Biotribological Mechanism Of Articular Cartilage

Articular cartilage is a tissue of excellent lubricating ability and bearingcapacity, which played an important role in human joint motion. After cartilagedamaged severely, artificial joint arthroplasty is the final treatment. Even for thesame cartilage vs. metal tribopair of artificial joint, the postsurgical result of hiphemiarthroplasty is much poorer than the knee arthroplasty without patellaresurfacing. Therefore it is essential to study cartilage wear, lesion modes and itsprogression in order to support the research of early cartilage diagnosis andtreatment.Biomechanical simulation of articular cartilage as the theoretical tool inthis study, analyzed the interstitial flow in cartilage. Next, phase contrastimaging with contrast agent based on synchrotron radiation verified simulatedinterstitial flow. On the other hand, friction experiment analyzed the frictionbehaviors of cartilage such as biphasic lubrication. Finally, three aspects aboveformed biotribological mechanism of articular cartilage lesion, which is appliedto analyze the biotribological problems among the hip hemiarthroplasty andknee arthroplasty without patella resurfacing.The primary content and conclusion of this study are as follows.Firstly, biomechanical model is established in COMSOL based on cartilage biphasic model theory. Accompanied with cartilage creep testing, the modelgave that the elastic module of cartilage is1MPa, permeability is2.2×10-14m4/Ns. Applying the model and parameters above, it calculated cartilageinterstitial flow in static, sliding and cyclic load and establishes the method ofmultiscale mechanical computation for chondrocyte. The biomechanical modelof cartilage is verified through the experiment of cartilage streaming potential,whose result is consistent with the models’.Secondly, cartilage interstitial flow experiment is carried out at ShanghaiSynchrotron Radiation Facility. One contrast agent is chosen whose one-dimensional diffusion coefficient is measured as2.28×10-11m2/s±0.71×10-11m2/s.Relying on the data and experience, the difficulties of cartilage interstitial flowexperiment are analyzed and corresponding technological proposal is found. Theproposal is theoretical analyzed by cartilage biomechanical model, verified inpilot experiment and optimized parameters. Using this method, normal andosteoarthritic (OA) cartilage groups are tested and compared. The interstitialflow direction of normal cartilage is consistent with its computational result.Thirdly, relying on cartilage vs. cartilage friction experiment and itsmodel calculation, the increasing friction coefficient was related to thedecreasing of interstitial pressurization of cartilage. And load sliding speed isrelated to the maintaining of such pressurization. On the other hand, the headgroups of DPPC and those phospholipids on cartilage are positive charged.The electric friction testing shows that negative potential surface adsorbs DPPCliposome, benefiting the lubrication while positive potential surface expelsDPPC, deteriorating the lubrication.Fourthly，wear lesion of articular cartilage starts from the failure oflubrication and superficial lesion primarily due to fatigue wear. With excessiveflow embedded into cartilage, it brings a series of biomechanical degenerationthat accelerates OA progression. Through multiscale mechanical computation ofchondrocyte, mechanical environment around the normal chondrocyte are in thenormal range of chondrocyte according to published experimental results. Incontrast，mechanical environment around OA chondrocyte are out of the rangeso that it influences physiological function of chondrocyte. These phenomenaare consistent with the observation on OA cartilage histological section.Finally, the primary factor of postsurgical difference between hiphemiarthroplasty and knee arthroplasty without patella resurfacing is that hiphemiarthroplasty changed original moving contact lubrication, leading toremarkably increasing friction coefficient between artificial head and naturalacetabular cartilage. And hip hemiarthroplasty decreases squeezing film time by62%comparing to natural hip. Sliding motion of patella keeps moving contactlubrication so that its friction coefficient is low. Mechanical level around chondrocytes of hip hemiarthroplasty was deteriorating with respect to the wear.For knee arthroplasty without patella resurfacing, the mechanical environmentof chondrocyte is same with natural hip joints’. This is a powerful support forthe knee arthroplasty without patella resurfacing.This study expended cartilage biotribology toward cartilage physiology.Through cartilage biomechanical model and multiscale mechanical computationof chondrocyte, it links cartilage mechanical lesion with its pathologicalphenomena and supports the multidisciplinary research in this field.