Study Of Molecular Transport Patterns Within Cartilage Tissue Under Static/Mechanical Loading

Articular cartilage is a non-vascular,non-neural connective tissue covering the subchondral bone surface that transmits loads,cushions shock absorption,and maintains normal joint motion.Since articular cartilage has no blood vessels,its nutrient transport mode is different from other tissues.Investigating the transport pattern of molecules within articular cartilage plays an important role in the treatment and repair of articular cartilage diseases.In this paper,the molecular transport pattern within the cartilage under static conditions was firstly investigated.Considering the different molecular transport pathways within cartilage,three molecular mass transfer pathways,namely surface mass transfer pathway,lateral mass transfer pathway and composite mass transfer pathway,were designed for three time periods of 2 h,12 h and 24 h.Also,considering the different sizes of various molecules when chondrocytes obtain nutrients and growth factors,three tracer molecules with molecular weights of 479 Da,40 KDa and150 KDa were used to study the mass transfer pattern.The results showed that the tracer molecules diffused to the whole cartilage layer in 2 h when passing through the cartilage surface pathway.In the lateral pathway,the distance of molecular transport increased with the increase of mass transfer time,and all three molecules showed a gradual decrease in the concentration of molecules in the cartilage layer with the increase of the length from the cartilage side.The mass transfer rate of molecules decreased with the increase of mass transfer time under all three path conditions,and also by comparing the mass transfer results under the three path conditions,it can be seen that the molecular mass transfer effect under the composite path condition is better than the surface path and the lateral path,and the composite path is the best molecular mass transfer path.Then,the effect of dynamic loading on molecular mass transfer within the cartilage was further investigated.The results of dynamic loading mass transfer experiments showed that under the same loading frequency conditions,the increase of loading stress promoted the molecular operation within the cartilage layer,among which the most obvious effect on the operation of small molecules was promoted.When the maximum stress value of loading is the same,changing the loading frequency has an effect on the transfer of small molecules within the cartilage layer,and the transfer of small molecules within the cartilage is promoted as the loading frequency increases,which may be caused by the increase in the number of cyclic loading within the same loading time.Finally,it was considered that deformation and recovery of deformation of cartilage due to mechanical loading may be the reason why mechanical loading promotes molecular mass transfer within cartilage.Therefore,the cartilage immersed in PBS solution was loaded and unloaded for recovery using the same mechanical conditions as dynamic loading for mass transfer,and the deformation and recovery of cartilage during loading were observed and collected using DIC throughout the loading process,and the results showed that the greater the maximum stress the greater the cumulative strain occurred in cartilage with the same loading frequency and loading time,while with the same maximum stress and loading time the change of frequency had less effect on the accumulated strain in cartilage.Also,it was observed by DIC that the accumulated strain in cartilage during loading could be well recovered but not completely recovered during the recovery time of 10 min.Comparing the results of cartilage deformation and recovery with the results of molecular transfer in cartilage under the same dynamic loading conditions,it can be concluded that the higher the accumulated strain generated in cartilage,the better the effect of molecular transfer in cartilage,provided that the recovery of cartilage strain can be ensured.In summary,this paper investigates the molecular mass transfer in cartilage under static and dynamic conditions and draws corresponding laws,which is expected to provide a theoretical basis for the later treatment of cartilage degeneration and repair of cartilage damage.