Exploring the role of manganese on the microstructure, mechanical

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Characterization, Synthesis, and Modifications

Exploring the role of manganese on the microstructure, mechanical properties, biodegradability and biocompatibility of porous iron-based scaffolds Matthew Dargusch, Ali Dehghan-Manshadi, Mahboobeh Shahbazi, Jeffrey Venezuela, Xuan Tran, Jing Song, Na Liu, Chun Xu, Qinsong Ye, and Cuie Wen ACS Biomater. Sci. Eng., Just Accepted Manuscript • DOI: 10.1021/ acsbiomaterials.8b01497 • Publication Date (Web): 26 Feb 2019 Downloaded from http://pubs.acs.org on March 5, 2019

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ACS Biomaterials Science & Engineering

Exploring the role of manganese on the microstructure, mechanical properties, biodegradability and biocompatibility of porous iron-based scaffolds M. S. Darguscha*, A. Dehghan-Manshadia*, M. Shahbazib, J. Venezuelaa, X. Trana, J. Songc,d, N. Liuc,d, C. Xuc, Q. Yec, C. Wene a

Queensland Centre for Advanced Materials Processing and Manufacturing (AMPAM)

School of Mechanical and Mining Engineering, The University of Queensland, St Lucia, QLD 4072, Australia b

Institute for Future Environments (IFE), Queensland University of Technology (QUT), Brisbane, QLD 4001, Australia c School

of Dentistry, The University of Queensland, Brisbane, Queensland, 4006, Australia d School e School

of Stomatology, Foshan University, Foshan, Guangdong, China

of Engineering, RMIT University Melbourne VIC 3001, Australia

*corresponding authors: [email protected], [email protected]

ABSTRACT In this work, the role that manganese plays in determining the structure and performance of sintered biodegradable porous Fe-Mn alloys is described. Powder metallurgy processing was employed to produce a series of biodegradable porous Fe-xMn (x= 20, 30 and 35 wt%) alloys suitable for bone scaffold applications. Increasing manganese content increased the porosity volume in the sintered alloys and influenced the ensuing properties of the metal. The Fe35Mn alloy possessed optimum properties for orthopaedic application. X-ray diffraction analysis and magnetic characterization confirmed the predominance of the antiferromagnetic 1

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austenitic phase and ensured the magnetic resonance imaging (MRI) compatibility of this alloy. The porous Fe-35Mn alloy possessed mechanical properties (tensile strength of 144 MPa, elastic modulus of 53.3 GPa) comparable to human cortical bone. The alloy exhibited high degradation rates (0.306 mm yr-1) in simulated physiological fluid, likely due to its considerable Mn content and the high surface area inherent to its porous structures, while cytotoxicity and morphometry tests using mammalian pre-osteoblast cells (MC3T3-E1) indicated good cell viability in the Fe-35Mn alloy. Keywords: Fe-Mn alloys, biodegradable metals, mechanical properties, magnetic properties, powder sintering, biocompatibility

1.0 INTRODUCTION The need to address the health issues of an ageing population is driving intensive research in new materials and manufacturing processes for medical implants. Metallic biomaterials have found application in a variety of medical implants from orthopaedics and cardiovascular system repair to wound closure applications

1-3.

Metals have the particular

advantage of not only having a good combination of mechanical strength, and fracture toughness

4

but also high levels of processability via a range of manufacturing techniques

enabling a wide range of designs including complex features and functionality from wirebased products for cardiovascular stents and wound closure devices through to orthopaedic implants produced via additive manufacturing5-6 or wrought processing followed by machining 7-15. Most metallic implants currently used are intended to be permanent and have been manufactured from biocompatible, corrosion-resistant materials that are very stable in the biological environment such as titanium, stainless steel, nitinol, and chromium-cobalt alloys 1, 2


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4, 16.

The attraction of these materials is their high strength and excellent corrosion resistance

making them very reliable during their entire service life. Corrosion resistance is essential as many of the elements used in these alloys, such as titanium, chromium, and cobalt, are toxic in even small quantities 16. Despite this, there is evidence that some quantity of the alloying elements in these materials may be released by wear and corrosion processes

17-20.

Another

weakness of biometallic materials in dental and orthopaedic application is the mismatch between the mechanical properties of these materials and that of the surrounding bone. Metals generally possess higher yield strength and elastic modulus than bone, and such difference leads to stress shielding effects that can cause low bone density or osteopenia

21.

Implants designed from these materials are intended for permanency in the body because of their high resistance to environmental degradation and corrosion. Unfortunately, there is an increasing occurrence of infection and associated failure of the implants in service which requires follow-up surgery to remove the implant. Tissue damage and inflammatory reactions can occur if implants are not removed

4, 17-24.

This surgery involves significant risks and

additional financial costs 4. An alternative approach is to develop implants from materials that are biodegradable. These materials are expected to safely dissolve in the body once the implant has served its purpose. This biodegradation eliminates the complications as mentioned above (i.e., the need for second surgery) associated with a permanent implant. The common biodegradable materials are polymers and metals. At this time very few biodegradable implants, most of these being polymer-based, have been successfully developed and commercially available. Synthetic biodegradable polymers have the advantage of good biocompatibility, formability and degradability 25-26. However, these materials suffer from poor mechanical properties, which challenge their suitability for hard tissue engineering including applications such as scaffolds for bone replacement. Biodegradable metals are 3



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promising alternatives as these can deliver the required set of mechanical properties. Alloys made from magnesium (Mg), iron (Fe) and zinc (Zn) are being investigated, as these are nontoxic elements and have known processing pathways in the human body 27-29. The most investigated family of biodegradable metals are Mg alloys including those that have been modified to improve biocompatibility through alloying, coating and surface modification 4, 27, 30-37. One issue with Mg is its relatively rapid degradation rate inside the body38-39. This degradation leads to a rapid loss in mechanical/functional integrity and thereby limits the applicability of Mg to short-term implant applications. Also, the rapid deterioration of Mg within

the body may produce by-products (i.e., Mg ions and micron-size particles) at a rate faster than what the body can manage to incorporate. Another issue with Mg is the release of hydrogen gas during its degradation process, which may cause the accumulation of large amounts of hydrogen as subcutaneous gas bubbles 31. Iron is another biocompatible metal that is important in a range of metabolic processes 40.

Fe alloys generally show higher strength and other superior mechanical properties

compared to magnesium alloys. However, preliminary animal tests have shown that in vivo degradation rates of Fe alloys including alloys used to fabricate stents are slow

27, 41.

The

ferromagnetic nature of Fe creates difficulties with magnetic resonance imaging (MRI) and this problem along with its slow degradation rate has resulted in the development and exploration of new Fe based alloys and surface treatments which promote a faster degradation rate and improve MRI compatibility 28, 42-46. The pioneering work of Hermawan et al.

47

started the numerous investigations on

biodegradable iron-manganese (Fe-Mn) alloys. Manganese (Mn) is a trace element that is necessary for many enzymatic reactions Schinhammer et al.

43

27.

Hermawan and co-workers

42, 47-48

along with

have reported on the positive role that Mn plays in accelerating the 4


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degradation rate of Fe and improving MRI compatibility by producing a fully austenitic microstructure when alloying at fractions over 29 wt%. Hermawan et al. 42, 47-48 have shown that the Fe-35Mn alloy has a set of properties appropriate for biodegradable cardiovascular stents. Liu et al.

49

and Xu et al.

50

studied Fe-30Mn and likewise confirmed good

biodegradability in the alloy. Recently, Capek et al. 51 fabricated biodegradable wrought (hot forged) Fe-30Mn with excellent biocompatibility. However, they noted that while potentiodynamic tests indicated higher corrosion rates in Fe-30Mn compared to pure Fe, static immersion results showed otherwise. This discrepancy was attributed to a localized increase in pH that inhibited the corrosion of the Fe-Mn alloy. Some ternary and quaternary alloys based on the Fe-Mn binary combination were also found to have potential as a future biodegradable metal. Liu et al. 52 noted that the addition of 6% silicon in Fe-30Mn created a shape memory alloy with improved strength and corrosion rate. Orinakova et al.

53

fabricated a phosphated iron-manganese (Fe/P-30Mn) alloy which

they found to be similarly biocompatible while showing three times higher degradation rate compared to pure Fe. Schinhammer et al. 54 observed that Fe-10Mn-1Pd, Fe-21Mn-0.7C, and Fe-21Mn-0.7C-1Pd twinning-induced plasticity (TWIP) steels were all biocompatible. Similarly, the biodegradability of Fe-10Mn-1.2C and Fe-30Mn-1C high manganese austenitic steel was confirmed by Mozou et al. 55 and Xu et al. 50, respectively. Recently, Hufenbach et al.

56

observed that the addition of minute amounts of carbon (C) and sulfur (S) effectively

strengthens Fe-30Mn without compromising biocompatibility. However, C caused a significant drop in the ductility of the Fe-30Mn alloy. Dense Fe-Mn alloys may be suitable for stent applications but are not ideal for implants and scaffolds used in bone surgery where a degree of porosity is essential. Integration of residual pores within the Fe-Mn structure improves the material’s biodegradability by increasing the exposed area of the material to the corrosive body environment. Therefore, any 5



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attempt to develop porous Fe-Mn alloys with mechanical properties comparable with that of human bone will increase their application range in biomedical engineering. Studies have also looked at different techniques to develop porous iron. Powder metallurgy is the typical approach to create porous materials. Capek et al.57 used powder metallurgy technique and ammonium bicarbonate (NH4HCO3) as a space-holder material to create porous iron with mechanical properties similar too cancellous bone. Similarly, Zhang and Cao

58

employed powder metallurgy and NH4HCO3 space holder to produce Fe-35Mn

alloys with different porosity volumes. However, their product exhibited inferior mechanical properties and was not suitable for implants. Recently, additive manufacturing or 3D printing techniques are becoming popular for fabricating biodegradable porous iron. Li et al.

59

reported on direct metal printed (DMP)

topologically ordered porous biodegradable iron. DMP is a type of additive manufacturing technique. The measured properties of the 3D-printed porous iron were within the range of values for trabecular bone while showing about ≈12 times higher degradation compared to cold-rolled (CR) iron. Sharma and Pandey

60-61

used 3D printing and pressure-less

microwave sintering to create open-cell porous Fe with properties (e.g., Ec = 200 to 850 MPa) similar to cancellous bone. In the current work, we describe a range of previously unreported phenomenon in biodegradable Fe-Mn alloys. We explore in detail the ability of Mn to influence the level of porosity in sintered Fe-Mn alloys and how this affects critical properties such as mechanical behaviour and biocorrosion performance. The work involved the production and assessment of a number of porous Fe-Mn alloys; i.e., Fe-xMn where x = 20, 30, and 35 wt%. The alloys were fabricated via traditional powder metallurgy techniques. The mechanical properties, microstructure, magnetic properties, degradation behaviour, and in vitro biocompatibility of 6


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the sintered alloys were characterized. The results of these test elucidated the role of manganese in controlling porosity levels and influencing the attendant properties of the FeMn alloys.

2.0 MATERIALS AND METHODS 2.1 Alloy preparation and fabrication Fe-Mn samples were prepared by mixing elemental Fe (97% purity,

Exploring the role of manganese on the microstructure, mechanical

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