title: The mesoporosity of microparticles spray dried from trehalose  and nanoparticle hydroxyapatite depends on the ratio of  nanoparticles to sugar and nanoparticle surface charge.
abstract: The ratio of hydroxyapatite (HA) nanoparticles (NP) to trehalose in composite microparticle (MP) vaccine vehicles by determining inter-nanoparticle space potentially influences antigen release. Mercury porosimetry and gas adsorption analysis have been used quantify this space. Larger pores are present in MPs spray dried solely from nanoparticle gel compared with MPs spray dried from nanoparticle colloid which have less inter-nanoparticle volume. This is attributed to tighter nanoparticle packing caused by citrate modification of their surface charge. The pore size distributions (PSD) for MP where the trehalose has been eliminated by combustion generally broaden and shifts to higher values with increasing initial trehalose content. Modal pore size, for gel derived MPs is comparable to modal NP width below 30% initial trehalose content and approximates to modal NP length (approximately 50 nm) at 60% initial trehalose content. For colloidally derived MPs this never exceeds the modal NP width. Pore-sizes are comparable, to surface inter-nanoparticle spacings observed by SEM.
authors.affiliation: Department of Physiology, Development and Neuroscience, Multi-Imaging Centre School of Biological Sciences, Anatomy Building, Downing Street, Cambridge CB2 3DY, UK. dmw31@cam.ac.uk
authors.forename: David M
authors.initials: DM
authors.lastname: Wright
authors.forename: Zlatko S
authors.initials: ZS
authors.lastname: Saracevic
authors.forename: Nigel H
authors.initials: NH
authors.lastname: Kyle
authors.forename: Michael
authors.initials: M
authors.lastname: Motskin
authors.forename: Jeremy N
authors.initials: JN
authors.lastname: Skepper
mesh_terms: D002241:Carbohydrates / Q000737:chemistry; D020099:Coated Materials, Biocompatible / Q000737:chemistry; D003890:Desiccation; D004337:Drug Carriers / Q000138:chemical synthesis / Q000737:chemistry; D017886:Durapatite / Q000737:chemistry*; D055724:Electrophysiological Phenomena; D006358:Hot Temperature; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D008863:Microspheres; D053758:Nanoparticles / Q000737:chemistry; D009779:Occlusive Dressings; D010316:Particle Size; D016062:Porosity; D011208:Powders / Q000138:chemical synthesis / Q000737:chemistry; D011312:Pressure; D013499:Surface Properties; D014199:Trehalose / Q000737:chemistry*
chemical_list: D002241:Carbohydrates; D020099:Coated Materials, Biocompatible; D004337:Drug Carriers; D011208:Powders; D017886:Durapatite; D014199:Trehalose