Effect Of Elastin Degradation On Tensile Mechanical Response And Microstructure Of Patellar Tendon

BackgroundPatellar tendon plays a stabilizing role in that knee joint.When the tendon experiences high loads,microstructural disruption of the internal structure occurs which affects the mechanical properties of the tendon.Under axial mechanical test,the patellar tendon exhibits characteristic nonlinear mechanical properties and viscoelasticity,but it is not clear how elastin affects the mechanical behavior of the patellar tendon under load and how it affects microstructures such as collagen fibers.Objective1.Explore how elastin affects the mechanical properties of three regions of the patellar tendon by degrading elastin in the patellar tendon.2.Describe the structural differences in different regions of patellar tendon and quantitatively analyze the real-time changes of patellar tendon tissue structure without the action of elastin under the mechanical action.Methods1.The fresh porcine patellar tendons were incubated in 5 different concentrations of elastase for 6 h and 5 different times in 5 U/mL elastase respectively to quantify the residual elastin content.2.Patellar tendons were incubated for 8 h in PBS or 5 U/mL elastase.Collagen,sGAG,total protein content assay,VVG and Masson staining were performed.3.Patellar tendons were divided into proximal,central and distal regions.After mechanical test,it was randomly divided into PBS group and elastase treatment group(n=9 for each group).After incubation,the same mechanical test was performed again.The mechanical properties before treatment were used as self-control.Fitting was performed using the hyperelastic Yeoh constitutive model and the viscoelastic Prony series.4.Three regions of fresh patellar tendon were stained with Movat’s stain,and the completed test pieces of each group were stained with VVG.Quantitative polarized light imaging combined with mechanics was used to quantify the changes in the arrangement direction of fiber structures of patellar tendon and the arrangement degree in this direction before and after enzyme or PBS treatment in real time.Results1.5 U/mL elastase solution incubated for 8 h could meet the requirements of this experiment.2.There was no statistical difference in mechanical properties between patellar tendon regions.The tensile stress and stiffness decreased and the transition strain increased after enzyme treatment.After enzyme treatment,the stress relaxation amount and slope increased and the relaxation time became longer.The enzyme treatment group showed greater effects on the mechanical properties than the PBS group.3.After enzyme treatment,the fitting parameters C10,C20 and C30 of Yeoh model showed a downward trend.Fitting parameter G0 of viscoelastic Prony series decreased significantly,and τ1 and τ2 presented an increasing trend,τ1 became longer and τ2 shortened.4.The three regions of patellar tendon had similar microstructures and composition.After elastin degradation,collagen fibers were loosened,curled smaller,and straightened longer.AVG DoLP of fiber structures augmented and STD AoP decreased with the increase of strain,but AVG DoLP of elastase-treated fiber structures were significantly reduced and STD AoP were significantly increased.Conclusions1.The similar microstructural composition and arrangement of the patellar tendon region may lead to its lack of region-specific mechanical properties under tension.2.The specific degradation of elastin changes the nonlinear mechanical behavior of patellar tendon,and the zero region of the stress-strain curve become longer;and there is a significant stress relaxation phenomenon.3.The patellar tendon tissue undergoes the sliding and restructuring of the fiber structures under tensile strain;After degradation of elastin,the fiber structures become more heterogeneous and loose.