title: Chemical and spatial analysis of protein loaded PLGA microspheres for drug delivery applications.
abstract: Polymer microspheres for controlled release of therapeutic protein from within an implantable scaffold were produced and analysed using complimentary techniques to probe the surface and bulk chemistry of the microspheres. Time of Flight - Secondary Ion Mass Spectrometry (ToF-SIMS) surface analysis revealed a thin discontinuous film of polyvinyl alcohol (PVA) surfactant (circa 4.5 nm thick) at the surface which was readily removed under sputtering with C(60). Atomic Force Microscopy (AFM) imaging of microspheres before and after sputtering confirmed that the PVA layer was removed after sputtering revealing poly(lactic-co-glycolic) acid(PLGA). Scanning electron microscopy showed the spheres to be smooth with some shallow and generally circular depressions, often with pores in their central region. The occurrence of the protein at the surface was limited to areas surrounding these surface pores. This surface protein distribution is believed to be related to a burst release of the protein on dissolution. Analysis of the bulk properties of the microspheres by confocal Raman mapping revealed the 3D distribution of the protein showing large voids within the pores. Protein was found to be adsorbed at the interface with the PLGA oil phase following deposition on evaporation of the solvent. Protein was also observed concentrated within pores measuring approximately 2 μm across. The presence of protein in large voids and concentrated pores was further scrutinised by ToF-SIMS of sectioned microspheres. This paper demonstrates that important information for optimisation of such complex bioformulations, including an understanding of the release profile can be revealed by complementary surface and bulk analysis allowing optimisation of the therapeutic effect of such formulations.
authors.affiliation: Laboratory of Biophysics and Surface Analysis, University of Nottingham, Nottinghamshire, NG7 2RD, UK.
authors.forename: A
authors.initials: A
authors.lastname: Rafati
authors.forename: A
authors.initials: A
authors.lastname: Boussahel
authors.forename: K M
authors.initials: KM
authors.lastname: Shakesheff
authors.forename: A G
authors.initials: AG
authors.lastname: Shard
authors.forename: C J
authors.initials: CJ
authors.lastname: Roberts
authors.forename: X
authors.initials: X
authors.lastname: Chen
authors.forename: D J
authors.initials: DJ
authors.lastname: Scurr
authors.forename: S
authors.initials: S
authors.lastname: Rigby-Singleton
authors.forename: P
authors.initials: P
authors.lastname: Whiteside
authors.forename: M R
authors.initials: MR
authors.lastname: Alexander
authors.forename: M C
authors.initials: MC
authors.lastname: Davies
mesh_terms: D004337:Drug Carriers / Q000737:chemistry*; D019344:Lactic Acid / Q000737:chemistry*; D008863:Microspheres; D009113:Muramidase / Q000737:chemistry*; D011100:Polyglycolic Acid / Q000737:chemistry*; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011142:Polyvinyl Alcohol / Q000737:chemistry; D016062:Porosity; D062206:Spatial Analysis; D018629:Spectrometry, Mass, Secondary Ion; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry
chemical_list: D004337:Drug Carriers; D013501:Surface-Active Agents; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D019344:Lactic Acid; D011142:Polyvinyl Alcohol; C421864:hen egg lysozyme; D009113:Muramidase