After numerous surgeries in the urinary system, stenting is often required to ensure complete urine discharge, prevent urine from flowing back into the kidneys, and maintain proper urine flow to avoid renal failure. The stents currently used in medical centers are primarily polymeric. Over time, the surface of these stents becomes covered with a crystalline layer and bacterial colonies, which, without secondary care, leads to reduced mechanical properties and potential infection. To address these issues, biodegradable stents have been introduced as an alternative. This research investigates the magnesium alloy, specifically the Mg-Ca-Mn alloy, as a biodegradable material for this purpose. Given the limited formability of magnesium alloys, rolling was selected as the fabrication method for the stents. Samples were rolled from an initial thickness of 5.0 mm down to 0.4 mm with a preheating duration of 10 minutes. The grain size of the specimens after rolling was significantly reduced from 200 ± 30 µm to 17 ± 5 µm. This reduction in grain size resulted in a notable increase in yield and ultimate tensile strength, from 108.30 ± 3.60 MPa to 231.45 ± 17.17 MPa. The microstructure and texture of the material were evaluated using optical microscopy, X-ray diffraction, and electron backscatter diffraction. The results indicate a significant reduction in grain size following rolling, along with changes in dislocation density and texture, as revealed by EBSD data. These factors contribute to a higher surface potential, leading to a higher corrosion rate in the initial seconds of the corrosion process. Nevertheless, a protective layer forms rapidly, thereby controlling the corrosion rate sooner and resulting in lower rates over time. The average corrosion rates calculated from hydrogen evolution and weight loss studies in artificial urine over 14 days, and from polarization assessments, were 0.889 mm/y, 1.616 mm/y, and 2.402 mm/y, respectively. Consequently, the stent produced through this process is expected to fully degrade within 10-12 weeks.
-Why there is a significant difference between the corrosion rate measured by 3 techniques?
For biodegradable ureteral stents, the device must provide support for 4–12 weeks. For a stent thickness of 400 um, the target corrosion rate is 0.6 to 2.4 mm/y for this application, necessitating a material with uniform degradation and high mechanical strength.
The alloy developed in our lab meets these requirements, as evidenced by comparisons with previous literature and our own work (DOI: 10.1016/j.jallcom.2020.158077). A key advantage is its controllable degradation rate, which can be further optimized via heat treatment.
Our findings indicate that while wrought alloys (rolled/coiled) experience a higher initial corrosion rate compared to cast alloys—due to increased grain boundary and dislocation density—they quickly develop a (quasi) passive layer. This leads to a lower overall degradation rate over time, making the wrought alloy an ideal candidate for coiling into a stent.
The alloy's high strength and tailored degradation rate ensure it supports the ureter for the required duration without blocking the flow.
For more information please let me know:
Ahmad Bahmani
a.bahmani@irost.ir
For biodegradable ureteral stents, the device must provide support for 4–12 weeks. For a stent thickness of 400 um, the target corrosion rate is 0.6 to 2.4 mm/y for this application, necessitating a material with uniform degradation and high mechanical strength.
The alloy developed in our lab meets these requirements, as evidenced by comparisons with previous literature and our own work (DOI: 10.1016/j.jallcom.2020.158077). A key advantage is its controllable degradation rate, which can be further optimized via heat treatment.
Our findings indicate that while wrought alloys (rolled/coiled) experience a higher initial corrosion rate compared to cast alloys—due to increased grain boundary and dislocation density—they quickly develop a (quasi) passive layer. This leads to a lower overall degradation rate over time, making the wrought alloy an ideal candidate for coiling into a stent.
The alloy's high strength and tailored degradation rate ensure it supports the ureter for the required duration without blocking the flow.
For more information please let me know:
Ahmad Bahmani
a.bahmani@irost.ir
