Particle Coating (Pharmaceutics)

Presenter
Mr. Ghulam Rasool Noor
Pharm.D. R.Ph.
gr8noor@gmail.com
M.Phil Pharmaceutics
Riphah institute of Pharmaceutical
Sciences, Lahore

• Introduction to Particle Coating
• Objective of Particle Coating
• Approaches of Particle Coating
• Solvent-less Coating
• Technologies
Learning Objectives

Particle Coating
DEFINITION:
• When a thin layer of a substance is placed
around a core particle it is called coating of
the particle.
Coating alters:
Surface Properties &/or Functionality
of fine particles or powders.
Reference:
Vivek P. Chavda*, M. M. S., Jayant R. Chavda (2013). "Particle coating: From
conventional to advanced." International Journal of Pharmaceutical and Medicinal
Research(1): 1-17.

Particle Coating
Coating layer is generally applied as:
 Film resulting from the spraying &
 Subsequent drying of solutions or
dispersions

Particle Coating
Rationale &/or Purpose:
 Improvement to powder Flowability.
 Protection of Unstable/Reactive Substances
(from Air, Humidity, Light & Oxidation etc.)
 Enhancement of Mechanical Properties
(Abrasion Resistance & Compressibility)
 Improvement of Aesthetic Appeal
(Texture, Appearance, Odor or Taste Masking)
 Controlled Release / Dissolution of APIs.

Particle Coating
Wet / Liquid Coating Methods
Solvent Coating Aqueous Coating

Particle Coating
Solvent Coating:
 Coating polymers & other excipients are dissolved into an
organic solvent to form a coating solution
 Coating solution is sprayed onto the surface of the solid
dosage forms to form a coating film by evaporating the
organic solvent.
 Evaporation is done by drying process resulting in uniform
film formation.
Disadvantages:
TOXICITY & ENVIRONMENTAL CONCERNS
Due to presence of organic solvents

Particle Coating
Aqueous Coating: A preferred approach over solvent coating
For water soluble polymers:
The coating process & film formation
mechanism are SAME as organic solvent
coating.
For water-insoluble polymers:
The coating process & film formation
mechanism are DIFFERENT.
Processes:
 Coating polymers & additives are firstly ground into fine
powders & mixed together.
 Those fine powders are dispersed into water to form a coating
suspension.
 Suspension is then sprayed onto the surface of solid dosage
form followed by an evaporating by a flow of hot air
 Curing step to allow the polymer particles coalescing into a
homogeneous film.

Particle Coating
Aqueous Coating: A preferred approach over solvent coating
Plasticizers: are often added into the coating formulation to reduce glass transition
temperature (Tg) the coating polymer.
Advantages:
 No toxicity
 No environment related problems
LIMITATIONS:
 Water is more difficult to be evaporated compared to the
organic solvents.
 Much longer processing time
 Much higher energy consumption
 Hot air handling
 Not appropriate for the moisture sensitive drugs

Particle Coating
Solvent Coating:
TECHNOLOGIES:
o Microencapsulation
o Fluidized bed coating techniques
o Solvent evaporation
o Coacervation & phase separation techniques
o Spray drying
o Interfacial polymerization
o Pan coating

Solvent-less Coating Methods
RATIONALE:
Solventless Coating Technologies can overcome following
disadvantages associated with use of solvent/water in coating process:
 Organic solvents used in liquid coating are Flammable & Toxic.
 Solvent vapors causes hazards to coating operators,
 Solvent residue in the formulation.
 High cost of solvents
 Strict Environmental & Occupational Safety Regulations.
 Heat & water involved in coating process can degrade the drug
 Validation of coating dispersion for controlling microbial presence
 Solvent removal processes is time consuming
 Extreme energy consumption in solvent removal process.

Solvent-less Coating Methods
1. Photocurable Coating
2. Compression Coating
3. Hot-melt Coating
4. Magnetically assisted impaction Coating
5. Powder/Dry Coating
6. Supercritical Fluid Coating
No drying or liquid/solvent evaporation step

Particle Coating
1-Photocuring Coating:
PHOTOCURING:
A process of rapid conversion of specially formulated (usually liquid)
solventless compositions into solid films by irradiation with
UV-more energetic, Visible light is preferred due to safety & ease.
The only chemical approach to form coating film.
Two groups:
 Free-radical Mechanism:
(Polymerization reaction to form a crosslinked network).
 Ionic Mechanism: Cationic & Ionic
Process Steps:
 Initiation
 Propagation
 Termination
UV or Visible Light

Particle Coating
Photocuring Coating:
Components:
 Prepolymers or monomers (Polydimethylsiloxane, Acrylic Siloxanes)
 Photoinitiators/Catalysts (Hydroxyketones, Benzoin Ether)
 UV/Vis-Light Source (Mercury Lamp: 200-320 λ)
 Pore forming Agents (for Functional Coating - Lactose, PEG 800).
Advantages:
 This process can be performed at or below room
temperature with an extremely rapid rate.
 Coating can be done in open systems i. e. Pan Coating.
Disadvantages:
 Not suitable for photosensitive drugs
 Use is limited by specific photocurable materials and
coating equipment.

Particle Coating
2-Compression Coating:
Mixture of core formulation is first compressed into an inner layer
CORE and then coating material is compressed around the core to
form an Outer Layer.
Finished product is a tablet within tablet.

Particle Coating
Compression Coating:
Method is being employed Recently for creating:
Compressible Excipients:
 Microcrystalline Cellulose
 Colloidal Silica
 Manitol
 Lactose
Advantages:
 Two incompatible drugs within same Dosage Form
(Physically separated)
Disadvantages:
 Mechanically complex method; requires specially designed equipment.
 Coating thickness is not uniform; issues of placement of core in the centre.
MODIFIED-RELEASED PRODUCTS

Particle Coating
3-Hot Melt Coating:
Coating materials are applied over the Substrate in their Molten
state & then solidified upon cooling.
Coating Materials: Lipids, Waxes & Fatty bases.
Weight gain with lipid materials are less than those commonly applied with polymers
to achieve same effect.
Choice of coating material:
Depends on its “functions in dosage form” i.e retardation drug
release rate, prevention of degradation, masking of unpleasant taste.
STEPS involved:
1. Coating equipment is warmed.
2. Substrate is preheated
3. Coating material is melted and sprayed onto the
surface of substrate
4. Cooling step to allow the film formation.

Particle Coating
Hot Melt Coating:
TECHNOLOGIES:
Fluidized Bed Coating: (Top Spray & Bottom Spray)
Capable of coating particles from 10 to 35 mesh (0.500 to 2.00mm) &
tablets upto 1g.
Spray Congealing/Coating:
Slurry of molten matrix material & substrate is sprayed through into a
Cooling chamber, where the droplets solidify rapidly.
Methods for spray automization:
 Ultrasonic Automization
 Hydraulic Automization
 Pneumatic automization
Pan Coating: Conventional pan coater can be used. Difference is that
coating agent is in molten state instead of solution state.
Types: Pan Spray & Pan Pour
Pan spray is the best--- uniform film coating.

Particle Coating
Hot Melt Coating:
KEY FACTORS: related to excipients
 Molecular Weight (Key Physicochemical Parameter)
 Thermal behaviour
 Rheology in molten state.
Complete investigation of thermal behaviour is required as the method requires
melting of coating excipients & exposure to high temperature (about 2000 ˚C)
Advantages:
 Necessity of solvent application is fully eliminated.
 Cost effective
Disadvantages:
 Only suitable for the drugs with stable properties at or
below congealing point of coating materials.
 Operational safety: high temperature close to 2000 ˚C.

Particle Coating
4- Magnetically Assisted Impaction Coating:
Soft coating method(s)
That attach the Guest particles (Coating material) on the host particles
(material to be coat) with a minimum degradation of particle size,
shape and composition caused by the build up of heat.
Advantages:
 Rise in temperature is negligible.
 Most suitable for temperature sensitive particles
MAIC Device:
It can coat soft organic host and guest particles without causing major
changes in material shape & size.

Particle Coating
Magnetically Assisted Impaction Coating:
MAIC Apparatus:
 A processing vessel surrounded by the series of
electromagnets connecting to alternate current.
 Host & guest particles are placed in vessel along with
measured mass of magnetic particles
 when magnetic field is present, magnetic particles
move furiously in the vessel, resembling a fluidized
bed system
 Agitated magnetic particles impart energy to host &
guest particles causing collision,
 Coating achieved by means of impaction or peening of
guest particles on to the host particles.

Particle Coating
MAIC Apparatus:

Particle Coating
Mechanism of coating in MAIC Process:
a) Excitation of magnetic
particles
b) De-agglomeration of
guest particles
c) Shearing & spreading of
guest particles on surface
of host particles
d) Magnetic-host-host
particle interaction
e) Magnetic-host wall
interaction
f) Formation of coated
products

Particle Coating
5-Powder/Dry Coating:
Principle:
 Dry coating refers to the technique where the core
materials are strongly surrounded by fine particles simply
by collision or by the use of non-aqueous plasticizer
Dry Coating Techniques
I. Plasticizer Dry Coating
II. Heat Dry Coating
III. Electrostatic Dry Coating

Particle Coating
I- Plasticizer Dry Coating:
Principle:
 In this method, powdered materials are spread onto the dosage
surface simultaneously with the plasticizer spraying from
separate spraying nozzle.
 The sprayed liquid plasticizer would wet the powder
particles and the dosage surface promoting the adhesion
of particles to the dosage surface.
 The coated dosage forms are then cured for predetermined
time above Tg of polymer to form continuous film.

Particle Coating
II- Plasticizer Dry Coating:
Uses:
Plasticizer Dry Coating can be used for following purposes
 Extended release
 Enteric coating
Advantages:
 Time saving
 Energy saving
 High Productivity
 Low Moisture level
Methods:
 Pan Coater (for Tablets)
 Fluidized bed coater (for pellets)
Drawback
 Can’t be used for some sensitive products such as
probiotics

Particle Coating
Heat Dry Coating:
Principle:
 In this method only heat is used as a binding force to realize the
dry coating of the tablets.
Pre-heating
• (uncoated tablets are heated to predetermined temperature)
Powdering
•Powder is transferred into the coating equipment
and distributed onto the core
Curing
•Polymeric particles adhere to the surface of
substrate to form a polymeric film coating
Process:
 Three stage process

Particle Coating
Controlled release from drug microparticles via
Solventless Dry-polymer Coating
MAXX CAPECE & colleagues developed a novel solvent-less dry-polymer
coating process employing high-intensity vibrations avoiding the use of
liquid plasticizers, solvents, binders, and heat treatments is utilized for the
purpose of controlled release.

Particle Coating
III- Electrostatic Powder Coating:
Most widely used coating method
Principle:
 Dry powders are charged by an electrostatic spray gun and then
move & adhere to the grounded substrate surface without using
any solvent or water.
 Then the grounded substrate with deposited coating powder is
put on oven and cured for a certain period of time under high
temperature to allow film formation.

Particle Coating
Electrostatic Powder Coating:
Types of spraying Units:
Two types Powder coating Guns according to the charging Mechanism:
 Corona Charging: Uses principle of Electrical Field
 Tribo Charging: Uses principle of Frictional charging
Advantages:
 Short coating process
 Energy saving
 Reduction of operation cost
 INCREASED COATING EFFICIENCY
(by enhancing coating powder adhesion)
 Control of coating powder feeding
 UNIFORM COATING FILM
(Controlled coating thickness & surface morphology)

Particle Coating
6-Supercritical Fluid Coating:
Used to coat small particles uniformly by encapsulating each core with
coating materials uniformly under Supercritical Conditions.
SUPERCRITICAL FLUID/MEDIUM:
Liquid like density &
Solvating power with
Gas-like transport properties
These are “HIGHLY COMPRESSED GASSES” that possess
several advantageous properties of both liquids and gases. E.g
CO2, Alkanes (C2 to C4) & Nitrous Oxide (N2O)
Most widely used Supercritical Fluid is CARBON DIOXIDE b/c of its :
 Low Critical Temperature (31 ˚C)
 Critical Pressure (74 bar)
 Nontoxic, non-flammable
 Highly pure & Cost effective

Particle Coating
Supercritical Fluid Coating:
Rapid Expansion of Supercritical Solutions (RESS):
Most common in pharmaceutical applications
PROCESS:
1. Coating Material is solubilized in Supercritical Fluid
(CO2) in a high pressure vessel.
2. APIs / Drug particles are dispersed in the Supercritical
Fluid / Medium.
3. Suspension is rapidly expanded by sudden drop in
pressure (released at atmospheric pressure through a
nozzle.)
4. Solvent Power of CO2 reduces (Desolvation of coating
material)
5. Coating material precipitates & deposits onto the
particles of drugs (forms a coating layer)

Particle Coating
For a successful coating SCF ideally:
 Dissolves only the Coating material,
 leaving the Core completely undissolved.
Coating Materials: (mainly Lipids)
 Mono, Di, Triglycerides of various Fatty Acids
 Fatty Acids & Fatty Alocohols
Advantages:
• Mild processing conditions
• Allows microencapsulation of sensitive ingredients e.g Albumin.
• Prevent agglomeration of fine particles during coating.
Disadvantages:
• Application is limited due to the poor solubility of most of coating
materials in supercritical fluid.
• Requirement of the core to be insoluble.

Particle Coating
Simultaneous microencapsulation of hydrophilic and
lipophilic bioactives in liposomes produced by an ecofriendly
supercritical fluid process
Research Problem:
Organic solvent residues are always a concern with the liposomes produced
by traditional techniques.
Objectives:
To encapsulate hydrophilic and lipophilic compounds in liposomes using a
newly designed supercritical fluid process coupled with vacuum-driven cargo
loading.
Reference:
Wen-ChyanTsai, S. S. H. R. (2017). "Simultaneous microencapsulation of
hydrophilic and lipophilic bioactives in liposomes produced by an
ecofriendly supercritical fluid process." Food Research International 99: 256-
262.

Particle Coating
 Supercritical carbon dioxide was chosen as the phospholipid-
dissolving medium and an ecofriendly substitute for organic solvents.
 Liposomal microencapsulation was conducted via a 1000-μm
expansion nozzle at 12.41 MPa, 90 °C, and aqueous cargo loading rate
of 0.25 ml/s.
 Vitamins C and E were selected as model hydrophilic and lipophilic
compounds encapsulated in the integrated liposomes.
 The average vesicle size was 951.02 nm with a zeta potential of
− 51.87 mV. The encapsulation efficiency attained was 32.97% for
vitamin C and 99.32% for vitamin E.
 Good emulsion stability was maintained during storage at 4 °C for
20 days. Simultaneous microencapsulation in the liposomes was
successfully achieved with this supercritical fluid process.

Particle Coating

Particle Coating
SUMMARY
Solventless coating techniques are being preferred over
other coating techniques because these reduces the overall
cost by overcoming the tedious & costly processes of
solvent disposal/treatment. Moreover these technologies
can reduce the processing time because there is no
drying/evaporation step.

Particle Coating
References:
1. Wen-ChyanTsai, S. S. H. R. (2017). "Simultaneous microencapsulation of hydrophilic
and lipophilic bioactives in liposomes produced by an ecofriendly supercritical fluid
process." Food Research International 99: 256-262.
2. Vivek P. Chavda*, M. M. S., Jayant R. Chavda (2013). "Particle coating: From
conventional to advanced." International Journal of Pharmaceutical and Medicinal
Research(1): 1-17.
3. Patel, V. R., et al. (2012). "A Novel Dry Coating Technology for Pharmaceutical Dosage
Forms." Journal of Pharmacy Research Vol 5(4): 2298-2305.
4. Capece, M., et al. (2015). "Controlled Release from Drug Microparticles via Solventless
Dry‐Polymer Coating." Journal of pharmaceutical sciences 104(4): 1340-1351.
5. Yang, Q., et al. (2017). "An update on electrostatic powder coating for
pharmaceuticals." Particuology.
6. Capece, M. and R. Davé (2014). "Solventless polymer coating of microparticles."
Powder Technology 261: 118-132.

Particle Coating (Pharmaceutics)

Particle Coating (Pharmaceutics)

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