Optimization of a thermochemical process and antibacterial properties for 3D printed prostheses of titanium
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Tutor / directorManero Planella, José María
CovenanteeUniversité de Lorraine
Document typeMaster thesis
Rights accessRestricted access - author's decision
A relevant aspect in the biomedical field is the research for optimizing the bone-implant coupling in order to avoid the stress-shielding effect. Bone requires a mechanical stimulus for growth; hence, in a bone-implant coupling, it is essential to use materials with stiffness properties similar to bone for improving the load-transfer and favoring bone healing and remodeling. One alternative method of lowering the elastic is developing porous materials (metallic foams) that have demonstrated their potential to allow rapid bone ingrowth. Another important aspect of the use of biomaterials is linked with medical device-related infections. These infections may cause an implant failure, with the corresponding implant revision or removal process and the associatedpatient’s pain and costs. Recently, it has been shown that functional metal ions such as Ca, Sr, Mg and Ag can be incorporated into the Ti surface by modifying the conditions or the thermochemical treatment . In this regard, silver (Ag)-based compounds have been used in this project to obtain porous titanium with antibacterial properties. AMES, a company in automotive is willing to expend its market to the biomedical domain. They want to launch their first functionalized prosthesis in titanium 3D printed and industrialize it. The bioactivation of the titanium process must be effective, cheap and as short as possible. There are many processes to bioactivate the titaniumlike the apatite plasma coatingor calcium phosphate deposition by sputtering, butthethermochemical treatment can homogeneously cover complex shapes so is the most adapted for industrializationof porous prostheses.This thermochemical process chosen by AMESis composed of 2 steps after cleaning the sample, attack the samplewith a 5M NaOH solution at 60°C for 24h and finally a 600°C heat treatment for 1 hour. The first step is the most time consumer,therefore,the first aim was to optimize the time process of alkaline etching. Three timeshave beenexperimented:6, 10 and 24 hours at 60°C under constant agitation.The surface topography has been characterized by SEM and showed a feather-like structureaccording to the literature.The chemical characterization has been done with Raman spectroscopyshowingthat 10 hours of chemical attack gave similar composition that 24 hours. Moreover, the bioactivity(bone bonding ability)has been experimented by soaking the samples into simulated body fluid (SBF). Both, SEM studiesand Raman spectroscopy corroborate the formation of hydroxyapatite after 3 days in SBF. To address concerns regarding deep infection during orthopedic surgery, the second aim was to modify the thermochemical treatment incorporating Ag+ions to impart antibacterial properties. The use of calcium acetate instead of calcium chloride during the treatment has allowed to introduce simultaneously and easily silver ions into a thin calcium titanate layer. The porous titanium samples formed apatite on their surface in an SBF, released 179ppb Ag+ion into the Hanks solution within 72h, without cytotoxicity, and exhibited a strong antibacterial effect against Staphylococcus epidermidis and Pseudomonas. The efficiency of the antibacterial coating has been carried out by the halo of inhibition test for both bacteria.
SubjectsBiomedical materials, Implants, Artificial, Titani -- Aplicacions mèdiques, Materials biomèdics, Implants artificials
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