title: Biodegradable recombinant human erythropoietin loaded microspheres prepared from linear and star-branched block copolymers: influence of encapsulation technique and polymer composition on particle characteristics.
abstract: Recombinant human erythropoietin (EPO) and fluorescein isothiocyanate labeled dextran (FITC-dextran) loaded microspheres were prepared by a modified W/O/W double-emulsion technique. Biodegradable linear ABA block copolymers consisting of poly(L-lactide-co-glycolide) A blocks attached to central poly(ethyleneoxide) (PEO) B blocks and star-branched AB block copolymers containing A blocks of poly(L-lactide) or poly(L-lactide-co-glycolide) and star-branched poly(ethyleneoxide) B blocks were investigated for their potential as sustained release drug delivery systems. Microsphere characteristics were strongly influenced by the polymer composition. In the case of the linear block copolymers, a reduced lactic acid content in a linear block copolymer yielded smaller particles, a lower encapsulation efficiency, and a higher initial drug release both in the case of EPO and FITC-dextran. The investigation of the effects of several manufacturing parameters on microsphere formation showed that the process temperature plays an important role. Microsphere formation in a +1 degrees C environment resulted in higher drug loadings without increasing the amount of residual dichloromethane inside the particles. Other parameters such as the homogenization of the primary W/O emulsion and of the W/O/W double-emulsion have less impact on microsphere characteristics. Branched block copolymers containing star-shaped PEO also showed potential for the preparation of drug loaded microspheres. A certain amount of glycolic acid in the copolymer was necessary for the successful preparation of non-aggregating microspheres at room temperature. Again, the processing temperature strongly affected particle characteristics. Microsphere preparation at +1 degrees C allows the formation of microspheres from a polymer not containing glycolic acid, a result which could not be achieved at room temperature. Moreover, compared to microsphere formation at room temperature, the effective FITC-dextran loading was increased. Concerning the EPO loaded microspheres, the amount of EPO aggregated was comparable to that using the linear ABA polymers. A continuous release of the protein from these star-shaped polymers could not be achieved. In conclusion, apart from microsphere preparation in a +1 degrees C environment the choice of the polymer represents the main factor for a successful entrapment of proteins into biodegradable microspheres.
authors.affiliation: Department of Pharmaceutics and Biopharmacy, Philipps-University, Marburg, Germany.
authors.forename: K F
authors.initials: KF
authors.lastname: Pistel
authors.forename: B
authors.initials: B
authors.lastname: Bittner
authors.forename: H
authors.initials: H
authors.lastname: Koll
authors.forename: G
authors.initials: G
authors.lastname: Winter
authors.forename: T
authors.initials: T
authors.lastname: Kissel
mesh_terms: D001673:Biodegradation, Environmental; D003692:Delayed-Action Preparations / Q000493:pharmacokinetics*; D003911:Dextrans / Q000737:chemistry; D004921:Erythropoietin / Q000737:chemistry*; D006801:Humans; D066298:In Vitro Techniques; D008832:Microchemistry / Q000379:methods*; D008855:Microscopy, Electron, Scanning; D008863:Microspheres; D010316:Particle Size; D011108:Polymers / Q000138:chemical synthesis / Q000737:chemistry*; D011994:Recombinant Proteins; D013696:Temperature
chemical_list: D003692:Delayed-Action Preparations; D003911:Dextrans; D011108:Polymers; D011994:Recombinant Proteins; D004921:Erythropoietin