The researchers have used highly branching Janus dendrimers that have a water repellent, hydrophobic, and a water-loving, hydrophilic face, to create structures that self-assemble to mimic cell membranes in terms of structure and thickness. The team produced a complete library of bilayer capsules and other structures with uniform size that are stable at a range of temperatures and soluble. The "cubosomes", disks, tubular vesicles and helical ribbons were characterised using cryogenic transmission electron microscopy and fluorescence microscopy. No other single class of molecules including block copolymers and lipids can self-assemble in water into such a diverse array of supramolecular structures, the team says.
Liposomes, which are assembled from natural phospholipids or from synthetic amphiphiles, mimic cell membranes but are not stable, even at room temperature, they als vary widely in size. Polymersomes, in contrast, are stable but their size and shape varies considerably even in a given synthetic batch. Moreover, the majority are not biocompatible and so require further manipulation for any nanomedicine application Dendrimersomes offer stability, monodispersity, tenability and versatility, and are naturally biocompatible. They could significantly advance biological and medical applications of nanotechnology.
The new synthetic biomaterials outclass the already well-known liposomes in terms of impermeability to encapsulated compounds but the fact that dendrimersomes are an equivalent thickness to natural bilayer membranes also means that all the techniques of cell membrane molecular biology could be exploited in their development. This should allow researchers to incorporate biological components, including receptors and channels, into the membranes in a relatively straightforward manner. For instance, they can also be incorporated with pore-forming proteins or directed into specific functional structures using phospholipids or block copolymers. Additionally, their chemistry means that the researchers can add peripheral chemical groups to extend the materials’ repertoire still further.
"Dendrimersomes marry the stability and mechanical strength obtainable from polymersomes, vesicles made from block copolymers, with the biological function of stabilized phospholipid liposomes," explains study leader Virgil Percec of the University of Pennsylvania, "but with superior uniformity of size, ease of formation and chemical functionalization." The team having used a modular synthesis strategy suggests that it is now possible to access myriad molecular structures and of self-assembled architectures through systematic tuning of the components.