MICROENCAPSULATION: ADVANCEMENTS IN TECHNOLOGY AND ITS PATENTS

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About Authors:
Arsh Chanana*, Mahesh Kumar Kataria, Ajay Bilandi
Department of Pharmaceutics, Seth. G.L. Bihani S.D. College of Technical Education,
Sri Ganganagar (Rajasthan) INDIA
*arshchanana806@gmail.com

Abstract-
Microcapsule is a tiny sphere including core material/internal phase or fill, coated with/surrounded by wall know as shell, coating or membrane. The usual size range of the microcapsule lies between 1 to 1000 μm. The technique is usually applied for targeted drug delivery, protection of the molecule and stability if the core material. Microencapsulation system offers potential advantages over conventional drug delivery systems and also established as unique carrier systems for many pharmaceuticals. This article contains the traditional and the recent techniques, including their patents, for the preparation of microcapsules. Solvent exchange method, coacervation, polymerization, hot melts etc are several recent techniques are used for the preparation of the microcapsules. The microencapsulation technique, as Novel drug Delivery System (NDDS), is widely applied for delivery of probiotics, drugs, pesticide, food etc. Although significant advances have been made in the field of microencapsulation, still many challenges need to be rectified during the appropriate selection of core materials, coating materials and process techniques.

REFERENCE ID: PHARMATUTOR-ART-1916

Introduction-
It is a process in which tiny particles or droplets are surrounded by a coating to give small capsules various useful properties. A microcapsule is a tiny sphere with a uniform wall around it. The inside material in microcapsule is referred to as the core, internal phase or fill, whereas the wall is sometimes called a shell, coating or membrane. This process produces small particles ranging in size from 1 to 1000 μm. It is a one of the most intriguing filed in the area of drug delivery system. Microencapsulation includes bioencapsulation which is more restricted to entrapment to the entrapment of a biologically active substance (from DNA to entire cell or groups of cells) generally to improve its performance & enhance its shelf life. The microencapsulation study would be encouraged with the motto “Small is better”.

Microcapsule Terminology & Basic Structures-
There are basically two phase of microcapsules. The upper phase called the wall, external phases coating or shell and the inner phase called core, as contain active material, internal phases or payload according to the formulation. The Microcapsules are of various types according to the arrangement of the core and the coating material. The simple microcapsules contain a single external phases where as it double in the case of double walled. In multi-core the internal phase is two or more. In matrix types the internal phase is mixed with the external phases. In particulate the active medicament is mixed in external phases and in the irregular type of microcapsules there are irregular structures of the microcapsule.

Figure No. 1:  Basic Structure & Type of Microcapsule

Various Techniques used for MICROENCAPSULATION
Microencapsulation is a process where the particles of an active agent are surface coated to provide change in the physicochemical properties of an active agent. Several processing techniques (Table No. 1) are used to prepare microencapsules depending on the desired properties of the final product, the properties of the agent being coated and the coating material.

Table No 1: Different Micro-encapsulation Techniques

Physical methods

Physico-chemical methods

Other methods

 Pan coating

Ionotropic gelation

Emulsion Solidification

Air-suspension coating

Coacervation

1.  Simple coacervation

2. Complex coacervation

Solvent evaporation

Centrifugal extrusion

Solvent extraction

Solvent Exchange

Vibrational Nozzle

Chemical methods

Hot-Melt Microencapsulation

Spray–drying

1. Fluid-bed coating (Air-suspension technique)

2. Pan coating

Interfacial polycondensation

 

Interfacial cross-linking

 

In-situ polymerization

 

Matrix polymerization

 

Conventional Microencapsulation Techniques
Pan Coating-The pan coating process, widely used in the pharmaceutical industry, is among the oldest industrial procedures for forming small, coated particles or tablets. The particles are tumbled in a pan or other device while the coating material is applied slowly. Relatively large particles can be encapsulated by pan coating. Size of solid particles should be greater than 600 mm to achieve effective coating using this method. This is a typical method used to apply sugar coatings on candies. This method employs a rotating drum containing core materials (such as candies), onto which warm sucrose solution is ladled. The rotation distributes the syrup evenly as a thin coat on the cores and increases the surface area of the syrup that aids in evaporation of the water. As the water evaporates, the sugar hardens and coats the cores. For pharmaceutical products, perforated pans are used and the coating solution, usually an aqueous solution, is sprayed onto the tumbling cores.

Air-suspension coating- This technique is also popularly termed as Wurster coating or Fluidised Bed Coating. Air-suspension coating of particles by solutions or melts gives better control and flexibility. The particles are coated while suspended in an upward-moving air stream. They are supported by a perforated plate having different patterns of holes inside and outside a cylindrical insert. Just sufficient air is permitted to rise through the outer annular space to fluidize the settling particles. Most of the rising air (usually heated) flows inside the cylinder, causing the particles to rise rapidly. At the top, as the air stream diverges and slows, they settle back onto the outer bed and move downward to repeat the cycle. The process of movement through the inner cylinder repeats several times in few minutes (en.wikipedia.org/wiki/Micro-encapsulation). Several patents have been granted for this technique and a few among this has been enlisted in Table no. 2.

Table No. 2: Patents Granted For Air Suspension Microencapsulation Technique

Patent NO. and Date

Name of Method

Discussion

Reference

US/ Patent 6022525, (Feb 8 2000)

Preparation of diagnostic agents

Microcapsules are prepared by a process comprising the steps of (i) spray-drying a solution or dispersion of a wall-forming material in order to obtain intermediate microcapsules and (ii) reducing the water-solubility of at least the outside of the intermediate microcapsules. Suitable wall-forming materials include proteins such as albumin and gelatin. The microcapsules have walls of 40-500 nm thick and are useful in ultrasonic imaging. The control of median size, size distribution and degree of insolubilisation and cross-linking of the wall-forming material allows novel microsphere preparations to be produced.

(freepatentsonline.com /6022525.html)

US/ Patent 8192841 (June 5 2012)

Microencapsulated delivery vehicle having an aqueous core

Microencapsulated delivery vehicles comprising an active agent are disclosed. The microencapsulated delivery vehicles may be introduced into products such that, upon activation, the product provides a functional benefit to a substrate, such as a user's skin.

(freepatentsonline.com/ 8192841.html)

US/ Patent 4749575 (June 7 1988)

Microencapsulated medicament in sweet matrix

Any orally administrable medicament is prepared into a dosage form which eliminates the unpleasant taste and mouth feel of the medicament and is easily and pleasantly ingested even by children, by microencapsulating the medicament into microcapsules of less than 300 microns diameter, and embedding the microcapsules into a soft, sweet, palatable matrix, such as chocolate

(freepatentsonline.com/ 4749575.html)

US/ Patent 4925674 (May 15 1990)

Amoxicillin microencapsulated granules

The invention disclosed is amoxicillin microencapsulated granules with activity densities greater than about 0.200 g/ml. These granules are unusually small having diameters less than about 1000 microns. The granules optionally have a taste mask coating, and are particularlyuseful in hand-held flowable material dispensers. A process for manufacturing such granules is also disclosed.

(freepatentsonline.com/ 4925674.html)

Spray–drying- The process produce microcapsules approaching a spherical structure in the size range of 5 to 600 microns .Spray drying yield products of low bulk density owing to the porous nature of the coated particles (Leon Lachman et al,1991). This method is a single-step, closed-system process applicable to a variety of materials. The drug is dissolved or suspended in a suitable (either aqueous or non-aqueous) solvent containing polymer materials. The solution or suspension is atomized into a drying chamber, and microparticles form as the atomized droplets are dried by heated carrier gas (Swarbrick James, 2007).

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