Polymersome
Encyclopedia
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. Most reported polymersomes contain an aqueous solution
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 encapsulated material from external materials, such as those found in biological systems.
Synthasomes are polymersomes engineered to contain channels (transmembrane protein
s) that allow certain chemicals to pass through the membrane, into or out of the vesicle. This allows for the collection or enzymatic modification of these substances.
The term "polymersome" for vesicles made from block copolymers was coined in 1999. Polymersomes are similar to liposomes, which are vesicles 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.
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.
Polymersomes have been used to create candidate 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. Thus, polymersomes are useful carriers for targeted medication.
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
Hydrophobic blocks
If enough of the block copolymer molecules that make up a polymersome are cross-link
ed, 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
.
Biotechnology
Biotechnology is a field of applied biology that involves the use of living organisms and bioprocesses in engineering, technology, medicine and other fields requiring bioproducts. Biotechnology also utilizes these products for manufacturing purpose...
, polymersomes are a class of artificial vesicles
Vesicle (biology)
A vesicle is a bubble of liquid within another liquid, a supramolecular assembly made up of many different molecules. More technically, a vesicle is a small membrane-enclosed sack that can store or transport substances. Vesicles can form naturally because of the properties of lipid membranes , or...
, 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. Most reported polymersomes contain an aqueous solution
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
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 encapsulated material from external materials, such as those found in biological systems.
Synthasomes are polymersomes engineered to contain channels (transmembrane protein
Transmembrane protein
A transmembrane protein is a protein that goes from one side of a membrane through to the other side of the membrane. Many TPs function as gateways or "loading docks" to deny or permit the transport of specific substances across the biological membrane, to get into the cell, or out of the cell as...
s) that allow certain chemicals to pass through the membrane, into or out of the vesicle. This allows for the collection or enzymatic modification of these substances.
The term "polymersome" for vesicles made from block copolymers was coined in 1999. Polymersomes are similar to liposomes, which are vesicles 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 dendrimerDendrimer
Dendrimers are repetitively branched molecules. The name comes from the Greek word "δένδρον" , which translates to "tree". Synonymous terms for dendrimer include arborols and cascade molecules. However, dendrimer is currently the internationally accepted term. A dendrimer is typically symmetric...
portion is hydrophilic.
In the case of diblock, comb and dendronized copolymers the polymersome membrane has the same bilayer
Lipid bilayer
The 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...
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
Monolayer
- Chemistry :A Langmuir monolayer or insoluble monolayer is a one-molecule thick layer of an insoluble 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 enzymes have been described as nanoreactors.Polymersomes have been used to create candidate controlled release drug delivery
Drug delivery
Drug delivery is the method or process of administering a pharmaceutical compound to achieve a therapeutic effect in humans or animals. Drug delivery technologies modify drug release profile, absorption, distribution and elimination for the benefit of improving product efficacy and safety, as well...
systems . Similar to coating liposomes with polyethylene glycol
Polyethylene glycol
Polyethylene glycol is a polyether compound with many applications from industrial manufacturing to medicine. It has also been known as polyethylene oxide or polyoxyethylene , depending on its molecular weight, and under the tradename Carbowax.-Available forms:PEG, PEO, or POE refers to an...
, polymersomes can be made invisible to the immune system
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor 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 vivo
In vivo
In vivo is 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 facto
De facto
De facto is a Latin expression that means "concerning fact." In law, it often means "in practice but not necessarily ordained by law" or "in practice or actuality, but not officially established." It is commonly used in contrast to de jure when referring to matters of law, governance, or...
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)Polyethylene glycolPolyethylene glycol is a polyether compound with many applications from industrial manufacturing to medicine. It has also been known as polyethylene oxide or polyoxyethylene , depending on its molecular weight, and under the tradename Carbowax.-Available forms:PEG, PEO, or POE refers to an...
(PEG/PEO) - Poly(2-methyloxazoline)
Hydrophobic blocks
- PolydimethylsiloxaneSiliconeSilicones are inert, synthetic compounds with a variety of forms and uses. Typically heat-resistant and rubber-like, they are used in sealants, adhesives, lubricants, medical applications , cookware, and insulation....
(PDMS) - Poly(caprolactonePolycaprolactonePolycaprolactone is a biodegradable polyester with a low melting point of around 60°C and a glass transition temperature of about −60°C. PCL is prepared by ring opening polymerization of ε-caprolactone using a catalyst such as stannous octoate. Recently a wide range of catalysts for the ring...
(PCL) - Poly(lactide)Polylactic acidPoly or polylactide is a thermoplastic aliphatic polyester derived from renewable resources, such as corn starch , tapioca products or sugarcanes...
(PLA) - Poly(methyl methacrylate)Acrylic glassPoly is a transparent thermoplastic, often used as a light or shatter-resistant alternative to glass. It is sometimes called acrylic glass. Chemically, it is the synthetic polymer of methyl methacrylate...
(PMMA)
If enough of the block copolymer molecules that make up a polymersome are cross-link
Cross-link
Cross-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 cell
Artificial cell
An 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 hemoglobin
Hemoglobin
Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...
and other components are added. The first artificial cell was made by Thomas Chang
Thomas Chang
Thomas Ming Swi Chang, is a Canadian physician and scientist.In 1957, while an undergraduate at McGill University he invented the world's first artificial cell...
.