3D printing of polymeric Coatings on AZ31 Mg alloy Substrate for Corrosion Protection of biomedical implants

Abstract

Magnesium (Mg) alloys show promise in biomedical implants due to their excellent mechanical strength, biocompatibility and biodegradability. However, their rapid degradation rates in vivo induce toxicity and reduce their mechanical strength thereby, limiting their widespread usage. Our group employs a 3D inkjet printing technique for polymeric surface modification of bioresorbable AZ31 Mg alloy towards corrosion control. Thin films of three proprietary formulations of elastomeric poly (ester urethane) urea (PEUU) embedded with an anti-proliferative drug paclitaxel (Taxol) were coated on biodegradable AZ31 Mg coupons. Multilayer coatings of 5 and 20 layers were deposited for virgin (PEUU-V), PEUU with phosphorylcholine (PEUU-PC) and PEUU with sulfobetaine (PEUU-SB). Coating thicknesses of 8 µm and 19 µm were observed for 5-layer and 20-layer coatings, respectively. Surface morphology results depicted the presence of Taxol beads on PEUU-V and PEUU-SB coatings due to precipitation. An equivalent circuit model was used to calculate the polarization resistance values and revealed that the polymeric coatings provided a significant protective effect on the corrosion rate of AZ31 Mg alloy. Electrochemical impedance spectroscopy measurements indicated that PEUU-SB offered the least resistance to corrosion and had the highest porosity (35.6%) among all the polymeric coatings. PEEU-V polymeric coatings offered the greatest polarization resistance with the least porosity (10.5%). Statistical analysis confirmed that the 20-layer coating thickness had a significantly higher polarization resistance than the 5-layer coatings. This research lays the foundation for developing corrosion control drug-eluting coatings for cardiovascular and other medical device applications via surface modification using 3D inkjet printing.