University of Sheffield and Polymer Center academic Professor Steven Armes et al. have demonstrated the encapsulation of silica nanoparticles and bovine serum albumin within synthetic polymeric vesicles, and the consequent triggered release of the payload.
The encapsulation and subsequent release of active ingredients on the micro or nanoscale has drawn considerable academic interest over the recent years. Such processes find application in a wide range of industrial formulations, from medicine to laundry science and agrochemicals.
Similarly, the ability of certain polymers to self-assemble in solution to form hollow spheres, known as vesicles or polymersomes, provides us with a convenient vessel within which to encapsulate desired active ingredients. These vesicles contain an inner lumen encased by a spherical polymeric bilayer, somewhat similar to the way eukaryotic cells are encased by a lipid bilayer.
In the recent work reported by Professor Armes, the particular block copolymer used to produce these vesicles was poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate), which abbreviated to PGMA-PHPMA. The use of a technique known as polymerisation-induced self-assembly (PISA) enabled the convenient synthesis of these PGMA-PHPMA vesicles at relatively high concentrations and short reaction times.
Poly(2-hydroxypropyl methacrylate) has an unusual property: in water it becomes more soluble at lower temperatures. Furthermore, by cooling a solution of PGMA-PHPMA vesicles down to around 0 °C, the PHPMA block becomes increasingly solvated which causes the vesicles to break apart. The ability to disintegrate the encapsulating vesicles by cooling provides a convenient thermal trigger to release any payload that may be loaded within them. By cooling the silica loaded vesicles in ice for 30 minutes, it was demonstrated that the vesicles disintegrated and the silica nanoparticles were released back into solution.
The encapsulation and release process was characterised by a number of analytical techniques, including transmission electron microscopy (TEM), disc-centrifuge photosedimentometry (DCP) and small-angle x-ray scattering (SAXS). In addition, this encapsulation process was not limited to inorganic silica nanoparticles; biological material could also be encapsulated. Bovine serum albumin (BSA), a model globular protein, was successfully encapsulated in the PGMA-PHPMA vesicles and then released upon cooling.
For the original publication please see C. J Mable, S. P. Armes et al. J. Am. Chem. Soc. 2015, 137, 16098 or visit http://pubs.acs.org/doi/abs/10.1021/jacs.5b10415
Article by Matt Rymaruk; a PhD Student on the EPSRC Polymers, Soft Matter and Colloids CDT programme. For more information, please contact Dr Joe Gaunt at the Polymer Centre.