Study On The Mechanical And Biological Properties Of Fully Degradable Artificial Ligaments

Anterior cruciate ligament(ACL)is an important ligament structure in the knee joint.It has high incidence of injury.Moreover,because of the low vascularization of ACL,endogenous healing is difficult to occur after injury.So,surgical intervention is required.At present,due to the shortage of sources and disease transmission of auto-transplantation and allotransplantation,the clinical demand for artificial ligament is increasing.In the early stage,the artificial ligament was gradually withdrawn from the market due to the problems of poor development of the tissues around the articular cavity and high complications after implantation.Subsequently,the products showed better short-term efficacy,but the medium and long-term tissues could not grow inward and the synovial foreign body responded seriously.Recently,LARS artificial ligament from France is the most widely used in clinical practice in China,and its strength is relatively high.Its porosity promote cell growth,but LARS artificial ligament used non-absorbable material(PET),debris generated by the interface between materials and bone and the wear between materials causes arthritis and other diseases,and its high strength during the service period has a stress shielding effect on the new tissue.At the same time,other materials do not have the function of inducing regeneration to form complete autologous ligament.Therefore,there is no ideal artificial ligament product to meet the clinical needs.In order to solve the problems of artificial ligament,a fully absorbable artificial ligament was designed and prepared from raw materials and structure.Based on the multistage structure of human ACL and the healing cycle after ACL repair,the core-shell structure of artificial ligament was designed,and PPDO,PGCL and PGLA were selected as raw materials.Through the analysis of the different components of the artificial ligament and the effect of the braided structure on its mechanical properties and the mechanism of action,the artificial ligament with 6 braided bundles and single shell layer as its nuclear layer was optimized.In terms of biomechanical properties,when the ratio of PPDO,PGCL and PGLA component was 6:4:2 and 4:6:2,the fracture strength of the sample was(110.88±2.08)and(102.97±2.70)MPa,and the young's modulus was(116.37±2.85)and(114.01±6.05)MPa,respectively,which were larger than the human ACL.The results show that the artificial ligament of this structure can recover its original length after sudden and rapid physiological activities,and the stress relaxation rate of the artificial ligament after repeated stretching is less than 7%,which has outstanding anti-stress relaxation performance and can maintain the stability of knee joint function.At the same time,the fracture strength of artificial ligament after cyclic tensile fatigue for 500 times is still much higher than that of human ACL,which has excellent anti-fatigue performance.In terms of biodegradation performance,based on in vitro heating acceleration simulation,the results showed that PGCL and PGLA gradually degraded within 12-36d(approximate in vivo temperature 8-24 weeks)at 50? in vitro,and the degradation rate basically matched the tissue regeneration rate(6-24 weeks),providing space for tissue growth.In addition,due to the heterogeneous degradation of multi-component materials,the accumulation of acidic degradation products per unit time is slowed down,and the risk of inflammatory response at the site of artificial ligament implantation is reduced.During the degradation process,the mechanical properties of the artificial ligament would decline and the fracture strength would decrease,but both of them were higher than the requirement for the minimum fracture strength of the artificial ligament in the ligament healing cycle.The decline rate of fracture strength basically met the regeneration rate of tissue.In terms of biocompatibility,the test results of cytocompatibility and histocompatibility showed that the cells could adhere to and proliferate on the artificial ligament scaffold,with high cell vitality and good growth form,and could absorb the artificial ligament without cytotoxicity.After subcutaneous implantation for 3 weeks,the internal tissues of the artificial ligament scaffold showed no obvious inflammatory reaction,and the color of the surrounding tissues was close to that of normal tissues,with collagen infiltration and good histocompatibility.Above all,nuclear layer for 6 root stocks weaving beam,shell of single-layer artificial ligament is a more ideal artificial ligament structure,excellent mechanical properties and biocompatibility,suitable degradation properties,meet the requirements of clinical performance of artificial ligaments,for follow-up study of fully degradable artificial ligament of tissue regeneration of the in situ degradation performance and matching laid the foundation theory and experiment.