Shervin Eslami Harandi

Effect of calcium content on the microstructure, hardness and in-vitro corrosion behavior of biodegradable Mg-Ca binary alloy

Effect of calcium addition on microstructure, hardness value and corrosion behavior of five different Mg-xCa binary alloys (x = 0.7, 1, 2, 3, 4 wt. (%)) was investigated. Notable refinement in microstructure of the alloy occurred with increasing calcium content. In addition, more uniform distribution of Mg 2 Ca phase was observed in α-Mg matrix resulted in an increase in hardness value. The in-vitro corrosion examination using Kokubo simulated body fluid showed that the addition of calcium shifted the fluid pH value to a higher level similar to those found in pure commercial Mg. The high pH value amplified the formation and growth of bone-like apatite. Higher percentage of Ca resulted in needle-shaped growth of the apatite. Electrochemical measurements in the same solution revealed that increasing Ca content led to higher corrosion rates due to the formation of more cathodic Mg 2 Ca precipitate in the microstructure. The results therefore suggested that Mg-0.7Ca with the minimum amount of Mg 2 Ca is a good candidate for bio-implant applications.

Characteristics of As-Cast and Forged Biodegradable Mg-Ca Binary Alloy Immersed in Kokubo Simulated Body Fluid

Biodegradable implant is an alternative to metallic implant and has the advantage of not being necessary to remove once the fracture has healed. Magnesium is particularly desirable since it is biocompatible and has a modulus of elasticity closer to bone. In addition, it shows ability to biodegrade in situ, when used as an implant material. In this research, different percentages of calcium were added to magnesium during melting of the alloy. A selected alloy was forged at different parameters. Both as cast and forged alloys were subjected to polarization test performed in Kokubo simulated body fluid. Immersion test in the fluid was conducted for 96 hours to investigate the formation, growth and morphology of the hydroxyapatite on the surface of the alloys. The results showed that similar electrochemical behaviour took place in the alloys regardless of the calcium content. However, an increase in corrosion rate was observed with increasing calcium content. It was also observed that forging process decreased the corrosion resistance of the alloy. Furthermore, increasing calcium content accelerated the growth of bone-like apatite in the alloy.

Resistance of Magnesium Alloys to Corrosion Fatigue for Biodegradable Implant Applications: Current Status and Challenges

Magnesium (Mg) alloys are attracting increasing interest as the most suitable metallic materials for construction of biodegradable and bio-absorbable temporary implants. However, Mg-alloys can suffer premature and catastrophic fracture under the synergy of cyclic loading and corrosion (i.e., corrosion fatigue (CF)). Though Mg alloys are reported to be susceptible to CF also in the corrosive human body fluid, there are very limited studies on this topic. Furthermore, the in vitro test parameters employed in these investigations have not properly simulated the actual conditions in the human body. This article presents an overview of the findings of available studies on the CF of Mg alloys in pseudo-physiological solutions and the employed testing procedures, as well as identifying the knowledge gap.

Understanding Corrosion-Assisted Cracking of Magnesium Alloys for Bioimplant Applications

Magnesium (Mg) alloys possess great potential for their use as temporary implants and devices (such as pins, wires, screws, plates, and stents). Use of Mg alloys as temporary implants will completely avoid the cumbersome procedure of second surgery (which is required when such implants are constructed out of traditional materials such as titanium alloys or stainless steels). However, there are some limitations of Mg as a temporary implant. Firstly, the high corrosion rates of Mg alloys in the physiological environment may lead to loss in mechanical integrity of the implants. Secondly, the simultaneous action of the corrosive human-body-fluid and the mechanical loading can cause sudden and catastrophic fracture due to corrosion-assisted expedited cracking, such as stress corrosion cracking (SCC) and/or corrosion fatigue (CF). SCC and CF of Mg alloy implants are vastly unexplored research areas. This article provides an overview of the experimental results on SCC and CF of different Mg alloys in corrosive environments including simulated body fluid (SBF), and discusses associated fracture mechanisms.

Appropriate Corrosion-Fatigue Testing of Magnesium Alloys for Temporary Bioimplant Applications

Magnesium (Mg) alloys are attractive for their great potential as temporary bio-implants. However, Mg alloys can suffer sudden cracking/fracture under the simultaneous action of cyclic loading and the corrosive physiological environment, i.e., corrosion fatigue (CF). Though there are reports on CF of Mg alloy, it is necessary that the investigations of such fracture should be performed under conditions that appropriately simulate those in actual human body conditions. This article describes a relatively more accurate testing procedure and preliminary data generated using this procedure.

Advanced Materials Research

Biodegradable implant is an alternative to metallic implant and has the advantage of not being necessary to remove once the fracture has healed. Magnesium is particularly desirable since it is biocompatible and has a modulus of elasticity closer to bone. In addition, it shows ability to biodegrade in situ, when used as an implant material. In this research, different percentages of calcium were added to magnesium during melting of the alloy. A selected alloy was forged at different parameters. Both as cast and forged alloys were subjected to polarization test performed in Kokubo simulated body fluid. Immersion test in the fluid was conducted for 96 hours to investigate the formation, growth and morphology of the hydroxyapatite on the surface of the alloys. The results showed that similar electrochemical behaviour took place in the alloys regardless of the calcium content. However, an increase in corrosion rate was observed with increasing calcium content. It was also observed that forging process decreased the corrosion resistance of the alloy. Furthermore, increasing calcium content accelerated the growth of bone-like apatite in the alloy.

Characteristics of as-cast and forged biodegradable Mg-Ca binary alloy immersed in Kokubo simulated body fluid

Biodegradable implant is an alternative to metallic implant and has the advantage of not being necessary to remove once the fracture has healed. Magnesium is particularly desirable since it is biocompatible and has a modulus of elasticity closer to bone. In addition, it shows ability to biodegrade in situ, when used as an implant material. In this research, different percentages of calcium were added to magnesium during melting of the alloy. A selected alloy was forged at different parameters. Both as cast and forged alloys were subjected to polarization test performed in Kokubo simulated body fluid. Immersion test in the fluid was conducted for 96 hours to investigate the formation, growth and morphology of the hydroxyapatite on the surface of the alloys. The results showed that similar electrochemical behaviour took place in the alloys regardless of the calcium content. However, an increase in corrosion rate was observed with increasing calcium content. It was also observed that forging process decreased the corrosion resistance of the alloy. Furthermore, increasing calcium content accelerated the growth of bone-like apatite in the alloy.