Comparison of adhesion strength of tricalcium phosphate coatings on Titanium versus on Titanium dioxide by first-principle calculations

To increase osseointegration, special bioactive coatings are surfaced upon implants. The most common biocompatible material for implants is titanium and typical coating material is tricalcium phosphate, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi>C</mml:mi> <mml:msub> <mml:mi>a</mml:mi> <mml:mn>3</mml:mn> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:mrow> <mml:mi>P</mml:mi> <mml:msub> <mml:mi>O</mml:mi> <mml:mn>4</mml:mn> </mml:msub> </mml:mrow> <mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mn>2</mml:mn> </mml:msub> </mml:math> , which is similar to the structure of bone tissue. Since cases of delamination at the implant-coating interface were observed in clinic, the focus of this paper is to study the adhesion strength of tricalcium phosphate coating with titanium. In air, titanium instantly oxidizes, without any other additional actions. That raises the question, and worth checking, what is better for the stronger adhesion of the coating, to be applied to the pure titanium or titanium dioxide? In this article, we perform numerical calculations of the adhesion strength of tricalcium phosphate first on titanium dioxide, according to the first principles of physical chemistry, and then on pure titanium. We then compare the results of the calculations and make recommendations for practitioners. The characteristic of adhesion strength is the binding energy. We synthesized tricalcium phosphate step by step, evaluating the bond energy between its constituents, first with titanium dioxide and then with pure titanium. To gain insight into the interactions and their effects on strength, we used the Gaussian09 DFT B3 LYP hybrid exchange-correlation functional (Becke, three-parameter, Lee-Young-Parr) with a 6-31G basis set to analyze structural properties including bond lengths, bond angles, dihedral angles, and charges. The program performs geometric optimization of structures and determines the position of all nuclei and such electron density functionality that provide a global minimum on the surface of potential energy.