Hollow colloidosomes prepared using accelerated solvent evaporation.

We demonstrate a new, scalable, simple, and generally applicable two-step method to prepare hollow colloidosomes. First, a high volume fraction oil-in-water emulsion was prepared. The oil phase consisted of CH2Cl2 containing a hydrophobic structural polymer, such as polycaprolactone (PCL) or polystyrene (PS), which was fed into the water phase. The water phase contained poly(vinylalcohol), poly(N-isopropylacrylamide), or a range of cationic graft copolymer surfactants. The emulsion was rotary evaporated to rapidly remove CH2Cl2. This caused precipitation of PCL or PS particles which became kinetically trapped at the periphery of the droplets and formed the shell of the hollow colloidosomes. Interestingly, the PCL colloidosomes were birefringent. The colloidosome yield increased and the polydispersity decreased when the preparation scale was increased. One example colloidosome system consisted of hollow PCL colloidosomes stabilized by PVA. This system should have potential biomaterial applications due to the known biocompatibility of PCL and PVA.

Gelation of microsphere dispersions using a thermally-responsive graft polymer.

Dispersions of microspheres (MSs) that form self-supporting particle gels are fundamentally interesting from the viewpoints of gel formation and mechanical properties. Here, we investigate model mixed MS/thermally responsive polymer dispersions that exist as particle gels at 37°C. The MS comprised poly(caprolactone) (PCL) and was prepared by solvent evaporation. The thermally responsive polymer contained a cationic backbone and poly(2-(2-methoxyethoxy)ethyl methacrylate) side chains and is abbreviated as PMA. Mixed PCL/PMA dispersions formed weak gels due to depletion at 20°C. At higher temperatures they formed stronger gels due to a combination of bridging of PCL MS by PMA and reinforcement by a PMA network. A key parameter controlling the mechanical properties of the reinforced MS particle gels was the volume fraction of PMA with respect to total polymer present (ΦPMA). Self-healing behaviour was observed for the gels using dynamic rheology and this depended on ΦPMA. The MS particle gel mechanical properties were conceptually described in terms of isostress and isostrain blending laws. At ΦPMA less than or greater than 0.057 the gels were dominated by the PCL or PMA networks, respectively. The latter value is suggested to be analogous to a phase inversion point.

Thermally triggered assembly of cationic graft copolymers containing 2-(2-methoxyethoxy)ethyl methacrylate side chains.

Thermoresponsive copolymers continue to attract a great deal of interest in the literature. In particular, those based on ethylene oxide-containing methacrylates have excellent potential for biomaterial applications. Recently, some of us reported a study of thermoresponsive cationic graft copolymers containing poly(N-isopropylacrylamide), PNIPAm, (Liu et al., Langmuir, 24, 7099). Here, we report an improved version of this new family of copolymers. In the present study, we replaced the PNIPAm side chains with poly(2-(2-methyoxyethoxy)ethylmethacrylate), PMeO(2)MA. These new, nonacrylamide containing, cationic graft copolymers were prepared using atom transfer radical polymerization (ATRP) and a macroinitiator. They contained poly(trimethylamonium)-aminoethyl methacrylate and PMeO(2)MA, i.e., PTMA(+)(x)-g-(PMeO(2)MA(n))(y). They were investigated using variable-temperature turbidity, photon correlation spectroscopy (PCS), electrophoretic mobility, and (1)H NMR measurements. For one system, four critical temperatures were measured and used to propose a mechanism for the thermally triggered changes that occur in solution. All of the copolymers existed as unimolecular micelles at 20 °C. They underwent reversible aggregation with heating. The extent of aggregation was controlled by the length of the side chains. TEM showed evidence of micellar aggregates. The thermally responsive behaviors of our new copolymers are compared to those for the cationic PNIPAm graft copolymers reported by Liu et al. Our new cationic copolymers retained their positive charge at all temperatures studied, have high zeta potentials at 37 °C, and are good candidates for conferring thermoresponsiveness to negatively charged biomaterial surfaces.