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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.

The synthesis of a series of thermo-responsive ABA triblock copolymers in which the outer A blocks comprise poly(2-hydroxypropyl methacrylate) and the central B block is poly(2-(methacryloyloxy)ethyl phosphorylcholine) is achieved using atom transfer radical polymerization. These novel triblock copolymers form thermo-reversible physical gels with critical gelation temperatures and mechanical properties that are highly dependent on the copolymer composition and concentration. TEM studies on dried dilute copolymer solutions indicate the presence of colloidal aggregates, which is consistent with micellar gel structures. This hypothesis is consistent with the observation that incorporating a central disulfide bond within the B block leads to thermo-responsive gels that can be efficiently degraded using mild reductants such as dithiothreitol (DTT) over time scales of minutes at 37 degrees C. Moreover, the rate of gel dissolution increases at higher DTT/disulfide molar ratios. Finally, these copolymer gels are shown to be highly biocompatible. Only a modest reduction in proliferation was observed for monolayers of primary human dermal fibroblasts, with no evidence for cytotoxicity. Moreover, when placed directly on 3D tissue-engineered skin, these gels had no significant effect on cell viability. Thus, we suggest that these thermo-responsive biodegradable copolymer gels may have potential applications as wound dressings.