Effects of Revision Rod Position on Spinal Construct Stability in Lumbar Revision Surgery: A Finite Element Study

Revision surgery (RS) is a necessary surgical intervention in clinical practice to treat spinal instrumentation–related symptomatic complications. Three constructs with different configurations have been applied in RS. One distinguishing characteristic of these configurations is that the revision rods connecting previous segments and revision segments are placed alongside, outside, or inside the previous rods at the level of facetectomy. Whether the position of the revision rod could generate mechanical disparities in revision constructs is unknown. The objective of this study was to assess the influence of the revision rod position on the construct after RS. A validated spinal finite element (FE) model was developed to simulate RS after previous instrumented fusion using a modified dual-rod construct (DRCm), satellite-rod construct (SRC), and cortical bone trajectory construct (CBTC). Thereafter, maximum von Mises stress (VMS) on the annulus fibrosus and cages and the ligament force of the interspinous ligament, supraspinous ligament, and ligamentum flavum under a pure moment load and a follower load in six directions were applied to assess the influence of the revision rod position on the revision construct. An approximately identical overall reducing tendency of VMS was observed among the three constructs. The changing tendency of the maximum VMS on the cages placed at L4-L5 was nearly equal among the three constructs. However, the changing tendency of the maximum VMS on the cage placed at L2-L3 was notable, especially in the CBTC under right bending and left axial rotation. The overall changing tendency of the ligament force in the DRCm, SRC, and CBTC was also approximately equal, while the ligament force of the CBTC was found to be significantly greater than that of the DRCm and SRC at L1-L2. The results indicated that the stiffness associated with the CBTC might be lower than that associated with the DRCm and SRC in RS. The results of the present study indicated that the DRCm, SRC, and CBTC could provide sufficient stabilization in RS. The CBTC was a less rigid construct. Rather than the revision rod position, the method of constructing spinal instrumentation played a role in influencing the biomechanics of revision.

Acute Effects of Ammoniac Nitrogen on Marine Copepod Acartia pacifica When Exposed to Different Temperature Conditions

Acute toxicity of ammoniac nitrogen on marine copepod Acartia pacifica when exposed to different temperatures of 10℃~25℃were performed under controlled lab conditions. The changing tendency of mortality was evaluated and the 48h LC50 was determined according to the observation. Results showed that the 48h LC50 in different temperature gradients were for Pacific spindle daphnia 48 h - LC50 is 65.889 mg/L for 25 ℃, 134.214 mg/L for 20 ℃, 71.247 mg/L for 15 ℃ and 27.318 mg/L for 10 ℃, respectively. Temperature seemed to exert impacts on the stress induced by ammoniac nitrogen, and the peak of 48h LC50 appeared in between 15 ℃ and 20 ℃. The toxicity of ammonia showed a tendency to decrease with the increase of temperature before the peak while the was significantly enhanced with temperature increasing thereafter.

Interactions and Optimizations Analysis between Stiffness and Workspace of 3-UPU Robotic Mechanism

The interactions between stiffness and workspace performances are studied. The stiffness in x, y and z directions as well as the workspace of a 3-UPU mechanism are studied and optimized. The stiffness of the robotic system in every single moveable direction is measured and analyzed, and it is observed that in the case where one tries to make the x and y translational stiffness larger, the z directional stiffness will be reduced, i.e. the x and y translational stiffness contradicts with the one in z direction. Subsequently, the objective functions for the summation of the x and y translational stiffness and z directional stiffness are established and they are being optimized simultaneously. However, we later found that these two objectives are not in the same scale; a normalization of the objectives is thus taken into consideration. Meanwhile, the robotic system’s workspace is studied and optimized. Through comparing the stiffness landscape and the workspace volume landscape, it is also observed that the z translational stiffness shows the same changing tendency with the workspace volume’s changing tendency while the x and y translational stiffness shows the opposite changing tendency compared to the workspace volume’s. Via employing the Pareto front theory and differential evolution, the summation of the x and y translational stiffness and the volume of the workspace are being simultaneously optimized. Finally, the mechanism is employed to synthesize an exercise-walking machine for stroke patients.

Study of Phase Function of the Biological Cell

In order to settle the influence of measuring results of cells with its shape-variety in the examination of biological cell, MCEM (modify co-central ellipse model) is adopted based on the theories of Rayleigh-Debye-Gans, and the changing tendency of scattering phase function of nucleated cells with different body factor, nuclear size and shooting angle are studied. These provide a useful theory foundation for improving the measurement and distinguishing of biological cell.