title: Critical review: Injectability of calcium phosphate pastes and cements.
abstract: Calcium phosphate cements (CPC) have seen clinical success in many dental and orthopaedic applications in recent years. The properties of CPC essential for clinical success are reviewed in this article, which includes properties of the set cement (e.g. bioresorbability, biocompatibility, porosity and mechanical properties) and unset cement (e.g. setting time, cohesion, flow properties and ease of delivery to the surgical site). Emphasis is on the delivery of calcium phosphate (CaP) pastes and CPC, in particular the occurrence of separation of the liquid and solid components of the pastes and cements during injection; and established methods to reduce this phase separation. In addition a review of phase separation mechanisms observed during the extrusion of other biphasic paste systems and the theoretical models used to describe these mechanisms are discussed.
  
  
  
  Occurrence of phase separation of calcium phosphate pastes and cements during injection limits their full exploitation as a bone substitute in minimally invasive surgical applications. Due to lack of theoretical understanding of the phase separation mechanism(s), optimisation of an injectable CPC that satisfies clinical requirements has proven difficult. However, phase separation of pastes during delivery has been the focus across several research fields. Therefore in addition to a review of methods to reduce phase separation of CPC and the associated constraints, a review of phase separation mechanisms observed during extrusion of other pastes and the theoretical models used to describe these mechanisms is presented. It is anticipated this review will benefit future attempts to develop injectable calcium phosphate based systems.
authors.affiliation: School of Mechanical and Aerospace Engineering, Queen's University Belfast, Ashby Building, Stranmillis Rd, Belfast BT9 5AH, United Kingdom.
authors.forename: R
authors.initials: R
authors.lastname: O'Neill
authors.affiliation: School of Pharmacy, Queen's University Belfast, 97 Lisburn Road, Belfast BT9 7BL, United Kingdom.
authors.forename: H O
authors.initials: HO
authors.lastname: McCarthy
authors.affiliation: Biomaterials, Biomechanics and Tissue Engineering Group, Department of Materials Science and Metallurgical Engineering, Universitat Politècnica de Catalunya. BarcelonaTech (UPC), Av. Diagonal 647, 08028 Barcelona, Spain; Institute for Bioengineering of Catalonia, C. Baldiri Reixach 10, 08028 Barcelona, Spain.
authors.forename: E B
authors.initials: EB
authors.lastname: Montufar
authors.affiliation: Biomaterials, Biomechanics and Tissue Engineering Group, Department of Materials Science and Metallurgical Engineering, Universitat Politècnica de Catalunya. BarcelonaTech (UPC), Av. Diagonal 647, 08028 Barcelona, Spain; Institute for Bioengineering of Catalonia, C. Baldiri Reixach 10, 08028 Barcelona, Spain.
authors.forename: M-P
authors.initials: MP
authors.lastname: Ginebra
authors.affiliation: Department of Chemical Engineering and Biotechnology, New Museums Site, Pembroke Street, University of Cambridge, CB2 3RA, United Kingdom.
authors.forename: D I
authors.initials: DI
authors.lastname: Wilson
authors.affiliation: School of Mechanical and Aerospace Engineering, Queen's University Belfast, Ashby Building, Stranmillis Rd, Belfast BT9 5AH, United Kingdom.
authors.forename: A
authors.initials: A
authors.lastname: Lennon
authors.affiliation: School of Pharmacy, Queen's University Belfast, 97 Lisburn Road, Belfast BT9 7BL, United Kingdom; Centre for Medical Engineering Research, School of Mechanical and Manufacturing Engineering, Dublin City University, Stokes Building, Collins Avenue, Dublin 9, Ireland; Trinity Centre for Bioengineering, Trinity Biomedical Sciences Institute, Trinity College Dublin, Dublin 2, Ireland. Electronic address: nicholas.dunne@dcu.ie.
authors.forename: N
authors.initials: N
authors.lastname: Dunne
mesh_terms: D000818:Animals; D001672:Biocompatible Materials / Q000737:chemistry* / Q000627:therapeutic use; D001843:Bone Cements / Q000737:chemistry* / Q000627:therapeutic use; D002130:Calcium Phosphates / Q000737:chemistry* / Q000627:therapeutic use; D003738:Dental Cements / Q000737:chemistry* / Q000627:therapeutic use; D006801:Humans; D016062:Porosity
chemical_list: D001672:Biocompatible Materials; D001843:Bone Cements; D002130:Calcium Phosphates; D003738:Dental Cements; C020243:calcium phosphate
keywords: Bone cements; Calcium phosphates; Injectability; Material properties; Phase separation