Effect of grain sizes on mechanical properties and biodegradation behavior of pure iron for cardiovascular stent application

Abstract

Pure iron has been demonstrated as a potential candidate for biodegradable metal stents due to its appropriate biocompatibility, suitable mechanical properties and uniform biodegradation behavior. The competing parameters that control the safety and the performance of BMS include proper strength-ductility combination, biocompatibility along with matching rate of corrosion with healing rate of arteries. Being a micrometre-scale biomedical device, the mentioned variables have been found to be governed by the average grain size of the bulk material. Thermo-mechanical processing techniques of the cold rolling and annealing were used to grain-refine the pure iron. Pure Fe samples were unidirectionally cold rolled and then isochronally annealed at different temperatures with the intention of inducing different ranges of grain size. The effect of thermo-mechanical treatment on mechanical properties and corrosion rates of the samples were investigated, correspondingly. Mechanical properties of pure Fe samples improved significantly with decrease in grain size while the corrosion rate decreased marginally with decrease in the average grain sizes. These findings could lead to the optimization of the properties to attain an adequate biodegradation-strength-ductility balance.

Influence of cross-rolling on the micro-texture and biodegradation of pure iron as biodegradable material for medical implants

“…On the other hand, these mechanical properties are grain-size dependent, and would be decreased with an increase in recrystallized grain size according to the Hall-Petch relationship [33]. It is notable that since the rotation of the metal sheet by 90°during bi-directional rolling gives no particular orientation to the grain boundary plane; annealed BD samples would have more isotropic and uniform mechanical properties.…”

Grain size evolution and mechanical properties of thermomechanically processed pure iron for biodegradable medical implant application

“…Its chemical composition (wt. %) was determined in a previous work [8] and was as follows: C: 0.006; Ni: 0.037; Cr: 0.032; Mn: 0.041; Cu: 0.017; Mo: 0.002; S: 0.014; Sn: 0.014; P: 0.019; Si: 0.008; Al: 0.010; Fe balance.…”

“…The ductility of two pure Fe samples (UD75%CR and UD85%CR) annealed at 550°C was greater than the minimum requirement (>15-18%) for metallic stent application. Since cardiovascular stents require sufficient strength to preserve their load-bearing function and adequate ductility for a safe deployment during implantation [8], the strength-ductility combination of the pure Fe samples cold deformed to 75% and 85% reduction and annealing at 550°C is adequate for the intended application. Table 2 compared the mechanical properties of ironbased alloys for medical applications and brought to the fore the challenges in controlling strength and ductility.…”

Influence of Al content on the corrosion resistance of micro-alloyed hot rolled steel as a function of grain size

“…Chen and Zhang [6] observed that corrosion resistance was considerably improved with refinement of grain size. Furthermore, Obayi et al [7] reported that corrosion resistance was slightly improved in cold rolled and annealed pure iron as a result of refining grain size. In addition, homogeneous distribution of grain size enhanced passivation status leading to lower corrosion rate.…”