Biaxial testing of canine annulus fibrosus tissue under changing salt concentrations

Abstract

The in vivo mechanics of the annulus fibrosus of the intervertebral disc is one of biaxial rather than uniaxial loading. The material properties of the annulus are intimately linked to the osmolarity in the tissue. This paper presents biaxial relaxation experiments of canine annulus fibrosus tissue under stepwise changes of external salt concentration. The force tracings show that stresses are strongly dependent on time, salt concentration and orientation. The force tracing signature of a response to a change in strain, is one of a jump in stress that relaxes partly as the new strain is maintained. The force tracing signature of a stepwise change in salt concentration is a progressive monotonous change in stress towards a new equilibrium value. Although the number of samples does not allow any definitive quantitative conclusions, the trends may shed light on the complex interaction among the directionality of forces, strains and fiber orientation on one hand, and on the other hand, the osmolarity of the tissue. The dual response to a change in strain is understood as an immediate response before fluid flows in or out of the tissue, followed by a progressive readjustment of the fluid content in time because of the gradient in fluid chemical potential between the tissue and the surrounding solution.

Refinement of Elastic, Poroelastic, and Osmotic Tissue Properties of Intervertebral Disks to Analyze Behavior in Compression

“…The swelling properties of tissues can be quantified by measuring hydration, osmotic swelling, and creep behavior in baths having differing osmolarity. 4,6,19,47,48 Disk degeneration is associated with loss of proteoglycans and decrease in pH that both reduce the fixed charge density (FCD). 16,39,48 …”

Experimental and model determination of human intervertebral disc osmoviscoelasticity

“…N um erous studies have reported the A F com pressive [9][10][11][12][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.…”

Osmo-inelastic response of the intervertebral disc annulus fibrosus tissue

“…Keeping bone is a solution 3 but limited by bone brittleness and potential bone failure during cutting and grips pressure. The annulus specimens may be also glued with cyanoacrylate to grips, [26][27][28] the cyanoacrylate stiffness being much higher than the annulus stiffness (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25) and its influence may be neglected. Here, the specimens were glued at metal plates using cyanoacrylate and then immerged in a 9-g/ L saline solution during 100 min to reach equilibrium swelling and to cancel all residual stresses due to specimen preparation.…”

“…The underlying coupling depends on the chemical state of the disc 20 with variations in fluid content inside extracellular matrix and modifications in chemical equilibrium. 10,[21][22][23][24] Although inelastic and osmotic effects in the disc usually appear together, the coupling between both effects is rarely studied. 1,[8][9][10]20,25 The evaluation of the intrinsic annulus mechanics including multiple lamellae in relation with the surrounding chemical environment should bring precious information on the implication of proteoglycans/collagen fibers as well as inter-lamellae interactions on the coupling between osmotic and inelastic effects (the interaction between inelastic effects and osmolarity effects will be termed as osmo-inelastic coupling).…”