Effect of PLLA coating on corrosion and biocompatibility of zinc in vascular environment

Zinc (Zn) has recently been introduced as a promising new metal candidate for biodegradable vascular stent applications with a favorable degradation rate and biocompatibility. Corrosion-resistant metal stents are often coated with drug-eluting polymer layers to inhibit harmful biological responses. Here, the authors aimed to investigate the interaction between biodegradable zinc metal and a conventional biodegradable polymer coating. Zinc wires with a diameter of 0·25 mm were surface-modified using 3-(trimethoxysilyl)propyl methacrylate (MPS) and then coated with a 1–12 μm film of poly(l-lactic acid) (PLLA). The corrosion behavior of PLLA/MPS-coated zinc wires was studied in simulated body fluid using electrochemical impedance spectroscopy. An increase in the impedance from <1000 to >15 000 Ω cm² was recorded for the zinc wires after being coated with PLLA. The PLLA/MPS-coated zinc specimens were implanted into the abdominal rat aorta to assess their biodegradation and biocompatibility compared to uncoated zinc wires. PLLA/MPS-coated wires corroded at approximately half the rate of unmodified zinc during the first 4·5 months. A histological analysis of the biological tissue surrounding the zinc implants revealed a reduction in the biocompatibility of the polymer-coated samples, as indicated by increasing cell toxicity and neointimal hyperplasia.