Biodegradable Materials for Medical Applications II: Magnesium Implants II
Sponsored by: TMS Functional Materials Division, TMS: Biomaterials Committee
Program Organizers: Jaroslaw Drelich, Michigan Technological University; Ehsan Mostaed, Michigan Technological University; Malgorzata Sikora-Jasinska, Michigan Technological University; Jan-Marten Seitz, Syntellix AG; Petra Maier, University of Applied Sciences Stralsund; Norbert Hort, Helmholtz-Zentrum Hereon; Huinan Liu, University Of California Riverside
Monday 2:30 PM
February 24, 2020
Room: Vista
Location: Marriott Marquis Hotel
Session Chair: Petra Maier, University of Applied Sciences Stralsund; Norbert Hort, Helmholtz-Zentrum Geesthacht
2:30 PM Keynote
Are those Biproducts of Bidegradable Metals Deleterious to Bone Healing?: Kelvin Yeung1; 1The University of Hong Kong
A variety of degradable metallic ions e.g. magnesium and zinc has been reported to alter different cellular functions including the transport of potassium and calcium ions, whilst it also modulates signal transduction, energy metabolism and cell proliferation due to the electro-potential change of cell membrane. It was recently reported that the presence of magnesium in the bone system is beneficial to bone growth and play a key role in bone remodeling and skeletal development. In the present study, we aim at reporting the potential mechanism of bone healing stimulated by Mg ions and its clinical applications as well as its bio-hazard.
3:05 PM Invited
On Contributors to Fracture in Absorbable Metals: Adam Griebel1; Jeremy Schaffer1; 1Fort Wayne Metals
Absorbable metal implants are designed to disintegrate, eventually. Various modes of material fracture may occur over the service life and it is key to ensure that fracture occurs in compliment to healing. For both iron- and magnesium-based absorbable metals, a host of intrinsic factors (e.g. chemistry, internal defects) and extrinsic factors (e.g. final microstructure, surface finish, in-service conditions) will impact these modes of fracture. This talk will review contributors to fracture in current-state medical metals with a focus on wire and how these may or may not apply to absorbable metals. The talk will also highlight observed fracture modes in ferrous and magnesium alloys and efforts to minimize them, and finally comment on standardization efforts in these areas.
3:30 PM
Non Invasive Degradation Tracking of Mg Implants in Humans: Jan-Marten Seitz1; Patrick Varady1; Tim Vockensohn1; 1Syntellix AG
Measurement of in vivo degradation progression for biodegradable metals such as magnesium remains of utmost importance for customer satisfaction and regulatory purposes. Current methods base on CT/X-ray or MRI approaches that generally provide results with inappropriate validity. Approaches via MRI are heavily impacted by the exact position and orientation of the implant in the magnetic field and final evaluation is affected by subjective assessment. CT scans expose the patients to radiation and based on their attenuation one cannot precisely distinguish between bone, the magnesium’s degradation products (e.g. MgOH2) and metal, which makes proper degradation tracking impossible.Syntellix developed non invasive routines to overcome these adverse and often inaccurate methods by combining H2-measurement and metal detection. Both methods are suitable to detect the state of degradation of magnesium implants in vivo directly or indirectly by means of periodically recurring standardized measurements.
3:50 PM
Tailoring Degradation Behavior of Mg-5Nd Alloy by Intermetallic Distribution: Yaping Zhang1; Yuanding Huang1; Frank Feyerabend1; Karl Ulrich Kainer1; Norbert Hort1; 1Helmholtz-Zentrum Geesthacht
The distribution of intermetallic phases (IM) largely influences corrosion resistance and strength of degradable magnesium alloys. In order to investigate its effects on the degradability, alloying element Nd was selected, which was reported to have a quite good cytocompatibility. The present investigation mainly focuses on the influence of distribution of Nd containing IM on the degradability of magnesium. The alloys with different distributions of second phases were prepared by various heat treatments. Microstructures were investigated by optical, scanning / transmission microscopy, and synchrotron radiation diffraction. Degradation behavior was explored by immersion in DMEM + 10% FBS under cell culture conditions. In T4 state, undissolved Mg41Nd5 phase distributed randomly in the matrix. Fine Mg41Nd5 precipitates forming inside the grains during T6 treatment facilitated intragranular corrosion, but its degradation rate was less than that of T4 microstructure.
4:10 PM Break
4:25 PM
Microstructure and Biodegradation Behavior of Additively Manufactured Magnesium: Leila Sorkhi1; James Tomich1; Joshua Hammel1; Grant Crawford1; 1South Dakota School of Mines and Technology
Magnesium has gained significant interest for use as biodegradable implants due to its excellent biocompatibility, comparable mechanical properties to natural bone, and unique ability to naturally degrade in the physiological environment. However, the high biodegradation rate of magnesium alloys may result in hydrogen gas evolution and associated patient discomfort, or loss of implant mechanical integrity. Additive manufacturing offers the potential to develop compositionally gradient biodegradable implants and complex implant designs for improved biological function. In this work, direct energy deposition was used to fabricate Mg parts with various compositions. Microstructure was characterized using optical microscopy, scanning electron microscopy, and energy dispersive x-ray spectroscopy. Furthermore, the corrosion behavior of the samples was evaluated using potentiodynamic polarization and immersion methods in simulated body fluid. Finally, the effect of post-processing on microstructure and degradation behavior of the additively manufactured samples was evaluated.
4:45 PM
In-vitro Corrosion and Mechanical Performance of Mg Alloy WE43 Processed by Spark Plasma Sintering: Julie Soderlind1; Subhash Risbud1; Joerg Loeffler2; 1University of California, Davis; 2ETH Zurich
Magnesium alloys are currently investigated for biodegradable implant applications due to their mechanical strength and biocompatibility. Processing by conventional methods (melt casting, extrusion) does not result in the refined microstructure required for controlled corrosion in a biological environment. Spark plasma sintering (SPS) is an attractive alternative processing method offering both densification and microstructure control. This study characterizes the in-vitro corrosion and mechanical performance of gas-atomized WE43 powder, sintered with two different SPS conditions. Samples were sintered at two distinct pressures, heating rates and hold times, with a Ts = 450°C. The resulting microstructures, observed in both SEM and TEM, show differences in the distribution of alloying elements. Both samples were immersed in an NaCl solution for three days and imaged to evaluate the impact of microstructural refinement on corrosion surface morphology. Mechanical performance of each sample was evaluated by simple compression and microhardness testing. Prepared by LLNL under Contract DE-AC52-07NA27344.
5:05 PM Cancelled
Evaluation of in vitro Fatigue Property of Grain Refined Mg-Ca Alloy: Naoya Kawamura1; Taichi Uemura1; Naoko Ikeo1; Toshiji Mukai1; 1Kobe University
Magnesium is expected as a new class of biomaterials due to the biodegradability and excellent biocompatibility. One drawback of magnesium implants is that they have a risk of premature fracture by fatigue in vivo. Therefore it is important to improve fatigue property in the degradable environment. Grain refinement is known to improve fatigue strength in air, but the effect on fatigue property in vivo is still unclear. Thus, the aim of this research is to clarify the effect of grain refinement on fatigue strength in vitro to study the fatigue properties in vivo. As a result of fatigue test in vitro, fatigue strength in a fine-grained alloy became almost the same in a high cycle region when compared with those of magnesium with large grain size. This suggest that in the high cycle region, effect of corrosion resistance decrease caused by grain refinement becomes bigger than fatigue strength improving.
5:25 PM
Effect of Secondary Processing on Microstructure, Mechanical and Corrosion Response of a Biodegradable Mg1Zn2Ca Alloy: Diksha Matta1; Gururaj Parande2; Sravya Tekumalla2; Manoj Gupta2; 1Vellore Institute of Technology; 2National University of Singapore
Magnesium and its alloys have often been evaluated for their application as temporary orthopaedic implants owing to several salient advantages over other light metals (aluminium and titanium) such as high specific strength, natural availability, non-toxic nature, similar elastic modulus as that of bone amongst others. However, its limited corrosion resistance restricts its application in real-time biomedical applications. By alloying with biocompatible elements, high corrosion rate can be alleviated without inducing any apparent toxicity in the host both at the local and systemic level. In this study, a novel magnesium-based alloy is synthesized using disintegrated melt deposition and the effect of the secondary extrusion process on the mechanical and corrosion response is studied. Mechanical properties like microhardness and compression displayed excellent results owing to superior grain refinement post extrusion. Corrosion rates evaluated using simulated body fluid(HBSS) displayed promising results with delayed and uniform degradation profile. Strucutre-property correlations are analyzed.