Effect Of Moderate Treadmill Exercise Together With Modified Hydroxyapatite Chitosan Composite Hydrogel (CS/HA-g-CS) Implantation On Repair Of Full-Thickness Defects Of Articular Cartilage In Rats

Background:The bony ends of synovial joints are lined with a layer of articular cartilage, which permits congruency between the two opposing skeletal elements, facilitates the transfer of forces between these and their practically frictionless movement, and acts as an absorber of weight during sustained static loading. Articular cartilage is a highly specialized tissue. Healthy cartilage is an essential condition for the activities of the body, all kinds of joint injury, bone and joint disease and bone and joint tumors will damage the articular cartilage. Cartilage is mainly composed of chondrocytes, extracellular reticular collagen fiber, glycosaminoglycan(GAG) and water. Because of its special structure, there are no blood vessels and nerves, and the way to get nutrition is different from other tissues. In the early age, the joint cartilage supply of nutrients via diffusion from the subchondral bone, and the adult was mainly depended on the material exchange with the joint fluid to get the nutrition. The reasons why lesions confined to the layer of adult articularcartilage do not heal lie mainly in the nature of this tissue’s structure and physiology. Moreover, the progression of such lesions is generally believed to forebode the onset of osteoarthritis (OA). Therefore, the repair of articular cartilage injury has been a hot issue in clinical practice.There is no gold standard method for the treatment of cartilage injury at present and the treatment method is still controversial. Now, there are drug therapy, biological therapy, surgical treatment, biological engineering materials implants etc. With the development of biomedical, biological therapy attracted more and more attention. The research of chondrocytes transplantation, cytokines transplantation, tissue-engineered cartilage and other methods has been develop quickly, but currently mostly limited to basic research, clinical research and application is not yet mature, and its long-term efficacy remains to be further clarified. Surgical procedures, such as abrasion chondroplasty, pridie drilling, microfracturing, osteochondral autografting, osteochondral allografting, autologous-chondrocyte implantation etc, although there are many methods, but there are limitations and shortcomings and use of surgical treatment of the repair and reconstruction of cartilage and normal cartilage tissue has some differences, and processing of micro fracture surgery, autologous cartilage transplantation will cause damage. In recent years, great progress has been made in biological tissue engineering materials, and a variety of tissue engineering gels and scaffolds have been proved to play a role in the repair of cartilage defects. The theory is formation of the structure and intensity similar to cartilage matrix biomaterial filling in a cartilage defect, fill the defect site in early time and maintain the articular surface its original form. Biological tissue engineering provide good environment of proliferation and differentiation for materials mesenchymal cells, so the regeneration of cartilage is closer to the normal cartilage morphological and histological characteristics. Chitosan (polyglusam) is a copolymer of glucosamine and N-acetylglucosamine, which may be cross-linked with polyanionic chondroitin-sulfate to form a hydrogel. Several in-vitro studies yield evidence of its potential value as a matrix to facilitate articular cartilage repair. It efficiently supports not only chondrogenic activities, but also the in-vitro expression of cartilage extracellular matrix proteins by human chondrocytes. It can also serve as a carrier for growth factors. The materials used in this experiment are modified hydroxyapatite chitosan composite hydrogel, which was prepared by physical crosslinking method that improved the compatibility of hydroxyapatite nanoparticles with chitosan, and can increase the compressive strength of the gel and prolong the time of degradation. Lack of nutritional support is an important reason for the repair of cartilage defects. A large number of literature reports that static can cause degeneration of articular cartilage. The reason is static will stop the nutrition exchange which is between cartilage and joint fluid and maintain the nutrition of articular cartilage. In the literature, there is a strong joint activity that can lead to cartilage degeneration. At present, it is generally considered that the appropriate stress stimulation is closely related to the physiological activities of the normal cartilage, and the appropriate exercise can improve the quality of the articular cartilage. Periodic changes pressure imposed on articular cartilage in the process of joint movement make cartilage like periodic water squeezing sponge, forming the so-called "cartilage pump", this is the cartilage to get nutrition mechanism. Moderate exercise can reduce the adhesion of the joint and outside of the joint, increase the muscle strength and the stability of the tendon and joint capsule. Scholars study found that moderate intensity treadmill exercise can improve content of Cartilage Glycosaminoglycans glycosaminoglycans (GAG) and type II collagen (College-Ⅱ) and can promote the non weight bearing area of the articular cartilage defect repair, high strength treadmill exercise will lead tocartilage destruction and low intensity havn’t significant effect. By consulting a lot of literature, we found that the study of treadmill exercise mostly in normal cartilage and cartilage defect that not be repaired, but treadmill exercise for cartilage defects that have been repaired have not reported. The mechanism of repairing cartilage defect is that the hemorrhage of the subchondral bone makes the defect site to form a hematoma, and the mesenchymal cells which have multiple differentiation tend enter the defect area and proliferate. Fibrin clot formed by red blood cells, white blood cells and undifferentiated cells was formed in the defect area, further Fibrin clot transform into granulation tissue, granulation tissue transform into a fibrous cartilage, and then again as a kind of cartilage like cartilage. We assume that the moderate intensity treadmill exercise rehabilitation exercise is used in rats which have been implanted tissue engineering in the cartilage defect, CS/HA-g-CS hydrogel can provide stable environment in the defect implanted for the early repair of the defect, reduce the stress influence on undifferentiated mesenchymal stem cells and form a cartilage matrix-like structure in the defects, conducive to mesenchymal stem cells to differentiate into cartilage cells. So as to obtain cartilage pump the role of nutritional support, prevent joint adhesion, and can avoid interference of treadmill exercise, then the moderate intensity treadmill exercise combined with CS/HA-g-CS hydrogel on rat patellofemoral articular cartilage defect repair effect is better to used alone treadmill exercise or CS/HA-g-CS hydrogel. In order to confirm our hypothesis, we conducted a study of this experiment.Objective:To investigate the effect of moderate treadmill exercise together with modified hydroxyapatite chitosan composite hydrogel (CS/HA-g-CS) implantation on repair of full-thickness defects of articular cartilage in rat.Method:Full-thickness cartilage defects were drilled in the patellar groove of bilateral femoral condyles in a total of 24 male SD rats before they were randomly assigned into four groups. In control group (BC group), no exercise was given and without a CS/HA-g-CS implant. In chitosan group (CHI group), rats only were performed with CS/HA-g-CS implant without exercise. On the contrary, in moderate treadmill exercise group (MIR group), rats were performed with exercise post-operation of 4 weeks without CS/HA-g-CS implant. While all these two treatments were performed is CHI+MIR group. Half of the animals were sacrificed at week 4 and half at week 12 after exercise. Femoral condyles were harvested for gross observation and histochemical measurement by O’Driscoll scoring system. mRNA expressions of glycosaminoglycan, collagen type Ⅱ and BMP-2 were detected by RT-PCR.Results:Both 8 and 16 weeks post-operation, the best results were observed in CHI+MIR group and the worst results appeared in BC group. The histochemisty scores and the expressions of collagen type Ⅱ, glycosaminoglycan and BMP-2 were significantly higher in CHI+MIR group than in other three groups (P<0.05).Conclusion:This study demonstrates that moderate treadmill exercise together with CS/HA-g-CS implantation has significant positive effects on rehabilitation in rat knee joint cartilage defect models.