Comparative mechanical and corrosion studies on magnesium, zinc and iron alloys as biodegradable metals

Abstract

In this paper, selected magnesium, zinc and iron biodegradable alloys were studied as prospective biomaterials for temporary medical implants like stents and fixation devices for fractured bones. Mechanical properties of the alloys were characterized with hardness and tensile tests. In-vitro corrosion behavior was studied using immersion tests in a simulated physiological solution (SPS, 9 g/L NaCl) to roughly estimate the in-vivo biodegradation rates of implants. It was found that the Mg and Zn alloys were limited by a tensile strength of 370 MPa, while the tensile strength of the Fe alloys achieved 530 MPa. The main advantage of the Mg alloys is that their Young's modulus of elasticity is similar to that of the human bone. However, the corrosion tests revealed that the Mg-based alloys showed the highest corrosion rates in the SPS, ranging between 0.6 mm and 4.0 mm per year, which is above the tolerable degradation rates of implants. The corrosion rates of the Zn alloys were between 0.3 mm and 0.6 mm per year and the slowest corrosion rates of approximately 0.2 mm per year were observed for the Fe alloys.The results indicate that all three kinds of alloys meet the mechanical requirements for the load-bearing implants. From the corrosion-behavior point of view, the Zn-and Fe-based "slowly corroding" alloys appear as promising alternatives to the Mg-based alloys. Keywords: biodegradable metal, magnesium, zinc, iron, mechanical properties, corrosion lanek obravnava {tudij izbranih magnezijevih, cinkovih in`elezovih potencialnih biorazgradljivih zlitin kot obetajo~ih biomaterialov za za~asne medicinske vsadke, kot so opornice in pripomo~ki za utrjevanje zlomljenih kosti. Mehanske lastnosti zlitin so bile dolo~ene z merjenjem trdote in z nateznimi preizkusi. Korozijski preizkusi in vitro so bili izvr{eni s pomakanjem v simulirano fiziolo{ko raztopino (SPS, 9 g/L NaCl) za grobo oceno in vivo hitrosti biorazgradnje implantatov. Ugotovljeno je, da so zlitine Mg in Zn omejene z natezno trdnostjo 370 MPa, medtem ko je natezna trdnost Fe-zlitin dosegla 530 MPa. Glavna prednost Mg-zlitin je v podobnem Young-ovem modulu elasti~nosti, ki je podoben kot pri~love{ki kosti. Vendar pa so korozijski preizkusi pokazali pri zlitinah na osnovi Mg najve~je korozijske hitrosti v SPS, med 0,6 mm in 4,0 mm na leto, kar je nad dopustno hitrostjo degradacije implantata. Korozijske hitrosti Zn zlitin so bile med 0,3 mm in 0,6 mm na leto, najni`je hitrosti korozije, okrog 0,2 mm na leto, pa so bile opa`ene pri Fe-zlitinah. Rezultati so pokazali, da vse tri vrste zlitin ustrezajo mehanskim zahtevam za obremenjene implantate. S stali{~a korozijskega vedenja so zlitine na osnovi Zn in Fe "zlitine s po~asno korozijo" in se ka`ejo kot obetajo~e nadomestilo za zlitine na osnovi Mg.

Influence of different production processes on the biodegradability of an FeMn17 alloy

“…A wide variety of biodegradability/corrosion studies have been made using the electrochemical testing of the desired designed materials due to aconvenient and easy method to evaluate the corrosion property by testing theOCP (open-circuit potential), polarization curves and EIS(electrochemical impedance spectroscopy) via a three-electrode system. [6][7][8]12,13,[15][16][17] Very similar results of corrosion testing with potentiodynamic testing were observed by H. Hermawan 13 with one distinctive difference, our pure Fe behaved biodegradability much more similar to the FeMn17 alloy than theirs.…”

“…1 Despite the immense potential of Fe and Mg alloys, experiments and clinical trials also exposed their weaknesses: too rapid degradation rates, poor mechanical properties and significant hydrogen evolution during the corrosion process of Mg-based alloys and a too slow degradation of Fe-based alloys. [5][6][7][8] Fe-based alloys may also present problems with certain imaging devices (magnetic resonance imaging, for example) due to the Fe's ferromagnetic nature. However, alloying and heat treatment can modify the mechanical, corrosion, and ferromagnetic properties of pure Fe.…”

Investigation on Mechanical Behavior of Biodegradable Iron Foams under Different Compression Test Conditions

“…Nevertheless, there exist studies that show iron-based materials are possibly suitable for temporary biodegradable implants [9,10]. They provide answers to the two major drawbacks of magnesium-based materials which are high degradation rate that limits the use of such materials on small implants with approximate life span of 6-12 months, and hydrogen evolution during corrosion that can disturb the healing process [7,[11][12][13]. Mechanical properties of iron-based alloys, e.g., strength and ductility, can be easily tailored to meet the criteria for some biomedical applications.…”

“…Mechanical properties of iron-based alloys, e.g., strength and ductility, can be easily tailored to meet the criteria for some biomedical applications. They are viewed as good candidates for load bearing biodegradable implants owing to their high mechanical properties, e.g., high strength [13], and biocompatible, non-toxic characteristics [7]. However, a major challenge of using iron as a biodegradable implant is its slow rate of degradation [7,14].…”

Building towards a standardised approach to biocorrosion studies: a review of factors influencing Mg corrosion in vitro pertinent to in vivo corrosion

“…Initial testing used immersion conditions in simple NaCl solutions, but these were found to be inappropriate [42]. Subsequently, a wide range of solutions and methodologies have been explored [36,[43][44][45][46], each with advantages and limitations, although some studies still continue to use NaCl solutions [47]. Table 1 provides a comparison of the constituent elements of several commonly used in vitro immersion solution [24,[48][49][50].…”