Novel biodegradable magnesium alloy clips compared with titanium clips for hepatectomy in a rat model.

BACKGROUND: The use of surgical metal clips is crucial for ligating vessels in various operations. The currently available metal clips have several drawbacks; they are permanent and interfere with imaging techniques such as computed tomography (CT) or magnetic resonance (MR) imaging and carry the potential risk of endo-clip migration. We recently developed a novel magnesium (Mg) alloy for biodegradable clips that reduces artifacts on CT imaging. This study aimed to examine the tolerance, biodegradability, and biocompatibility of the Mg alloy clips compared with those of standard titanium (Ti) clips in hepatectomy. METHODS: Thirty Wistar rats were divided into two groups based on the clip used (groups A and B). The vascular pedicle, including hepatic artery, portal vein, bile duct, and hepatic vein of the left lateral lobe, was ligated with the Ti clip in group A or the Mg alloy clip in group B, and then the left lateral lobe was removed. The rats were sacrificed at 1, 4, 12, 24, and 36 weeks after surgery. Clinical and histological evaluations were performed. Absorption rate was calculated by measuring the clip volume. RESULTS: Although the Mg alloy clips showed biodegradability over time, there were no significant differences in the serum concentration of Mg between the two groups. The remaining volume ratio of Mg alloy clips was 95.5, 94.3, 80.0, 36.2, and 16.7% at 1, 4, 12, 24, and 36 weeks, respectively. No side effects occurred. Most of the microscopic changes were similar in both groups. CONCLUSIONS: The new biodegradable Mg alloy clips are safe and feasible in vessel ligation for hepatectomy in a rat model and reduce artifacts in CT imaging compared with the standard Ti clips.

Trace impurities in sodium phosphate influences the physiological activity of Escherichia coli in M9 minimal medium.

In the field of applied microbiology, reproducibility and experimental variability are important factors that influence both basic research as well as process development for industrial applications. Experimental reproducibility and accuracy depend not only on culture conditions such as temperature and aeration but also on raw materials and procedures used for media preparation. The M9 minimal medium is one of the most common synthetic media for culturing Escherichia coli and other bacteria. This synthetic medium can be used to observe and evaluate the physiological activity of microbes under minimal nutritional requirements and determine the limiting factor for the desired phenotype. Although one of the advantages using the M9 medium is that its composition can be modulated, it is difficult to control presence of trace components and impurities from the reagents for preparing this medium. Herein, we showed that trace ingredients present in the reagents used for M9 media preparation affect the bacterial physiological activities (e.g., cell growth, substrate consumption, and byproduct formation). Additionally, we systematically identified the trace ingredient that influenced phenotypic differences. Our results showed that the selection of reagents and accuracy during reagent preparation is important for experimental reproducibility in the field of bio-engineering and systems biology focused on the systematic and continuous development of biomolecular systems (e.g., biorefinery, metabolic engineering, and synthetic biology).

Shootins mediate collective cell migration and organogenesis of the zebrafish posterior lateral line system.

The zebrafish sensory posterior lateral line is an excellent model system to study collective cell migration and organogenesis. Shootin1 is a cytoplasmic protein involved in neuronal polarization and axon guidance. Previous studies have shown that shootin1 couples actin filament retrograde flow with extracellular adhesive substrates at the leading edge of axonal growth cones, thereby producing mechanical force for the migration and guidance of axonal growth cones. However, the functions of shootin in peripheral cells remain unknown. Here we identified two novel shootin family members, shootin2 and shootin3. In zebrafish, shootin1 and shootin3 are expressed in the posterior lateral line primordium (PLLP) and neuromasts during embryonic development. A shootin1 mutant displayed a reduced speed of PLLP migration, while shootin1;shootin3 double mutation inhibited cell proliferation in the PLLP. Furthermore, our results suggest that shootin1 and shootin3 positively regulate the number of neuromasts and the number of cells in deposited neuromasts. Our study demonstrates that shootins mediate collective cell migration of the posterior lateral line primordium and formation of neuromasts in zebrafish.

Fabrication of a magnesium alloy with excellent ductility for biodegradable clips.

To develop a biodegradable clip, the equivalent plastic strain distribution during occlusion was evaluated by the finite element analysis (FEA) using the material data of pure Mg. Since the FEA suggested that a maximum plastic strain of 0.40 is required to allow the Mg clips, the alloying of magnesium with essential elements and the control of microstructure by hot extrusion and annealing were conducted. Mechanical characterization revealed that the Mg-Zn-Ca alloy obtained by double extrusion followed by annealing at 673K for 2h possessed a fracture strain over 0.40. The biocompatibility of the alloy was confirmed here by investigating its degradation behavior and the response of extraperitoneal tissue around the Mg-Zn-Ca alloy. Small gas cavity due to degradation was observed following implantation of the developed Mg-Zn-Ca clip by in vivo micro-CT. Histological analysis, minimal observed inflammation, and an only small decrease in the volume of the implanted Mg-Zn-Ca clip confirmed its excellent biocompatibility. FEA using the material data for ductile Mg-Zn-Ca also showed that the clip could occlude the simulated vessel without fracture. In addition, the Mg-Zn-Ca alloy clip successfully occluded the renal vein. Microstructural observations using electron backscattering diffraction confirmed that dynamic recovery occurred during the later stage of plastic deformation of the ductile Mg-Zn-Ca alloy. These results suggest that the developed Mg-Zn-Ca alloy is a suitable material for biodegradable clips. STATEMENT OF SIGNIFICANCE: Since conventional magnesium alloys have not exhibited significant ductility for applying the occlusion of vessels, the alloying of magnesium with essential elements and the control of microstructure by hot extrusion and annealing were conducted. Mechanical characterization revealed that the Mg-Zn-Ca alloy obtained by double extrusion followed by annealing at 673K for 2h possessed a fracture strain over 0.40. The biocompatibility of the alloy was confirmed by investigating its degradation behavior and the response of extraperitoneal tissue around the Mg-Zn-Ca alloy. Finite element analysis using the material data for the ductile Mg-Zn-Ca alloy also showed that the clip could occlude the simulated vessel without fracture. In addition, the Mg-Zn-Ca alloy clip successfully occluded the renal vein. Microstructural observations using electron backscattering diffraction confirmed that dynamic recovery occurred during the later stage of plastic deformation of the ductile Mg-Zn-Ca alloy.