Date of Award
Doctor of Philosophy
Chemical and Biochemical Engineering
undamental and applied research on the reinforcement of polymeric materials using nanotechnology is of tremendous potential importance to many industrial and scientific areas, such as the biomedical, automobile and aeronautical industries. In the biomedical industry, there is a sustained interest to develop novel bone cements with enhanced mechanical properties. Bone cement is a self-polymerizing composite material of poly(methyl methacrylate) (PMMA) which has been used in joint replacement surgeries since the 1950s. Bone cement fills the space between the prosthesis and bone to stabilize the implant and transmit functional loading. Joint replacement failure is due to a number of factors, one of which is known to be bone cement mantle failure resulting from the cement’s poor mechanical properties. The aim of this research was to test the efficacy of using nanotechnology to improve the mechanical properties of PMMA based bone
cement. This was accomplished through a range of different investigations. Focusing on nanostructured titania (n-TiC>2) initially, titania nanofibers (n-Ti02 fiber) and nanotubes (n-TiC>2 tube) were introduced into a commercial PMMA matrix with the achievement of increased fracture toughness (Kic), flexural strength (FS) and flexural modulus (FM) of the resulting nanocomposites. The n-TiC>2 fiber/tubes were surface treated to improve dispersion and ensure compatibility with the PMMA matrix using the bifunctional monomeric coupling agent, methacrylic acid (MA). MA has two distinct centers of reactivity, one links with the inorganic nanofiller through a molecular bridge, while the other establishes a covalent bond with the polymer chain. On the basis of the determined mechanical properties, an optimum composition was found at 2 wt% loading of n-Ti02
which provided a significant increase in Kic (10-20%), FS (20-40%) and FM (96-122%) when compared with the unfilled PMMA matrix (P<0.05, one way ANOVA). These improvements were attributed to a high level of interaction and strong chemical adhesion between the n-TiC>2 and PMMA matrix. However, both the n-TiC>2 fibers and tubes did not provide sufficient radiopacity to the PMMA matrix at their optimum level of loading in the composites, which restricts the application of the resulting composites as bone cements.
Secondly, the n-TiC>2 tubes were modified through an in-situ integration process incorporating strontium into tube at the time of the tube synthesis. The modified n-TiC>2 tubes were shown to provide reasonably higher radiopacity to the PMMA matrix than the unmodified tubes at the same level of loading, attributed to the presence of the highly radiopaque strontium atom. While keeping the KiC values of the nanocomposites the same as those reinforced by n-TiC>2 tubes, the strontium modified tubes were shown to enhance the in vitro biocompatibility of the PMMA matrix with rat calvariar osteoblast cells.
Finally, the functionalized n-TiC>2 fibers and tubes were introduced into a clinically used commercial radiopaque bone cement CMW®1, with the n-TiC>2 acting as a reinforcing phase. Mechanical and other important physical characteristics of the reinforced cements were analyzed according to the universal bone cement standard ISO 5833. Based on the determined mechanical properties of the reinforced cements, the optimum composition was found at 1 wt% loading of the n-Ti02 fibers and tubes separately. The observed optimum loading provided a significant increase in Kic (63-73%), FS (20-42%) and FM (22-56%) of the reinforced cements when compared to the as received CMW®1 cement
(P<0.05, one way ANOVA). In addition, the setting and rheological characteristics of the curing cement as well as its in vitro biocompatibility were shown to remain unaltered at the optimized small loading (1%). This study demonstrated a novel pathway to augment the mechanical properties of PMMA based bone cement by providing an enhanced interfacial interaction and strong adhesion between functionalized n-TiC>2 and PMMA matrix. This approach enhanced the effective load transfer within the cement while providing excellent biocompatibility. From the studied experimental outcomes, it is considered that nanotechnology using modified n-TiC>2 provides a new vehicle to improve the mechanical properties of acrylic bone cement.
Khaled, S.M. Zahangir, "DEVELOPMENT OF A NEW GENERATION OF BONE CEMENTS USING NANOTECHNOLOGY" (2009). Digitized Theses. 3937.