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Title: Investigation of mechanisms and factors influencing the delivery of calcium phosphate pastes for minimally invasive surgical applications
Author: O'Neill, Rory Edward
ISNI:       0000 0004 6059 5114
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2016
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Calcium phosphate (CaP) materials have shown great potential in orthopaedic applications due to their ability to mimic the mineral phase of bone. However applications requiring injection or extrusion of CaP paste (e.g. percutaneous vertebroplasty and kyphoplasty, or producing scaffolds by robocasting) are frequently inhibited by the separation of the powder and liquid components. This phase separation has a detrimental effect on the quality of extrudate due to a higher liquid content than desired. Currently there is an effort to reduce or eliminate phase separation and produce fully injectable CaP pastes and cements to better exploit their advantageous properties in orthopaedic applications. This research programme contributes to this effort by increasing the understanding of the mechanism and dominant drivers influencing phase separation during ram extrusion of CaP pastes. The phase separation of CaP pastes was examined by determining the flow of the liquid and powder components throughout the extrusion process. Experimental and theoretical methods were investigated to measure the flow properties and permeability of different compositions of CaP pastes. The influence of these two properties on phase separation was determined. It was found that increasing flowability and reducing permeability reduced phase separation, and it was flowability that was the dominant influencing property. Using different theories and characterisation techniques a semi-empirical theoretical model was developed. The model predicted the difference between the pressure required for homogeneous extrusion and pressure required to cause the liquid to travel through the powder network. The predicted pressure difference corroborated well with phase separation values measured within this project and several other studies, demonstrating the model can estimate the extent of phase separation over a range of variables including: liquid content, powder morphology, plunger rate and syringe geometry.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available