Review Article: Recent advances in bulk metallic glasses for biomedical applications

This summary is based on the article published in Acta Biomaterialia: “Recent advances in bulk metallic glasses for biomedical applications” (May 2016)

H.F. Li, Y.F. Zheng, Department of Materials Science and Engineering, College of Engineering, Peking University

Context

• With a continuously increasing aging population and the improvement of living standards, large demands of biomaterials are expected for a long time to come. Further development of novel biomaterials, that are much safer and of much higher quality, in terms of both biomedical and mechanical properties, are therefore of great interest for both the research scientists and clinical surgeons.
• Compared with the conventional crystalline metallic counterparts, bulk metallic glasses have unique amorphous structures, and thus exhibit higher strength, lower Young’s modulus, improved wear resistance, good fatigue endurance, and excellent corrosion resistance. For this purpose, bulk metallic glasses (BMGs) have recently attracted much attention for biomedical applications.
• Bulk metallic glasses (BMGs), also known as amorphous alloys or liquid metals, are relative newcomers in the field of biomaterials. They have gained increasing attention during the past decades, as they exhibit an excellent combination of properties and processing capabilities desired for versatile biomedical implant applications.
• The present work reviewed the recent developments and advances of biomedical BMGs, including Ti-based, Zr-based, Fe-based, Mg-based, Zn-based, Ca-based and Sr-based BMG alloying systems. Besides, the critical analysis and in-depth discussion on the current status, challenge and future development of biomedical BMGs are included. The possible solution to the BMG size limitation, the brittleness of BMGs has been proposed.

Purpose of the Review

• This review discusses and summarizes the recent developments and advances of bulk metallic glasses, including Ti-based, Zr-based, Fe-based, Mg-based, Zn-based, Ca-based and Sr-based alloying systems for biomedical applications.
• Future research directions will move towards overcoming the brittleness, increasing the glass forming ability (GFA) thus obtaining corresponding bulk metallic glasses with larger sizes, removing/reducing toxic elements, and surface modifications.

Review Highlights 

Mechanical properties of biomedical Ti-based BMGs

• Mechanical properties of materials have great importance due to their role for applications. Ti-based BMGs have relatively low Young’s modulus (80–120 GPa), high fracture strength (1700–2500 MPa), and excellent specific strength.

Corrosion behavior of biomedical Ti-based BMGs

• The study of the corrosion behavior of BMGs is of great importance to understand their chemical and environmental stability. Corrosion processes in humid environment are mostly based on electrochemical reactions.
• Researchers have studied the corrosion behavior of Ti-based BMGs in different kinds of simulated body fluids, including phosphate buffered solution (PBS), Ringer’s solution, Hank’s balanced salt solution (HBSS), 1 mass% Lactic acid, and specific simulated body fluid (SBF).
• Studies have shown that Ti-based BMGS exhibited passive behavior at the open-circuit potential with a low corrosion rate; a susceptibility to localized corrosion in the form of pitting corrosion; the localized corrosion resistance was statistically equivalent to, or better than, the conventional crystalline biomedical alloys, including 316L stainless steel, pure Ti and Ti-based biomedical alloys (such as Ti-6Al-4V).

Biocompatibility of biomedical Ti-based BMGs

• Biocompatibility is described as the ability of the material to exist in contact with tissues of the human body without causing a non-acceptable degree of harm.
• Researchers have studied the biocompatibility of Ti-based BMGs via both in vitro cell response (via MTT/CCK8 assay and cell morphology observations) and in vivo animal implants.  And results have demonstrated that Ti-based BMGs showed better biocompatibility than the conventional crystalline Ti-6Al-4V and Ti-45Ni alloys for both the in vitro human osteoblast SaOS2 cells, murine fibroblast cells (L929 cell and NIH3T3 cell) culture and in vivo beagle dogs implantation.

Mechanical properties of biomedical Zr-based BMGs

• The biomedical Zr-based BMGs have been featured with a high hardness that is about twice to three times of that for conventional crystalline biomedical 316L SS, Ti alloys and Zr alloys, and high yield strength that is considerably higher than that of those above mentioned conventional crystalline metallic biomaterials.

Corrosion behavior of biomedical Zr-based BMGs

• Results demonstrated that in comparison with conventional crystalline 316L stainless steel, Zr and Zr-based alloys and Ti and Ti-based alloys, the BMGs show evidently a lower passive current density, much higher pitting potential, suggesting that the passive films formed on the Zr-based BMGs are more protective than on the above mentioned control groups, indicating their enhanced corrosion resistance behavior.

Biocompatibility of biomedical Zr-based BMGs

• Many studies have investigated the biocompatibility of Zr-based BMGs via both in vitro cell response and in vivo animal implants. And results have shown that Zr-based BMGs showed better biocompatibility than the conventional crystalline 316L stainless steel Zr and Zr-based alloys and Ti and Ti-based alloys.

Corrosion behavior of biomedical Fe-based BMGs

• The developed Fe-based BMGs have higher pitting potential values and lower corrosion current density values both in Hank’s solution and in artificial saliva solution and have quite lower ion releasing than that of 316L SS [67], together with good biocompatibility in vitro.

Future research directions and challenges for BMGs as potential biomaterials

BMG Composites

• Future studies need to focus on BMG Composites performances under physiological circumstances, including bio-mechanical properties, bio-corrosion behavior and biocompatibility evaluations.

BMG Foams

• Future studies need to focus on their performances under physiological circumstances, including bio-mechanical properties, biocorrosion behavior and biocompatibility evaluations.

Removing toxic and noble alloying elements

• Removing the toxic and noble alloying elements in BMGs while still keep their high GFA at the same time is another research direction and challenge for the further research and development of biomedical BMGs.

Conclusion

• BMGs have great potential in biomedical applications ranging from orthopedic, cardiovascular to dental implants and fillers.
• As non-degradable BMGs, Ti-based, Zr-based and Febased BMGs with combined excellent mechanical properties and corrosion resistance can be used as biomedical devices, such as surgical blades, pacemakers, medical stapling anvils, and minimally invasive surgical devices; and biomedical implants, such as articulating surfaces, artificial prostheses and dental implants, which are needed to serve a long time in the severe human body environments.
• On the other hand, biodegradable BMGs, including Mg-based, Ca-based, Zn-based and Sr-based BMGs have great potential as fracture repair materials (such as intramedullary needles, bone plates and bone screws) as well as cardiovascular stent materials, absorbable sutures, fillers around dental implants, and fillings of bone after cyst/tumor removal in arthroplasty; as they will degrade gradually in human body after completing their temporary mission (would dissolve completely upon fulfilling the mission of fixing or supporting) during which arterial/bone remodeling and healing would occur.

References (PDF)