pelletisation_6 Flashcards
definition of pellets
small, round,, ball/tube shaped compressed massed of a substance
definition of spheroids
solid geometrical figure similar in a shape of a sphere
how does round shape minimise energy
reduce friction during motion
therapeutic advantages of spheroids as multi-unit dose form
- minimise local irritation
- maximise absorption/ bioavailability
- less susceptible to dose dumping
- reduction in gastric emptying rates
technological advantage of spheroids as multi-unit dose
- superiority for coating
- uniformity in packing
- spherical in shape
- good flow ability
- low friability
types of direct pelletisation
- aqueous-based pelletisation
2. melt-based pelletisation
types of pelletisation through extrusion step
- extrusion spheronisation
2. hot-melt extrusion
types of pelletisation by layering onto starter seed
- powder layering
- solution layer
- suspension layering
types of pelletisation through formation of droplets
- spray drying
- spray congealing
- cyro-pelletisation
what is layering
similar to coating, deposition of successive coats onto seed particles without agglomerative growth, the coating medium is solution or suspension of the core material
how is pelletisation in rotary processor works
carried out by spraying the agglomeration media directly onto the powder mass rotating in a spheroniser on a frictional base. Pellets are formed in situ and they can be directly coated by changing the spray media to a coating media with the introduction of drying air into the chamber
extrusion spheronisation
- highly spherical aggregates
- pellets of narrow size distribution
- pellets of smooth surface
- pellets of low friability
extrusion spheronisation process steps
- dry blending
- wet massing
- extrusion
- spheronisation
- drying
- coating
ideal extrudate for spheronising
jagged, feature with regular spaced shark-skinned protuberance
formulation requirements for extrusion-spheronisation
- specific requirement for extrusion (cohesive, plastic wet mass with inherent fluidity and self-lubricating properties)
- specific requirement or spheronisation (extrudates with sufficient plasticity)
- basic formulation (pelletisation aid, drug, filler, moistening fluid)
choice of pelletisation aid and properties
microcrystalline cellulose (MCC) - pelletisation aid of choice
- good binding property
- good cohesiveness
- large surface area
- high internal porosity
- gives unparallel efficiency for preparing highly spherical granules of narrow size distribution and with the desired mechanical properties
molecular sponge model of MCC
- MCC absorbs water like molecular sponge during extrusion (forms cohesive yet plastic wet mass)
- helps in binding and lubrication during spheronisation (increases surface plasticity, and helps in rounding extrudates into pellets)
crystalline gel model of MCC
MCC particles are broken down into single crystallites of colloidal size which are able to form a crystalline gel and immobilise the liquid
function of MCC
- absorbs water like molecular sponge
- extrusion gives a cohesive yet plastic wet mass, helping to bind and lubricate
- spheronisation increases surface plasticity, helping to round extrudates into pellets
example of other pelletisation aids
- powdered cellulose
- hydroxypropyl methylcellulose/ hypromellose
- hydroxyethyl cellulose
- chitosan
- carrageenan
- cross-linked polyvinyl pyrrolidone (v successful)
bad examples of pellet formation during spheronisation step
- poorly formed extrudates
- fragments
- build up pellets slowly
good examples of pellet formation during spheronisation
- well formed extrudates
- break into short lengths
- round quickly
ideal size of components
1/6-1/8 of desired pellet size
note: the smaller the particles, the more favoured it is
what mean torque to use for pellet making
@ Tmax, usually at capillary stage
what happens when cohesive forces < forces during spheronisation
irregular shaped, wide size distribution, leading to
- spheronisation speed decreasing (reduces the force of spheronisation
- wet amss/ extrudate cohesive strength increases (increases mechanicam strength)
what happens when cohesive forces ~ forces during spheronisation
round, narrow size distribution, leading to:
what happens when cohesive forces > forces during spheronisation
spheronisation speed increase, leading to:
- breaking and rounding of extrudate
- particle size dereases
- causing surface area to increase
- hence greater cohesivity
importance of packability of component particles
- influences the spheroid formation
- dependent on particle size, size of distribution of its component, and force exerted during wet processing
functionality of spheronsation aid dependent on
- in process particle size
- overall matrix cohesiveness during wet processing steps of extrusion-spheronisation
cohesivity is important for pelletisation but:
- cannot have migratable stickiness (eg. use PVP or HPMC or melt)
- use immobile adhesive particles (micronised powder , MCC)
what does migratable stickiness do
make a process less robust, for controlling final product size (eg. in melt pelletisation)
examples of direct pellisation
- fluid bed layering
- balling process
- one-pot rotary process (expensive)
