pelletisation

Question 1

What are pellets:

Answer 1

Small rounded compressed/tube shaped mass of substance

Question 2

Advantages of spheronisation:

Answer 2

Therapeutic:

• Minimise local irritation
• Maximise absorption/bioavailability
• Less susceptible to dose dumping
• Reduction in GER

Technological:

• superiority for coating
• uniformity in packaging
• spherical in shape
• good flowability
• low friability

Question 3

List of pelletisation techniques

Answer 3

Direct pelletisation
Pelletisation through extrusion step
Pelletisation by layering onto starter seeds
Pelletisation through formation of droplets

Question 4

Direct pelletisation methods:

Answer 4

Fluid bed layering: pelletisation by layering onto starter seeds –> disposition of successive coats onto seed particles without agglomerative growth (coating medium is solution/suspension of core material)
Balling process: involves disc/rotatory drum pelletiser – pellets will not be highly uniform – not for drug loaded ones
Pelletisation in rotatory processor: agglomeration media sprayed directly onto powder mass rotating in spheroniser on frictional base – size distribution of pellets not very tight

Question 5

Why is extrusion-spheronisation often used:

Answer 5

• Ease of operation
• High throughput, low wastage
• Highly efficient
• Highly spherical
• Pellets of narrow size distribution - no need to sieve particles that are too big/small
• Pellets with smooth surface
• Pellets with low friability

Question 6

Steps involved in extrusion-spheronisation:

Answer 6

1. Dry blending
2. Wet blending
3. Extrusion
4. Spheroisation
5. Drying
6. Coating

Question 7

What is involved in the extrusion step:

Answer 7

Moistened powder mixture introduced and processed in extruder to form high density, cylinder shaped extrudates – pass through screen of desired aperture size

Question 8

What are the features of ideal extrudates:

Answer 8

Jagged, featured with regular spaced shark-skinned protuberances – broken up easily

Question 9

What is involved in the spheronisation step:

Answer 9

1. Cylindrically shaped extrudates broken into uniform lengths and rounded in spheroniser with rotating frictional plate
2. Rapid process rounds break extrudates by rope like motion
3. Highly spherical, narrow distributed pellets of size close to extruder screen aperture formed

As spheronisation time increases, size distribution decreases

Question 10

Formulation requirements for extrusion-spheronisation

Answer 10

Extrusion:
- Cohesive, plastic wet mass with inherent fluidity and self-lubricating properties

Spheronisation:
- Extrudates with sufficient plasticity

Basic formulation:

• Pelletisation aid
• Drug
• filler
• Moistening liquid

Question 11

Most commonly used pelletisation aid:

Answer 11

Microcrystalline cellulose

Question 12

What are desirable properties of microcrystalline cellulose:

Answer 12

Good binding property
Good cohesiveness
Large surface area
High internal porosity

Question 13

Molecular sponge model

Answer 13

MCC absorbes water like sponge during extrusion –> cohesive and plastic wet mass –> liquid present helps it stay together and be extruded

Helps in binding and lubrication during spheronisation by increasing surface plasticity and help with rounding extrudates into pellets

Question 14

Crystallite gel model:

Answer 14

MCC particles broken down into single crystallites of colloidal size – form crystallite gel and immobilise liquid

Plasticity and lubricative properties also increased

Question 15

Function of MCC in extrusion-spheronisation

Answer 15

Extrusion:

• Form cohesive and plastic wet mass
• Help with binding ad extrusion

Spheronisation:

• increase surface plasticity
• Help round extrudates into pellets

Question 16

Types of pelletisation aids (dont memorise unless you have brain power)

Answer 16

powdered cellulose
hydroxylpropyl methylcellulose/hypromellose
hydroxyethyl cellulose
chitosan
carrageean
cross-linked polyvinyl pyrrolidone (2nd best after MCC)

Question 17

How do quality of extrudates impact quality of pellets:

Answer 17

Poorly formed extrudates fragment and build up pellets slowly
Well-formed extrudates break into short lengths and round quickly

Question 18

Why are smaller particles favoured in spheronisation:

Answer 18

smoother surfaces and narrower size distributions

Question 19

optimal amount of liquid used in spheronisation:

Answer 19

80-90% Tmax – capillary form

Question 20

How to get round pellets with narrow distribution:

Answer 20

Cohesive forces close to forces added during spheronisation

if cohesive forces< forces:
decrease spheronisation speed 
repeat extrusion step 
reduce component particle size 
Widen component particle size distribution for better packability 

if cohesive forces> forces:
Increase spheronisationn speed

Question 21

factors affecting packability of component particles in pelletisation

Answer 21

depends on particle size and size distribution of components and forces exerted during wet processing

critical in spheroid formation

Question 22

Factors for successful spheronisation process:

Answer 22

in process particle size and overall matrix cohesiveness during wet processing steps

Ability of components to pack well

Optimal balance of forces and processing conditions that promote rounding

Question 23

Impt point related to cohesivity and pelletisation (sry i cant think of a better description)

Answer 23

Cohesivity is important for pelletisation but cannot have migratable stickiness cos if binder can migrate with flud, pellet will keep growing and sizes will be variable

use immobile adhesive particles

Question 24

Types of particles related to type of pellets formed:

Answer 24

Coarse particles – loosely packed friable pellets
Small particles – well packed strong pellets
Wide size distribution of particles – well packed strong pellets

Question 25

Example of immobile adhesive particles:

Answer 25

micronised powders, MCC