Nucleus pulposus (NP) cells of the intervertebral disk (IVD) have unique

Nucleus pulposus (NP) cells of the intervertebral disk (IVD) have unique morphological characteristics and biologic reactions to mechanical stimuli that may regulate maintenance and health of the IVD. of cell-PCM regions of the mature rat NP measured using confocal microscopy. Three-dimensional geometries of the extracellular matrix and representative cell-matrix S(-)-Propranolol HCl devices were used to construct 3D finite element models of the constructions as isotropic and biphasic materials. In response to compressive strain of the extracellular matrix NP cells and PCM areas were predicted to experience volumetric strains that were 1.9-3.7 and 1.4-2.1 instances greater than the extracellular matrix respectively. Volumetric and deviatoric strain concentrations were generally found at the cell/PCM interface while von Mises stress concentrations were associated with the PCM/extracellular matrix interface. Cell-matrix devices containing higher cell numbers were associated with higher maximum cell strains and lower rates of fluid pressurization upon loading. These studies provide fresh model predictions for micromechanics of NP cells that can contribute to an understanding of mechanotransduction in the IVD and S(-)-Propranolol HCl its changes with aging and degeneration. sections of the NP from the mature rat lumbar disk immunolabeled for type VI collagen (Cao et al. 2007). A total of six distinct cell-matrix units (CMU) were chosen for FEM presented here as representative of a majority of CMU observed for the NP region. These CMU models were chosen with aspect ratios around the mean values in each CMU subgroup (1 cell 2 cells and 3 or 4 4 cells 2 representative models for each CMU group Fig. 1). The reconstructed surfaces of the PCM and enclosed cell(s) in the CMU were separately registered as 3D solid geometry objects in COMSOL by custom programs written in MATLAB (The Mathworks Inc. Natick MA) and COMSOL Script (COMSOL Inc. Burlington MA) as described previously (Cao et al. 2009). A cube representing the ECM with dimensions (× × is the width of the transverse plane of the ECM and is the height of the ECM along the longitudinal direction (the principal axis of the CMU). A preliminary study confirmed that the choice of this ECM size was S(-)-Propranolol HCl sufficient to accurately predict viscoelastic responses in all sub-domains that were independent of dimension and associated with acceptable computational cost. Thus a 3D solid geometry model with three sub-domains including the extracellular matrix PCM and enclosed cell(s) was built based on their in situ 3D morphologies. These three sub-domains were exclusive to each other but physically connected via enforcement of continuity of displacement and pressure boundary conditions. Fig. 1 Registered 3D solid geometries in tetrahedron meshes in the nucleus pulposus. Models include different cell-matrix unit (CMU) subgroups: 1 cell CMUs 1 and 2; 2 cell CMUs 3 and 4; and 3 or 4 4 cell CMUs 5 and 6. For clarity only meshes on the surfaces … The combined 3D solid objects were meshed using tetrahedron elements in COMSOL Multiphysics (Fig. 1). The registered 3D geometries required a large number of tetrahedron elements to generate good quality meshes due to the curvature and roughness on the surfaces of the PCM and cells as seen in examples of meshed CMUs within the NP area. The meshes generally contains 28 0 0 tetrahedron components and around 120 0 0 IL19 examples of freedom reliant on the CMU decoration. The average minimal component quality index across all versions was ~0.15 fulfilling the necessity for tetrahedral elements in COMSOL (>0.1). Within the elemental interpolation the form function for pressure (linear) was arranged to become one order less than displacements (quadratic) S(-)-Propranolol HCl to acquire convergence in COMSOL. 2.3 Materials properties FEM definitions closely follow those created previously for anulus fibrosus and PCM domains within the IVD S(-)-Propranolol HCl (Cao et al. 2009) apart from the isotropic materials assumption that’s invoked for S(-)-Propranolol HCl many material domains within the NP right here. In short the extracellular matrix PCM and cell sub-domains had been assumed to become isotropic linearly flexible biphasic materials having a continuous permeability (Mow et al. 1980). The materials constants had been chosen through the books for the extracellular matrix (Iatridis et al. 1997; Johannessen et al. 2004; Elliott and Johannessen 2005; Perie et al. 2005; Cloyd et al. 2007) PCM (Alexopoulos et al. 2003 2005 b) and cells (Guilak et al. 1999) (Desk 1). Desk 1 Materials properties selected for the extracellular matrix pericellular cells and matrix within the nucleus pulposus 2.4 Boundary conditions The 3D solid models had been used to.