Nanocapsules

A nanocapsule is a nanoscale shell made from a nontoxic polymer. They are vesicular systems made of a polymeric membrane which encapsulates an inner liquid core at the nanoscale. Nanocapsules have many uses, including promising medical applications for drug delivery, food enhancement, nutraceuticals, and for self-healing materials. The benefits of encapsulation methods are for protection of these substances to protect in the adverse environment, for controlled release, and for precision targeting. Nanocapsules can potentially be used as MRI-guided nanorobots or nanobots, although challenges remain. A nanocapsule is a nanoscale shell made from a nontoxic polymer. They are vesicular systems made of a polymeric membrane which encapsulates an inner liquid core at the nanoscale. Nanocapsules have many uses, including promising medical applications for drug delivery, food enhancement, nutraceuticals, and for self-healing materials. The benefits of encapsulation methods are for protection of these substances to protect in the adverse environment, for controlled release, and for precision targeting. Nanocapsules can potentially be used as MRI-guided nanorobots or nanobots, although challenges remain. The typical size of the nanocapsule used for various applications ranges from 10-1000 nm. However, depending on the preparation and use of the nanocapsule, the size will be more specific. Nanocapsule structure consists of nanovesicular system that is formed in a core-shell arrangement. The shell of a typical nanocapsule is made of a polymeric membrane or coating. The type of polymers used is of biodegradable polyester, as nanocapsules are often used in biological systems. Poly-e-caprolactone (PCL), poly(lactide) (PLA), and poly(lactide-co-glicolide) (PLGA) are typical polymers used in nanocapsule formation. Other polymers include thiolated poly(methacrylic acid) and poly(N-vinyl Pyrrolidone). As synthetic polymers have proven to be more pure and reproducible when compared naturally occurring polymers, they are often preferred for the construction nanocapsules. However, some natural occurring polymers such as chitosan, gelatin, sodium alginate, and albumin are used in some drug delivering nanocapsules. Other nanocapsule shells include liposomes, along with polysaccharides and saccharides. Polysaccharides and saccharides are used due to their non-toxicity and biodegradability. They are attractive to use as they resemble biological membranes. The core of a nanocapsule is composed of an oil surfactant that is specifically selected to coordinate with the selected drug within the polymeric membrane. The specific oil used must be highly soluble with the drug, and non-toxic when used in a biological environment. The oil-drug emulsion must have low solubility with the polymer membrane to ensure that the drug will be carried throughout the system properly and be released at the proper time and location. When the proper emulsion is obtained, the drug should be uniformly dispersed throughout the entire internal cavity of the polymeric membrane. The encapsulation method depends on the requirements for any given drug or substance. These processes depend on the physiochemical properties of the core material, the wall material, and the required size. The most common ways to produce nanocapsules are nanoprecipitation, emulsion-diffusion, and solvent-evaporation. In the nanoprecipitation method, also termed solvent displacement method, nanocapsules are formed by creating a colloidal suspension between two separate phases. The organic phase consists of a solution and a mixture of organic solvents. The aqueous phase consists of a mixture of non-solvents that forms a surface film. The organic phase is slowly injected in the aqueous phase which then is agitated to form the colloidal suspension. Once the colloidal suspension is formed it will be agitated until nanocapsules begin to form. The size and shape of the nanocapsule depend on the rate of injection along with the rate of agitation. Another common way to prepare nanocapsules is the emulsion diffusion method. This method consists of three phases: organic, aqueous, and dilution phase. In this method the organic phase is added to the aqueous phase under conditions of high agitation which form an emulsion. During this process water is added to the emulsion which causes the solvent to diffuse. The result of this emulsion-diffusion is nanocapsule formation. Solvent evaporation is another effective method to prepare nanocapsules. In this process, single or double emulsions are formed from solvents and are used to formulate a nanoparticle suspension. High speed homogenization or ultrasonication is used to form small particle size in the nanoparticle suspension. Once the suspension is stable, the solvents are evaporated using either continuous magnetic stirring at room temperature, or by reducing the ambient pressure. The table below displays how nanocapsules exhibit different traits based on the method by which they were prepared. Nanocapsule types vary by size, drug concentration, and active substance release time.