Layered double hydroxide/poly-dopamine composite coating with surface heparinization on Mg alloys: improved anticorrosion, endothelialization and hemocompatibility

Magnesium (Mg) and its alloys are promising cardiovascular stent materials due to their favourable physical properties and complete degradation in vivo. However, rapid degradation and poor cytocompatibility hinder their clinical applications. To enhance the corrosion resistance and endothelialization of the AZ31 alloy, a layered double hydroxide (LDH)/poly-dopamine (PDA) composite coating (LDH/PDA) was successfully fabricated. Polarization curves and the electrochemical impedance spectroscopy Nyquist spectrum test proved that the corrosion resistance of the LDH/PDA sample was significantly improved in vitro. The LDH/PDA sample greatly improved the adherence process and the proliferation rate of human umbilical vein endothelial cells (HUVECs). After culturing for 10 days, the number of living HUVECs on the LDH/PDA sample was comparable to that on the Ti sample whereas the cells barely survived on the AZ31 or LDH coating. Furthermore, heparin was immobilized on LDH/PDA via a covalent bond (LDH/PDA/HEP). The corrosion resistance and long-term proliferation of HUVECs after the introduction of heparin were mildly decreased compared with the L/P sample, but were still greatly improved compared with AZ31, the LDH coating and the PDA coating. Furthermore, the LDH/PDA/HEP sample greatly improved the HUVEC migration rate compared with the LDH/PDA sample, and inhibited platelet adhesion which was intense on the LDH/PDA sample. Both LDH/PDA and LDH/PDA/HEP samples had a low hemolysis rate (2.52% and 0.65%, respectively) in vitro and eliminated the adverse biocompatible effects of the direct PDA coating on the AZ31 substrate in vivo. Our results suggest that the LDH/PDA composite coating with further heparinization is a promising method to modify the surface of Mg alloys by significantly improving corrosion resistance, endothelialization and hemocompatibility.