Biocompatible Materials Based on Self-Assembling Peptides on Ti25Nb10Zr Alloy: Molecular Structure and Organization Investigated by Synchrotron Radiation Induced Techniques

Valeria Secchi, Stefano Franchi, Marta Santi, Alina Vladescu, Mariana Braic, Tomáš Skála, Jaroslava Nováková, Monica Dettin, Annj Zamuner, Giovanna Iucci, Chiara Battocchio
2018 Nanomaterials  
In this work, we applied advanced Synchrotron Radiation (SR) induced techniques to the study of the chemisorption of the Self Assembling Peptide EAbuK16, i.e., H-Abu-Glu-Abu-Glu-Abu-Lys-Abu-Lys-Abu-Glu-Abu-Glu-Abu-Lys-Abu-Lys-NH 2 that is able to spontaneously aggregate in anti-parallel β-sheet conformation, onto annealed Ti25Nb10Zr alloy surfaces. This synthetic amphiphilic oligopeptide is a good candidate to mimic extracellular matrix for bone prosthesis, since its β-sheets stack onto each
more » ... er in a multilayer oriented nanostructure with internal pores of 5-200 nm size. To prepare the biomimetic material, Ti25Nb10Zr discs were treated with aqueous solutions of EAbuK16 at different pH values. Here we present the results achieved by performing SR-induced X-ray Photoelectron Spectroscopy (SR-XPS), angle-dependent Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy, FESEM and AFM imaging on Ti25Nb10Zr discs after incubation with self-assembling peptide solution at five different pH values, selected deliberately to investigate the best conditions for peptide immobilization. for use in high load-bearing applications, total hip, and total knee replacements. However, some concerns related to the toxicity of various alloying elements do exist [3] . In particular, Ti6Al4V alloy is commonly used in clinical practice as biocompatible material for prosthetics applications and dental implants [4] [5] [6] [7] [8] [9] . In the last years, the in vitro and in vivo tests performed on Ti6Al4V alloy showed that this alloy has a toxic effect resulting from released V and Al and that its elastic modulus is very distant from the bone value [10-16], restricting its use in biomaterial applications. On this basis, a lot of experiments have been carried out to develop a novel Ti based alloy consisting only of biocompatible elements, which could replace the Ti6Al4V alloy in clinical practice [9, [17] [18] [19] . For example, Ti6Al7Nb (ASTM F1295), Ti13Nb13Zr (ASTM F1713), and Ti12Mo6Zr (ASTM F1813) were proposed as candidates for manufacturing surgical implants. It is worth mentioning that there are a lot of other proposed alloys in the literature, such as Ti-Nb-Zr- Ta [20-24], Ti-Mo-Zr-Fe [25,26], Ti-Al-Zr [27], Ti-Al-Fe [18], Ti-Nb-Fe [28,29], Ti-Nb-Zr-Sn [30] and Ti-Nb [31] systems, but no standards have been published. The here reported Ti-Zr-Nb system was selected for the following reasons: all of the constituent elements are considered to be highly biocompatible [32] [33] [34] and show high affinity to oxygen, leading to the formation of stable oxides which improve the corrosion resistance [35] [36] [37] [38] [39] ; moreover, Zr is added in the alloy due to its capacity to stabilize the β phase. In fact, Abdel-Hady et al. showed that a Zr content ranging from 6 to 30 at % stabilized the β phase in alloys [40] . In the literature, there are few papers dealing with the effect of Zr content on the mechanical, tribological, and anticorrosive properties of Ti-Zr-Nb systems used for biomedical applications. In all published literature, the Zr content is up to 10 at % [41] [42] [43] [44] [45] [46] or of about 30 at % [43] . Nb addition is also required because it maintains the β phase formed during the annealing. Furthermore a possible strategy to promote osseo-integration and enhance the biological acceptance of the implants is the biofunctionalization of the Ti25Nb10Zr surface with bioactive molecules that can be grafted on the surface in order to establish a molecular dialogue with host cells [47] . Among other bioactive molecules, self-assembling peptides (SAPs) are extremely promising candidates, since thanks to their on-purpose designed sequence they are able to self-assemble in a beta-sheet secondary structure [48, 49] . They can then aggregate in the presence of saline creating hydrogels that can be used either as drug delivery vehicles, in the case of factors to release with a precise kinetic, or can be decorated with adhesive sequences or proteins, appropriately conjugated with a self-assembling sequence, allowing the functionalization of the scaffold with adhesive signals in a 3D structure by simple co-aggregation. The chemically stable SAP adhesion to the substrate is usually obtained by covalently and selectively functionalizing the alloy surface of the ion complementary peptide [50, 51] . In this work, we present the characterization, carried out by synchrotron radiation-induced X-ray Photoemission Spectroscopy (SR-XPS), angle-dependent Near Edge X-rays Absorption Fine Structure (NEXAFS) spectroscopy, Field Emission Scanning Electron Microscopy (FE-SEM) and Atomic Force Microscopy (AFM) investigations of Ti25Nb10Zr alloy surfaces functionalized by the SAP EAbuK16 (Abu stands for α-aminobutyric acid), i.e., H-Abu-Glu-Abu-Glu-Abu-Lys-Abu-Lys-Abu-Glu-Abu-Glu-Abu-Lys-Abu-Lys-NH 2 . The proposed SAP is able to self-assemble in aqueous solution in the presence of monovalent cations. To prepare the material, Ti25Nb10Zr discs were exposed to self-assembling peptide solutions at pH values ranging from 2 to 12, in order to understand the best conditions for peptide immobilization. Materials and Methods Samples Preparation Ti25Nb10Zr Alloy Preparation and Preliminary Characterization Ti25Nb10Zr (in wt %) was manufactured by Romanian Company (R&D Consulting and Services, Bucharest, Romania). Ti25Nb10Zr alloy was casted by a cold crucible levitation melting technique (CCLM), using a FIVES CELES-CELLES MP 25 furnace with nominal power 25 kW (Fives Celes, Lautenbach, France). The alloy was produced by mixing ultra-pure raw metals, subsequently annealed
doi:10.3390/nano8030148 pmid:29518968 pmcid:PMC5869639 fatcat:b6znr7ua2bewnflbhofiqn6c4y