Mechanical Properties Of The Knee Ligaments

The knee ligament is one of the main load bearing tissues of the knee joint,stabilizing the joint and limiting joint position.Hence,it is crucial to investigate the mechanical properties of ligament,which can provide reference information for the design of artificial transplant materials and the understanding of the failure mechanism.At present,the considerable studies have been performed on the tensile properties of ligaments.However,few studies have focused on the compression properties of ligament and the effects of loading rate on the compression constitutive relations of ligament are largely ignored.In addition,most measurements are conducted using in vitro preserved ligament samples.But there is no standard method for the preservation of ligament samples in vitro and the influence of preservation conditions is still unrevealed.As such,in this thesis,the rabbit patellar ligaments are used to build the constitutive relation of ligament in compression,and the effects of different cryopreservation durations on the compression property of ligaments are investigated.Also,a serrated occlusal clamp is designed for the tensile test of fresh human anterior cruciate ligament,which can avoid the slippage of ligament specimen under high strain loading.In order to characterize the rate-dependent compression response of the ligament,the uniaxial unconfined compression and compression relaxation experiments are carried out on fresh rabbit patellar ligaments at four strain rates of 0.1%/s,1%/s,10%/s and 100%/s.The results show that the stress at the strain of 40% increases significantly with the increase of strain rate.Three constitutive models,Gent,Fung and Ogden,are used to fit the mean curves of uniaxial compression at different strain rates.By introducing strain rate variables,the strain rate-dependent compression constitutive equation is obtained through fitting.The Prony series fitting are carried out for compression relaxation results at different strain rates.After fitted with strain rate variables,the strain rate-dependent compression constitutive equation is obtained.To study the effect of different cryopreservation durations on the properties of ligament in compression,the compressive performance of ligament samples after preserved for different cryopreservation durations are compared.It is found that the stress value at the strain of 40% continuously increases within 3 days,and reaches the peak value in the third day,which is 5.77 times of the fresh sample.Then the stress decreases until it achieves the stable value after 18 days,where the stress value is 2.67 times of fresh samples.The biological mechanisms of the mechanical properties change of patellar ligament are explored by scanning electron microscopy,differential scanning calorimetry,Western blotting and dimethyl-methyl blue colorimetry.The results show that the degree of collagen cross-linking might be the main factor that affects the compression properties of the patellar ligament during preservation.Finally,the human anterior cruciate ligament is used to explore the clamping method and the serrated occlusal clamp is designed to reduce the slippage of the ligament under high strain.Then,the finite element simulation is carried out to discuss the effects of the clamping feed amount and the sawtooth profile on the stress distribution of the ligament.The results indicate that the crushing and the end slippage during clamping can be avoided by reasonably selecting the diameter of the chamfering tooth and the clamping feed amount.The tensile experiments indicate that the tensile strength and the elongation ratio of ligament are 16.85±1.99 MPa and 25.32±0.76%,respectively.