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• W61332104 abstract "Polyurethanes have long been attractive polymeric biomaterials due to their biocompatibility, processability and tailorable mechanical properties. Nonetheless, for future designs of some next generation medical device components, the mechanical properties of existing polyurethanes are inadequate. As an example, the advancement of Cochleart implants requires new insulation materials which are capable of accommodating a smaller and more intricate design of electrode arrays. Existing insulation materials, silicone elastomers, have limited overall mechanical and tear properties, which therefore hamper the realization of the next generation Cochleart implants. Furthermore, the incorporation of organoclays in a polymer matrix has been widely shown to simultaneously enhance the mechanical, thermal, and barrier properties of several host polymer types, including polyurethanes.Considering these potential benefits, the viability of silicone-based polyurethane/organoclay nanocomposites as potential candidates for long-term implantable medical devices, particularly for the next generation of Cochleart implants, is investigated in this thesis. Since these proposed biomaterials incorporate nanoparticles (organoclays), in addition to enhanced mechanical performance, the safety of these materials needs to be demonstrated in order to progress the technology towards applications and commercialization. It is particularly important to investigate both mechanical and biological performance in parallel because the published cytotoxicity data for organoclays is very limited and contradictory, and robust data surrounding the leaching of nanofillers is non-existent. In order to address this knowledge gap, a range of single and dual modified organo hectorites (aspect ratio ~ 25 nm/1 nm) and organo fluoromicas (aspect ratio ~ 650 nm/1 nm) with varying degrees of surface hydrophobicity were prepared and characterized. Octadecyltrimethylammonium bromide (ODTMA), dimethyldioctadecylammonium chloride (DMDO), and choline chloride (CC) were employed to modify the clay surface via an aqueous ion exchange reaction. The dual-modified organoclays incorporated 25% CC and 75% ODTMA or DMDO. The results showed that d-spacing expansion, thermal stability and surface hydrophobicity of the resultant organoclays was strongly affected by the chemical structure of the surfactants, single/dual modification, and type of clays. Furthermore, the physicochemical properties of organoclays influence the clay dispersion state (exfoliated/intercalated nanocomposites or microcomposites), determine the suitable polymer processing methods, and affect the mechanical properties of polyurethane nanocomposites (tensile, creep, and tear properties). The release of leachables from the nanocomposites was quantified and the toxicity was subsequently investigated. It was established that the cytotoxicity of organoclays is affected by the chemical structure of surfactants and the type of cell line employed. The toxicity of organoclays investigated in this thesis was found to increase in the following order: unmodified fluoromica l M75D (fluoromica modified with 75%/25% DMDO/CC) l M75O (fluoromica modified with 75%/25% ODTMA/CC). Moreover, the mouse neuroblastoma (Neuro 2A) cell line was more susceptible to the surfactants and organoclays when compared to the human epithelial carcinoma (HeLa) cell line. In addition to the inherent cytotoxicity of organoclays, the clay dispersion state in the host polyurethanes is another important factor to be considered when selecting suitable nanofillers, since the well dispersed organoclays are less likely to leach out and pose safety risk compared to the incompatible organoclays, which form large tactoids and tend to phase separate from the polyurethane matrix. In general, organoclays have been shown to enhance the in vitro biostability of silicone-based polyurethane nanocomposites. Nonetheless, it was the most well-dispersed organoclays, L75D (hectorite modified with 75%/25% DMDO/CC), which was capable of most effectively reducing the rate of surface degradation by minimizing the interactions of susceptible bonds and oxidative reagents. Finally, the importance of conducting mechanical testing in physiological conditions (PBS, 37 dC) instead of in dry ambient conditions wasn demonstrated. It was shown that a minimum amount of absorbed water may alter the mechanical properties ofn polyurethane nanocomposites." @default.
• W61332104 created "2016-06-24" @default.
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• W61332104 date "2013-01-01" @default.
• W61332104 modified "2023-09-26" @default.
• W61332104 title "Biocompatibility and toxicity of synthetic organoclay nanofillers and biomedical polyurethane nanocomposites" @default.
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