title: Multiple characterization study on porosity and pore structure of calcium phosphate cements.
abstract: Characterization of the intricate pore structure of calcium phosphate cements is a key step to successfully link the structural properties of these synthetic bone grafts with their most relevant properties, such as in vitro or in vivo behaviour, drug loading and release properties, or degradation over time. This is a challenging task due to the wide range of pore sizes in calcium phosphate cements, compared to most other ceramic biomaterials. This work provides a critical assessment of three different techniques based on different physical phenomena, namely mercury intrusion porosimetry (MIP), Nitrogen sorption, and thermoporometry (TPM) for the detailed characterization of four calcium phosphate cements with different textural properties in terms of total porosity, pore size distribution (PSD), and pore entrance size distribution (PESD). MIP covers a much wider size range than TPM and Nitrogen sorption, offering more comprehensive information at the micrometer level. TPM, and especially Nitrogen sorption, are non-destructive techniques and, although they cover a limited size range, provide complementary information regarding pore structure associated with crystal shape at the nanoscale, recording both PSD and PESD in a single experiment. MIP tended to register smaller sizes, especially at low L/P ratios, due to the network effect, which has a strong influence on the outcome of this technique.
  
  
  CONCLUSIONS
  The detailed characterisation of the porosity of calcium phosphate cements is of paramount importance, since it is a key parameter influencing some of the most relevant features, like mechanical properties, degradation rate or drug loading and release kinetics. However, this is a challenging task because, once hardened, calcium phosphate cements present an intricate morphology, consisting of a network of precipitated crystals, which generate a high intrinsic micro/nano porosity, with pore sizes covering six orders of magnitude. This work provides for the first time a critical assessment of the advantages and limitations of three different techniques, namely mercury intrusion porosimetry, Nitrogen sorption and Thermoporometry, for the characterisation of the porosity of four calcium phosphate cements with different textural properties.
authors.affiliation: Biomaterials, Biomechanics and Tissue Engineering Group, Department of Materials Science and Metallurgy, Universitat Politècnica de Catalunya. BarcelonaTech (UPC), Av. Diagonal 647, 08028 Barcelona, Spain; Centre for Research in Nanoengineering, Technical University of Catalonia (UPC), c/Pascual i Vila 15, 08028 Barcelona, Spain. Electronic address: david.pastorino@upc.edu.
authors.forename: David
authors.initials: D
authors.lastname: Pastorino
authors.affiliation: Biomaterials, Biomechanics and Tissue Engineering Group, Department of Materials Science and Metallurgy, Universitat Politècnica de Catalunya. BarcelonaTech (UPC), Av. Diagonal 647, 08028 Barcelona, Spain; Centre for Research in Nanoengineering, Technical University of Catalonia (UPC), c/Pascual i Vila 15, 08028 Barcelona, Spain. Electronic address: cristina.canal@upc.edu.
authors.forename: Cristina
authors.initials: C
authors.lastname: Canal
authors.affiliation: Biomaterials, Biomechanics and Tissue Engineering Group, Department of Materials Science and Metallurgy, Universitat Politècnica de Catalunya. BarcelonaTech (UPC), Av. Diagonal 647, 08028 Barcelona, Spain; Centre for Research in Nanoengineering, Technical University of Catalonia (UPC), c/Pascual i Vila 15, 08028 Barcelona, Spain. Electronic address: maria.pau.ginebra@upc.edu.
authors.forename: Maria-Pau
authors.initials: MP
authors.lastname: Ginebra
mesh_terms: D000327:Adsorption; D001843:Bone Cements; D002130:Calcium Phosphates / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D016062:Porosity; D014961:X-Ray Diffraction
chemical_list: D001843:Bone Cements; D002130:Calcium Phosphates; C020243:calcium phosphate
keywords: Calcium phosphate cement; Mercury intrusion porosimetry; Nanostructured materials; Nitrogen sorption; Pore size distribution; Porosity; Synthetic bone graft; Thermoporometry