Age-related Biomechanical Properties Of NZW Rabbit Knee Articular Cartilage

Objective:The purpose of this study is to fully demonstrate the alterations about the biomechanical properties of chondrocytes in nature degeneration of articular cartilage.Methods:15 female New Zealand White rabbits were divided into 3 groups: young group(about 6 weeks age),adult group(about 7 months age),old group(about 31 months age).All NZW rabbits were sacrificed and evaluated using macroscopical observing in their left knees.At the same time,we observed the histologic changes of cartilage with increasing ages using HE staining.We also observed the ultrastructure of the chondrocytes using the transmission electron microscope and measured the diameters of the chondrocytes using the laser confocal scanning microscope.The micropipette aspiration combined with Half-space model was used to quantify changes in biomechanical properties of chondrocytes isolated from different age groups.Results:Articular cartilage had a obvious degeneration with increasing age,especially in old group.There are some changes at ultrastructure of the chondrocytes,especially in old group too.The mean diameter of chondrocytes in young,adult and old groups was 8.84±0.97μm,9.77±1.41μm and 11.5±1.76μm respectively,and were significantly different each other(p＜0.001).Experimental studies have shown that the viscoelastic properties of chondrocytes in old group exhibited a significantly lower instantaneous modulus E₀(Median±Quartile range=0.56±0.08kPa),equilibrium modulus E_∞(0.28±0.05 kPa),and apparent viscosityμ(4.06±0.71 kPa·s)compared with young group(0.68±0.15 kPa,0.38±0.16 kPa,6.42±1.36 kPa·s)(p＜0.005)and adult group(0.63±0.10 kPa,0.33±0.06 kPa,5.84±1.35 kPa·s).(p＜0.005).But no difference were found in the viscoelastic properties between young group and adult group(p＞0.1).Conclusion:In response to a step pressure,chondrocytes in each group exhibited viscoelastic solid creep behavior;There were significantly alterations in the diameter of chondrocytes with increasing age;The viscoelastic properties of the chondrocytes may be altered in old group.