| Objective (1) Part 1:Study of the basic physicochemical properties of the novel magnesium phosphate cement (MPC). (2) Part 2:Study of the biomechanical characteristics of the MPC strengthen pedicle screws in osteoporotic condition. (3) Part 3:Investigation of whether the MPC can cause animals'pyrogen reaction and supplement of the biocompatibility evidences.Methods (1) Part 1:Description of the producing method of the novel magnesium phosphate cement, we observed the microstructure of MPC, analysed the reaction end products of MPC, and measured the maximum reaction exothermic temperature, setting time together with compressive strength of MPC. (2) Part 2:The experiment was divided into two groups, one group was used the MPC to strengthen pedicle screws (group A) and another group was applied traditional polymethyl methacrylate (PMMA) bone cement to strengthen pedicle screws (group B), by measuring two groups'the maximum axial pullout force (N) of pedicle screws at cement solidified 30 min,12 h, 24 h,72 h, and pedicle screws'maximum torque (N.mm) at 24 h, as well as the maximum axial pullout force (N) after 20000 cycles of stress at 24 h, we evaluated the biomechanical characteristics in two groups. (3) Part 3:Twenty New Zealand white rabbits were randomly divided into MPC group (group A) and control group (group B), ten rabbits in each group. Preparation of the MPC leaching solution and preheating the leaching solution to 38?,the leaching solution was injected into the rabbits of group A by ear vein with volume of 10 ml/Kg. By the same way, rabbits of group B was injected into the saline; injection speed was 2 ml/min. The temperature of every rabbit was recorded before injection, and the body temperature was measured every 0.5 h after injection, for total six times.Results (1) Through electron microscopy scanning we observed that in the MPC the particles diameter was more homogeneous, inter particle bonded closely, and no obvious cracks affect the bonding strength after reaction; the main products of cement hardening was MgNH4PO4-6H2O, a small amount of by-products was Mg(NH4HPO4)2-4H2O, and excess unreacted magnesium oxide; the highest average cement exothermic temperature was 43.5?, the average solidification time was 9.33 min and the compressive strength of cement was 45.50 ± 2.08 MPa. (2) The MPC augmentation of pedicle screws'maximum axial pull-out force was at cement solidification 30 min,12 h,24 h,72 h were obviously higher than PMMA bone cement augmentation of pedicle screws, the difference was statistically significant (P< 0.05); The maximum torque of MPC augmentation of pedicle screws compared with PMMA bone cement augmentation of pedicle screws at cement solidification 24 h showed no statistical difference (P>0.05); After the fatigue test, the maximum axial pull-out force of MPC strengthening pedicle screws was obviously higher than PMMA bone cement strengthening pedicle screws, with statistical significance (P< 0.05); After the fatigue test, the maximum axial pull-out force of MPC strengthening pedicle screws compared with the 24h maximum axial pull-out force, indicated no difference (P=0.24>0.05); In contrast, the maximum axial pull-out force of PMMA bone cement strengthening pedicle screws compared to the 24h maximum axial pull-out force after the fatigue test, the difference was statistically significant (P=0.03<0.05). (3) After injection leaching solution at time point of 0.5h?1h?1.5h?2h? 2.5h 3h, there was no statistical difference in the body temperature between MPC group and control group(P>0.05). There was no statistical difference in maximum temperature between MPC group and control group after injection (P>0.05).Conclusions (1) The exothermic reaction of novel magnesium phosphate cement stay low temperature, stable microstructure after solidification, with good compressive strength, appropriate setting time, and the fine biocompatibility of final product of reaction. (2) The MPC can significantly increase the stability of pedicle screws under osteoporotic condition, comparing with PMMA bone cement, it can provide better biomechanical stability in vitro. (3) In animal models, it will not cause pyrogen reaction of MPC injection, and the preliminary results show that the pyrogen testing of MPC is safe and reliable. |
PDF Full Text Request