|Tuesday, August 24|
Enhancing mechanical property of Mg-Zn-Nd alloy wire by a combination of equal channel angular pressing, extrusion and hot drawing
* Lili Tan, Institute of Metal Research, Chinese Academy of Sciences, China
Ming Gao, Institute of Metal Research, Chinese Academy of Sciences
Ke Yang, Institute of Metal Research, Chinese Academy of Sciences
INTRODUCTION: Biodegradable magnesium alloys wires have great potential as surgical staples. Most of the metal wires were prepared by drawing, which includes cold drawing and hot drawing. The material after cold drawing has higher strength, but the severe work hardening occurs during the cold drawing process, which has a negative influence on the ductility of the material. The magnesium alloy wire prepared by hot drawing with higher processing efficiency has good ductility, but the strength is usually too low to meet the requirement for staples [1-2]. Therefore, it is essential to coordinate the strength and ductility of magnesium alloy wires for the application of staples. In this study ECAP and extrusion were combined with hot drawing to fabricate biodegradable Mg alloy wires with high strength and ductility. METHODS: Mg-2Zn-0.5Nd (ZN20) alloy with a composition of 1.84% Zn, 0.52% Nd and remaining Mg, was extruded. Cylindrical specimens (10 mm in diameter and 100 mm in length) were cut from extruded bars. The cylindrical specimens were processed by four passes equal channel angular pressing (ECAP), and rotated 90° along extrusion direction after each pass. ZN20 alloy after ECAP was extruded into wires with diameter of 1 mm (Extrusion-2) and then was followed by hot drawing to the final size of wires. RESULTS: A bi-ultrafine (BU) microstructure with similar diameter of matrix grains (1-3 μm) and second phase particles (composed of larger granular phase with an average diameter of 2.54 μm and smaller granular phase with an average diameter of 1.08 μm) was formed in ZN20 alloy after a combined process of ECAP, extrusion and hot drawing. After such a combined process, the ultimate tensile strength was increased to 332 MPa, and the ductility (7.9%) was also increased by 3.5 times. DISCUSSION & CONCLUSIONS: The strength of ZN20 alloy wire after a combined process of ECAP, extrusion and hot drawing was increased to 332 MPa by texture strengthening, grain boundary strengthening and precipitates strengthening. Figure 1 shows schematic illustration of crack initiation mechanism in ZN20 alloy with coarse grain microstructure and bi-ultrafine microstructure. The ductility was improved obviously due to the formation of BU microstructure, because it could promote shear bands nucleation and inhibit their prolongation, and profuse shear bands could coordinate the deformation . While in ZN20 alloy with coarse grain microstructure, stress concentration caused by dislocation accumulation around second phase and grain boundary had a negative influence on the ductility .
Copper-incorporated polydopamine coatings on biodegradable Mg alloy vascular stent with corrosion-resistant and re-endothelialization multifunctionality
* ling-yu Li, Shanghai Jiao Tong University, China
Jia Pei, Shanghai Jiao Tong University
Biodegradable magnesium stents are promising applied to treating coronary artery diseases, as they can provide short-term functional support and facilitate full recovery of arteries 1. However, overfast degradation of Mg alloys limit its wider application in biomedical implant field. This work developed Copper-incorporated polydopamine coatings on Mg alloys with corrosion-resistant and re-endothelialization multifunctionality.
A biodegradable multifunctional 3D woven Magnesium-based scaffold for orthopedic implants
* Ju Xue, Johns Hopkins University, United States
Srujan Singh, Johns Hopkins University
Alexander Pantoja, Johns Hopkins University
Yuxiao Zhou, Johns Hopkins University
Timothy Witham, Johns Hopkins University
Warren Grayson, Johns Hopkins University
Timothy Weihs, Johns Hopkins University
Porous Magnesium (Mg) is considered a promising biodegradable scaffold when treating critical-size bone defects. In this study, we manufactured 3D weaves with various architecture using Mg wires, and we optimized them for stiffness and porosity using topology optimization. Once woven, we dip-coated the weaves into polylactic acid (PLA) that includes Mg oxide nanoparticles (nMgO) to tailor the strength of the weaves, as well as their rate of degradation and the local pH within physiological conditions.
Extrusion-based additive manufacturing of MgZn alloy scaffolds
* Jiahui Dong, Delft University of Technology, Netherlands
Nazli Tümer, Delft University of Technology
M.A Leeflang, Delft University of Technology
L.E Fratila-Apachitei, Delft University of Technology
A.A Zadpoor, Delft University of Technology
Jie Zhou, Delft University of Technology
Extrusion-based additive manufacturing technique was successfully employed to fabricate MgZn scaffolds and the in vitro biodegradation behavior, mechanical properties, electrochemical response and biological responses of an osteoblast cell line to the fabricated MgZn scaffolds were studied.
In-vitro degradation assessment of bioresorbable Mg-Li-Zn-Ca alloys
* Chiamaka Okafor, Florid International University, United States
Norman Munroe, Florid International University
The development of Mg-Li-Zn-Ca alloy system is aimed at improving uniform biodegradation. Studies carried out show that these alloys can provide uniform degradation, improve mechanical strength and ductility without posing toxic reactions to the human body. These improvements are because of microstructural phase transformations and presence of superior passivating oxides.
Optimization of SLM parameters for 3D printing pure magnesium
* Agnieszka Chmielewska, The Ohio State University, United States
Bartomiej Wysocki, Cardinal Stefan Wyszynski University in Warsaw
Karolina Bogdanowicz, Warsaw University of Technology
ukasz rodowski, Warsaw University of Technology
Wojciech wieszkowski, Warsaw University of Technology
Alan Luo, The Ohio State University
David Dean, The Ohio State University
This study presents the optimization of printing parameters of pure magnesium Selective Laser Melting (SLM) technique to achieve high density and reliable mechanical and resorption properties. Process parameters that allowed for the fabrication of solid magnesium samples with density up to 93% are reported.
Discussion - Short Oral Presentation