ABSTRACT
Ligament tissue engineering is currently a novel approach to the treatment of ligament injury, which can replace the deficiency of autografts. Ligament tissue engineering consists of four basic elements:seed cells, nanoscaffolds, growth factors, and mechanical stimulation. At present, the main problem in ligament tissue engineering is how to control seed cells to ligament cells more controllly. The study found that each physical property of the natural bio ligament and mechanical stimulation (uniaxial stretching) plays an important role in the differentiation of stem cells into ligament cells. Therefore, the design of nanofiber scaffolds must consider the elastic modulus of the material and the material. Structure(material arrangement, porosity and diameter, etc.), elastic modulus and material structure in different ranges will guide cells to differentiate into different lineages. Considering that the ligament is the main force-bearing tissue of the human body, mechanical stimulation is also essential for stem cell differentiation, especially uniaxial stretching, which best meets the stress of the ligament in the body. A large number of studies have found the frequency and amplitude of stretching. And time will also lead the cells to differentiate in different directions. RhoA/ROCK plays a regulatory role in cytoskeletal remodeling and cell differentiation. It is also found that RhoA/ROCK protein participates in the process of nanofiber arrangement and uniaxial stretching to guide stem cells to differentiate into ligament cells, specifically how to influence stem cell differentiation. It is not clear at present that understanding the effects of physical properties on stem cell differentiation and understanding the mechanism of action of RhoA/ROCK protein will provide a new theoretical basis for further optimization of ligament tissue engineering.
Subject(s)
Humans , Cell Differentiation , Environment , Ligaments , Research , Tissue Engineering , Tissue ScaffoldsABSTRACT
BACKGROUND: Once the articular cartilage has a crack defect, its mechanical properties will change. In previous studies, the investigation of damaged articular cartilage mostly focused on compression, and there were few studies on tensile properties. OBJECTIVE: To measure the uniaxial quasi-static tensile properties by preparing crack defects on the cartilage layer samples. METHODS: The articular cartilage of the fresh adult pig knee joint was selected to prepare a cartilage specimen containing a crack defect. The tensile properties were tested at different stress rates (0.001, 0.01 and 0.1 MPa/s) and the creep properties were tested under different constant stresses (1, 2 and 3 MPa). RESULTS AND CONCLUSION: (1) In the tensile test at different stress rates, as the stress rate increases, the stress required to reach the same strain increased gradually, and the Young's modulus of the test piece increases with the increase of the stress rate. (2) The tensile stress-strain curves of the articular cartilage with cracks at different stress rates did not coincide, indicating that the tensile properties of the articular cartilage with crack defects are rate-dependent. (3) In the creep experiment under different constant tensile stress levels, the creep strain increased with the increase of the tensile stress level, the creep compliance decreased with the increase of the tensile stress level, and with the creep time. The creep strain increased rapidly and then increased slowly. (4) To conclude, different stress rates and different constant stresses have great influence on the tensile mechanical properties of articular cartilage with crack defects. The experimental results provide a mechanical reference for the repair of defective articular cartilage.
ABSTRACT
Objective To observe the expression changes of inflammatory cytokines of human tendon-derived stem cells (TDSCs) under uniaxial stretching.Methods TDSCs were isolated from human gracilis tendon by collagenase digestion at very low density.Cells were detected for surface markers by flow cytometry,and tested for multi-differentiation potential in vitro.Repetitive uniaxial stretching was applied on the cells at 0％,4％,8％ or 10％ strain.Under the microscopy,cell alignment was observed after mechanical stretching.Expressions of inflammation factors COX-2 and MMP-1 were detected by qPCR and western blotting.Results TDSCs were successfully isolated from human gracilis tendon.Inflammatory cytokines CD29,CD44 and CD105 were positive,but CD45 and CD14 were negative.TDSCs could differentiate into osteocytes,adipocytes and chondrocytes in vitro.Cells were not realigned4 hours after mechanical stretching.MMP-1 mRNA expression was significantly down-regulated at 4％ strain (0.090 ± 0.007) compared to that at 0％ strain (0.247 ± 0.032,P ＜ 0.05).No significant difference was found in COX-2 mRNA expression at 4％ and 8％ strain (both was 0.005 ±0.001,P ＞0.05).MMP-1 and COX-2 mRNA expressions at 8％ strain (0.168 ± 0.040 and 0.007 ± 0.001)revealed no significant differences from those at 0％ strain (0.134 ±0.075 and 0.006 ±0.003) (P ＞0.05),whereas at 10％ strain MMP-1 and COX-2 mRNA expressions were significantly up-regulated (0.047 ± 0.003 and 0.496 ± 0.036) compared to those at 0％ strain (0.011 ± 0.003 and 0.005 ± 0.003)(P ＜ 0.05).Changes in MMP-1 and COX-2 protein expressions revealed similar trend as their mRNA expressions.In contrast to the setting of 0％ strain,4％ strain induced down-regulated MMP-1 and COX-2 proteins,8％ strain induced no significant changes in MMP-1 and COX-2 proteins,and 10％ strain induced up-regulated COX-2 protein despite minor increase in MMP-1 protein.Conclusions Mechanical stretching can affect the secretion of inflammatory cytokines.Low tensile stretch is associated with decreased expression of inflammatory cytokines while high tensile stretch promotes secretion of inflammatory cytokines.