טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentRemennik Sergei
SubjectDevelopment of Magnesium Alloys for Bio-Medical Applications
DepartmentDepartment of Materials Science and Engineering
Supervisor Research Professor E Dan Shechtman
Full Thesis textFull thesis text - English Version


Abstract

Current approaches to reduce initial corrosion rates of biodegradable magnesium alloys include alloying with different elements, mechanical processing, coatings and the use of metallic glasses. Alloys produced this way have limited ductility and therefore low fracture toughness that may render the alloy useless. Furthermore, slow corroding magnesium alloys, coatings or metallic glasses have not proven to be fully dissolvable in-vivo.

We have developed a new class of biocompatible, biodegradable ductile magnesium alloys with up to 40 percent elongation at room temperature. The alloys are based on the Mg-Bi and Mg-Zn-Y-RE (RS66) systems and undergo a series of production routes, which include rapid solidification (RS) and various extrusion processes like forward (EX) and Reciprocating (RE) extrusion. In preliminary bone, intramuscular and subcutaneous implant sites studies in rabbits, the alloys corrode fast without any clinically visible gas formation in bone sites. Only 50% of RS66-RE4 implant and 30% of the Mg-Bi-Ca implant remains uncorroded 4 weeks post implantation, while for HP-B-BX samples, prepared from low iron magnesium, about 70% of the bone implant remained uncorroded after 4 weeks of implantation. However, the corrosion rates in intramuscular and subcutaneous implantation site were significantly higher for all alloys.

The foreign body reaction was very mild and enhanced bone formation could be observed in the vicinity of the corroding implant. Thus, these new magnesium alloys may be promising biomaterials, although more detailed in-vivo studies of the alloys need be performed in actual implant situations.

We also designed and made high strength high ductility alloys based on the Mg-Li system. These new alloys contain previously unknown intermetallic phases that we were able to analyze. One such phase is the quaternary Mg-Zn-Ca-Li with space group (SG) Pm3  (200) and lattice parameter: a=9.386(8) Å. Its atomic positions were determined by XRD Rietveld refinement. Two more quaternary phases, Mg-Zn-Y-Li and Mg-Zn-Y-Al-Li were also identified.