Electrochemical deposition and evaluation of electrically conductive polymer coating on biodegradable magnesium implants for neural applications
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In an attempt to develop biodegradable, mechanically strong, biocompatible, and conductive nerve guidance conduits, pure magnesium (Mg) was used as the biodegradable substrate material to provide strength while the conductive polymer, poly(3,4-ethylenedioxythiophene) (PEDOT) was used as a conductive coating material to control Mg degradation and improve cytocompatibility of Mg substrates. This study explored a series of electrochemical deposition conditions to produce a uniform, consistent PEDOT coating on large three-dimensional Mg samples. A concentration of 1 M 3,4-ethylenedioxythiophene in ionic liquid was sufficient for coating Mg samples with a size of 5 × 5 × 0.25 mm. Both cyclic voltammetry (CV) and chronoamperometry coating methods produced adequate coverage and uniform PEDOT coating. Low-cost stainless steel and copper electrodes can be used to deposit PEDOT coatings as effectively as platinum and silver/silver chloride electrodes. Five cycles of CV with the potential ranging from −0.5 to 2.0 V for 200 s per cycle were used to produce consistent coatings for further evaluation. Scanning electron micrographs showed the micro-porous structure of PEDOT coatings. Energy dispersive X-ray spectroscopy showed the peaks of sulfur, carbon, and oxygen, indicating sufficient PEDOT coating. Adhesion strength of the coating was measured using the tape test following the ASTM-D 3359 standard. The adhesion strength of PEDOT coating was within the classifications of 3B to 4B. Tafel tests of the PEDOT coated Mg showed a corrosion current (ICORR) of 6.14 × 10−5 A as compared with ICORR of 9.08 × 10−4 A for non-coated Mg. The calculated corrosion rate for the PEDOT coated Mg was 2.64 mm/year, much slower than 38.98 mm/year for the non-coated Mg.
KeywordsCyclic Voltammetry Adhesion Strength Simulated Body Fluid Electrochemical Deposition Tape Test
This material is based upon study supported by the National Science Foundation under Grant 1125801. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. The authors would also like to thank the University of California for financial support. We would like to thank the Central Facility for Advanced Microscopy and Microanalysis (CFAMM) at the University of California, Riverside, thank Drs. X. Luo, X.T. Cui, and V. Vullev for their advice on electrochemistry, and thank Mitch Boretz for proofreading.
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