Abstract
3D printable biopolymer nanocomposites are an exciting novel class of materials with potential as biomaterials for skeletal reconstruction. In recent years, there has been an increasing demand for synthetic bone graft substitute materials. Development of these biomaterials would reduce the dependence on natural bone grafts and metal prostheses, which have significant practical and clinical issues associated with their use. Using additive manufacturing technologies, such as masked stereolithography, and biopolymer nanocomposites, complex, accurate, robust, and customizable biomaterials can be produced. Novel nanocomposite biomaterials composed of functionalized plant-based monomers and hydroxyapatite (HA) nanoparticle fillers developed previously in our laboratory have achieved mechanical performance exceeding those of commercial bone cement biomaterials. However, these materials have not been evaluated under physiologically relevant conditions. Exposure to physiological temperature of 37 °C and a hydrated environment can result in significant mechanical consequences, such as reduced mechanical strength and stiffness due to swelling, hydrolysis or osmotic cracking. To create a successful bone graft substitute, along with competent mechanical properties, it is essential that the material be degradable and resorbable to allow remodeling to natural bone tissue. One of the methods to evaluate a material’s eventual in vivo degradation performance is to assess its susceptibility to oxidative degradation, as this is a naturally occurring mechanism in cell metabolism, inflammation responses, and osteoclast resorption. In this thesis, a set of experiments with controllable environmental factors was developed to assess the responses of our biopolymer nanocomposites to physiological temperature, water absorption, and oxidative degradation. It was determined that the biomaterials investigated in this study were susceptible to these effects, with significant evidence of water absorption and surface degradation due to oxidation. This led to consequences in mechanical performance, in particular tensile and compressive strengths and moduli. For example, a 10 vol% HA nanocomposite exposed to elevated temperatures had 62 and 68 % reductions in compressive yield strength resulting from 14-day incubations in phosphate-buffered saline and hypochlorous acid, respectively. This thesis has demonstrated the importance of evaluating biomaterials under physiologically relevant conditions in vitro throughout the material development process and provides a fundamental basis and clear recommendations for further development of these materials.
Presenter
Elizabeth Diederichs, MASc candidate in Systems Design Engineering