Biomechanical And Degradation Characteristics In Vitro Of New Magnesium Alloy Bone Screws

Compared with the commonly used bone screw materials in clinic,the new magnesium alloy are more suitable for the treatment of fracture healing in terms of biodegradability,biocompatibility and mechanical properties,and have higher costeffectiveness.It is an ideal orthopedic implant material.Previous studies have shown that the degradation rates of magnesium alloys are too fast to match the healing rate of human fracture.The New magnesium alloy is made of magnesium and zinc,calcium,neodymium,zirconium,tweezers,copper,iron and other elements.The corrosion resistance of new magnesium alloy bone screws have been greatly improved by adding proper amount of zinc and rare earth elements,due to the role of solution strengthening and aging strengthening of zinc.Firstly,the biomechanical characteristics of bone screws were studied: three types of bone screw models were designed and constructed according to the national standard "Metal Bone Screws for Bone Joint Implants";The tibial fracture model was established by reverse modeling method for CT data,and the three-dimensional structure model of bone screw-bone composite models were assembled with bone screws.These models have high accuracy and are more conducive for dividing the finite element mesh;The bone screw-bone composite finite element models were established and calculated to obtain the maximum equivalent stress and stress distribution of the screws.Then,the degradation characteristics of bone screws in vitro were studied.According to the established bone screw-bone composite models,the parameters(including the location of fracture seam,the thickness of bone wall at fracture site and the width of bone marrow cavity)of animal bone(sheep bone)degradation experiment in vitro were determined and treated;Referring to the fact that bone screws are often subjected to stress in vivo,the in vitro degradation experimental device of bone screws in mechanical environment was designed and the experiments were carried out.By measuring hydrogen production and weightlessness,observing surface morphology and analyzing corrosion products,the effects of axial pressure and structure of bone screws on degradation rate in vitro were obtained.Finally,the biomechanical properties and degradation characteristics in vitro of bone screws were compared and analyzed,which showed that:(1)Biomechanical properties of bone screws: when the axial pressures on thetibial plateau were the same,the stress levels of the three types of bone screws from high to low were HA-3,HA-1 and HA-2.When the axial pressures acting on the tibial plateau were different,the stress levels of the new magnesium alloy bone screws increased with the increase of axial pressure.(2)Degradation characteristics in vitro of bone screws: axial pressure had a significant effect and the structure had little effect on the degradation in vitro of new magnesium alloy bone screws;(3)Comparing the biomechanical and degradation characteristics in vitro of bone screws: the higher the axial pressure was,the higher the stress level of new magnesium alloy bone screw was,and the faster the degradation rate in vitro was.Stress could promote the degradation rate in vitro.By studying the biomechanical properties and in vitro degradation characteristics of new magnesium alloy bone screws,this paper provides data support and theoretical guidance for material selection,design and clinical application of new magnesium alloy bone screws.