title: Gamma irradiation of active self-healing PLGA microspheres for efficient aqueous encapsulation of vaccine antigens.
abstract: OBJECTIVE
  To investigate the effect of γ-irradiation of poly(lactic-co-glycolic acid) (PLGA)/Al(OH)₃/0 or 5 wt% diethyl phthalate (DEP) microspheres for active self-healing encapsulation of vaccine antigens.
  
  
  METHODS
  Microspheres were irradiated with ⁶⁰Co at 2.5 and 1.8 MRad and 0.37 and 0.20 MRad/h. Encapsulation of tetanus toxoid (TT) was achieved by mixing Al(OH)₃-PLGA microspheres with TT solution at 10-38°C. Electron paramagnetic resonance (EPR) spectroscopy was used to examine free radical formation. Glass transition temperature (T(g)) and molecular weight of PLGA was measured by differential scanning calorimetry and gel permeation chromatography, respectively. Loading and release of TT were examined by modified Bradford, amino acid analysis, and ELISA assays.
  
  
  RESULTS
  EPR spectroscopy results indicated absence of free radicals in PLGA microspheres after γ-irradiation. Antigen-sorbing capacity, encapsulation efficiency, and T(g) of the polymer were also not adversely affected. When DEP-loaded microspheres were irradiated at 0.2 MRad/h, some PLGA pores healed during irradiation and PLGA healing during encapsulation was suppressed. The molecular weight of PLGA was slightly reduced when DEP-loaded microspheres were irradiated at the same dose rate. At the 0.37 MRad/h dose rate, these trends were not observed and the full immunoreactivity of TT was preserved during encapsulation and 1-month release. Gamma irradiation slightly increased TT initial burst release. The small increase in total irradiation dose from 1.8 to 2.5 MRad had insignificant effect on the polymer and microspheres properties analyzed.
  
  
  CONCLUSIONS
  Gamma irradiation is a plausible approach to provide a terminally sterilized, self-healing encapsulation PLGA excipient for vaccine delivery.
authors.affiliation: Department of Pharmaceutical Sciences and the Biointerfaces Institute, University of Michigan, NCRC, 2800 Plymouth Road, Ann Arbor, Michigan 48109, USA.
authors.forename: Kashappa-Goud H
authors.initials: KG
authors.lastname: Desai
authors.forename: Samer
authors.initials: S
authors.lastname: Kadous
authors.forename: Steven P
authors.initials: SP
authors.lastname: Schwendeman
mesh_terms: D016503:Drug Delivery Systems; D005720:Gamma Rays; D019344:Lactic Acid / Q000737:chemistry*; D008863:Microspheres; D011100:Polyglycolic Acid / Q000737:chemistry*; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D013242:Sterilization / Q000379:methods; D013745:Tetanus Toxoid / Q000008:administration & dosage*; D044366:Transition Temperature
chemical_list: D013745:Tetanus Toxoid; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D019344:Lactic Acid