Hydroxyapatite Surfaces Functionalized with a Self-Assembling Peptide: XPS, RAIRS and NEXAFS Study

Valeria Secchi,Klára Beranová,Alina Vladescu,Annj Zamuner,Stefano Franchi,Monica Dettin,Giovanna Iucci,Chiara Battocchio,Luca Tortora,Valerio Graziani

doi:10.3390/nano10061151

Abstract

Hydroxyapatite (HAP) coatings can improve the biocompatibility and bioactivity of titanium alloys, such as Ti6Al4V, commonly used as material for orthopedic prostheses. In this framework, we have studied the surface of HAP coatings enriched with Mg and either Si or Ti deposited by RF magnetron sputtering on Ti6Al4V. HAP coatings have been furtherly functionalized by adsorption of a self-assembling peptide (SAP) on the HAP surface, with the aim of increasing the material bioactivity. The selected SAP (peptide sequence AbuEAbuEAbuKAbuKAbuEAbuEAbuKAbuK) is a self-complementary oligopeptide able to generate extended ordered structures by self-assembling in watery solutions. Samples were prepared by incubation of the HAP coatings in SAP solutions and subsequently analyzed by X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared (FTIR) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopies, in order to determine the amount of adsorbed peptide, the peptide stability and the structure of the peptide overlayer on the HAP coatings as a function of the HAP substrate and of the pH of the mother SAP solution. Experimental data yielded evidence of SAP adsorption on the HAP surface, and peptide overlayers showed ordered structure and molecular orientation. The thickness of the SAP overlayer depends on the composition of the HAP coating.

Highlights

Titanium and its alloys are renowned biocompatible materials that are commonly used for dental and orthopedic prostheses
We have studied the surface of HAP coatings enriched with Mg and either Si or Ti deposited by RF magnetron sputtering on Ti6Al4V
Samples were prepared by incubation of the HAP coatings in self-assembling peptide (SAP) solutions and subsequently analyzed by X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared (FTIR) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopies, in order to determine the amount of adsorbed peptide, the peptide stability and the structure of the peptide overlayer on the HAP coatings as a function of the HAP substrate and of the pH of the mother SAP solution

Summary

Introduction

Titanium and its alloys are renowned biocompatible materials that are commonly used for dental and orthopedic prostheses. Ti6Al4V, for instance, is typically employed in clinical practice as a biocompatible material in the manufacturing of hip and artificial knee joints and dental implant prostheses components [1,2,3,4,5]. Improved biocompatibility and bioactivity of the implant can be obtained by appropriate modifications of the alloy surface by bioactive coatings. Hydroxyapatite (HAP) coatings show good bioactive ability and are known to support bone growth at the interface between the implant and the extracellular matrix [6,7]; HAPs have been used to coat orthopedic and dental implants [8,9,10]. Titanium was chosen due to its biocompatibility and ability to promote cell growth [15]

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Conclusion