POE-PEG-POE triblock copolymeric microspheres containing protein: I. Preparation and characterization

Yi Yan Yang*, Jin Ping Wan, Tai-Shung Chung, Pramoda Kumari Pallathadka, Steve Ng, Jorge Heller

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

52 Scopus citations


Poly(ortho ester) (POE)-poly (ethylene glycol) (PEG) triblock copolymers (POE-PEG-POE) with different PEG contents were synthesised as carriers for controlled protein delivery. POE-PEG-POE microspheres containing bovine serum albumin (BSA) were prepared using a double-emulsion (water-in-oil-in-water) process. In this first paper of a two-part series, we report the fundamentals of the fabrication and characterization of POE-PEG-POE microspheres. Because the triblock copolymer is more hydrophilic than neat poly(ortho ester), the triblock copolymer yields a more stable first emulsion (water-in-oil) and a greater BSA encapsulation efficiency (90% vs. 30%). No BSA is found on POE-PEG-POE microsphere surfaces measured by X-ray photoelectron spectroscopy, while uniform BSA distributions are observed within the microspheres by confocal microscopy. SEM pictures show that an increase in PEG content results in microspheres with a denser cross-section because of a more stable first emulsion and better affinity between the copolymer and water. POE-PEG(20%)-POE suffers significant swelling during the fabrication process and yields the biggest microspheres. However, the POE-PEG(30%)-POE microspheres are much smaller since the dissolution loss of POE-PEG(30%)-POE in the external water phase may be much higher than that of POE-PEG(20%)-POE. The salt concentration in the external water phase significantly affects the morphology of the resultant microspheres. Microspheres with a dense wall are produced when using pure water as the external water phase. Polymer concentration has less impact on BSA encapsulation efficiency but has a considerable effect on microsphere size and morphology. Increasing the concentration of the polyvinyl alcohol emulsifier does not cause an obvious decrease in microsphere size. However, increased BSA loading results in bigger microspheres.

Original languageEnglish (US)
Pages (from-to)115-128
Number of pages14
JournalJournal of Controlled Release
Issue number1-2
StatePublished - Jul 10 2001


  • Microspheres
  • POE-PEG-POE triblock copolymer
  • Poly(ortho ester)
  • Protein encapsulation efficiency

ASJC Scopus subject areas

  • Pharmaceutical Science


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