Adele Carradò

Structural, Microstructural, and Residual Stress Investigations of Plasma-Sprayed Hydroxyapatite on Ti-6Al-4 V

Plasma-spray (PS) is a classical technique usually employed to cover orthopaedic titanium implant surfaces with hydroxyapatite (HA - Ca(10)(PO(4))(6)(OH)(2)). The objective of the current study is to investigate the structure and microstructure of HA plasma-spray 50 mum thick coating on titanium alloy (Ti-6Al-4 V) and residual stress due to processing in the substrate and in HA coating. The structure of the coatings was determined by high-energy synchrotron X-ray diffraction in energy dispersive (HESXRD), selected area electron diffraction (saed), Scanning Electron Microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). No impurity phases in the HA were identified by HESXRD to keep away from the decomposition of HA at high temperature. hcp phase of HA substrate was detected with slight amorphous background. FTIR spectrum of a HA powder shows a typical spectrum for HA material with the characteristic phosphate peaks for HA at wavenumbers of 1090, 1052, 963, 602, and 573 cm(-1) are present. The morphology of HA powder observed by SEM exhibits grains of ca. 0.1 mum well-adapted for cell proliferation. HA/Ti-6Al-4 V interface observed by cross-section scanning and transmission electron microscopy (TEM) presents microcracks. Residual stresses were analyzed by sin(2) Psi X-ray diffraction method on titanium substrates and HA coating. Although the Ti substrates are in a slightly tensile residual state, the coated ones show a compressive state.

Harnessing the Multifunctionality in Nature: A Bioactive Agent Release System with Self-Antimicrobial and Immunomodulatory Properties

Major problems with biomedical devices in particular implants located in nonsterile environments concern: (i) excessive immune response to the implant, (ii) development of bacterial biofilms, and (iii) yeast and fungi infections. An original multifunctional coating that addresses all these issues concomitantly is developed. A new exponentially growing polyelectrolyte multilayer film based on polyarginine (PAR) and hyaluronic acid (HA) is designed. The films have a strong inhibitory effect on the production of inflammatory cytokines released by human primary macrophage subpopulations. This could reduce potential chronic inflammatory reaction following implantation. Next, it is shown that PAR, due to its positive charges, has an antimicrobial activity in film format against Staphylococcus aureus for 24 h. In order to have a long-term antimicrobial activity, a precursor nanoscale silver coating is deposited on the surface before adding the PAR/HA films. Moreover, the PAR/HA films can be easily further functionalized by embedding antimicrobial peptides, like catestatin (CAT), a natural host defense peptide. This PAR/HA+CAT film proves to be effective as an antimicrobial coating against yeast and fungi and its cytocompatibility is also assessed. Finally, this all-in-one system constitutes an original strategy to limit inflammation and prevents bacteria, yeast, and fungi infections.

Determination of residual stresses in materials and industrial components by neutron diffraction

We present a review of the determination of residual stresses in materials and components of industrial interest by using the non-destructive technique of neutron diffraction. The fundamental aspects are discussed, together with a brief description of the experimental facilities. Several experimental results are then reported, particularly concerning applications to materials and components for power plants (CrMo steel, AISI304 stainless steel and 2.25Cr1Mo ferritic steel), aerospace and automotive technology (Al alloys, metal matrix composites, nickel superalloy gas-turbine components) and fusion-reactor technology (AISI316L for the first wall). A few thermomechanical treatments are considered, such as welding, cold-expanded holes, thermoelastic coupling and thermal and mechanical fatigue. Moreover, a few applications to general industrial problems are shown, namely brazed ceramic-steel components, coatings and fatigue-cracked samples. In some cases, experimental results are compared with numerical models or results from x-ray diffraction measurements.

Production of Customized High-Strength Hybrid Sandwich Structures

The production process and the forming behaviour of locally reinforced steel/polymer/steel (316L/PP-PE/316L) hybrid sandwich composite materials (SMS) have been investigated. The effect of simple plate reinforcements with different size, shape and geometry on the forming limits of SMS was studied. As a local reinforcement, the simple solid steel and mesh steel plate inlays with central and edge positions were chosen instead of a polymer core as a sandwich laminate. In order to increase the adhesion properties between the metal and polymer layers, corona discharge and plasma preliminary surface treatments were applied prior to the sandwich production. Both, deep drawing and stretching cup-forming tests were performed in order to analyse the forming behaviour as well as the failure of SMS with and without local inlays subject to different tensile loadings. The influence of the local reinforcement on the bending behaviour was determined by three and four-point bending processes. Stress-strain curves and thinning behaviour of SMS with local reinforcements under the different forming loads were determined using digital image correlation via photogrammetry. The forming behaviour strongly depends on the quality, geometry and size of the local plate inlays. Owing to the different positions of reinforcement as well as to the different polymer content around of inlays, failure of SMS by bending and drawing differs. The sandwich samples with mesh reinforcement demonstrate better formability by drawing and bending than that of samples with solid plates. In order to minimise the loss in formability of sandwich samples during deep drawing, the size of the centred reinforcement has to be larger than the punch diameter.

Press Joining Rolling Process for Hybrid Systems

The press joining rolling process used for the production of metal/polymer/metal systems is introduced. In the first step three-layer sandwich sheet, 316L/polypropylene- polyethylene/316L (316L/PP-PE/316L) with and without local reinforcement, were processed by roll bonding at approx. 250°C of two steel sheets with a pre-rolled PP-PE - core sheet. Mechanical and forming behaviour of the parts had been investigated by tensile, bending and deep drawing tests. It could be shown that for moderate drawing depths deep drawing behaviour is close to the one of the mono-material.

Biomimetic calcium–phosphates produced by an auto-catalytic route on stainless steel 316L and bio-inert polyolefin

A melange of hydroxyapatite and calcium phosphate hydrate coatings have been deposited on the surfaces of 316L type stainless steel and polyolefin (PP-PE), both components of 316L/PP-PE/316L sandwich, by an auto-catalytic route using an acidic bath. Coatings on 316L are made of spherules size ranged from 100 nm to 1 μm while those observed on PP-PE are smaller in the 50–600 nm range. Cell viability is much higher in samples with novel auto-catalytic layer of Ca–P than in the uncoated ones. Furthermore, our results show that the Ca–P coating produced by an auto-catalytic route act as promoter for osteoblasts proliferation. Osteoblasts morphology investigated by immunofluorescence proves that they are attached and well spread confirming the cytocompatibility.

Investigation on the Residual Stress State of Drawn Tubes by Numerical Simulation and Neutron Diffraction Analysis

Cold drawing is widely applied in the industrial production of seamless tubes, employed for various mechanical applications. During pre-processing, deviations in tools and their adjustment lead to inhomogeneities in the geometry of the tubes and cause a gradient in residuals. In this paper a three dimensional finite element (3D-FE)-model is presented which was developed to calculate the change in wall thickness, eccentricity, ovality and residual macro-stress state of the tubes, produced by cold drawing. The model simulates the drawing process of tubes, drawn with and without a plug. For finite element modelling, the commercial software package Abaqus was used. To validate the model, neutron strain imaging measurements were performed on the strain imaging instrument SALSA at the Institute Laue Langevin (ILL, Grenoble, France) on a series of SF-copper tubes, drawn under controlled laboratory conditions, varying the drawing angle and the plug geometry. It can be stated that there is sufficient agreement between the finite element method (FEM)-calculation and the neutron stress determination.

Neutron and Synchrotron Evaluation of Residual Stresses in Coatings

Abstract The present study is dedicated to the evaluation of residual stresses at surfaces, in the bulk of materials and at interfaces, by classical X-ray and neutron diffraction and high-energy synchrotron measurements. It is mainly focused on the improvement of these experimental techniques. The new developed methods have been applied to a coating that consists of leucite moulded on a Palladium alloy substrate. These materials are employed in dental applications.

Characterisation of Microstructure and Residual Stresses in Hydroxyapatite Coatings on Titanium Prostheses

Hydroxyapatite (HA) is one of the most used biomaterials in modern orthopaedics. It allows good chemical bonding to human bones, as it is one of its constituents. HA coatings on prostheses of different nature are currently used to improve their functional performances. Substrates of Titanium and Ti6Al4V Titanium alloy are largely used as they have good mechanical properties. However, they do not induce any osteointegration. Good mechanical properties and good osteointegration processes are achieved when Titanium base prostheses are coated with HA via plasma spray deposition. This work aims to characterise the mechanism of adhesion at the coating-substrate interface in orthopaedic prostheses. Microstructural information is obtained by using optical microscopy, electron microscopy and X-ray diffraction techniques. The residual strain and residual stress gradients close to the interface are investigated by using synchrotron radiation.

Alternative technique for calcium phosphate coating on titanium alloy implants

As an alternative technique for calcium phosphate coating on titanium alloys, we propose to functionalize the metal surface with anionic bath containing chlorides of palladium or silver as activators. This new deposition route has several advantages such as controlled conditions, applicability to complex shapes, no adverse effect of heating, and cost effectiveness. A mixture of hydroxyapatite and calcium phosphate hydrate is deposited on the surface of Ti–6Al–4V. Calcium phosphate coating is built faster compared with the one by Simulated Body Fluid. Cell morphology and density are comparable to the control one; and the results prove no toxic compound is released into the medium during the previous seven days of immersion. Moreover, the cell viability is comparable with cells cultivated with the virgin medium. These experimental treatments allowed producing cytocompatible materials potentially applicable to manufacture implantable devices for orthopedic and oral surgeries.