Experimental and model determination of human intervertebral disc osmoviscoelasticity

Abstract

Finite elem ent (FE )m odels have becom e an im portant toolto study load distribution in the healthy and degenerated disc. H ow ever,m odelpredictions require accurate constitutive law sand m aterialproperties.A s the m echanicalpropertiesofthe intervertebral disc are regulated by its biochem icalcom position and fiber-reinforced structure,the relationship betw een the constitutive behavior ofthe tissue and its com position requirescarefulconsideration.W hile num erousstudieshave investigated the annulusfibrosuscom pressive and tensileproperties,specificconditionsrequired todeterm inem odelparam etersfortheosm oviscoelasticm odelareunavailable.Therefore,the objectivesofthisstudy w ere(1)to com plem entthe existing m aterialtesting in thel iterature w ith confined com pression and tensile testson hum an annulus fibrosus and (2)to use these data,togetherw ith existing nucleus pulposus com pression data to tune a com position-based, osm oviscoelasticm aterialconstitutive law .The osm oviscoelasticm aterialconstitutive law and the experim entaldata w ere used to describe thefiberand nonfiberpropertiesofthehum an disc.Thecom pressivem aterialpropertiesofnorm aldisctissuew ereG m ¼ 1. Keywords: three-dim ensi onalfinite elem ent;confined com pressi on test;tensile test;vi scoelasticity;porom echanics;com position-based Finite elem ent (FE )m odels have becom e an im portant tool to study load distribution in the healthy and degenerated disc. H ow ever, m odel predictions require accurate constitutive law s and m aterialproperties.1 A s the m echanicalproperties ofthe intervertebraldisc are regulated by its biochem ical com position and fiberreinforced structure, the constitutive law describing this com pl ex tissue requires careful consideration. The annulus fibrosus (A F) consi sts of collagen, w hich provides tensile strength, and proteoglycans (PG s), w hi ch due to their strong sw el ling ability 3 provide tissue hydration. 4,5 This sw el ling tendency is am pl ified by the partialshielding ofthe w ater by the collagen. 4 A high intradiscal pressure in the nucleus is the consequence ofthe sw elling and is balanced by the external load and tensile stresses in the dense collagen fiber structure of the annulus. W e previously presented a three-dim ensi onal (3D ) osm oviscoelastic FE m odel 6,7 that accounts for the interdependency of the sw elling ability and the collagen prestressing. The m odel predicts intradiscal pressures in the order of 0. 1 to 0. 2 M Pa i n unloaded discs,in agreem ent w ith in vi vo m easurem ents.8 H ow ever,l ack ofexperim entaldata to determ ine som e of the m odel param eters lim i ts the applicability ofthis m odel.N um erous studies have reported the A F com pressive 9-13 and tensile properties, 11, 14-17 but specific conditions required to determ ine m odelparam eters for the osm oviscoelasticm odelare unavailable.In com pression, previous studies quantified the load distribution and shiftbetw een fibrillarand solid m atri cesin the annulus.H ow ever, i n these studies the ...

Intervertebral Disk Tissue Engineering Using Biphasic Silk Composite Scaffolds

“…39 The mechanical property of the human AF tissue is reported at 7.2-27.2 MPa for tensile modulus and 1.23 MPa for compressive modulus. [40][41][42] In our previous study, silk scaffolds with lamellar structure exhibited 0.26 MPa for tensile modulus and 164.80 kPa for compressive modulus, whereas silk scaffolds with a porous structure showed 1.30-1.41 MPa for tensile modulus and 293.78-347.58 kPa for compressive modulus. 32 Even though the mechanics of general silk scaffolds are lower than native IVD tissues, new strategies have been sought to enhance silk biomaterial mechanical properties, for example, by reinforcing silk sponges with silk particles (up to 1.93 MPa for compressive modulus).…”

A biochemical/biophysical 3D FE intervertebral disc model

“…Constitutive laws acquired on isolated samples of nucleus and annulus tissue through confined compression experiments and uniaxial tensile tests enabled us to describe the anisotropic, non-linear behavior of the annulus and nucleus tissue (Schroeder et al 2008). Accounting for the difference between nucleus and annulus tissue through its biochemical composition reduced the number of constituent parameters (Schroeder et al 2008).…”

“…Accounting for the difference between nucleus and annulus tissue through its biochemical composition reduced the number of constituent parameters (Schroeder et al 2008). This is of special interest, as variation in the experimental data entails a large variability in the material properties describing the disc tissue behavior (Jones and Wilcox 2008).…”

“…This is of special interest, as variation in the experimental data entails a large variability in the material properties describing the disc tissue behavior (Jones and Wilcox 2008). This paper presents a novel FE model at a wholeorgan level; the 3D OVED model describes the overall disc behavior as a function of annulus and nucleus tissue biochemical composition, organization and the specific material properties of each of these constituents (Schroeder et al 2006;Schroeder et al 2008). The description of the 3D collagen network in the 3D OVED model is (Table 1) enhanced to account for smaller fibril structures.…”

Biaxial testing of canine annulus fibrosus tissue under changing salt concentrations

“…Different modelling strategies have been proposed to grasp its coupled electro-chemo-mechanical properties (Huyghe 1999, Iatridis et al 2003, van Loon et al 2003, Schroeder et al 2006 Selected paper presented at the IUTAM Symposium on Swelling and Shrinking of Porous Materials: From Colloid Science to Poromechanics -August 06-10 2007, LNCC/MCT. E-mail: j.m.r.huyghe@tue.nl Schroeder et al 2008). The constitutive relationships of an intervertebral disc tissue are subdivided into 2 categories .…”