Sharp Rachael, Pelletier Matthew H, Walsh William R, Kelly Cambre N, Gall Ken
Surgical and Orthopaedic Research Laboratories, Prince of Wales Clinical School, University of New South Wales, Sydney 2052, Australia.
Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC 27708, USA.
Materials (Basel). 2022 Jul 9;15(14):4805. doi: 10.3390/ma15144805.
Corrosion of medical implants is a possible failure mode via induced local inflammatory effects, systemic deposition and corrosion related mechanical failure. Cyclic potentiodynamic polarisation (CPP) testing was utilized to evaluate the effect of increased porosity (60% and 80%) and decreased wall thickness in gyroid lattice structures on the electrochemical behaviour of LPBF Ti6Al4V structures. The use of CPP allowed for the landmarks of breakdown potential, resting potential and vertex potential to be analysed, as well as facilitating the construction of Tafel plots and qualitative Goldberg analysis. The results indicated that 60% gyroid samples were most susceptible to the onset of pitting corrosion when compared to 80% gyroid and solid samples. This was shown through decreased breakdown and vertex potentials and were found to correlate to increased lattice surface area to void volume ratio. Tafel plots indicated that despite the earlier onset of pitting corrosion, both gyroid test groups displayed lower rates of corrosion per year, indicating a lower severity of corrosion. This study highlighted inherent tradeoffs between lattice optimisation and corrosion behaviour with a potential parabolic link between void volume, surface area and corrosion being identified. This potential link is supported by 60% gyroid samples having the lowest breakdown potentials, but investigation into other porosity ranges is suggested to support the hypothesis. All 3D printed materials studied here showed breakdown potentials higher than ASTM F2129's suggestion of 800 mV for evaluation within the physiological environment, indicating that under static conditions pitting and crevice corrosion should not initiate within the body.
医用植入物的腐蚀是一种可能的失效模式，可通过诱发局部炎症反应、全身沉积以及与腐蚀相关的机械故障引发。循环动电位极化（CPP）测试用于评估在类螺旋晶格结构中孔隙率增加（60%和80%）以及壁厚减小对激光粉末床熔融（LPBF）Ti6Al4V结构电化学行为的影响。CPP测试的应用使得能够分析击穿电位、静止电位和顶点电位的特征，同时也有助于绘制塔菲尔曲线和进行定性的戈德堡分析。结果表明，与孔隙率为80%的类螺旋样品和实心样品相比，孔隙率为60%的类螺旋样品最易发生点蚀。这通过击穿电位和顶点电位的降低得以体现，并且发现其与晶格表面积与孔隙体积比的增加相关。塔菲尔曲线表明，尽管点蚀更早发生，但两个类螺旋测试组每年的腐蚀速率都较低，表明腐蚀的严重程度较低。本研究突出了晶格优化与腐蚀行为之间固有的权衡关系，并确定了孔隙体积、表面积和腐蚀之间可能存在的抛物线关系。孔隙率为60%的类螺旋样品具有最低的击穿电位，这支持了这种潜在关系，但建议对其他孔隙率范围进行研究以支持该假设。此处研究的所有3D打印材料的击穿电位均高于ASTM F2129中对于生理环境下评估所建议的800 mV，这表明在静态条件下，体内不应引发点蚀和缝隙腐蚀。
