Emulsion electrospinning has been sought as a method to prepare fibrous materials/scaffolds for growth factor delivery. Emulsion conditions, specifically sonication and the addition of a surfactant, were evaluated to determine their effect on the release and bioactivity of proteins from electrospun scaffolds. Polycaprolactone (PCL) and poly(ethylene oxide) (PEO/PCL) blends were evaluated where PEO, a hydrophilic polymer, was shown to enhance the incorporation of proteins. Electrospun scaffolds prepared with the addition of the nonionic surfactant Span (R) 80 at a concentration greater than the critical micelle concentration followed by mild sonication (10% amplitude) released lysozyme, the model protein, with a higher level of bioactivity as compared with other surfactant and sonication conditions. These conditions were then used to prepare emulsions of platelet-derived growth factor-BB (PDGF-BB) in PEO/PCL blends. Electrospun mats prepared by emulsions consisting of PDGF-BB incorporated with Span (R) 80 and sonicated at 10% amplitude exhibited a controlled release of PDGF-BB over 96 h as compared with a more rapid release from solutions that were not emulsified (Direct Addition) or emulsions that did not receive Span (R) 80 or sonication. Bioactive PDGF-BB incorporated in electrospun scaffolds enhanced the osteogenic differentiation of human mesenchymal stem cells as evidenced by increased alkaline phosphatase activity, improved cell attachment and reorganized cytoskeletal filaments. The findings in this study provide improved methods for achieving controlled release of bioactive proteins from electrospun materials. (c) 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 674-684, 2014.