Introduction.
Microencapsulation is the technique of enclosing or wrapping solids, liquids, or even gases within a second material with a continuous layer of polymeric components that results in minute particles (ranging from less than 1 micron to several hundred microns in size).
Small discrete solid particles or small liquid droplets and dispersions are wrapped and enclosed by a thin coating in this technique to provide protection and control the release.
The microencapsulation procedure is commonly used to adjust and postpone medication release from various pharmaceutical dosage forms.
The components contained or encased within the microcapsules are referred to as core materials, pay-load materials, or nucleus, whereas the encircling materials are referred to as coating materials, wall materials, shell materials, or membrane.
Microparticles:
“Microparticles” refers to particles having a diameter range of 1-1000 μm.
Microspheres:
“Microspheres" particularly refer to the spherically shaped microparticles within the broad category of microparticles.
Microcapsules:
“Microcapsules”refer to microparticles having a core surrounded by a coat or wall material(s) distinctly different from that of the core or pay-load or nucleus, which may be solid, liquid, or even gas.
Microcapsules can be classified into three types :
i)Mononuclear: containing the shell around the core.
ii)Polynuclear: Having many cores enclosed within a shell.
iii)Matrix type: distributed homogeneously into the shell material.
The advantages of microencapsulation:
Providing environmental protection to the encapsulated active agents or core materials.
Liquids and gases can be changed into solid particles in the form of microcapsules.
Surface as well as colloidal characteristics of various active agents can be changed.
modify and delay drug release from different pharmaceutical dosage forms.
Formulation of sustained controlled release dosage forms can be done by modifying or delaying the release of encapsulated active agents or core materials.
Disadvantages of microencapsulation:
Expensive techniques.
This causes a reduction in the shelf-life of hygroscopic agents.
Microencapsulation coating may not be uniform and this can influence the release of encapsulated materials.
Methods of preparation of microencapsulation:
Air suspension,
Coacervation phase separation
Pan coating,
Fluidized-bed technology,
Spray drying and spray congealing,
Multiorifice-centrifugation,
Solvent Evaporation,
Solvent Evaporation,
Interfacial cross-linking
Air suspension:
The air suspension method of microencapsulation entails dispersing solids and particulate core materials in a supporting air stream and spray coating on the air suspended particles.
Particulate core materials are suspended in an upward moving air stream within the coating chamber.
The design of the chamber and its operating parameters affect the recirculating flow of particles through the coating-zone portion of the coating-chamber, where a coating material is sprayed onto the moving particles.
The core material receives a coat during each pass through the coating-zone, and this cyclic process is repeated depending on the purpose of microencapsulation.
The supporting air stream also helps to dry the product while it is being manufactured / encapsulated.
The drying rate is proportional to the temperature of the supporting air stream.
Coacervation phase separation:
Microencapsulation by the coacervation phase separation method consists of 3 steps:
The formation of three immiscible phases: liquid manufacturing, core material, and coating material.
The core material is coated with a liquid polymer coating.
To stiffen the coating, thermal, cross linking, or desolvation techniques are commonly used. to form microcapsules.
Coacervation phase separation microencapsulation requires jacketed tanks with variable speed agitators.
Pan coating:
Microencapsulation of relatively large particles larger than 600 in size can be accomplished using the pan coating method, which is widely used for the preparation of controlled release particulates.
In this method, various spherical core materials are coated with a variety of polymers.
In the coating pan, the coating is applied as a solution or as an atomized spray to the desired solid core material.
As the coatings are applied, warm air is passed over the coated materials in the coating pans to remove the coating solvent.
In some cases, the drying oven is used to complete the final solvent removal process.
Fluidized-bed technology:
Fluidized-bed technology is used for microencapsulation of solid core materials, including liquids absorbed into porous solids.
This microencapsulation technique is widely used to encapsulate pharmaceuticals.
The solid particles to be encapsulated are suspended in an air jet and then covered with a spray of liquid coating material.
The capsules are transported to a location where their shells will be solidified through cooling or solvent vaporization.
The processes of suspending, spraying, and cooling are repeated until the desired thickness of the capsule-wall is achieved.
When the spray nozzle is located at the bottom of the fluidized particle bed, this is known as the Wurster process.
Spray drying and spray congealing:
Both the spray drying and the spray congealing techniques for microencapsulation involve dispersing the core material in a liquefied coating agent and spraying or introducing the core coating mixture into an environment that influences the relatively quick solidification of the coating.
The method of coating solidification is the main distinction between these two microencapsulation techniques.
In the spray drying process, the coating solidification is influenced by the speedy evaporation of a solvent that contains the coating material.
In the spray congealing method, coating solidification is achieved by thermally congealing molten coating material or by solidifying a dissolved coating by dissolving the coating core material mixture in a nonsolvent.
Sorption extraction or evaporation are frequently used to remove solvents or non-solvents from coated products.
Multiorifice-centrifugation:
The centrifugal forces of the multiorifice-centrifugation method are used to propel a core particle through an encasing membrane.
The multiorifice centrifugation method's various processing parameters include
(i) the cylinder's rotational speed,
(ii) the core and coating materials' flow rates, and
(iii) the core material's concentration, viscosity, and surface tension
With a variety of coating materials, the multiorifice centrifugal method can microencapsulate liquids and solids of various sizes.
The encapsulated product can be delivered as a dry powder or as a slurry in the hardening medium.
Solvent Evaporation:
The O/W emulsion, which is made by agitating two immiscible liquids, can be produced using the solvent evaporation method.
The microcapsule coating (polymer) is dissolved using the solvent evaporation method in a volatile solvent that is incompatible with the liquid manufacturing vehicle phase.
In the coating polymer solution, a core substance (drug) to be microencapsulated is dissolved or dispersed.
With agitation, the core–coating material mixture is dispersed in the liquid manufacturing vehicle phase to obtain the appropriate sized microcapsules.
The system continues to agitate until the solvent separates into the aqueous phase and is eliminated by evaporation.
Microcapsules are hardened as a result of this process.
The oil phase can be dispersed in the continuous phase using a variety of techniques.
The most popular technique involves using a variable speed motor and a blade with the appearance of a propeller.
The selection of the vehicle phase and solvent for the polymer coating, as well as solvent recovery systems, are the most crucial variables to take into account when creating microcapsules using the solvent evaporation method.
There are many different liquid and solid core materials that can be used with the solvent evaporation method for microencapsulation.
Either water-soluble or water-insoluble materials can make up the core components.
Coatings can be made from a wide range of polymers that form films.
Polymerization:
In situ production of protective microcapsule coatings uses the polymerization method of microencapsulation.
The process involves the reaction of monomeric units that are positioned at the interface between a dispersed core material and a continuous phase.
The polymerization reaction takes place at the interfaces of liquid-liquid, liquid-gas, solid-liquid, or solid-gas because the continuous or core material supporting phase is typically a liquid or gas.
Interfacial cross-linking:
A biosourced polymer, such as a protein, is used in place of the small bifunctional monomer that contains active hydrogen atoms in an interfacial cross-linking method of microencapsulation.
When the reaction is carried out at the emulsion's interface, the acid chloride interacts with the protein's various functional groups to create a membrane.
For cosmetic or pharmaceutical applications, the interfacial cross-linking microencapsulation technique is very useful.
Applications:
Microencapsulation can be used to formulate various sustained controlled release dosage forms by modifying or delaying the release of encapsulated active agents or core materials.
Microencapsulation can also be employed to formulate enteric-coated dosage forms, so that the drugs will be selectively absorbed in the intestine rather than the stomach.
Gastric irritant drugs are being microencapsulated to reduce the chances of gastric irritation.
The taste of bitter drug candidates can be masked by employing microencapsulation techniques.
Through microencapsulation, liquids and gases can be changed into solid particles in the form of microcapsules.
Microencapsulation can be employed to aid in the addition of oily medicines to tableted dosage forms to overcome the problems of tacky granulations and in direct compression.
The volatility can be reduced using microencapsulation.
Volatile substances that are microencapsulated can be kept for longer periods of time without experiencing significant evaporation.
The encapsulated active agents are protected by microencapsulation from a variety of environmental hazards, including light, heat, humidity, oxidation, etc.
Many core materials' hygroscopic properties can be lessened by microencapsulation.
Microencapsulation can be used to separate incompatible substances. For instance, microencapsulation can be used to separate pharmaceutical eutectics.
Before mixing, both aspirin and chlorpheniramine maleate are microencapsulated to improve the stability of the incompatible mixture.
To reduce the potential risk associated with handling toxic substances, microencapsulation is used.
Commonly Asked Questions.
What is “microencapsulation"? Give its pharmaceutical applications.
Describe the various methods used to manufacture microencapsulation.