Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Biomedical Engineering

Collaborative Specialization

Musculoskeletal Health Research

Supervisor

Rizkalla, Amin S.

Abstract

The goal of this study was to develop and validate finite element analysis (FEA) models to predict static and dynamic mechanical properties of porous titanium 6-aluminum 4-vanadium (Ti6Al4V) constructs. Dumbbell-shaped and square prism porous computer models were created with simple cubic unit cell structures with a size of 1 mm and strut thicknesses varying between 250 and 650 µm. The pore diameters ranged between 350 and 750 µm. Constructs were manufactured using selective laser melting (SLM). These constructs were scanned using computed tomography (CT) and scanning electron microscopy (SEM). These constructs were then tested under tensile and flexural static loading using a screw-type universal testing machine and under dynamic flexural loading using a servo-hydraulic testing machine. The FEA models were designed with mechanical properties calibrated to mimic those of the real-life constructs and omit the structural imperfections. The models’ predictions were compared to the real-life mechanical testing results. A novel intraosseous porous implant was designed with numerical models to assess the mechanical properties of the implant under physiological loading conditions. The strength and modulus predictions of the FEA models matched those of the SLM-built constructs within a deviation of < 11 %, while the deviation of the fatigue strength from the numerical models was ≈ 10%. The larger deviations in the toughness predictions of the computer models from the real-life tests were associated with the diminished plastic strain of the SLM-built constructs, which the structural imperfections of the SLM-built constructs might have caused. In addition, SLM-built Ti6Al4V porous constructs with strut thicknesses ranging between 350 and 450 µm were viable for use in the intraosseous mandibular implant design. The implant was intact when exposed to physiological molar clenching. When the implant was exposed to cyclic masticatory forces ranging between 50 and 100 N, its predicted life expectancy was between 4 years at 100 N and 119 years at 50 N, exceeding the time for healthy bone ingrowth to osseointegrate and stabilize within the constructs. The FEA models can swiftly and accurately predict the static and dynamic mechanical properties of SLM-built constructs within a short period, making them suitable for use in clinical settings.

Summary for Lay Audience

This study focused on developing computer models to validate and predict porous titanium alloy constructs' static and dynamic mechanical properties. The aim of using these models was to design intraosseous porous implants that could be used for mandible (jaw) reconstruction. A series of porous models were built with void volumes and sizes to 3D-print porous titanium alloy constructs using selective laser melting (SLM). The microstructural features of these constructs were analyzed using computed tomography (CT) and scanning electron microscopy (SEM). The porous constructs were subjected to pull tensile loading and static and dynamic three-point bending to evaluate their mechanical properties. The results of these tests were used to develop and validate finite element analysis (FEA) models to predict the mechanical behaviour of these constructs. The results of these tests demonstrated a close correlation with real-life SLM-built porous constructs, particularly when a low force was applied. The deviations in the strain values were presumed to be an outcome of the structural imperfections detected within the constructs. Using these computer models, an intraosseous jaw implant was built with a porous structure that followed the stiffness of a dried cadaveric jaw model. The analysis showed that the implant can withstand chewing for up to 119 years of service. The computer models developed in this study can be used to create clinical procedures whereby patient-specific orthopedic implants can be designed, tested, and manufactured for implantation within a short time.

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