Nanocapsules
Nanocapsules have recently generated lot of interest in the area of controlled release with availability of biocompatible and biodegradable polymers. Nanocapsules are a specific class of nanoparticles composed of one or more active materials (core) and a protective matrix (shell). Nanocapsules are submicroscopic colloidal drug carrier systems composed of an oily or an aqueous core surrounded by a thin polymer membrane. The interfacial polymerization of a monomer or the interfacial nano deposition of a preformed polymer is the two technologies used to obtain such nanocapsules.
Preparation of nanocapsules
Nano precipitation method is used to prepare nanocapsules. The organic phase containing solvent, polymer, oil, and drug is pressed through the pores of an ultra filtration membrane via the filtrate side. The aqueous phase containing water and surfactant is made to circulate inside the membrane module, and sweep away the nanocaspules forming at the pore outlets.
Encapsulation technique
Encapsulation technology can be used to prepare micro/nanocapsules with specific application properties in several areas including food, biology and medicine. Nanocapsules can be synthesized via mini emulsion and interfacial polymerization techniques. Most reviewed nanocapsule technologies used in drug carrier systems employ encapsulation techniques using isocyanates in either solvent or bulk to form shell (or matrix) materials for encapsulating functional materials, releasable fill materials, or making pressure sensitive copying paper. The inherent reactivity of isocyanates with water makes it difficult to encapsulate them in aqueous media.
The nanocapsules can be characterized via Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and transmission electron microscopy (TEM).
Two steps technique
The nanocapsules can be through two steps of pre-emulsification (to form a pre-emulsion) and emulsion polymerization. This gives a new method for synthesizing nanocapsules containing either blocked or free isocyanates in aqueous media. The thermally dissociated isocyanate can be utilized as an active functional group in coatings and adhesive applications. Nanocapsules containing blocked isocyanates are of interest in self-healing systems where the isocyanate can be liberated by thermal treatment or extracted via solvent or reactive agents such as amines. Nanocapsule shells functionalized with amines and hydroxyls provide a ready moiety for the isocyanate to react once it is liberated from the protective shell of the nanocapsule.
Nanocapsules of diltiazem
Diltiazem drug is widely used in the treatment of chronic conditions such as hypertension and angina which require prolonged therapy. Nanocapsules can be prepared by the interfacial deposition technique by taking different concentrations of polymers and phospholipid mixture. Nanocapsules of diltiazem can be prepared for achieving controlled release of the drug in order to reduce the frequency of administration of drug, to obtain more uniform plasma concentration, and to improve patient compliance.
The morphology of nanocapsules can be assessed by scanning electron microscope.
These nanocapsules are found to be smooth, spherical having distribution with particle size in the range of 20 to 380 nm, stable at 4°C but unstable at 25°C, and require storage in refrigeration. Thus nanocapsules are a useful technology for controlled release of diltiazem.