BACKGROUND:Al oying is a convenient and effective method to alter the microstructure and control the corrosion behavior of magnesium al oy.
OBJECTIVE:To explore the in vitro and in vivo degradation of Mg-Nd-Zn-Zr al oy as a degradable medical biomaterial.
METHODS:(1) In vitro static immersion test:The immersion tests were carried out at (37.0±0.5) thermostatic bath. Six Mg-Nd-Zn-Zr al oy samples and six pure magnesium samples were immersed in the 250 mL simulated body fluid and vibrated without agitation during immersion. After 3, 7 and 30 days static immersion, the samples were taken out from the simulated body fluid. Then the in vitro corrosion properties were evaluated using scanning electron microscope and energy dispersive spectrometer analysis. (2) In vivo animal experiment:After bone tunnel was established in the left femur of adult New Zealand rabbits, the Mg-Nd-Zn-Zr al oy rods were embedded in the Mg-Nd-Zn-Zr al oy group, titanium al oy rods were embedded in the titanium al oy group, and only bone tunnel was established in the sham-operated group. At 1, 2, 4, 8 weeks after implantation, an X-ray of the implanted region was taken to determine the location and the degradation behavior℃in a of Mg-Nd-Zn-Zr al oy. At 4, 8 weeks after implantation, the corrosion product and its element composition were observed using scanning electron microscope with an energy dispersive spectroscopy system.

Magnesium stents have gained increasing interest as an ideal stent of future intervention. In order to study the deformation behavior of magnesium alloy stents in the interventional treatment, the finite element method was used to analysis the effects of different crimp and expansion dimensions on the mechanical properties (maximum stress, radial recoil rate, longitudinal shortening rate and radial strength). The results showed that crimping and expanding have a minimal influence on the stent radial strength. When the expansion size is same, the maximum equivalent stress and recoil rate decrease with the crimp size. When the crimp size is same, in contrast with the radial recoil rate, the maximum equivalent stress and longitudinal shortening rate increase with the expansion size. In addition the paper verified the radial strength-radial displacement curve obtained by FEM. Results are basically consistent, indicating the finite element method can efficiently provide researchers with reliable, high-quality design.
Alloys ; Finite Element Analysis ; Magnesium ; Stents

Objective To discuss the feasibility of biodegradable covered magnesium alloys stent for a rabbit model of lateral aneurysm in the common carotid artery (CCA). Methods The left CCA was ligated in 20 conventional New Zealand rabbits. MRA of the neck was performed 1 month after ligation. The rabbits with thickening of the right CCA and non-or slight thickening of the bilateral vertebral arteries were selected for lateral aneurysm model making. The venous pouch and the right CCA wall by discontinuous extroversion sutures, to form a lateral aneurysm model. The biodegradable covered magnesium alloys stents or Willis covered stents were inserted two weeks after model making. Angiography was performed prior to the procedure, 3, 6 and 12 months after stent implantation to evaluate the disappearance of the aneurysms and patency of the right CCA. The degradation behaviour is invastagated with molybdenum target 2 weeks, 1, 2, 4, 6,9 and 12 months after stent placement. Results The left CCAs were successful ligated in all rabbits. MRA 1 month after ligation showed thickening of the right CCA and non-thickening of the bilateral vertebral arteries in 17 of 20 rabbits. In these animals, the CCA lateral aneurysm model was deemed successful, and biodegradable covered magnesium alloys stents and Willis covered stents were implanted in 9 and 8 aneurysms, respectively. DSA after biodegradable covered magnesium alloys stent placement displayed disappearance of the aneurysms and patency of the CCA in all 9 rabbits during follow-ups. DSA 3 months after Willis stent placement displayed patency of the CCA in 7 rabbits and occlusion of the artery in one. No occlusion of the right CCA was observed on angiography at 6 and 12 months. The degradation of the biodegradable covered magnesium alloys stent was investigated with molybdenum target during follow-ups, and no changes was observed in Willis covered stent. Conclusion Biodegradable covered magnesium alloys stent is a feasible approach for the treatment of a lateral aneurysm in the right CCA.

The purpose of this paper is to investigate the altered brain areas activated in functional magnetic resonance imaging before and after escitalopram antidepressant treatment in patients with major depressive disorder. Functional magnetic resonance studies showed abnormal activity in brain regions such as prefrontal cortex， cingulate cortex and striatum in patients prior to treatment， meantime， the abnormal activation of anterior cingulate， dorsolateral prefrontal and thalamus reflected the outcomes of escitalopram antidepressant therapy. Following the treatment with escitalopram， the fMRI activation of brain areas returned to normal， and those changes were significantly correlated with the improvement of depressive symptoms. So this paper provides a review of the brain functional activity changes in patients with major depressive disorder before treatment and at different time point of medication， as well as the correlation between altered brain functional activity and clinical symptoms.