Development and Characterisation of Bioactive Coatings Based on Biopolymer and Bioactive Glass Obtained by Electrochemical Means
Creators: name: Pishbin, Fatemehsadat
Publisher: name: Imperial College London
Year: 2012

description: In spite of their widespread application, metallic orthopaedic prosthesis failure still occur due to lack of sufficient bone-bonding and the incidence of post-surgery microbial infections. The goal of this research was to develop multifunctional composite polymer/bioactive glass coatings as a potential strategy to improve surface properties of metallic implants. Using this approach, the bioactive glass improves osseointegration and the polymer plays a dual role: firstly to improve mechanical properties and secondly as a carrier for the release of therapeutics at the implantation site. Electrophoretic deposition (EPD) was chosen as the fabrication method, as it is a room temperature technique in which deposition properties can be effectively tuned and complex architectures can be coated homogenously. 45S5 Bioglass® (BG) powder (~10 μm) and chitosan (CS); a natural polysaccharaide (85% deacetylated); were utilised for coating AISI 316L stainless steel substrate. In aqueous EPD of CS, the electrophoretic mobility and deposition rate were shown to increase with increasing pH from 2.9 to 4.1. Aqueous EPD from BG and composite CS/BG suspensions were optimised by the Taguchi design of experiments approach. For BG suspensions, the pH and the electric field had the most and the least effects on deposition rate, respectively, and a high deposition rate of BG was attained at pH=7. For CS/BG suspensions, co-deposition was very sensitive to the concentration of BG due to its effect on suspension pH, conductivity and particles mobility. Composites with smoother surface morphology and more uniform distribution of BG particles in the CS matrix were obtained at lower glass concentrations. Structural and physical evaluations of CS and different CS/BG coatings showed that they were amorphous and also confirmed the formation of hydrogen-bonding between BG and CS in the EPD suspension. Dissolution profiles and bioactivity study of the coatings confirmed hydroxycarbonate apatite (HCA) formation in simulated body fluid (SBF) for composites in the higher range of BG loading. The bioactivity response of coatings was elucidated considering the EPD suspension preparation step and the role of surface charge on HCA formation. Tape-testing showed improvement of coating adhesion with addition of BG (for up to~ 60 wt% BG) and Vickers micro-hardness testing revealed that the composite hardness increased with the amount of BG in the films. Two types of antibacterial agents were incorporated in the composites via EPD: nano-particulate silver (Ag-np) and gentamicin (GS) antibiotic. For the first time, single step processing, in-situ formation and incorporation of Ag-np during EPD of chitosan-based composite films was shown. The release of Ag ion and GS in SBF was measured showing an initial burst release followed by a reduced release rate. Although about 40% of GS was released in 5 days, less than 7% of the loaded silver was released within 28 days. Disk diffusion tests demonstrated inhibition of S. aureus growth up to 10 and 2 days for Ag-np and GS samples, respectively. A preliminary 7 day culture study of MG-63 osteoblast like-cells on coatings indicated cellular attachment and proliferation for all coatings, except for Ag-np-containing films. The high amount of silver release was identified as the reason for cytotoxicity. Overall, the results presented in this thesis demonstrate the potential of EPD as a suitable fabrication technology for preparing multifunctional CS/BG composite bioactive coatings for orthopaedic applications.