Dr Amirpasha Moetazedian's Qualifications (3)

Biomedical Materials Science
BSc

Status	Complete
Part Time	No
Years	2013 - 2016
Awarding Institution	University of Birmingham

Biomaterials
MRes

Status	Complete
Years	2016 - 2018
Project Title	Modification of novel Portland based cement for orthopaedic application
Project Description	Portland cement (PC) is a ceramic hydraulic cement which has been used in construction for decades and more recently for dental applications. PCs possess high durability and compressive strength and demonstrate good biological responses, that are generating interest as a potential material for orthopaedic applications. The present study investigated the addition of porogens to induce large macropores e.g. > 100 µm to promote potential bone ingrowth, whilst retaining appropriate mechanical and physical properties for vertebroplasty used to stabilise fractured vertebral bodies. The cements containing 20 wt% bismuth oxide (radiopacifying agent) and 5 wt% calcium chloride (setting accelerant) were prepared using a range of powder-to-liquid ratios and porogens (including mannitol, sucrose and sodium bicarbonate or foaming agents) were added from 1-20 wt% to induce macroporosity either after or during setting of the cement. Increasing the concentration of sugars increased the initial setting time 3-fold, whilst causing the cement paste to behave as a liquid. The compressive strengths of modified cements were reduced by up to 90 % after 7 days of storage through increasing flaws and porosity. The macrostructural analysis using scanning electron microscopy (SEM) showed no major difference between the modified cements and controls. 10 wt% foamed gelatine (FG) was found to improve the viscosity of the paste so that it was readily injectable, and demonstrated sufficient cohesion after injection. FG doubled the setting time approximately and generated large interconnected pores ranging from 100-400 µm in diameter according to SEM images. The compressive strengths of foamed cements were sufficiently high after 7 and 30 days of storage to stabilise fractured vertebral bodies. The addition of 10 wt% FG has shown the potential to modify PC by inducing large pores, whilst maintaining high injectability and compressive strength, which warrants further testing for clinical application in verterbroplasty
Awarding Institution	University of Birmingham

Mechanical Engineering
PhD / DPhil

Status	Complete
Years	2018 - 2021
Project Title	Hydrolytic degradation of polylactide in extrusion additive manufacturing
Project Description	The combined use of material extrusion additive manufacturing (MEAM) and biodegradable polymers such as polylactide (PLA) is one of the most versatile and valuable manufacturing strategies for biomedical applications. MEAM enables rapid production of personalised PLA medical devices as they degrade by hydrolysis over a period of months or years. Although MEAM presents a range of opportunities, there are a number of limitations, the most critical of which is mechanical anisotropy, specifically low strength in the direction normal to the print platform (Z direction). This limits its use for long-term mechanical application. Numerous studies have attributed the diffusion of the polymer chains across the interface between layers as the main underlying mechanism of mechanical anisotropy. However, attempts to understand mechanical anisotropy of MEAM parts have resulted in considerable inconsistencies, with no consensus on the degree of anisotropy or its dependency on printing parameters. In this thesis, experimental studies describe the development of a new microscale uniaxial tensile specimen, based on the idea of COntinuously Varied EXtrusion (CONVEX) by direct GCode scripting to reduce geometrical complexities of current testing standards and to enable improved manufacturing control. The newly devised PLA specimen comprised of stacked individual extruded filaments enabled an improved fundamental analysis of extruded filaments (F specimens, representing bulk-material properties when extruded filament printed along the print platform) and the interface (Z specimens when extruded filament printed normal to the print platform) between them. Geometrical analysis of specimens by microscopy allowed accurate cross-sectional area measurements to be used in strength calculations and generated new understanding about the effect of testing orientation on mechanical properties of MEAM parts. Mechanical and thermal characterisations of both specimen types were conducted to consider the effects of physiological temperature (PT), hydration and in-aqua testing against the control (non-hydrated specimens tested in air at room temperature). Mechanical studies showed bulk-material bond strength between layers. The filament-scale geometries in Z specimens (i.e. grooves between layers) were responsible for strain concentrations and significantly reducing strain at fracture and toughness. In contrast, for F specimens, the grooves were aligned in the direction of loading and did not impact mechanical properties. Furthermore, the importance of submerged tests at PT for PLA was confirmed by demonstrating a combined plasticisation effect of water and higher temperature, highlighting an important risk of conventional laboratory testing overestimating properties by two-fold. The testing environment has a similar effect on both F and Z specimens. Moreover, during long-term hydrolytic degradation experiments, it was found that the interface degraded in a similar manner to the bulk polymer material. Comparison of thermal and chemical properties revealed that during the early stage of hydrolytic degradation, crystallinity was the dominating factor, whilst at later stages, mechanical properties were mainly defined by the molecular weight. The new understanding developed in this thesis highlights that for MEAM parts, the interface does not affect its long-term properties. This improves confidence in using the MEAM process for high-value applications.
Awarding Institution	Loughborough University