Thermal spray of a drug delivery system onto femoral orthopaedic implant
Chebbi, Ahmed (2011) Thermal spray of a drug delivery system onto femoral orthopaedic implant. PhD thesis, Dublin City University.
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Hydroxyapatite bioceramics are proven to be good materials for bone replacement and repair applications, due to their similarity in chemical composition to bone. Plasma spraying has been commonly used to apply hydroxyapatite coatings onto metallic implants for use in orthopaedic surgeries. The addition of HA coatings was successful in improving the performance of titanium implants. However, this type of implant has shown some limitations with regards to mechanical (implant loosening) and biological (infections) behaviour. It is thought that local drug delivery would be useful to prevent implant failures that could be treated with therapeutic agents (drug/growth factor). It is hypothesised in this work that polymers proven in drug delivery for other applications could be successfully applied to implants using existing technology in the sector. This research aims to introduce biodegradable materials (polymers) to the existing HA-titanium combination and to bare titanium implants in order to act as a drug-delivery vehicle. The proposed materials (PCL, PMMA and PHBV) consisted of biodegradable and non-biodegradable polymers (used separately or as a composite) that are widely used as drug delivery systems. The method used to apply these drug delivery systems in this project was flame spraying, due to its superior mechanical advantages over other techniques. Taking into account the thermal sensitivity of the chosen polymers and the high process temperature generated by the process, the mains challenges of this study were to obtain viable coatings with regards to all coating properties (chemical, physical, biological) and to control the mechanical characteristics of such coatings by varying the process parameters. Screening tests were conducted to determine the spraying parameters suitable for each polymer, followed by a more thorough Design of Experiments analysis to understand the relationship between three process factors: traverse speed, number of passes and spraying distance, and four coatings properties: thickness, roughness, adhesion and wettability. Chemical, physical, physiological and biological tests were also performed in order to study the suitability of the proposed polymers for such an application. The optimal process parameters to spray the PCL and PHBV matrices were: traverse speed of 0.152 m/s and 0.33 m/s, spraying distance of50 cm and 42.5 cm number of passes of 6 and 14, respectively. Viable polymer composites were obtained with the optimised spraying parameters on bare titanium and on HA coatings. These polymer coatings were not chemically damaged following flame spraying and all physiological and biological indicators suggested that the deposition technique used in this project is well suited for applying polymeric materials on orthopaedic implants for use as bioactive and drug delivery systems.
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