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Cell cytosol and the different subcellular organelles house the most important biochemical processes that control cell functions. Effective delivery of bioactive agents within cells is expected to have an enormous impact on both gene therapy and the future development of new therapeutic and/or diagnostic strategies based on single-cell-bioactive-agent interactions. Herein a biomimetic nanovector is reported that is able to enter cells, escape from the complex endocytic pathway, and efficiently deliver actives within clinically relevant cells without perturbing their metabolic activity. This nanovector is based on the pH-controlled self-assembly of amphiphilic copolymers into nanometer-sized vesicles (or polymersomes). The cellular-uptake kinetics can be regulated by controlling the surface chemistry, the polymersome size, and the polymersome surface topology. The latter is controlled by the extent of polymer-polymer phase separation within the external envelope of the polymersome.

We have recently achieved efficient cytosolic delivery by using pH-sensitive poly(2-(methacryloyloxy)ethylphosphorylcholine)-co-poly(2-(diisopropylamino)ethylmethacrylate) (PMPC-PDPA) diblock copolymers that self-assemble to form vesicles, known as polymersomes, in aqueous solution. It is particularly noteworthy that these diblock copolymers form stable polymersomes at physiological pH but rapidly dissociate below pH 6 to give molecularly-dissolved copolymer chains (unimers). These PMPC-PDPA polymersomes are used to encapsulate nucleic acids for efficient intracellular delivery. Confocal laser scanning microscopy and fluorescence flow cytometry are used to quantify cellular uptake and to study the kinetics of this process. Finally, we examine how PMPC-PDPA polymersomes affect the viability of primary human cells (human dermal fibroblasts (HDF)), paying particular regard to whether inflammatory responses are triggered.

Nature has the exquisite ability to design specific surface patterns and topologies on both the macro- and nanolength scales that relate to precise functions. Following a biomimetic approach, we have engineered fully synthetic nanoparticles that are able to self-organize their surface into controlled domains. We focused on polymeric vesicles or "polymersomes"; enclosed membranes formed via self-assembly of amphiphilic block copolymers in water. Exploiting the intrinsic thermodynamic tendency of dissimilar polymers to undergo phase separation, we mixed different vesicle-forming block copolymers in various proportions in order to obtain a wide range of polymersomes with differing surface domains. Using a combination of confocal laser scanning microscopy studies of micrometer-sized polymersomes, and electron microscopy, atomic force microscopy, and fluorescence spectroscopy on nanometer-sized polymersomes, we find that the domains exhibit similar shapes on both the micro- and nanolength scales, with dimensions that are linearly proportional to the vesicle diameter. Finally, we demonstrate that such control over the surface "patchiness" of these polymersomes determines their cell internalization kinetics for live cells.