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• W3184403783 abstract "For treatment of severe bone fractures and damage, synthetic bone grafts have extensively been used as substituting natural bone tissue. Hydroxyapatite (HA) is being extensively used for numerous biomedical applications, specially in orthopaedics and bone replacement applications because of its resemblance to the inorganic part of natural bone. This work aimed to develop novel substituted hydroxyapatite materials having antibacterial properties, as a potential approach to address infection problems in orthopaedic surgeries. This thesis presents a variety of novel single and co-substituted HA powders synthesized by wet precipitation and solid-state methods; afterwards, characterisation of the new materials was carried out using several techniques to determine the crystallographic structure, physiochemical properties, elemental composition, antibacterial and cellular properties of novel substituted HA powders. The new compositions are characterized by substitution of different metal ions in HA, namely: selenite/selenate (SeO3 2- or SeO4 2-), cerium (Ce3+ or Ce4+), copper (Cu+ or Cu2+), and strontium (Sr2+) in various concentrations to improve antibacterial activity, and so to prevent the demand for the usage of antibiotics. Crystallographic studies by X-ray diffraction (XRD) and Rietveld refinement were performed to explain the effect of ion substitution on the HA lattice structure. The compositional and morphological analysis was carried out by using X-ray powder fluorescence (XRF) and Scanning Electron Microscopy (SEM), respectively. Complete chemical recognition was carried out with Fourier transform infrared (FTIR) and Raman spectroscopy to reveal the functional groups present in substituted HA. Biological studies of substituted HA using both direct and in-direct cell culture routes revealed positive cell response with MG-63 and MC3T3-E1 cell lines. Disc diffusion method and turbidity measurements were used to evaluate antibacterial properties of samples against Gram-positive bacteria Staphylococcus carnosus (S. carnosus) and Gram-negative bacteria Escherichia coli (E. coli). The crystallographic results confirmed the substitution of metal ions in the HA crystal structure, as the change in lattice parameters, crystallinity and crystallite size was evidenced, which shows the impact of ion substitution in the HA lattice structure. The substituted ions showed a small deviation of the achieved concentration from the predictable reaction stoichiometry. Moreover, surface charge (evaluated by zeta potential measurements) was revealed to be contingent on the type of substitution. The HA powders immersed in simulated body fluid (SBF) exhibited moderate release of ions which were measured using Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). The levels of released ions were directly proportional to the concentration of substituted ions in HA. The type and concentration of substituted ions had a significant influence on cellular activity. HA substituted with SeO3 2-/SeO4 2-, Ce3+/Ce4+, and Cu+/Cu2+ ions exhibited different levels of antibacterial properties against both bacterial strains, which was ascribed to the type and concentration of substituted ions and also to the ion release profiles. The successfully substituted HA materials showing best results in term of significant antibacterial and biological properties were selected for coatings on metallic implants. Electrophoretic deposition (EPD) techniques (AC and DC) were used to fabricate bioactive and antibacterial composite coatings based on chitosan and substituted HA (pure HA, selenium substituted HA (Se-HA), strontium substituted HA (Sr-HA), and selenium-strontium co-substituted HA (Se-Sr-HA)), as a prospective approach to tackle intrinsic limitation of metallic implants, for example lack of bioactivity and antibacterial effects. In this approach, the substituted HA particles acted as carriers of metal ions for antibacterial activity while chitosan acted as matrix to improve the mechanical properties and to promote osseointegration of the metallic implants. The processing parameters of EPD techniques (AC and DC) were optimized to obtain the desired properties of coatings. The composite coatings exhibited significant adhesion strength, wetting behaviour, and in vitro bioactivity. The release of SeO3 2-/SeO4 2- ions confers antibacterial activity against both S. carnosus and E. coli bacterial strains. Moreover, the chitosan/Se-Sr-HA based composite coatings revealed significant cell viability of 75 % (determined by the WST-8 assay). Furthermore, the co-substitution of Sr2+ was shown to improve cell viability of the coatings. Likewise, the adhesion of MC3T3-E1 cells on the coating surface was significant revealing strong cell-matrix adhesion and cell spreading morphology. To summarize, EPD was confirmed as an appropriate coating method for fabricating substituted HA-based composite coatings for orthopaedic implants. To the best of the authors’ knowledge Se-Sr-HA using wet precipitation method, and cerium substituted HA (Ce-HA) using solid-state route were synthesized and characterized for the first time in this thesis. Moreover, chitosan/Se-Sr-HA composite coatings as bioactive and antibacterial coatings were developed and tested for the first time, with successful results which indicate that such novel coatings could be potentially used in orthopaedic implants applications." @default.
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• W3184403783 date "2021-01-01" @default.
• W3184403783 modified "2023-09-27" @default.
• W3184403783 title "Substituted hydroxyapatites for antibacterial applications" @default.
• W3184403783 hasPublicationYear "2021" @default.
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