Electrophoretic deposition of organic/inorganic composite coatings on metallic substrates for bone replacement applications: mechanisms and development of new bioactive materials based on polysaccharides

Please always quote using this URN: urn:nbn:de:bvb:29-opus4-65631
  • Regarding the need to improve the usually encountered osteointegration of metallic implants with the surrounding body tissue in bone replacement applications, bioactive organic/inorganic composite coatings on metallic substrates were developed in this work using electrophoretic deposition (EPD) as coating technology. In the present work three polysaccharides, namely alginate, chondroitin sulfate and chitosan were used as the organic part, acting as the matrix of the coating and enabling the coating attachment to the metallic substrates (stainless steel AISI 316L, titanium alloy TI6Al4V and magnesium alloy AD91D). Different types of ceramic fillers were investigated as the inorganic phase ofRegarding the need to improve the usually encountered osteointegration of metallic implants with the surrounding body tissue in bone replacement applications, bioactive organic/inorganic composite coatings on metallic substrates were developed in this work using electrophoretic deposition (EPD) as coating technology. In the present work three polysaccharides, namely alginate, chondroitin sulfate and chitosan were used as the organic part, acting as the matrix of the coating and enabling the coating attachment to the metallic substrates (stainless steel AISI 316L, titanium alloy TI6Al4V and magnesium alloy AD91D). Different types of ceramic fillers were investigated as the inorganic phase of the coatings. Different bioactive glasses were used to impart osteoconductive and osteoinductive properties to the coating, while nanoparticles of titania and zinc oxide were used to bring antibacterial properties, improve the mechanical stability and control the degradation behavior of the coatings. In this work the possibility to develop stable suitable suspensions to produce coatings by EPD is shown, based in the three selected biopolymers and containing one or more types of ceramic particles in different size ranges from 20 nm to 30 µm. The investigation of different solvents for EPD, namely water and ethanol, was carried out (single or in mixtures of both) to develop stable suspensions to reduce the negative effect of the water hydrolysis in the coating morphology. The suspension stability was studied via ζ–potential measurements finding that the suspension mechanism is controlled by the polymer, which, by esterification effect, suspends the ceramic particles in the liquid media. A variety of more than 20 coatings were studied and developed during this thesis. The major goal was to develop suitable EPD technology to produce coatings with: adequate (i) homogeneity, (ii) attachment to the substrate, (iii) ceramic/polymer ratio, (iv) wettability and morphology, (v) electrochemical behavior, (vi) bioactivity and (vi) degradation behavior. Other properties were also analyzed such as: antibacterial activity and drug delivery function (by incorporation of simvastatin). Alginate based coatings containing nanoparticles of TiO2 or ZnO were developed by anodic EPD. Bioactive glass 45S5® (BG) was successfully incorporated to those coatings with the aim to provide bioactivity to the coating by the formation of hydroxyapatite. However not all the coatings were able to show bioactivity, mainly by an interaction of the anodic alginate with the ions coming from the simulated body fluid (SBF) and the BG particles. It was confirmed that all coatings imparted corrosion protection to the substrate when evaluated via potentiostatic polarization curves by immersion in Dulbecco´s MEM, also to the highly reactive magnesium alloy AZ91D, in the initial immersion stages. For the first time, in this project chondroitin sulfate (CS) was deposited by EPD. Even when the deposition was successful the coating degraded considerably fast when immersed in water based fluids. To tackle the fast degradation and impart bioactivity to CS coatings, a multilayer approach was chosen, where chitosan was used in the production of "sandwich-type" multilayers with the presence of BG in some of the layers. By this method the coating degradation was considerable reduced and the development of a bioactive composite coating was possible. The most successful coatings, in terms of degradation behavior and bioactivity, were the chitosan based coatings. The bioactive glass/chitosan (BG/Ch) system was studied in a comparative study using three different bioactive glasses. In this study all the coatings exhibited bioactivity, independently of the bioactive glass composition. The best coating in terms of homogeneity, degradability and bioactivity was produced using Bioglass 45S5®. For the system Bioglass/Chitosan considerable improvements were done compared with previous reported works, obtaining more stable suspensions and better coating homogeneity. To tailor the coating degradability and improve adhesion to the substrate, titania was added to the BG/Ch coating. In addition, simvastatin, a drug currently proposed to promote bone formation, was added to the system confirming the drug delivery potential of the coatings. Cell test studies with MG-63 human osteosarcoma cells were done on selected coatings to evaluate cell vitality and the effect of the simvastatin on cell behavior. In this work EPD has shown to be a highly versatile, low-cost and convenient method to produce organic/inorganic coatings on metallic substrates based on the chosen materials. Different approaches were studied: from single to multilayers, from coatings on flat surfaces to complex 3D structures, as well as the drug delivery potential. Coatings with tailored composition and thickness were successfully produced exhibiting the versatility of EPD as coating production technique.show moreshow less

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Metadaten
Author:Luis Eduardo Cordero Arias
URN:urn:nbn:de:bvb:29-opus4-65631
Referee:Aldo Boccaccini, Sannakaisa Virtanen
Document Type:Doctoral Thesis
Language:English
Year of Completion:2015
Embargo Date:2015/09/09
Publishing Institution:Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)
Granting Institution:Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Technische Fakultät
Date of final exam:2015/08/28
Release Date:2015/09/17
SWD-Keyword:Bioglass; Electrophoretic Deposition; Chitosan; Alginate; Chondroitin sulfate; coating; Bone; Titania
Pagenumber:278
Institutes:Technische Fakultät
Dewey Decimal Classification:6 Technik, Medizin, angewandte Wissenschaften / 62 Ingenieurwissenschaften / 620 Ingenieurwissenschaften und zugeordnete Tätigkeiten
open_access (DINI-Set):open_access
Licence (German):Creative Commons - CC BY-NC-ND - Namensnennung - Nicht kommerziell - Keine Bearbeitungen 3.0