In biotechnology, polymersomes are a class of artificial vesicles, tiny hollow spheres that enclose a solution. Polymersomes are made using amphiphilic synthetic block copolymers to form the vesicle membrane, and have radii ranging from 50 nm to 5 μm or more.
The term "polymersome" for vesicles made from block copolymers was coined in 1999. where the backbone block is hydrophilic and the comb branches are hydrophobic, and dendronized block copolymers, where the dendrimer portion is hydrophilic.
In the case of diblock, comb and dendronized copolymers the polymersome membrane has the same bilayer morphology of a liposome, with the hydrophobic blocks of the two layers facing each other in the interior of the membrane. In the case of triblock copolymers the membrane is a monolayer that mimics a bilayer, the central block filling the role of the two facing hydrophobic blocks of a bilayer.
In general they can be prepared by the methods used in the preparation of liposomes. Film rehydration, direct injection method or dissolution method.
Uses
Polymersomes that contain active enzymes and that provide a way to selectively transport substrates for conversion by those enzymes have been described as nanoreactors.
Polymersomes have been used to create controlled release drug delivery systems. Similar to coating liposomes with polyethylene glycol, polymersomes can be made invisible to the immune system if the hydrophilic block consists of polyethylene glycol. Their permeability can be modulated by exogenous factors, for example by incorporation of stimuli-responsive molecules such as photoswitches, or pH responsive groups. Thus, polymersomes are useful carriers for targeted drug delivery.
For in vivo applications, polymersomes are de facto limited to the use of FDA-approved polymers, as most pharmaceutical firms are unlikely to develop novel polymers due to cost issues. Fortunately, there are a number of such polymers available, with varying properties, including:
Hydrophilic blocks
- Poly(ethylene glycol) (PEG/PEO)
- Poly(2-methyloxazoline)
If enough of the block copolymer molecules that make up a polymersome are cross-linked, the polymersome can be made into a transportable powder.
Polymersomes can be used to make an artificial cell if hemoglobin and other components are added. The first artificial cell was made by Thomas Chang.
See also
- Cell (biology)
- Liposome
- Polymer
- Copolymer
- Artificial cell