RESUMO
Zinc shows great promise as a bio-degradable metal. Our early in vivo investigations implanting pure zinc wires into the abdominal aorta of Sprague-Dawley rats revealed that metallic zinc does not promote restenotic responses and may suppress the activities of inflammatory and smooth muscle cells. However, the low tensile strength of zinc remains a major concern. A cast billet of the Zn-Li alloy was produced in a vacuum induction caster under argon atmosphere, followed by a wire drawing process. Two phases of the binary alloy identified by x-ray diffraction include the zinc phase and intermetallic LiZn4 phase. Mechanical testing proved that incorporating 0.1wt% of Li into Zn increased its ultimate tensile strength from 116±13MPa (pure Zn) to 274±61MPa while the ductility was held at 17±7%. Implantation of 10mm Zn-Li wire segments into abdominal aorta of rats revealed an excellent biocompatibility of this material in the arterial environment. The biodegradation rate for Zn-Li was found to be about 0.008mm/yr and 0.045mm/yr at 2 and 12months, respectively.
Assuntos
Ligas/química , Aorta Abdominal , Animais , Lítio , Magnésio , Teste de Materiais , Ratos , Ratos Sprague-Dawley , ZincoRESUMO
The present work aimed to investigate the influence of acetone and formalin as well as the duration and type of storage on magnesium based implants by means of microscopic, µ-computed tomographic, scanning electron microscopic, EDX and metallographic investigations. In contrast to storing in acetone, storage in formalin led to an increase in surface to volume ratio, and a decrease of the volume and the density. The various types of storage exerted no differing effects on the implants but with increasing storage duration, a spreading of oxygen rich areas on the surface, increased precipitations and a decrease in grain size could be observed.
Assuntos
Magnésio , Próteses e Implantes , Acetona/química , Formaldeído/química , Microscopia Eletrônica de Varredura , Tomografia Computadorizada por Raios XRESUMO
Magnesium alloys are promising implant materials for use in orthopaedic applications. In the present study, screws made of the Mg-alloy ZEK100 (n = 12) were implanted in rabbit tibiae for four and six weeks, respectively. For degradation analysis, in vivo µ-computed tomography (µCT), a determination of the weight changes and SEM/EDX examinations of the screws were performed. Screw retention forces were verified by uniaxial pull-out tests. Additionally, soft-tissue biocompatibility was estimated using routine histological methods (H&E staining) and the immunohistological characterization of B- and T-cells. After six weeks, a 7.5% weight reduction occurred and, in dependence of the implant surrounding, the volume loss (µCT) reached 9.6% (screw head) and 5.0% for the part of the thread in the marrow cavity. Pull-out forces significantly decreased to 44.4% in comparison with the origin value directly after implantation. Soft tissue reactions were characterized by macrophage and lymphocyte infiltration, whereas T-cells as well as B-cells could be observed. In comparison to MgCa0.8-screws, the degradation rate and inflammatory tissue response were increased and the screw holding power was decreased after six weeks. In conclusion, ZEK100-screws seem to be inferior to MgCa0.8-screws, although their initial strength was more appropriate.