Evaluation of a new Mg-Zn-Ca-Y alloy for biomedical application.

In this study, a new Mg-Zn-Ca-Y alloy was evaluated for blood compatibility and in vivo biocompatibility in rabbits after implantation in the sacral crest muscle. Blood test and HE staining was performed to examine the host response, and scanning electron microscope was used to observe the fibrous membrane and corrosion of the magnesium alloy. The results showed that hemolysis rate decreased with the Mg(2+) concentration, in particularly, the hemolysis rate was 47.24 % for the magnesium alloy 100 % mixture solution, while was 0.1372 % for the 1 % extract solution. After implantation, the rabbits showed generally good condition, without swelling and wound secretions. One week after implantation, in the experimental group, a few lymphocytes and macrophages could be observed around the local muscle tissue, and fiber membrane structure had not yet formed; after 2 weeks, loose fiber membranes formed, while the number of inflammatory cells decreased; the fiber membrane became thinner at 4 and 12 weeks,. The fiber membrane thickness at 24 weeks were measured by scanning electron microscopy, at about 15-25 µm, which accord with the U.S. ASTM-F4 implant requirements (<30 µm). Acceptable degradation and corrosion were observed after implantation into rabbits. Through the in vivo study, the new magnesium alloy exhibited good biocompatibility and non-toxic in the experimental animals. Addition of Zn, Ca and Y can slow the degradation rate, and have acceptable side effects in vivo, resulting in improved corrosion properties and desirable biocompatibility at the same time.

Ti-24Nb-4Zr-8Sn Alloy Pedicle Screw Improves Internal Vertebral Fixation by Reducing Stress-Shielding Effects in a Porcine Model.

To ensure the biomechanical properties of Ti-24Nb-4Zr-8Sn, stress-shielding effects were compared between Ti-24Nb-4Zr-8Sn and Ti-6Al-4V fixation by using a porcine model. Twelve thoracolumbar spines (T12-L5) of 12-month-old male pigs were randomly divided into two groups: Ti-24Nb-4Zr-8Sn (EG, n = 6) and Ti-6Al-4V (RG, n = 6) fixation. Pedicle screw was fixed at the outer edge of L4-5 vertebral holes. Fourteen measuring points were selected on the front of transverse process and middle and posterior of L4-5 vertebra. Electronic universal testing machine was used to measure the strain resistance of measuring points after forward and backward flexion loading of 150 N. Meanwhile, stress resistance was compared between both groups. The strain and stress resistance of measurement points 1, 2, 5, 6, 9, and 10-14 in Ti-24Nb-4Zr-8Sn fixation was lower than that of Ti-6Al-4V fixation after forward and backward flexion loading (P < 0.05). The strain and stress resistance of measurement points 3, 4, 7, and 8 was higher in Ti-24Nb-4Zr-8Sn fixation than that of Ti-6Al-4V fixation (P < 0.05). Stress-shielding effects of Ti-24Nb-4Zr-8Sn internal fixation were less than that of Ti-6Al-4V internal fixation. These results suggest that Ti-24Nb-4Zr-8Sn elastic fixation has more biomechanical goals than conventional Ti-6Al-4V internal fixation by reducing stress-shielding effects.