The microgravity environment of a long-term space flight may induce acute changes in an astronaut＇s musculo-skeletal systems. This study explores the effects of simulated microgravity on the mechanical characteristics of articular cartilage. Six rats underwent tail suspension for 14 days and six additional rats were kept under normal earth gravity as controls. Swelling strains were measured using high-frequency ultrasound in all cartilage samples subject to osmotic loading. Site-specific swelling strain data were used in a triphasic theoretical model of cartilage swelling to determine the uniaxial modulus of the cartilage solid matrix. No severe surface irregularities were found in the cartilage samples obtained from the control or tail-suspended groups. For the tail-suspended group, the thickness of the cartilage at a specified site, as determined by ultrasound echo, showed a minor decrease. The uniaxial modulus of articular cartilage at the specified site decreased significantly, from （6.31 ± 3.37） MPa to （5.05 ± 2.98）MPa （p 〈 0.05）. The histology- stained image of a cartilage sample also showed a reduced number of chondrocytes and decreased degree of matrix staining. These results demonstrated that the 14 d simulated microgravity induced significant effects on the mechanical characteristics of articular cartilage. This study is the first attempt to explore the effects of simulated microgravity on the mechanical characteristics of articular cartilage using an osmotic loading method and a triphasic model. The conclusions may provide reference information for manned space flights and a better understanding of the effects of microgravity on the skeletal system.
Hai-Jun NiuQing WangYue-Xiang WangAng LiLian-Wen SunYan YanFan FanDe-Yu LiYu-Bo Fan
The purpose of this study was to explore the triphasic mechanical properties of osteoarthritic cartilage with different pathological grades.First,samples of cartilage from rabbits with different stages of osteoarthritis (OA) were graded.Following this,the cartilage was strained by a swelling experiment,and changes were measured using a high-frequency ultrasound system.The result,together with fixed charge density and water volume fraction of cartilage samples,was used to estimate the uniaxial modulus of the cartilage tissue,based on a triphasic model.For the control cartilage samples,the uniaxial elastic modulus on the cartilage surface was lower than those in the middle and deep layers.With an increase in the OA grade,the uniaxial elastic modulus of the surface,middle and deep layers decreased.A significant difference was found in the surface elastic modulus of different OA grades (P<0.01),while no significant differences were identified for OA cartilages of Grades 1 and 2 in the middle and deep layers (P<0.01).Compared with Grades 1 and 2,there was a significant reduction in the elastic modulus in the middle and deep layers of Grade 3 OA cartilage (P<0.05).Overall,this study may provide a new quantitative method to evaluate the severity of OA using the mechanical properties of cartilage tissue.
Subtle changes of articular cartilage(AC) can lead to tissue degeneration and even osteoarthritis(OA).The early degeneration of AC is closely related to a change in proteoglycans(PG) content.The observation of PG is therefore an appropriate way of studying OA and evaluating the degree of AC degeneration.In this study,20 cartilage-bone samples were prepared from normal porcine femoral condyle cartilage and 10 samples were digested over 2 h using 0.25% trypsin solution.The dynamic process of PG-digestion was explored using a conventional A-mode ultrasound(US) experimental system with a 10 MHz center frequency.Quantitative acoustic parameters were calculated from ultrasonic radio-frequency echo signals and included US speed(USS),US amplitude attenuation coefficient(UAA) and broadband US attenuation coefficient(BUA).The experimental results showed that the conventional A-mode ultrasound is valuable for tracking the degree of PG-digestion.Histology also confirmed the validity of the ultrasound observations.For every AC sample,the degree of PG-digestion within a given time was different and was affected by individual differences.After two hours of degeneration,USS showed a mean decrease of 0.4%(P<0.05).UAA was significantly lower after a two-hour PG depletion period(from(2.45±0.23) to(2.28±0.41) dB mm?1).BUA showed no significant differences during this process.In conclusion,conventional ultrasound can provide useful information about trypsin-induced progressive PG depletion in AC and can reflect variations of PG content via the quantitative acoustic parameters USS and UAA.The results of this study may be used to identify an indirect indicator of cartilage matrix integrity and OA disease progression.
