Polymersomes represent a class of
vesiclesA vesicle is a bubble of liquid within a cell. More technically, a vesicle is a small, intracellular, membrane-enclosed sac that stores or transports substances within a cell. Vesicles form naturally because of the properties of lipid membranes ...
, tiny hollow spheres that enclose a solution. Polymersomes are made using amphiphilic synthetic block copolymers to form the vesicle membrane, and range in size with radii ranging from 50 nm to 5 um or more.. Most reported polymersomes contain an
aqueous solutionWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
in their core and are useful for encapsulating and protecting sensitive molecules, such as drugs, enzymes, other proteins and peptides, and DNA and RNA fragments.
Polymersomes represent a class of
vesiclesA vesicle is a bubble of liquid within a cell. More technically, a vesicle is a small, intracellular, membrane-enclosed sac that stores or transports substances within a cell. Vesicles form naturally because of the properties of lipid membranes ...
, tiny hollow spheres that enclose a solution. Polymersomes are made using amphiphilic synthetic block copolymers to form the vesicle membrane, and range in size with radii ranging from 50 nm to 5 um or more.. Most reported polymersomes contain an
aqueous solutionWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
in their core and are useful for encapsulating and protecting sensitive molecules, such as drugs, enzymes, other proteins and peptides, and DNA and RNA fragments. The polymersome membrane provides a physical barrier that isolates the encapulated material from external materials, such as those found in biological systems. The term "polymersome" for vesicles made from block copolymers was coined in 1999
Polymersomes are similar to liposomes, which are formed from naturally occurring lipids. While having many of the properties of natural liposomes, polymersomes exhibit increased stability and reduced permeability. Furthermore, the use of synthetic polymers enables designers to manipulate the characteristics of the membrane and thus control permeability, release rates, stability and other properties of the polymersome.
Preparation
Several different morphologies of the block copolymer used to create the polymersome have been used. The most frequently used are the linear diblock or triblock copolymers. In these cases, the block copolymer has one block that is hydrophobic; the other block or blocks are hydrophilic. Other morphologies used include comb copolymers, where the backbone block is hydrophilic and the comb branches are hydrophobic, and dendronized block copolymers, where the dendromer portion is hydrophilic.
In the case of diblock, comb and dendronized copolymers the polymersome membrane has the same
bilayerA lipid bilayer is a thin membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around cells. The cell membrane of almost all living organisms and many viruses are made of a lipid bilayer, as are the membranes surrounding the cell nucleus and...
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- Chemistry :A Langmuir monolayer or insoluble monolayer is a one-molecule thick insoluble layer of an organic material spread onto an aqueous subphase. Traditional compounds used to prepare Langmuir monolayers are amphiphilic materials that possess a hydrophilic headgroup and a hydrophobic tail...
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 enyzmes have been described as nanoreactors.
Polymersomes have been used to create candidate controlled release
drug deliveryDrug delivery is the method or process of administering a pharmaceutical compound to achieve a therapeutic effect in humans or animals. Drug delivery technologies are patent protected formulation technologies that modify drug release profile, absorption, distribution and elimination for the benefit...
systems.
Similar to coating liposomes with
polyethylene glycolPoly , also known as poly , polyoxyethylene and under the tradename Carbowax is the most commercially important type of polyether. PEG, PEO or POE refers to an oligomer or polymer of ethylene oxide...
, polymersomes can be made invisible to
the immune systemAn immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumour cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
if the hydrophilic block consists of polyethylene glycol. Thus, polymersomes are useful carriers for targeted medication.
For
in vivoIn vivo refers to experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research...
applications, polymersomes are
de factoDe facto is a Latin expression that means "by [the] fact". In law, it is meant to mean "in practice but not necessarily ordained by law" or "in practice or actuality, but without being officially established"...
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)
Poly , also known as poly , polyoxyethylene and under the tradename Carbowax is the most commercially important type of polyether. PEG, PEO or POE refers to an oligomer or polymer of ethylene oxide...
(PEG/PEO)
- Poly(2-methyloxazoline)
Hydrophobic blocks
- Polydimethylsiloxane
Silicones are largely inert, man-made compounds with a wide variety of forms and uses. Typically heat-resistant, nonstick, and rubber-like, they are commonly used in cookware, medical applications, sealants, adhesives, lubricants, insulation, and breast implants.Silicones are polymers that include...
(PDMS)
- Poly(caprolactone
Polycaprolactone is a biodegradable polyester with a low melting point of around 60°C and a glass transition temperature of about −60°C. PCL is derived by chemical synthesis from crude oil. It can be prepared by ring opening polymerization of ε-caprolactone using a catalyst such as stannous...
(PCL)
- Poly(lactide)
Polylactic acid or polylactide is a biodegradable, thermoplastic, aliphatic polyester derived from renewable resources, such as corn starch or sugarcanes...
(PLA)
- Poly(methyl methacrylate)
Poly poly is a transparent thermoplastic. Chemically, it is the synthetic polymer of methyl methacrylate...
(PMMA)
If enough of the block copolymer molecules that make up a polymersome are
cross-linkCross-links are bonds that link one polymer chain to another. They can be covalent bonds or ionic bonds. "Polymer chains" can refer to synthetic polymers or natural polymers . When the term "cross-linking" is used in the synthetic polymer science field, it usually refers to the use of...
ed, the polymersome can be made into a transportable powder.
Polymersomes can be used to make an
artificial cellAn artificial cell is a minimal cell from artificial parts and is an emerging technology. Until recently, most attempts have generally created only a package that can do many things a cell can do, such as transcribe and translate proteins and generate ATP but not yet a fully operational cell...
if
hemoglobinHemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of vertebrates, and the tissues of some invertebrates....
and other components are added. The first artificial cell was made by
Thomas ChangThomas Ming Swi Chang, OC is a Canadian physician and scientist.In 1957, while an undergraduate at McGill University he invented the world's first artificial cell...
.