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Int J Pharma Res Health Sci. 2017; 5 (5): 1823-30
DOI:10.21276/ijprhs.2017.05.01
Farheen et al CODEN (USA)-IJPRUR,e-ISSN: 2348-6465
International Journal of Pharma Research and Health Sciences
Available online at www.pharmahealthsciences.net
Review Article
A Review on a Process: Microencapsulation
1,* 1 2
Talat Farheen , Azmat Shaikh , Sadhana Shahi
Y.B. Chavan College of Pharmacy, Department of Pharmaceutics, Aurangabad-431001, Maharashtra, India.
Government College of Pharmacy, Department of Pharmaceutics, Aurangabad-431005, Maharashtra, India
ARTICLE INFO ABSTRACT
The review of microencapsulation include preparation, modification in preparative
Received: 23 Aug 2017
Accepted: 01 Oct 2017
techniques, properties and uses of microcapsules in various fields like industrial,
engineering, pharmaceutical, biotechnology, and research applications. The article covers
encapsulation material, advantages and difficulties associated with microcapsules,
mechanism of release through capsule wall, techniques of preparation, some of the
modifications in preparation techniques, uses of microcapsules.
Key Words: Microencapsulation, microcapsules, core material, coating material,
________
coacervation, Wruster coater
1. INTRODUCTION
Microencapsulation, as a process, is application of relatively
thin coatings to small particles of solids or droplets of liquids
and dispersions. It is a process of surrounding, capsulating or
enclosing a substance inside a small capsule. Extremely tiny
droplets or particles of liquid, dispersion or solid material,
are packed within a second material or coating polymer film
for shielding the active material from surrounding
environment. The size of microcapsule ranges from one
micron to seven millimeter. Microencapsulation provides the
Corresponding author * means of converting liquids to solids, altering colloidal
Talat Farheen surface properties, providing environmental protection and
Y.B. Chavan College of Pharmacy, Department of controlling the release characteristics or availability of
Pharmaceutics, Aurangabad-431001, Maharashtra, India
Email ID: talat0326@gmail.com
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IIIIIIIII© International Journal of Pharma Research and Health Sciences. All rights reserved
Int J Pharma Res Health Sci. 2017; 5 (5): 1823-30
coated materials. Several of these properties can be attained release also depend upon whether the polymer degrades by
by macro-packaging techniques, however, the uniqueness of homogeneous or heterogeneous mechanism.
microencapsulation is the smallness of the coated particles 3. Diffusion controlled reservoir system:
and there subsequent use and adaptation to a wide variety of The active agent is encapsulated by a rate controlling
dosage forms and product application. The materials to be membrane through which the agent diffuses and the
coated are referred to as core, internal phase, active membrane erodes only after its delivery is completed. In
ingredient, fill, payload or nucleus, whereas the coatings of these systems delivery of drugs remain unaffected by the
microcapsules are termed as wall, shell, external phase, degradation of matrix.
membrane or coating. Microcapsules may have one or 4. Erosion:
multiple coatings arranged in strata of varying thicknesses Erosion of the coating due to pH and enzymatic hydrolysis
around core material. All the three states of material i.e. causes drug release with certain coating materials like
solid, liquid and gas, may be encapsulated and affect shape glyceryl mono stearate, bees wax and stearyl alcohol.4
and size of resultant capsules.1 Major Elements of Microcapsule System
Microencapsulation also includes bio-encapsulation which is Core material
more restricted to the entrapment of a biologically active The “core material” is defined as the specific material to be
substance (DNA, entire cell or group of cells) generally to coated, can be liquid or solid in nature. The composition of
improve its performance and to enhance its shelf life. the core material can be varied, as the liquid core can include
Because of the smallness of the particles, drug moieties can dispersed or dissolved material and the solid core can be a
be widely distributed throughout the GIT, thus potentially mixture of active constituents, stabilizers, diluents,
improving drug sorption.2 excipients and release rate retardants or accelerators. The
Need of Microencapsulation ability to vary the core material composition provides
To achieve sustained or prolonged drug release. definite flexibility and utilization of these characteristics
To mask unpleasant taste and odor of drugs to improve often allows effectual design and development of the desired
patient compliance. microcapsule properties.
Environment sensitive drugs can be stabilized by this Coating material
technique. Bakan and Anderson reported that The selection of the appropriate coating material is
microencapsulated vitamin A palmitate had enhanced responsible for the resultant physical and chemical
stability.3 properties of the microcapsules. The coating materials
Microencapsulation can be used for converting liquid should be capable of forming film that is cohesive with the
drugs into free flowing powders. core material, be chemically compatible and non-reactive
Drug-drug and drug-excipient incompatibility can be with the core material provide the desired coating properties
prevented by microencapsulation. such as strength, flexibility, impermeability, optical
Vaporization of volatile drugs such as methyl salicylate properties and stability.3
and peppermint oil can be prevented. Process Selection
Alteration in site of absorption can also be achieved by The factors to be considered during process selection are:
microencapsulation. Whether the core is solid or liquid,
Reduction in toxicity and GI irritation caused by various The solubility characteristics of the core,
drugs can be possible. The reactivity of the core with the wall material and
Toxic chemicals such as insecticides may be solvent,
microencapsulated to reduce possibility of sensitization The size of desired capsule,
of factorial person. The method of attaching the capsule to the desired
Release Mechanisms substrate,
The coated drug is release from microcapsules by following The method of core release,
mechanisms And the process and product economics.5
1. Degradation controlled monolithic system:
In this system drug is dissolved in matrix and is distributed 2. TECHNIQUES TO MANUFACTURE
uniformly. The drug is strongly attached to matrix and is MICROCAPSULES
released on degradation of matrix. Thus diffusion of drug is A. Physical methods:
slow as compared with matrix degradation. 1. Air suspension
2. Diffusion controlled monolithic system: 2. Coacervation
These systems are characterized by release of active agent 3. Coacervation phase separation
by diffusion prior to or concurrent with the degradation of 4. Centrifugal extrusion
polymer matrix. Thus the rate of diffusion of drug is higher 5. Pan coating
or equal to the rate of degradation of polymer. Rate of 6. Spray drying
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IIIIIIIII© International Journal of Pharma Research and Health Sciences. All rights reserved
Int J Pharma Res Health Sci. 2017; 5 (5): 1823-30
B. Chemical methods:1. Solvent evaporation precipitate from the solution. The shell material forms a
2. Polymerization: a) Interfacial polymerization continuous coating around the core droplets.
b) In-situ polymerization A. Cooling and hardening phase
c)Matrix polymerization • The shell material is cooled down to harden and forms the
Air suspension final capsule.
Also known as Wruster process, consist of the dispersing of • Hardening agents like formaldehyde can be added to the
solid, particulate core materials in a supporting air stream process.
and the spray coating of the air suspended particles. • The microcapsules are now stable in the suspension and
ready to be dried.
B. Drying phase
• The suspension is dried in a spray dryer or in a fluidized
bed drier.
• Spray Drying is a suitable method for heat sensitive
Products.
• The atomized particles assume a spherical shape. The rapid
flow of the coating material keeps the core material below
Fig 1:Wruster coater 100°C, even if the temperature in the drying chamber is
Air-suspension coating of particles by solutions or melts much greater.
gives better control and flexibility. The particles are coated • Microencapsulation makes the spray drying process easier
while suspended in an upward-moving air stream. They are for sticky products like fruit pulp or juice, with a high
supported by a perforated plate having different patterns of content of invert sugar.
holes inside and outside a cylindrical insert. Just sufficient Coacervation phase separation
air is permitted to rise through the outer annular space to The process consists of three steps carried out under
fluidize the settling particles. Most of the rising air flows continuous agitation:
inside the cylinder, causing the particles to rise rapidly. At 1.Formation of three immiscible chemical phases – A liquid
the top, as the air stream diverges and slows, they settle back manufacturing vehicle phase,A core material phase, andA
onto the outer bed and move downward to repeat the cycle. coating material phase.
The particles pass through the inner cylinder many times in a To form the three phases, the core material dispersed in a
few minutes. solution of the coating polymer, the solvent for the polymer
Process variables that affect the encapsulation: being the liquid manufacturing vehicle phase. The coating
Density, surface area, melting point, solubility, material phase, an immiscible polymer in a liquid state, is
volatility, crystallinity and flowability of the core formed by utilizing one of the methods of the methods of
material. phase separation-coacervation, i.e., by
Coating material concentration. a)Changing the temperature of the polymer solution; or
Coating material application rate. b)By adding a salt, non-solvent, or incompatible polymer to
Volumes of air required to support and fluidize the core the polymer solution; or
material. c)By inducing a polymer-polymer interaction.
Amount of coating material required. 2.Deposition of the coating –
Inlet and outlet operating temperature. It consists of depositing the liquid polymer coating upon the
The process has the capability of applying coating in the core material. This is accomplished by controlled, physical
form of solvent solutions, aqueous solutions, emulsions, mixing of the material in the manufacturing vehicle
dispersions or hot melts. In regard to particle size, the air deposition. If the liquid polymer coating around the core
suspension technique is applicable to both micro- material occurs if the polymer is adsorbed at the interface
encapsulation and macro-encapsulation coating processes.4 formed between the core material and the liquid vehicle
Coacervation phase, and this adsorption phenomenon is a prerequisite to
The core material will be added to the solution. The core effective coating. The continued deposition of the coating
material selected should not react or dissolve in water material is promoted by a reduction in the total free
(maximum solubility 2%). The core material is dispersed in interfacial energy of the system, brought about by the
the solution. The particle size will be defined by dispersion decrease of the coating material surface area.6
parameter, as stirring speed, stirrer shape, surface tension 3.Rigidization of the coating –
and viscosity. Size of the particles ranges from 2 - 1200μm. It involves rigidizing the coating, usually by thermal, cross-
Coacervation starts with a change of the pH value of the linking, or desolvation techniques, to form a self-sustaining
dispersion, e.g. by adding H2SO4, HCl or organic acids. The microcapsules.
result is a reduction of the solubility of the dispersed phases
(shell material). The shell material (coacervate) starts to
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IIIIIIIII© International Journal of Pharma Research and Health Sciences. All rights reserved
Int J Pharma Res Health Sci. 2017; 5 (5): 1823-30
E.g. Coacervation microencapsulation of talc particles with
poly (methyl methacrylate) by pressure-induced phase
separation of CO2- expanded ethanol solutions.6
Genc L et al. has prepared microcapsules of Ketorolac
tromethamine by means of a coacervation-phase separation
technique induced by the addition of non-solvent.7
Multi-orifice centrifugal extrusion
Liquids are encapsulated using a rotating extrusion head Fig 2: Representation of a typical pan coating
containing concentric nozzles. In this process, a jet of core Spray drying
liquid is surrounded by a sheath of wall solution or melt. As Spray drying serves as a microencapsulation technique when
the jet moves through the air it breaks, owing to Rayleigh an active material is dissolved or suspended in a melt or
instability, into droplets of core, each coated with the wall polymer solution and becomes trapped in the dried particle.
solution. While the droplets are in flight, a molten wall may The main advantages is the ability to handle labile materials
be hardened or a solvent may be evaporated from the wall because of the short contact time in the dryer, in addition,
solution. Since most of the droplets are within ± 10% of the the operation is economical.
mean diameter, they land in a narrow ring around the spray Spray drying and spray congealing processes are similar in
nozzle. Hence, if needed, the capsules can be hardened after that both involve dispersing the core material in a liquefied
formation by catching them in a ring-shaped hardening bath. coating substance and spraying or introducing the core -
This process is excellent for forming particles of 400– coating mixture into some environmental condition,
2,000μm diameter. Since the drops are formed by the whereby, relatively rapid solidification and formation of the
breakup of a liquid jet, the process is only suitable for liquid coating is affected. The principal difference between the two
or slurry. A high production rate can be achieved, i.e., up to methods is the means by which coating solidification is
22.5 kg of microcapsules can be produced per nozzle per accomplished. Coating solidification in the case of spray
hour per head. Heads containing 16 nozzles are available. drying is effected by rapid evaporation of a solvent in which
The process utilizes centrifugal forces to core material the coating material is dissolved. Coating solidification in
particles through an enveloping microencapsulation spray congealing methods is accomplished by thermally
membrane, thereby affecting microencapsulation.8 congealing a molten coating material or by solidifying a
Process variables include; rotational speed of cylinder, flow dissolved coating by introducing the coating - core material
rate of the core and coating material, the concentration and mixture into a non-solvent. Removal of the non-solvent or
viscosity of the coating material, viscosity and surface solvent from the coated product is then accomplished by
tension of core material.4 sorption, extraction, or evaporation techniques.
Pan coating Microencapsulation by spray drying is conducted by
The pan coating process, widely used in the pharmaceutical dispersing a core material in a coating solution, in which the
industry, is among the oldest industrial procedures for coating substance is dissolved and in which the core material
forming small, coated particles or tablets. The particles are is insoluble, and then by atomizing the mixture into air
tumbled in a pan or other device while the coating material stream. The air, usually heated, supplies the latent heat of
is applied slowly. With respect to microencapsulation, solid vaporization required to remove the solvent from the coating
particles greater than 600 microns in size are generally material, thus forming the microencapsulated product. The
considered essential for effective coating, and the process equipment components of a standard spray dryer include an
has been extensively employed for the preparation of air heater, atomizer, main spray chamber, blower or fan,
controlled - release beads. Medicaments are usually coated cyclone and product collector.
onto various spherical substrates such as nonpareil sugar Microencapsulation by spray congealing can be
seeds, and then coated with protective layers of various accomplished with spray drying equipment when the
polymers.9 protective coating is applied as a melt. Coating solidification
Generally the coating is applied as a solution, or as an (and microencapsulation) is accomplished by spraying the
atomized spray, to the desired solid core material in the hot mixture into a cool air stream. Waxes, fatty acids and
coating pans. To remove the coating solvent, warm air is alcohols, polymers and sugars, which are solids at room
passed over the coated materials as the coatings are being temperature but meltable at reasonable temperatures, are
applied in the coating pans. In some cases, final solvent applicable to spray congealing techniques. Typically, the
removal is accomplished in a drying oven. particle size of spray congealed products can be accurately
controlled when spray drying equipment is used, and has
been found to be affected by the feed rate, the atomizing
wheel velocity, dispersion of feed material viscosity, and
variables.10
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IIIIIIIII© International Journal of Pharma Research and Health Sciences. All rights reserved
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