Innovative processes for electropolishing of medical devices made of stainless steels

Currently, many medical devices are made of implantable metals such as 316LVM stainless steel. Electropolishing is a common process to obtain a smooth surface, free of contaminants and more passive, which allows for minimizing the foreign body response and cell adhesion. However, polishing of small implants with a highly complicated geometry and nonuniform metallurgy might result in unsatisfactory results. The objective of this work was to develop an electropolishing process effective for complex metallic implants such as artificial heart valve frames and miniature glaucoma implants. Polishing in an ultrasonic bath and pulsed voltage polishing processes were studied and compared to the standard ASTM process. Current-voltage curves were constructed for different solutions and bath temperatures. The polished parts were evaluated by stereomicroscopy, optical microscopy, atomic force microscopy, noncontact surface profilometry, and X-ray diffraction. Pulse polishing was found useful in eliminating the erosion effects of gas bubbles in solution. Electropolishing in an ultrasonic bath was found useful when a rough, patterned surface is needed, e.g. for osseointegration purposes. Preliminary animal studies followed by histopathology indicated that the polished surfaces stimulated only a moderate body reaction, as desired in such applications. The pronounced dependence of the measured roughness values on both the measurement technique and scanned area should inspire the preparation of a new test-method standard.