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In order to evaluate the biomechanical stability of titanium alloy screw with different structural parameters under bone remodeling, some three-dimensional finite element models were established and the bone remodeling process after implanting the screw was simulated. Three-dimensional finite element models consist of bone and screw with different lengths and diameters. Bone remodeling process was simulated by user-defined subroutine. It is found that the stress on the bone is concentrated on the groove and root of the internal thread. The screw stress is mainly on the beginning of the thread, and the whole stress decreases along the long axis of the screw. The stress distribution trend of bone and screw did not change significantly during the bone remodeling. The maximum equivalent stress value was different, the maximum equivalent stress on the screw and cancellous bone increased while the maximum equivalent stress value on the cortical bone decreased.
Subject(s)
Biomechanical Phenomena , Bone Remodeling , Bone Screws , Finite Element Analysis , Stress, Mechanical , TitaniumABSTRACT
Objective To evaluate the effects of locked plates with different screw layouts on stability of the internal fixation system for femoral shaft fracture, so as to provide guidance for clinical study on screw layout of the internal fixation system for femoral shaft fracture. Methods Orthogonal test design method was used with 4 groups of screws at 3 parametric levels. Biomechanical properties of the internal fixation system for femoral shaft fracture under 9 screw layouts were analyzed respectively by the finite element method, and 4 inspection indices, namely, the maximum equivalent stress of the plate, the screw and the femur, and the maximum axial displacement of the internal fixation system were obtained from each group of the experiment, and the orthogonal test weight matrix analysis method was conducted for data analysis. Results The influences of different screw parameters on stability of the internal fixation system varied, and the maximum weights of the 4 sets of screw parameters in stability of the internal fixation system were 13.86%, 7.57%, 7.53% and 5.91%, respectively. Conclusions The best scheme for screw layout in orthogonal test is the screw with none-fixed threaded holes in the first group, the single cortical screws with fixed threaded holes in the second group and the double cortical screws with fixed threaded holes in the third and fourth group.
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Objective To explore the effects of screw configurations on bone healing, so as to provide the basis for related fracture treatment. Methods The process of bone healing under different screw configurations was studied by finite element method, and the change in the process of callus growth during healing periods was simulated by interfragmentary strain theory (IFS). The iterative process for renewing callus modulus in every finite element was conducted by the second-developed ABAQUS based on Python scripting language, thus the process of fracture healing was simulated. Results The effect from different numbers of screws on bone healing was smaller than that from different working length of bone plates. On the premise of stable fixation, given the certain working length of bone plates, the effect from different screw numbers on stress distributions in plates or screws was relatively small, while the effect from different working length on stress distributions in plates or screws was relatively large, and the stress distribution in plates was larger than that in screws at different working length. Conclusions It is necessary to take more consideration on working length of bone plates than the number of screws when they are under a stable fixed situation, and it is a wise choice to reduce the screw numbers and choose a suitable working length for bone healing process.
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Objective To observe the protective effect of α-lipoic acid (LA) pretreatment on hypoxia/reoxyg-enation injury in vascular endothelial cells and preliminary explore its mechanism. Methods HUVEC were cultured intro and devided into control group,hypoxia/reoxygenation model group and LA group. Cell morphology was observed under inverted phase contrast microscope,cell viability was detected by MTT,total antioxidant capacity (TAOC),nitric oxide(NO),malondialdehyde (MDA),superoxide dismutase (SOD) activity or level were measured by various commercial kits respectively. Apoptosis of HUVEC in each group were detected by flow cytometry , cleaved caspase-3 level was measured by western blot. Results As compared to control group, the survival rate, TAOC, SOD, NO activity were significantly lower(P<0.05), and MDA level, apoptosis rate and apoptosis protein levels were significantly higher (P < 0.05) in model group. However,LA can increase the survival rate,TAOC, SOD,NO activity (P < 0.05),reduce MDA level and cell apoptosis (P < 0.05)in a dose dependent manner. Conclusion LA pretreatments provide protection against hypoxia/reoxygenation injury in HUVEC. LA exerts protective effects through inhibition of HUVEC apoptosis.
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The aim of this paper is to report the study on gene silencing efficiency of siRNA targeted against mouse VEGFR2 (siVEGFR2) in vitro mediated by polyethyleneimine (PEI) and its anti-tumor effect in vivo. CY3-labeled siRNA was compounded into PEI and transfected into MS1 cells. Confocal microscopy was used to image the subcellular distribution of siRNA in MS1 cells. Semi-quantitative RT-PCR and Western blotting were used to evaluate VEGFR2 gene silencing induced by siVEGFR2/PEI complexes. A tumor-bearing nude mice model was established to compare the anti-tumor effect after delivered by local and systemic routes. siVEGFR2/PEI complex-transfected cells exhibited much fluorescence in cytoplasm with no evidence of nuclear accumulation. The expression levels of VEGFR2 mRNA and protein in PEI-transfected cells were significantly down-regulated compared with that in blank group, the silencing efficiency were 28.2% and 23.6% respectively. The tumor sizes in mice intratumorally injected with siVEGFR2/PEI complexes (189.429 +/- 17.562 mm3) were reduced definitely compared to that in mice injected with siVEGFR2/PEI complexes via vein route (315.507 +/- 20.491 mm3), or to saline groups (365.844 +/- 20.713 mm3). The study demonstrated that PEI could effectively transfect siRNA into cells and silence the VEGFR2 gene expression. Intratumoral delivery is more suitable for non-targeted modified PEI/siRNA complexes to inhibit the tumor growth in vivo. The present data lay a solid foundation to further study on the gene silencing mechanism for PEI-medicated RNAi and its anti-tumor efficiency in vivo.
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OBJECTIVE:To establish an HPLC method for the determination of lipoic acid in lipoic acid sustained-release tablets.METHODS:HPLC was conducted on a Hypersil ODS with acetonitrile-0.05 mol?mL-1 potassium dihydrogen phosphate(45∶55,adjust pH to 2.0)as mobile phase at a flow rate of 1.0 mL?min-1.The injection volume was 10 ?L;the detection wavelength was set at 219 nm and the column temperature was 25 ℃.RESULTS:The linear range of lipoic acid was 9.99～399.70 ?g?mL-1(r=0.999)with an average recovery rate of 99.17%(RSD=0.40%);the intra-day and inter-day RSD were all less than 2.6%.CONCLUSION:The method is simple and accurate,and suitable for the determination of the content of lipoic acid in lipoic acid sustained-release tablets.
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Objective To investigate the effect of pronuciferine on apoptosis of cultured human umbilical vein endothelium cells(HUVECs) induced by angiotensin Ⅱ(AngⅡ).Methods HUVECs cell line ECV304 was cultured in vitro,pretreated with Captopril(10 ?mol/L) or pronuciferine 10,1,0.1,0.01 ?mol/L for 30 min,respectively,then treated with AngⅡ(1 ?mol/L).Cell-morphosis was observed by light microscope.Cells viability was assessed by MTT assay.Production of nitric oxide(NO),activities of total nitric oxide synthase(tNOS),and inducible nitric oxide synthase(iNOS) were measured by colorimetry.Apoptosis rate was measured by Flow Cytometer(FCM).Results AngⅡ induced typical endothelial cell apoptosis and the apoptosis rates were significantly higher than those of the control group((P