Biodegradable Materials for Medical Applications II: Magnesium Implants
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 8:00 AM
February 24, 2020
Room: Vista
Location: Marriott Marquis Hotel

Session Chair: Jaroslaw Drelich, Michigan Technological University; Jan-Martin Seitz, Syntellix AG


8:00 AM Introductory Comments

8:05 AM  Keynote
Proteins and Flow Conditions: How They Influence the Degradation of Mg: Ruiqing Hou1; Frank Feyerabend1; Regine Willumeit Romer1; 1Helmholtz Center Geesthacht
    To understand the magnesium (Mg) degradation mechanism in vivo, a variety of in vitro investigations were conducted. However, there is still a discrepancy of in vitro results with in vivo observations. Herein, the combined effect of proteins and medium flow condition on magnesium degradation was studied. Bovine serum albumin (BSA) and fetal bovine serum (FBS) were applied as the commonly used protein components for in vitro tests. Static condition, a medium changing method (semi-static) and continuous medium flow (dynamic) were used to present different conditions. The results showed the largest degradation inhibition efficiency of BSA and FBS to Mg degradation under static condition, while the efficiency largely decreased when the semi-static or dynamic condition were used, especially for BSA. The possible explanations are related to the composition of degradation products and the integrity of degradation layer. These results emphasis the importance of considering effects from different factors during magnesium degradation.

8:40 AM  Invited
Biodegradable Magnesium Implants – From Alloy Development to In Vivo Testing: Hans Maier1; Peter Wriggers1; Andrea Meyer-Lindenberg2; 1Leibniz Universität Hannover; 2 Ludwig-Maximilians-Universität München
    Magnesium-based implants are attractive for the treatment of large bone defects, as they combine good mechanical strength with biocompatibility and can be resorbed by the body. In addition, open-pored structures provide for enhanced bone ingrowth. In the present study, such structures were produced by investment casting and their degradation behavior was tailored by application of various surface coatings including magnesium fluoride, polylactic acid and calcium phosphate. Fused deposition modeling was employed to generate the initial form of the wax model used for investment casting. This in turn allowed for easy modification of pore sizes and arrangements. The implants were then tested both in-vitro and in-vivo. It turned out that the degradation rate can be tailored such that it is slow enough for use in implants. Moreover, the mechanical strength of the porous implants is sufficiently large to bear the loads experienced under actual loading scenarios.

9:05 AM  Invited
An Mg-Zn-Ca-based Alloy and a Biocompatible Ceramic Coating Towards Resorbable Bone Fixation Devices: Hamdy Ibrahim1; Alan Luo2; David Dean2; Rigoberto Advincula3; Mohammad Elahinia4; 1University of Tennessee at Chattanooga; 2Ohio State University; 3Case Western Reserve University; 4University of Toledo
    Mg and its alloys have recently been attractive for developing biomedical devices that can bioresorb completely after the healing of the body tissue. This can be attributed to the biodegradable nature, low density and biocompatibility of Mg alloys. While some Mg alloys are potentially strong enough for some bone implant applications, the strength, corrosion rates and biocompatibility of these alloys are not suitable for load-bearing skeletal reconstruction applications. We developed a patent-pending alloy, Mg-1.2Zn-0.5Ca-0.5Mn produced using biocompatible alloying elements, and a heat treatment process that is likely to provide the needed mechanical stability during bone healing and reliably resorb following the healing of a reconstructed skeletal segment. Our results confirmed the significant role of Zn content and age hardening temperature on the mechanical and corrosion properties of heat-treated Mg-Zn-Ca-based alloys. We also developed a composite ceramic-based coating to delay device corrosion using micro arc oxidation and sol-gel coating techniques.

9:30 AM  Invited
In-Vivo and In-Vitro Performance of Bioabsorbable BioMg 250 Mg Alloy Implants: Jacob Edick1; Raymond Decker1; Stephen LeBeau1; 1Nanomag LLC
    BioMg 250 is a microalloyed Mg-based alloy which can be strengthened by nutrient elements to reach yields strength levels greater than 300 MPa, while maintaining ductility of at least 10%. Its composition and processing have been optimized by in-vitro corrosion and toxicity testing. This presentation will report on follow-on in-vivo campaigns in animal models that demonstrate the bioabsorption rates, lack of toxicity (biocompatibility) and positive preclinical results of BioMg 250.

9:55 AM Break

10:10 AM  
Hydrogen Sensors for Noninvasively Monitoring the Status of Bioresorbable Magnesium Implants: William Heineman1; Daoli Zhao1; 1University of Cincinnati
    Bioresorbable magnesium offers advantages over permanent stainless steel for implants such as plates and screws that are used for repairing damaged bone. Magnesium bioresorbs by reacting with water to form hydrogen gas, magnesium ion, and hydroxide ion. Hydrogen has proven to be especially useful for monitoring magnesium biodegradation during in vivo evaluation of Mg alloys and devices implanted in test animals because the hydrogen gas generated during bioresorption rapidly permeates through biological tissue. Both electrochemical and visual sensors that are sufficiently sensitive to measure the very low levels of hydrogen involved have been developed for this application. Monitoring hydrogen is easily done by placing the sensor on the skin above the implant where it responds to the hydrogen gas permeating through the skin. This simple, non-invasive procedure is potentially useful for point-of-care applications such as doctor’s office surgery follow-ups to check the corrosion status of implants in patients.

10:30 AM  Cancelled
Current Development Status of Surgical Stapler and Clip Made of Mg Alloy in Kobe University: Takumi Fukumoto1; Masahiro Kido1; Naoko Ikeo1; Toshiji Mukai1; 1Kobe University
    Surgical instruments used for tissue ligation or intestinal anastomosis are usually made of titanium. They remain in the body permanently and form metallic artifacts in computed tomography images, which impair accurate diagnosis. In addition, it may pose a potential risk of a bacterial infection. Although biodegradable magnesium instruments have been developed in other fields, the physical properties necessary for tissue ligation or intestinal anastomosis differ from those of other instruments. Besides suitable biodegradability, these require the sufficient ductility and mechanical strength for applying tissue ligation or intestinal anastomosis. We have developed a biodegradable magnesium-zinc-calcium alloy clip and stapler with good biological compatibility and enough clamping or stapling capability. In this presentation, we show the current development status of these instruments. We believe that our new surgical instrument be useful in the clinical setting in near future.

10:55 AM  
Influence of Solution Heat Treatment on Microstructure, Hardness and Corrosion Behavior of Extruded RESOLOY: Petra Maier1; Benjamin Clausius1; Norbert Hort2; 1Stralsund University of Applied Sciences; 2Helmholtz-Zentrum Geesthacht
    Microstructural changes of RESOLOY, a resorbable Mg-Dy based alloy, is focus of this study. Hardness and bending tests are used to monitor the changes in mechanical properties. Overall, stress corrosion on C-Ring tests are planned to evaluate the corrosion behavior. Hot-extruded tubes were solution heat-treated at different temperatures and times. The as-extruded condition shows a rather homogeneous fine-grained microstructure. Solution heat treatment at lower annealing temperatures and times does not change the microstructure much, but reduces the hardness by relieving work-hardening. Solution heat treatment at higher annealing temperatures and times (24 and 48h) causes grain growth and reduces hardness, the spread of data distribution increases. On the other hand, annealing at 72h increases hardness with reducing mean grain size. Earlier research showed that LPSO phases form during post heat treatment. As-extruded RESOLOY is not free of pitting corrosion, especially not near strain-hardened areas. Solution heat treatment improves the corrosion behavior.

11:15 AM  
High Strength Rare Earth Free Mg Alloys with Controlled Degradation Behavior Through Microstructural Manipulation: Ehsan Mostaed1; Malgorzata Sikora-Jasinska1; Jaroslaw W. Drelich1; 1Michigan Technological University
    Magnesium (Mg) alloys have received increasing attention as potential bioresorbable medical materials for orthopedic load-bearing applications due to their excellent biocompatibility. Unfortunately, Mg rapid degradation in physiological environments, accompanied with a large amount of hydrogen gas release, affects tissue regeneration and delays the bone healing. Addition of rare earth elements (REEs) improves the degradation performance of Mg alloys. However, concerns about their biosafety have recently been raised. We have produced several REE-free nanostructured Mg alloys containing nutrient elements of Zn, Ca and Sr using a combination of novel non-equilibrium rapid solidification and severe plastic deformation (SPD) techniques. The SPD induced ultrafine-grained structure and dynamic precipitation of MgZn, Ca2Mg6Zn3 and Mg17Sr2 intermetallics resulted in remarkable enhancement of the alloys strength. Moreover, owing to the uniformly distributed nanosized precipitates within the Mg matrix, nanostructured alloys exhibited nearly an order of magnitude lower corrosion rate than their conventionally processed counterparts.