| Objective:To determinate the biomechanical performance of nano-hydroxyapatite ( n-HA) /polylactic acid ( PLA) compound material and evaluate the biomechanical capability of the interbody fusion cage of n-HA/PLA , to provided referenced data for the advance study of this bioactive material.Materials and Methods: This study was divided into two parts. Part one:The HA and PLA(MW=500000)solution were mixed by ultrasound then the mixture was dried.The mixture was further heating-molded in 170℃and under the pressure of 110Mpa to produce the composite specimens. Co-mixture of the compound craft preparation was applied to prepare n-HA/PLA compound material of different n-HA mass fraction (0,5%,10%,15%,20%,25%). Its mechanics performance(pressure strength,bending strength,curving module) were tested. Part two: To evaluate the immediate stability, 8 fresh lumber spine specimens(L1～L5) from young male cadavers were used ,Thespecimens were classified into 3 groups:the control group , auto iliac bone group and n-HA/PLA interbody fusion cage group. Load-displacement tests were performed in pure compression,flexion, extension, and lateral bending on each group, The axial stiffness of various group were analysed by stress analysis method, The results were statistically analyzed. Part three: The lumber vertebrae L1～L5 were obtained from twelve fresh adult male corpse and were randomly divided into three groups which were control group, iliac bone group, the bioactive interbody fusion cage group. To-be-tested experimental groups were set on the electronic universal material testing machine to test the load displacement,taking down the curve of the load displacement. When the vertebrae began to dent or fracture compressed,the load displacement curve came to the highest point,and the load of the vertebrae began to drop.Information of the load was taken by computer data collection system,testing the highest load and displacement respectively by analyzing the test accordingly.Results: With the percentage of n-HA inereasing, the pressure strength of the composites increas .The bending strength of compound material increased at first and then decreased.When the mass fraction of HA was 15%, the bending strength appeared the peak value (159.6 MPa). During extension,left and right bending, Comparing with the intact group,the mean axis compression stiffness of auto iliac bone group was decreased by 13.8%,15.3%,14.0% , and n-HA/PLA interbody fusion cage group was decreased byl2.6%,14.3%,16.4% respectively.but no significant difference was detected between the two devices ( P>0.05). The ultimate load and displacement of the iliac bone group is the lowest,only 60.4% of the control group.The bioactive interbody fusion cage group group has very good load capacity better than iliac bone group.Conclusions: 15 percent of n-HA in the compound material is considered as the best pereentage.It can meet the biomechanics performance requirement of spinal reconstruction. The n-HA/PLA interbody fusion cage could meet the demands of lumbar biomechanical stability and has good biological activity,load capacity of axial compress as well as vertebrae supporting capacity with excellent biomechanic performance,which can be an excellent material for vertebral replacement with promising prospect for application.
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