title: Extent and mechanism of phase separation during the extrusion of calcium phosphate pastes.
abstract: The aim of this study was to increase understanding of the mechanism and dominant drivers influencing phase separation during ram extrusion of calcium phosphate (CaP) paste for orthopaedic applications. The liquid content of extrudate was determined, and the flow of liquid and powder phases within the syringe barrel during extrusion were observed, subject to various extrusion parameters. Increasing the initial liquid-to-powder mass ratio, LPR, (0.4-0.45), plunger rate (5-20 mm/min), and tapering the barrel exit (45°-90°) significantly reduced the extent of phase separation. Phase separation values ranged from (6.22 ± 0.69 to 18.94 ± 0.69 %). However altering needle geometry had no significant effect on phase separation. From powder tracing and liquid content determination, static zones of powder and a non-uniform liquid distribution was observed within the barrel. Measurements of extrudate and paste LPR within the barrel indicated that extrudate LPR remained constant during extrusion, while LPR of paste within the barrel decreased steadily. These observations indicate the mechanism of phase separation was located within the syringe barrel. Therefore phase separation can be attributed to either; (1) the liquid being forced downstream by an increase in pore pressure as a result of powder consolidation due to the pressure exerted by the plunger or (2) the liquid being drawn from paste within the barrel, due to suction, driven by dilation of the solids matrix at the barrel exit. Differentiating between these two mechanisms is difficult; however results obtained suggest that suction is the dominant phase separation mechanism occurring during extrusion of CaP paste.
authors.affiliation: School of Mechanical and Aerospace Engineering, Queen's University Belfast, Stranmillis Road, Belfast, BT9 5AH, UK. roneill20@qub.ac.uk.
authors.forename: Rory
authors.initials: R
authors.lastname: O'Neill
authors.affiliation: School of Pharmacy, Queen's University Belfast, Lisburn Road, Belfast, BT9 7BL, UK. h.mccarthy@qub.ac.uk.
authors.forename: Helen O
authors.initials: HO
authors.lastname: McCarthy
authors.affiliation: School of Mechanical and Aerospace Engineering, Queen's University Belfast, Stranmillis Road, Belfast, BT9 5AH, UK. e.cunningham@qub.ac.uk.
authors.forename: Eoin
authors.initials: E
authors.lastname: Cunningham
authors.affiliation: Biomaterials, Biomechanics and Tissue Engineering Group, Department of Materials Science and Metallurgy, Technical University of Catalonia, BarcelonaTech (UPC), Av. Diagonal 647, 08028, Barcelona, Spain. edgar.benjamin.montufar@upc.edu.
authors.forename: Edgar
authors.initials: E
authors.lastname: Montufar
authors.affiliation: Biomaterials, Biomechanics and Tissue Engineering Group, Department of Materials Science and Metallurgy, Technical University of Catalonia, BarcelonaTech (UPC), Av. Diagonal 647, 08028, Barcelona, Spain. maria.pau.ginebra@upc.edu.
authors.forename: Maria-Pau
authors.initials: MP
authors.lastname: Ginebra
authors.affiliation: Department of Chemical Engineering and Biotechnology, New Museums Site, University of Cambridge, Pembroke St, Cambridge, CB2 3RA, UK. diw11@cam.ac.uk.
authors.forename: D Ian
authors.initials: DI
authors.lastname: Wilson
authors.affiliation: School of Mechanical and Aerospace Engineering, Queen's University Belfast, Stranmillis Road, Belfast, BT9 5AH, UK. a.lennon@qub.ac.uk.
authors.forename: Alex
authors.initials: A
authors.lastname: Lennon
authors.affiliation: School of Mechanical and Aerospace Engineering, Queen's University Belfast, Stranmillis Road, Belfast, BT9 5AH, UK. n.dunne@qub.ac.uk.|School of Mechanical and Manufacturing Engineering, Dublin City University, Dublin 9, Glasnevin, Ireland. n.dunne@qub.ac.uk.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Dunne
mesh_terms: D001843:Bone Cements / Q000737:chemistry*; D002130:Calcium Phosphates / Q000737:chemistry*; D002626:Chemistry, Pharmaceutical / Q000379:methods; D007267:Injections; D008422:Materials Testing; D009824:Ointments; D010316:Particle Size; D044367:Phase Transition; D011208:Powders / Q000737:chemistry; D011312:Pressure
chemical_list: D001843:Bone Cements; D002130:Calcium Phosphates; D009824:Ointments; D011208:Powders; C020243:calcium phosphate