Ligand‐conjugated polymer (polyplex) gene delivery vectors have strong potential as targeted, in vivo gene transfer vehicles; however, they are currently limited by low delivery efficiency. A number of barriers to polyplex‐mediated delivery have been previously identified, including receptor binding, internalization, endosomal escape, and nuclear localization. However, based on understanding of viral gene delivery systems, yet another potential barrier may exist; a limited ability to unpackage the plasmid DNA cargo following localization to the nucleus. We have developed a model system that employs a cationic polymer linked to epidermal growth factor (EGF) as a ligand to target delivery of plasmid DNA encoding the green fluorescent protein to mouse fibroblasts bearing the EGF receptor. Using fluorescence microscopy to simultaneously trace both the plasmid and polymer during gene delivery in combination with an in vitro transcription assay, we provide evidence that plasmid unpackaging can indeed be a limiting step for gene expression for sufficiently large polymer constructs. Short‐term expression is significantly enhanced by using short polycations that dissociate from DNA more rapidly both in vitro and in vivo. Finally, we describe a thermodynamic model that supports these data by showing that shorter polycations can have a higher probability of dissociating from DNA. This work demonstrates that vector unpackaging should be added to the list of barriers to receptor‐mediated polyplex gene delivery, thus providing an additional design principle for targeted synthetic delivery vehicles. © 2000 John Wiley & Sons, Inc. Biotechnol Bioeng 67: 598–606, 2000.

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We calculate the membrane-induced interaction between inclusions, in terms of the membrane stretching and bending moduli and the spontaneous curvature. We find that the membrane-induced interaction between inclusions varies nonmonotonically as a function of the inclusion spacing. The location of the energy minimum depends on the spontaneous curvature and the membrane perturbation decay length, where the latter is set by the membrane moduli. The membrane perturbation energy increases with the inclusion radius. The Ornstein-Zernike theory, with the Percus-Yevick closure, is used to calculate the radial distribution function of inclusions. We find that when the spontaneous curvature is zero, the interaction between inclusions due to the membrane deformation is qualitatively similar to the hard-core interaction. However, in the case of finite spontaneous curvature, the effective interaction is dramatically modified.

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We investigate the formation of polymer vesicles, or polymersomes, of polystyrene-block-poly(ethylene oxide) diblock copolymers using double emulsion droplets of controlled architecture as templates. To engineer the structure of the polymersomes, it is important to consider the concentration of diblock copolymer in the middle phase of the double emulsion. We describe how the presence of excess polymer can induce a transition from complete wetting to partial wetting of the middle phase, resulting in polymer shells with inhomogeneous thicknesses.