive after nucleotomy. In the neutral position, the axial deformation after nucleotomy correlated with degeneration (as quantified by T1ρ in the NP), with minimal alteration in nondegenerated discs. Nucleotomy altered the radial displacements and strains in the neutral position, such that the inner AF radial bulge decreased and the radial strains were more tensile in the lateral AF and less tensile in the posterior AF. In the bending loading positions the radial strains were not affected by nucleotomy.
Nucleotomy alters the internal radial and axial AF strains in the neutral position, which may leave the AF vulnerable to damage and microfractures. In bending, the effects of nucleotomy were minimal, likely due to more of the applied load being directed over the AF. Some of the nucleotomy effects are modulated by degeneration, where the mechanical effect of nucleotomy was magnified in degenerated discs and may further induce mechanical damage and degeneration.
Spine 03/2011; 36(21):1765-71. · 2.08 Impact Factor
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ABSTRACT: Early diagnosis is a challenge in the treatment of degenerative disc disease. A noninvasive biomarker detecting functional mechanics of the disc is needed. T1rho-weighted imaging, a spin-lock magnetic resonance imaging technique, has shown promise for meeting this need in in vivo studies demonstrating the clinical feasibility of evaluating both intervertebral discs and articular cartilage. The objectives of the present study were (1) to quantitatively determine the relationship between T1rho relaxation time and measures of nucleus pulposus mechanics, and (2) to evaluate whether the quantitative relationship of T1rho relaxation time with the degenerative grade and glycosaminoglycan content extend to more severe degeneration. It was hypothesized that the isometric swelling pressure and compressive modulus would be directly correlated with the T1rho relaxation time and the apparent permeability would be inversely correlated with the T1rho relaxation time.
Eight cadaver human lumbar spines were imaged to measure T1rho relaxation times. The nucleus pulposus tissue from the L1 disc through the S1 disc was tested in confined compression to determine the swelling pressure, compressive modulus, and permeability. The glycosaminoglycan and water contents were measured in adjacent tissue. Linear regression analyses were performed to examine the correlation between the T1rho relaxation time and the other measured variables. Mechanical properties and biochemical content were evaluated for differences associated with degeneration.
A positive linear correlation was observed between the T1rho relaxation time on the images of the nucleus pulposus and the swelling pressure (r = 0.59), glycosaminoglycan content per dry weight (r = 0.69), glycosaminoglycan per wet weight (r = 0.49), and water content (r = 0.53). No significant correlations were observed between the T1rho relaxation time and the modulus or permeability. Similarly, the T1rho relaxation time, swelling pressure, glycosaminoglycan content per dry weight, and water content were significantly altered with degeneration, whereas the modulus and permeability were not.
T1rho-weighted magnetic resonance imaging has a strong potential as a quantitative biomarker of the mechanical function of the nucleus pulposus and of disc degeneration.
The Journal of Bone and Joint Surgery 05/2008; 90(4):796-802. · 3.27 Impact Factor
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ABSTRACT: Biomechanical study and literature review.
To quantify the acute effect of needle diameter on the in vitro mechanical properties of cadaver lumbar discs in the rat and sheep. To review published in vivo animal studies and evaluate disc changes with respect to the relative needle size.
There are many cases where a disc needle puncture or injection is applied to animal models: puncture injuries to induce degeneration, chemonucleolysis to induce degeneration, and delivery of disc therapies. It is not clear what role the size of the needle may have in the outcome.
Mechanics were measured after sham phosphate buffered saline injection with a 27 G or 33 G needle in the rat and with a 27 G needle in the sheep. A literature review was performed to evaluate studies in which animal discs were treated with a needle puncture or a sham injection. For each study, the ratio of the needle diameter to disc height (needle:height) was calculated.
When the rat was injected with a 27 G needle (52% of disc height), the compression, tension, and neutral zone stiffnesses were 20% to 60% below preinjected values and the neutral zone length was 130% higher; when injected with a 33 G needle (26% of disc height), the only affected property was the neutral zone length, which was only 20% greater. When the sheep was injected with a 27 G needle (10% of disc height), none of the axial properties were different from intact, the torsion stiffness was not different, and the torque range was 15% smaller. Twenty-three in vivo studies in the rat, rabbit, dog, or sheep were reviewed. The disc changes depended on the ratio of needle diameter to disc height as follows: significant changes were not observed for needle:height less than 40%, although between 25% and 40% results were variable and some minor nonsignificant effects were observed, disc changes were universal for needle:height over 40%.
A needle puncture may directly alter mechanical properties via nucleus pulposus depressurization and/or anulus fibrosus damage, depending on the relative needle size. As more basic science research is aimed at treating disc degeneration via injection of therapeutic factors, these findings provide guidance in design of animal studies. Such studies should consider the relative needle size and include sham control groups to account for the potential effects of the needle injection.
Spine 04/2008; 33(6):588-96. · 2.08 Impact Factor
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ABSTRACT: Experimental measurement and normalization of in vitro disc axial compression mechanics and glycosaminoglycan and water content for several animal species used in intervertebral disc research.
To compare normalized axial mechanical properties and glycosaminoglycan and water content from other species to those of the human disc to aid in selection and interpretation of results in animal disc studies.
There is a lack of mechanical and biochemical comparative data from animal intervertebral discs with respect to the human disc.
Intervertebral disc axial mechanical properties, glycosaminoglycan, and water content were evaluated for 9 disc types in 7 mammalian species: the calf, pig, baboon, sheep, rabbit, rat and mouse lumbar, and the cow and rat tail. Disc area and height were used for calculation of the normalized mechanical parameters. Glycosaminoglycan content was normalized by dry weight.
Many directly measured mechanical parameters varied by orders of magnitude. However, these parameters became comparable and often did not show significant differences after geometric normalization. Both glycosaminoglycan and water content revealed similarity across species.
Disc axial mechanics are very similar across animal species when normalizing by the geometric parameters of disc height and area. This suggests that the disc tissue material properties are largely conserved across animal species. These results provide a reference to compare disc axial mechanics and glycosaminoglycan and water composition of experimental animal models to the human lumbar disc, to aid in both selection and interpretation of experimental disc research.
Spine 04/2008; 33(6):E166-73. · 2.08 Impact Factor
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ABSTRACT: Internal deformations and strains were measured within intact human motion segments.
Quantify 2-dimensional internal deformation and strain in compression of human intervertebral discs using MRI.
Experiments using radiographic or optical imaging have provided important data for internal disc deformations. However, these studies are limited by physical markers and/or disruption of the disc structural integrity.
MR images were acquired before and during application of a 1000 N axial compression. Two-dimensional internal displacements, average strains, and the location and direction of peak strains were calculated using texture correlation, a pattern matching algorithm.
The average height loss was 0.4 mm, which corresponded to 4.4% compressive strain. The inner AF radial displacement was outward, even with degeneration; the average outward displacement of the inner AF (0.16 mm) was less than the outer AF (0.36 mm). High shear peak strains (2%-26%) occurred near the endplate and at the inner AF. Shear was higher in the anterior AF compared to the posterior.
This technique allows quantification of displacement and strain within the intact disc. The radial displacements of inner AF suggest NP translation under compression. Peak tensile radial strains occurred as vertical bands throughout the anulus, which may contribute to radial tears and herniations. The tensile axial and shear strains at the interface between the AF and endplate could be related to the occurrence of rim lesions. Peak strains at the endplate are likely due to the AF curvature and the oblique fibers angle at fiber insertion sites. In the future, this technique may be used to measure disc strain under a variety of loading conditions, such as bending or torsion, and could also be used to study the mechanical effects of disc degeneration and potential clinical interventions.
Spine 01/2008; 32(25):2860-8. · 2.08 Impact Factor
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ABSTRACT: Measurement and normalization of disc geometry parameters for several animal models used in disc research.
To compare normalized values of disc geometry to the human disc geometry to aid in the selection and interpretation of animal model studies.
Animal models are widely used to study intervertebral disc degeneration and to evaluate disc treatment methods because of the availability of the tissue, the decreased variability between subjects compared with humans, and the feasibility to perform in vivo experiments. There is a general lack of comparative data with respect to the human disc analog for animal models.
The disc height, lateral width, AP width, area, and the nucleus pulposus lateral width, AP width, area, and centroid offset were all measured and normalized by 2 scaling factors, lateral width and disc area, for comparison to human.
The species studied were ranked according to the average percent deviation of the normalized disc height, AP width and nucleus pulposus area from human geometry as: mouse lumbar (12%), rat lumbar (15%), mouse tail (18%), baboon (19%), bovine tail (22%), rabbit (26%), sheep (31%), and rat tail (46%).
This paper provides a reference to compare disc geometries of experimental animal models to the human lumbar disc, to aid both in interpretation of and in planning for experimental disc research, and to provide normalized disc geometry parameters for computational models.
Spine 03/2007; 32(3):328-33. · 2.08 Impact Factor
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ABSTRACT: Mechanical function of the intervertebral disc is maintained through the interaction between the hydrated nucleus pulposus, the surrounding annulus fibrosus, and the superior and inferior endplates. In disc degeneration the normal transfer of load between disc substructures is compromised. The objective of this study was to explore the mechanical role of the nucleus pulposus in support of axial compressive loads over time. This was achieved by measuring the elastic slow ramp and viscoelastic stress-relaxation mechanical behaviors of cadaveric sheep motion segments before and after partial nucleotomy through the endplate (keeping the annulus fibrosus intact). Mechanics were evaluated at five conditions: Intact, intact after 10,000 cycles of compression, acutely after nucleotomy, following nucleotomy and 10,000 cycles of compression, and following unloaded recovery. Radiographs and magnetic resonance images were obtained to examine structure. Only the short time constant of the stress relaxation was altered due to nucleotomy. In contrast, cyclic loading resulted in significant and large changes to both the stiffness and stress relaxation behaviors. Moreover, the nucleotomy had little to no effect on the disc mechanics after cyclic loading, as there were no significant differences comparing mechanics after cyclic loading with or without the nucleotomy. Following unloaded recovery the mechanical changes that had occurred as a consequence of cyclic loading were restored, leaving only a sustained change in the short time constant due to the trans-endplate nucleotomy. Thus the swelling and redistribution of the remaining nucleus pulposus was not able to fully restore mechanical behaviors. This study reveals insights into the role of the nucleus pulposus in disc function, and provides new information toward the potential role of altered nucleus pulpous function in the degenerative cascade.
Journal of Biomechanical Engineering 01/2007; 128(6):823-9. · 1.90 Impact Factor
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ABSTRACT: Knowledge of the functional role of the nucleus pulposus is critical for the development and evaluation of disc treatment strategies to restore mechanical function. While previous motion segment studies have shown that nucleotomy alters disc mechanics, disruption of the annulus fibrosus may have influenced these experiments. The objective of this study was to determine the mechanical role of the nucleus pulposus in support of axial loads via a trans-endplate nucleotomy procedure. Sheep motion segments were randomly assigned to three groups: control, limited nucleotomy, and radical nucleotomy. Mechanical testing consisted of 20 cycles of compression-tension, a 1-h creep, and a slow constant-rate compressive ramp test. Nucleotomy led to increased axial deformations, in particular an elongated neutral zone, a greater range of motion, and altered creep behavior. In general, the elastic properties exhibited a graded response with respect to the amount of nucleus material removed. This graded effect can be attributed to swelling of the nucleus pulposus in the limited nucleotomy group, whereas little swelling was observed in the radical group. The findings of the present study indicate that functional evaluation of nucleus pulposus replacements and disc implants should include range of motion measures (including neutral zone) and viscoelastic creep experiments in addition to considering compressive stiffness.
Annals of Biomedical Engineering 05/2006; 34(4):687-96. · 2.37 Impact Factor
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The Journal of Bone and Joint Surgery 06/2005; 87(5):1098-103. · 3.27 Impact Factor
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ABSTRACT: To examine the impact of hypoxia, rat nucleus pulposus cells were maintained in monolayer culture in 2% O2 and survival and signal transduction pathways identified.
To elucidate the signaling pathways that allow nucleus pulposus cells to adapt to low oxygen environment.
Mammalian cell function is critically dependent on a continuous supply of oxygen. Interestingly, some specialized cell types that include nucleus pulposus cells of the intervertebral disc reside in a hypoxic environment. However, the mechanism of their adaptation to this low oxygen environment is not known.
Rat nucleus pulposus cells were harvested from explant cultures and grown to confluence in monolayer. Cells from passage 3-7 were maintained under hypoxia (2% O2) and normoxia (20% O2) for various time periods in complete or serum-free medium. Cells were also treated with pharmacologic agents that block PI3K and MAPK signaling pathways. Cell survival was assessed by MTT assay, annexinV-PI dual-color flow cytometry, and the TUNEL procedure. Expression of signaling proteins was evaluated by Western blot analysis. Cell phenotype was studied by semiquantitative RT-PCR.
Under hypoxic conditions, rat nucleus pulposus cells were resistant to apoptosis induced by serum starvation. Protection was also observed after treatment of the nucleus cells by desferrioxamine, a compound that mimics many of the effects of hypoxia. Cell survival in hypoxia was related to activation of phosphatidylinositol 3-kinase (PI3K)/Akt and mitogen-activated protein kinase (MEK)/extracellular signal-regulated kinase (ERK) pathways. Induction of Akt activation and ERK1/2 activationunder hypoxic condition was detected at 12 hours and correlated with inactivation of glycogen synthase kinase-3beta (GSK-3beta), an effector protein involved in regulation of apoptosis. Finally, inhibition of PI3K/Akt and MEK/ERK pathway using the inhibitors LY294002 and PD98059, respectively, impaired cell survival.
It is concluded that under hypoxic conditions, rat nucleus pulposus cells are adapted for survival by regulation of expression of critical genes, downregulation of apoptosis through activation of the PI3K/Akt and MAPK survival pathways.
Spine 05/2005; 30(8):882-9. · 2.08 Impact Factor
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ABSTRACT: Biodegradable, controlled-release carrier materials with non-toxic degradation products are valuable for local delivery of biologically active molecules. Previously, it was shown that room-temperature processed silica sol-gels (or xerogels) are porous, resorbable materials that can release molecules of various sizes in a controlled, time dependent manner. Previous in vitro studies also demonstrated benefits of silica xerogels as controlled-release materials for the treatment of bone infections. Herein the tissue and cell response to xerogels is documented using a subacute implantation procedure. The tissue response was correlated to composition, surface properties, resorption rate and incorporation of the antibiotic vancomycin. Ca- and P-free and Ca- and P-containing xerogels, with and without apatite (AP) surface, were used. Xerogels were implanted either as discs in a subcutaneous site, or as granules in the iliac crest of New Zealand white rabbits. The samples with surrounding tissue were retrieved after 2 and 4 weeks of implantation. Silica xerogels implanted either as discs subcutaneously or as granules in the iliac crest showed a favorable tissue response. The granules, either with or without Ca and P content, gradually resorbed over time. The resorption was accompanied by extensive trabecular bone growth and a minimal inflammatory response. Ca- and P-containing granules with an AP-surface layer showed a slower resorption rate and more extensive new bone growth than those without AP layer. Among AP-coated granules, those with incorporated vancomycin showed the most favorable tissue response. The present in vivo data together with prior in vitro data suggest that these xerogels have potential as controlled-release materials for the treatment of bone infections and as carrier materials for a variety of other applications.
Biomaterials 04/2005; 26(9):1043-52. · 7.40 Impact Factor
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ABSTRACT: Because mesenchymal stem cells can differentiate into chondrocyte-like cells, we ask the question, can mesenchymal stem cells commit to the nucleus pulposus phenotype?
Back pain, a significant source of morbidity in our society, is linked to degenerative changes of the intervertebral disc. Absence of suitable graft tissue limits therapeutic approaches for repair of disc tissue. For this reason, there is considerable interest in developing "tissue engineering" strategies for the regeneration of the nucleus pulposus.
Rat mesenchymal stem cells were immobilized in 3-dimensional alginate hydrogels and cultured in a medium containing transforming growth factor-beta1 under hypoxia (2% O2) and normoxia (20% O2). Mesenchymal stem cells were examined by confocal microscopy to evaluate their viability and metabolic status after labeling with Celltracker green, a thiol sensitive dye, and Mitotracker red, a dye sensitive to the mitochondrial membrane potential. Flow cytometry, semiquantitative reverse transcription polymerase chain reaction and Western blot analysis were carried out to evaluate phenotypic and biosynthetic activities and the signaling pathways involved in the differentiation process.
Under hypoxic conditions, mesenchymal stem cells formed large aggregates and exhibited positive Celltracker and Mitotracker signals. Glucose transporter-3, matrix metalloproteinase-2, collagen type II and type XI, and aggrecan mRNA and protein expression was upregulated, whereas there was no change in the levels of decorin, biglycan, fibromodulin, and lumican. Hypoxia maintained the expression of CD44 (hyaluronan receptor), ALCAM (CD166), and endoglin (transforming growth factor-beta receptor). Likewise, expression of beta3 and alpha2 integrin was upregulated. Transforming growth factor-beta treatment increased MAPK activity and Sox-9, aggrecan, and collagen type II gene expression. Basal levels of the phosphorylated MAPK isoform ERK1/2, but not p38, were higher under hypoxic conditions than normoxia, and its activation was further augmented by treatment of cells with transforming growth factor-beta. In hypoxia, transforming growth factor-beta sustained phosphorylated p38 expression for an extended time period. Pharmacological inhibition of ERK1/2 and p38 enzymatic activity resulted in a decrease in Sox-9, aggrecan, and collagen type II mRNA levels.
Our results indicate that hypoxia and transforming growth factor-beta drive mesenchymal stem cell differentiation towards a phenotype consistent with that of the nucleus pulposus. Measurement of selected signaling molecules and response to specific inhibitors suggest involvement of MAPK signaling pathways. It is concluded that mesenchymal stem cells could be used to repopulate the damaged or degenerate intervertebral disc.
Spine 01/2005; 29(23):2627-32. · 2.08 Impact Factor
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ABSTRACT: Spinal injuries occur frequently in the patient with polytrauma making the knowledge of the evaluation and treatment of these injuries invaluable to the trauma team. In the immediate moments after these injuries, critical steps can be taken to prevent additional injury and insure maximum neurologic and functional recovery of the patient. A simple, standardized approach to treating the patient at the scene, examining the patient in the trauma admitting area, ordering appropriate radiographic studies, and instituting early treatment can markedly influence a patient's maximal recovery. Furthermore, background knowledge in the classification and ultimate treatment goals allows for an effective communication between the initial treating team and the spinal surgeons involved. The work on indicators of potential spinal instability by White and Panjabi and the three-column classification of spinal injuries of Denis lends insight to the potential consequences of spinal trauma. A thorough appreciation of these concepts puts evaluation and treatment of these injuries into a logical framework with which spinal injuries initially can be approached.
Clinical Orthopaedics and Related Research 06/2004; · 2.53 Impact Factor
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ABSTRACT: The objectives of this study were (1) to quantify changes in the mechanical behavior of the intervertebral disc in response to cyclic compressive loading and (2) to determine whether mechanical behavior would be restored following a period of unloading. The elastic and viscoelastic compressive mechanical behaviors of adult sheep motion segments were assessed. Ten thousand cycles of compressive loading resulted in increased elastic stiffness and decreased stress-relaxation. After 18 h of unloading in a PBS bath stiffness and relaxation were fully restored. Cyclic loading did not cause structural damage as determined by radiographs and magnetic resonance images. After cyclic loading, average stiffness increased from 603 to 800 N/mm (p = 0.015) and returned to initial levels after the recovery period. Cyclic loading caused a decrease in total relaxation (from 92 to 38 N, p < 0.001) that also returned to initial levels after recovery. The reversible, repeatable effects of cyclic loading and recovery demonstrated in this in vitro study may be attributed to fluid flow. Intervertebral disc fluid transport during the diurnal recovery cycle may be key to understanding intervertebral disc degeneration, as fluid exudation and recovery may be integral to maintaining adequate disc nutrition.
Annals of Biomedical Engineering 02/2004; 32(1):70-6. · 2.37 Impact Factor
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ABSTRACT: The goal of this study was to develop a methodology to maintain intervertebral discs in organ culture, thereby preserving tissue architecture and metabolic function in a three-dimensional environment.
Using a microdissection technique, intervertebral discs were removed from rat lumbar vertebrae. The discs were maintained in organ culture, and cell viability was evaluated histochemically and using probes that measured mitochondrial function and thiol status. The biosynthetic activity of the cells was evaluated by Western blot and RT-PCR analysis.
The in vitro organ culture system maintained the vitality of the nucleus pulposus cells. Cells exhibited a high membrane potential for 1 week. When cells were exposed to carbonyl cyanide 4-trifluoromethoxy phenylhydrazone, a known protonophore, the fluorescence was lost, indicating that the staining was specific for viable cells. In many cells, Celltracker Green, probe for reduced thiols, colocalized with the membrane potential. Histologic studies revealed that in culture for 1 week, normal nucleus pulposus structure was maintained; after this time period, alterations were observed. We evaluated the two tissues for characteristic phenotypic markers HIF-1alpha and MMP-2. We noted that the nucleus pulposus expressed these proteins. The RT-PCR profile at 7 days indicated that the cells also expressed collagen type II, aggrecan, and decorin.
Three factors contributed to success in maintaining the vitality of the nucleus pulposus in vitro. First, the cells were confined within the disc itself; second, the medium was hyperosmotic; third, the medium was supplemented with transforming growth factor-beta. The fluorescence measurement provided a rapid method for evaluation of the status of nucleus pulposus cells. Histologic analysis confirmed that the cells remained viable for at least 1 week. Viability in terms of biosynthetic activity was further confirmed using RT-PCR and Western blot analysis. We conclude that short-term intervertebral disc organ culture can be used as a suitable in vitro model to study effects of environmental factors linked to disc degeneration and/or regeneration.
Spine 01/2004; 28(24):2652-8; discussion 2658-9. · 2.08 Impact Factor
