Systems Design Engineering

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This is the collection for the University of Waterloo's Department of Systems Design Engineering.

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Browsing Systems Design Engineering by Subject "3D printing"

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    Experimental and Computational Micromechanical Investigations for Developing Mechanically Competent 3D Printable Nanocomposite Biomaterials
    (University of Waterloo, 2023-09-19) Saadatmand Hashemi, Sanaz
    The development of mechanically competent biomaterials that can also facilitate new bone formation is a major challenge in the field of bone repair, especially critically-sized bone defect reconstruction. 3D printed synthetic bone grafts are a possible alternative to conventional bone-substitutes if engineered to provide appropriate structure with adequate mechanical properties and biocompatibility. Nanocomposites may provide better mechanical properties and cell-material interactions compared to other classes of biomaterials due to their nano-scale reinforcements with advantageous surface-to-volume ratio and surface chemistry. In the context of 3D printed bone grafts, nanohydroxyapatite (nHA)-based biopolymer nanocomposites are attractive. The biopolymer matrix component represents the organic phase of natural bone, while nHA, the primary constituent of bone mineral, represents the mineral phase. The mechanical properties of these 3D printable biopolymer nanocomposites can be enhanced through different strategies such as optimizing the processing and manufacturing techniques, biopolymer matrix selection and optimization, surface functionalization of nanoparticles and improved dispersion and interfacial bonding between matrix and nanoparticle, all of which are attributed to improving the mechanical behavior at the micron and sub-micron scales. The focus of the current thesis was to conduct experimental and computational micromechanical investigations toward the development of mechanically competent 3D printable nanocomposite biomaterials (with a focus on strength). The objective was to enhance the mechanical properties of these nanocomposites at the nano-to-micro scales. To achieve this goal, various strategies were employed, including optimizing material design and fabrication techniques. Using a custom-designed direct ink writing (DIW) 3D printer, shear stress was varied during extrusion to force the nHA nanoparticles and/or polymer chains into alignment. The high shear extrusion led to improved mechanical properties through the formation of polymer chain crystallites and nanoconfined thermoset crystallinity phenomena, while no nHA alignment was observed. Another approach focused on optimizing the composition of the matrix by additional functionalization of the biopolymer matrix as well as heat-treating the nHA particles to remove absorbed moisture to improve the dispersion. The high shear extruded functionalized biopolymer nanocomposite system demonstrated Young’s modulus of 6.6 GPa and ultimate tensile strength of 75.5 MPa, providing a strength safety factor of approximately 1.5 against the minimum required standard mechanical properties for bone cement according to ISO standard 5833. It also improved the shape-holding properties of ink, making it suitable for printing objects using the DIW printing system. As part of the effort to enhance the mechanical properties, a novel processing technique and surface functionalization vii were introduced to achieve a homogeneous dispersion of nHA particles and enhance the interfacial bonding between nHA and the biopolymer matrix. This new approach significantly improved the nHA dispersion with few sub-micron scale agglomerations detected. Additionally, interfacial bonding was improved. Interestingly, the enhanced dispersion and interface properties resulted in greater ductility. Finally, an elastoplastic micromechanical computational model as a design tool was developed and biopolymer matrix characterization experiments were conducted to calibrate the elastoplastic material model used for predicting the elastoplastic behaviour of the biopolymer matrix. The model was developed to provide a design tool for virtual investigations of the effect of nHA distribution and orientation on the elastoplastic properties of the nanocomposite systems reported in this thesis. The model was validated using data from tensile tests conducted on these nanocomposite systems. The findings of the current thesis may pave the way for the fabrication of mechanically competent 3D printable nanocomposite grafts for use in bone reconstruction technology.
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    mSLA-based 3D printing of acrylated epoxidized soybean oil - nano-hydroxyapatite composites for bone repair
    (Elsevier, 2021-11) Mondal, Dibakar; Haghpanah, Zahra; Huxman, Connor J.; Tanter, Sophie; Sun, Duo; Gorbet, Maud; Willett, Thomas L.
    Structural bone allografts are used to treat critically sized segmental bone defects (CSBDs) as such defects are too large to heal naturally. Development of biomaterials with competent mechanical properties that can also facilitate new bone formation is a major challenge for CSBD repair. 3D printed synthetic bone grafts are a possible alternative to structural allografts if engineered to provide appropriate structure with sufficient mechanical properties. In this work, we fabricated a set of novel nanocomposite biomaterials consisting of acrylated epoxidized soybean oil (AESO), polyethylene glycol diacrylate (PEGDA) and nanohydroxyapatite (nHA) by using masked stereolithography (mSLA)-based 3D printing. The nanocomposite inks possess suitable rheological properties and good printability to print complex, anatomically-precise, ‘by design’ grafts. The addition of nHA to the AESO/PEGDA resin improved the tensile strength and fracture toughness of the mSLA printed nanocomposites, presumably due to small-scale reinforcement. By adding 10 vol% nHA, tensile strength, modulus and fracture toughness (KIc) were increased to 30.8 ± 1.2 MPa (58% increase), 1984.4 ± 126.7 MPa (144% increase) and 0.6 ± 0.1 MPa·m1/2 (42% increase), respectively (relative to the pure resin). The nanocomposites did not demonstrate significant hydrolytic, enzymatic or oxidative degradation when incubated for 28 days, assuring chemical and mechanical stability at early stages of implantation. Apatite nucleated and covered the nanocomposite surfaces within 7 days of incubation in simulated body fluid. Good viability and proliferation of differentiated MC3T3-E1 osteoblasts were also observed on the nanocomposites. Taken all together, our nanocomposites demonstrate excellent bone-bioactivity and potential for bone defect repair.