Study On Quasi-static Mechanical Properties And Ratcheting Behavior For Young And Adult Articular Cartilage

Osteoarthritis(OA)is a degenerative disease primarily characterized by the progressive destruction of the articular cartilage,subchondral bone thickening,osteophyte formation and inflammation of the synovium.Although all of the tissue in the joint is affected,cartilage destruction is deemed to be the major mediator of OA pathogenesis.Articular cartilage covers the ends of bones in the knee joint,supports and distributes loads and pressure over the surface of a joint.It can absorb shock during the movement of the joint.Articular cartilage maturation is the postnatal development process that adapts joint surfaces to their site-specific biomechanical demands.Maturation involves gross morphological changes that occur through a process of synchronised growth and resorption of cartilage and generally ends at sexual maturity.Since the mechanical fatigue was assumed as the original cause of OA.So it is very important to investigate the mechanical behavior of the adult and young articular cartilage for prevention and cure of cartilage diseases and the development of artificial cartilage.In this paper,the fresh articular cartilage obtained from 1-month-old pig and 8-month-old pig was used as experimental subject.The static and dynamic behavior of adult and young articular cartilage was tested under compressive loads and different layers of adult and young cartilage were observed by applying the non-contact digital image correlation technique.The results of the adult tests and young tests were compared.It is found that the creep strain and the creep rate in the initial stage of young cartilage were faster than adult cartilage,and the gap between adult and young cartilage increases with the increasement of stress;the creep strain and creep rate of young cartilage in each layer were higher than that in adult cartilage,the gap between two ages is the largest at the superficial layer,and the gap is not so obvious at the deep lauer;adult cartilage and young cartilage had their own rate of correlation,and Young’s modulus of adult cartilage was higher than the young cartilage during loading.The ratcheting behavior of the adult cartilage and young cartilage were compared,it is found that the ratcheting strain of young cartilage was higher than that of adult cartilage at the same number of cycles,stress amplitude and loading rate,and the differences between the two groups were obvious in the early stage of cyclic loading;the change of the stress amplitude has a great influence on the differences in the ratcheting behavior of the adult cartilage and young cartilage.The tests of static-dynamic behavior of articular cartilage were conducted.The effects of creep,creep-recovery and holding time on cyclic compressing were investigated.It is found that creep strain increased with the time increasing.The eternal deformation which could not disappear during recovery time was large.The ratcheting strain increased with stress level and peak time increasing.And the longer peak stress holding time improved the ratcheting strain accumulation rate.Ratcheting strain stage-grew when creep was in the ratcheting test.Articular cartilage was enhanced by pre-loading creep.The resistance of ratcheting was improved by pre-loading creep,but recovery decreased this enhancement.