A new strategy for developing chitosan conversion coating on magnesium substrates for orthopedic implants

Abstract

Chitosan as a natural biopolymer was immobilized and chelating-deposited with and without bioactive glass (BG) onto Mg substrates by means of a chemical conversion process at 75 °C to provide anti-corrosion properties, good adhesion and biocompatibility. The aim of the present work was to integrate the surface of biodegradable Mg as a part of the corrosion resistant coating via metal-chitosan complexation process.The surface morphology and composition of the coatings were characterized by Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS). The results provided evidence of the formation of a chitosan coating as well as its chelating reaction and immobilization on magnesium by a chemical conversion process. The non-alkalization of the chitosan solution was ascribed to the protective layer of Mg (II)-chitosan complex, which inhibits the further migration of Mg ions. The in vitro bioactivity of both chitosan (CHI)-coated and chitosan/BG (CHI/BG)-coated surfaces in simulated body fluid (SBF) proved the complete retention of chitosan and BG on the magnesium substrates. The XRD analysis of the (CHI/BG) coating after 2 weeks immersion in SBF showed mainly the formation of magnesium hydrogen phosphate hexahydrate and undetected amorphous (Ca, Mg) phosphate. The present study represents a novel attempt to modify the surface of Mg by a simple, one-step chemical conversion treatment in chitosan to form a Mg (II)-chitosan complex layer. Mechanisms for the Mg-chitosan complexation process and for the coating bioactivity behavior in SBF were discussed.