Therapeutic proteins are generally potent but their effect in vivo is short-lived. The extension of this therapeutic timescale has motivated recent work on protein encapsulation in drug delivery devices (i.e. liposomes, microparticles, hydrogels) or modification by polyethylene glycol (PEG). We are investigating the ability of PEG-based block copolymer vesicles - or polymersomes - to encapsulate such proteins for controlled release, and in the process studying the interactions between block copolymers and complex, aggregating proteins. We are using recombinant human insulin as one therapeutic protein for encapsulation and tuned release. Initial results indicate that the encapsulation of fluorescein-labeled insulin in polymersomes is possible. Insulin-loaded polymersomes can then be processed to a 100nm diameter and separated from unencapsulated insulin. These insulin-loaded nano-polymersomes are shown to be stable for months at 4„aC as well as in whole blood in vitro. However, insulin is a complex protein that is readily capable of aggregating to form dimers, hexamers, and higher molecular weight aggregates. This aggregation results from exposure to agitation, high temperature, and hydrophobic interfaces such as the air-water interface. Because high molecular weight PEG molecules have been shown to have little interaction with proteins or even to stabilize proteins in such adverse conditions, it is thought that the 100% PEGylated surface of the polymersome membrane will have minimal interaction with the proteins - making the aqueous lumen of the polymersome a stable environment for encapsulated proteins. We intend to further examine the effect of polymersome encapsulation on the structure of insulin as a model protein therapeutic.