Effects Of Formalin And Saline Preservation On The Mechanical Properties Of Cortical Bone

Cortical bone biomechanics test samples often come from frozen or formalin and other solution preservation,and the physiological saline is widely used during the preparation,preservation and testing of cortical bone samples.Freezing is thought to not affect the mechanical properties of the cortical bone,so the fresh-frozen bone is often used as a reference group for the biomechanical test.However,formalin and other chemical solutions will cause changes in bone tissue composition and structure,so fixed bone by these solutions may affect the mechanical properties of cortical bone.In addition,the effect of saline on the mechanical properties of cortical bone in the whole process of biomechanics is also unknown.Therefore,it is necessary to study the effects of formalin solution and saline on the mechanical properties of cortical bone,and guide the preservation of bone and the rational use of physiological saline during biomechanical testing.The specimens of this study were cut from the mid-diaphysis of seven male bovine femora.Cuboid specimens from the each anterior,lateral,posterior and medial anatomical quadrants of the femur were obtained,each with dimensions of 12 mm × 2 mm × 0.5 mm.The prepared samples were assigned to multiple groups with different preservation conditions,including fresh frozen(-20? for 60 days)?storage in formalin(25?)for 4 and 8 weeks and storage in saline(25?)for 3,10,36 and 60 days.All samples underwent quasi-static three-point bending test with a rate of 0.02 mm/s,the loading force-displacement curve was thereby obtained.Using the optimization method combined with specimen-specific finite element(FE)models to acquire the following constitutive parameters:elastic modulus,tangent modulus,yield stress and effective plastic strain.The one-way ANOVA or Kruskal-Wallis test was used to study whether the formalin and saline preservation can significantly alter the constitutive parameters of cortical bone.The Tukey method or Dunnett's T3 method was used to study the time effect of formalin and saline preservation on cortical bone constitutive parameters.The results showed that the optimization(FE)method can provide accurate values for the elastic modulus,yield stress,tangent modulus and effective plastic strain of cortical bone specimens.The elastic modulus of fresh frozen samples was in agreement with the literature.ANOVA and Kruskal-Wallis tests showed that the constitutive parameters of cortical bone were significantly affected by formalin fixation,and the elastic modulus and yield stress decreased with increased preservation time.Saline short-term preservation(<3 days)does not significantly change the mechanical properties of cortical bone,but long-term preservation(? 10 days)can significantly reduce the elastic modulus and yield stress of cortical bone.When considering the four anatomical quadrants,the effect of formalin solution on all constitutive parameters of four anatomical sites was different,and the effect of physiological saline on elastic modulus and yield stress of four anatomical sites was different.In conclusion,formalin and saline fixation changed the mechanical properties of the cortical bone,and the influence on the constitutive parameters is related to the preservation time and the anatomical quadrants.Therefore,the formalin fixed bone should be used with caution in biomechanical test,and when subjecting cortical bone to biomechanical tests at room temperature,the samples should not be placed in saline solution for extended periods of time to avoid significant deviations from the in vivo condition.