Quantitative Characterization of the Elasticity,Net Creep,and Swelling of the Intervertebral Disc:An In Vitro Experiment

During the in vitro creep of intervertebral discs,both applied loads and osmosis of solution influence their biomechanical behaviors.More specifically,the total displacement can be attributed to three parts:the elastic response during the loading period that results from instant tissue deformation;the nonlinear displacement during the creep period that is due to the poro-elastic fluid flow and visco-elastic deformation;and the swelling of discs that are affected by the osmolality.However,their respective contributions to the total displacement are unknown.To this end,this study aims to discern contributions of the above three parts in ex vivo experiments quantitively.Specimens were compressed for 4 h after 0.5 h preload.Displacement and strain were recorded and curve-fitted.The instant elastic displacement was positively related to the applied load,and its proportion rose from 18.09 to 21.46% as the load elevated.While the contribution of the net creep was inversely related to the applied load,dropping from 74.49 to 60.16%.An increase of 0.74 MPa of the osmolality induced a rise in displacement by 7.42-18.38%.Moreover,with the help of the non-contact measurement,researchers are able to know the contribution of each part quantitatively,which is of importance in understanding the creep mechanisms and developing biomaterials with mechanical mimicry of natural discs.