Enhancement of adhesion strength and in-vivo evaluation of electrodeposited calcium phosphate/chitosan biocoatings on titanium substrate

Abstract

Chitosan/calcium phosphate nanocomposites are widely used as a biocompatible coatings for titanium bioimplants in the fields of dentistry and orthopedics to enhance the integration between the implants and the hard bone. However, the poor adhesion strength between the coating and the metal substrate was found to be one of the major problems in the clinical application of these implants. In the current study, we reported the formation of Ca/P coating on titanium (Ti) substrate using electrodeposition. The key factor of the bath ingredients is the change of chitosan's solvent from a commonly used acetic acid to acrylic acid in the electrolyte. The structural analysis including X-ray diffraction (XRD), Raman spectroscopy, and attenuated total reflectance (ATR) confirmed the formation of three phases of Ca/P octacalcium phosphate (OCP), dicalcium phosphate dihydrate (DCPD) brushite, and hydroxyapatite (HA). The bond strength was performed by the tape test (ASTM D3359-09) which showed that nearly 65% of the coatings were removed in the case of using 2, 4, and 6% (v/v) acetic acid as chitosan solvent, while only 5% of the coatings were removed when high concentrations (4 and 6%) of acrylic acid is used in addition to increasing of the surface wettability. Furthermore, the morphology and thickness of the calcium phosphate layer coated on the surface of Ti metal were inspected by scanning electron microscopy (SEM). Finally, an in vivo application was conducted on the optimized coating by surgically placing the coated and control discs into rats’ clavicular bones for 2-weeks healing period. Then biomechanical evaluation was performed to verify the effect of treatment on the interface resistance to shear force, and histological analysis was performed to evaluate the bone tissue reactions to coated discs. The results showed that using acrylic acid instead of acetic acid to dissolve chitosan before in-situ electrodeposition might be an innovative approach to enhance the adhesion strength between chitosan/calcium phosphate-based coatings and titanium metal to be used in orthopedic and dental implant technology.