In Vivo Degradation Performance of High-Purity Magnesium Subjected to Quantitative Mechanical Load / 医用生物力学

Objective To study the effects of mechanical load on in vivo degradation performance of high-purity magnesium (HP Mg, 99.99 wt.%) quantitatively. Methods Cylindrical Mg specimens, with a 2 mm diameter and a 14 mm length, were mounted in polyetheretherketone (PEEK) rings to bear compressive stresses ［（6.2±0.6） MPa］, tensile stresses ［（4.6±0.1） MPa］ or no stress (as control). The specimens under different stress states were implanted subcutaneously in dorsal abdominal regions of SD rats for 4 weeks. The mass loss, residual volume and surface morphology of the specimens and staining of surrounding soft tissues were used to analyze the degradation rate of HP Mg. Results Specimens and rings were completely encapsulated by membranous tissues after implantation for 4 weeks. No significant differences in the degradation rates were noted between specimens bearing stress and the control. The corrosion layers of specimens under each stress state were uniform. Conclusions The compressive and tensile stresses (4-6 MPa) could not affect significantly HP Mg degradation performance in vivo. The research findings provide theoretical references for the design and clinical application of Mg-based degradable implants.

Distribution, quantitative load and characterization of Salmonella associated with swine farms in upper-northern Thailand

This study was conducted to analyze the prevalence and quantitative loads of Salmonella spp. on pig farms in Chiang Mai, Lamphun, Thailand to assess loading levels before slaughtering. The serotype diversity, antimicrobial-resistance pattern and pulse-field type of Salmonella spp. were also characterized to assess the dynamic propagation of the pathogen. The Salmonella-positive prevalence was 246/805 (30.56%), and the quantitative loads varied from 1.48~4.04 Log10MPN/g, with a mean +/- standard deviation of 2.11 +/- 0.57. AMP/S/TE (ampicillin/streptomycin/tetracycline) was the highest frequency antimicrobial resistance pattern found in this study. In addition, Salmonella Rissen was the primary serotype in this region. PFGE results indicated the occurrence of infection by cross contamination among pig farms. Our study showed that pork is easily contaminated with this pathogen. Farm control programs must be based on strict biosecurity and hygienic measures, which could further reduce the contamination pressure at slaughterhouses or retail shops.