PH2107 - Emulsions 1

Question 1

What is an emulsion?

Answer 1

A dispersed system comprised of two or more immiscible liquids

• oily
• aqueous

Question 2

What are the two phases that make up an emulsion?

Answer 2

Disperse phase

Continuous phase

Question 3

What state are emulsions in?

Answer 3

Emulsions may be semi solids or liquids

Question 4

What determines the state of an emulsion?

Answer 4

The oil and water proportions

Route of administration

Question 5

How is an emulsion formed?

Answer 5

High energy input needed as they are thermodynamically incompatible

Question 6

Why are emulsions thermodynamically unstable ?

Answer 6

Globules tend to:
adopt a spherical shape, due to surface tension
coalesce, merge with other globules – without an emulsifier

Question 7

What can be added to an emulsion to increase kinetic stability?

Answer 7

An emulsifier (emulgent)

Question 8

What is the general size of an emulsion ?

Answer 8

Emulsions can have broad droplet sizes not always nano, often micro range, but generally a mean diameter of ~1µm

Mini-emulsions and nano-emulsions can be formed with droplet sizes in the 100-500 nm range.

Question 9

What are microemulsions typically used for?

Answer 9

To kill microbes (bacteria, viruses), blood and sperm

Question 10

How much force is needed to make a microemulsion?

Answer 10

The smaller the droplet, the greater the surface tension and thus the greater the force to merge with other lipids

Question 11

How is a microemulsion made?

Answer 11

The oil is emulsified with a high shear mixer with detergents to stabilise the emulsion, so when they encounter lipids in the membrane or envelope of bacteria/viruses, they force the lipids to merge with themselves, disintegrating pathogen membrane

Question 12

What is a vesicle?

Answer 12

A supramolecular assembly of lipid molecules in an aqueous environment

Question 13

What is a bilayer?

Answer 13

A fundamental structural feature of a biological membrane

Question 14

What is a micelle?

Answer 14

A spherical aggregate, ~150nm of surfactant molecules dispersed in a liquid colloid

Question 15

What is a normal phase micelle?

Answer 15

A micelle with the headgroups facing away from the centre (oil-in-water micelle)

Question 16

What is an inverse micelle?

Answer 16

A micelle with the headgroups at the centre with the tails extending out (water-in-oil micelle)

Question 17

What are the two types of emulsions?

Answer 17

Oil in water (o/w)

Water in oil (w/o)

Question 18

What is a multiple layer emulsion?

Answer 18

Multiple emulsions - concentric multi-layer structures

Question 19

Give some uses for multiple layer emulsions

Answer 19

• carrier systems for protein or peptide drugs e.g. insulin
• to encapsulate drugs to protect them from physiological environment
• controlled release drug delivery e.g. synthesis of PLGA nanoparticles

Question 20

What is the ‘double emulsion technique’?

Answer 20

Encapsulation of hydrophilic or lipophilic molecules in polymeric nanoparticles

Question 21

What are the advantages of using emulsions for oral use?

Answer 21

• convenient way of giving water insoluble drugs (o/w)
• mask unpleasant tasting drugs (only taste continuous phase)
• some oil soluble compounds have increased absorption from GI tract when emulsified than when given as an oily oral solution

Question 22

What are the advantages of using emulsions for parenteral use?

Answer 22

• some parenteral formulations work better/faster as an emulsion than as an oil
• w/o injections given intra-muscularly (IM) can act as depots (slow drug release)

Question 23

What is TPN?

Answer 23

Total parenteral nutrition - a method of feeding that bypasses the gastrointestinal tract
- fluids are given into a vein to provide most of the nutrients the body needs

Question 24

What are used to supply total nutrition or specific components e.g. lipids in IV nutrition?

Answer 24

o/w systems

Question 25

What are the advantages of using emulsions for ocular use?

Answer 25

Eye is sensitive - emulsions have a more pleasant feel

Question 26

Give an example of an emulsion used to treat dry eye

Answer 26

Cationorm - o/w emulsion formulation to treat dry eye. It restores moisture (moisturises) from water + electrolytes but also helps to prevent fluid loss or evaporation (oil)
- oil phase also helps lubricate movements

Question 27

What is a common form of drug delivery?

Answer 27

Topical delivery

• skin
• mucous membranes
• gingiva
• rectum
• vagina

Question 28

What are creams?

Answer 28

Emulsions, as semi-solid (high viscosity) preparations of oil and water

Question 29

Give two examples of unmedicated creams that are used in a variety of skin conditions (dermatoses)

Answer 29

Emollients

Humectants

Question 30

What is an emollient?

Answer 30

Cosmetic preparations used for protecting, moisturising and lubricating the skin (barrier)

Question 31

What is a humectant?

Answer 31

Have an emollient effect but they act by drawing water or urea into stratum corneum

Question 32

What is a medicated emulsion?

Answer 32

Facilitate drug uptake

- oil absorbed into skin along with the drug

Question 33

What are the properties of o/w emulsions?

Answer 33

• absorbs water
• used for local effects
• washable
• non-greasy

Question 34

What are the properties of w/o emulsions?

Answer 34

• occlusive
• water repellant
• decreases water loss from skin
• enhances drug penetration
• feels greasy

Question 35

How can you determine the emulsion type?

Answer 35

Feel
- emulsions feel like the continuous phase (water or oil)
Miscibility
- o/w emulsion should dilute readily upon adding more water
Staining
- water soluble dye (e.g. food colourant) will colour o/w emulsion
Conductivity
- o/w conducts electricity
- w/o does not conduct electricity

Question 36

Why are emulsifiers essential in keeping the oil dispersed throughout the water phase?

Answer 36

Emulsions are thermodynamically unstable

Question 37

What happens when an emulsifier is added to a mixture of water and oil?

Answer 37

Polar groups associate with water molecules while non-polar parts enter the oil phase

Question 38

Where is an emulsifier located in an emulsion?The globule/continuous phase interface

Answer 38

The globule/continuous phase interface

Question 39

What factors determine the effectiveness of an emulsifier?

Answer 39

Balance between its hydrophilic and lipophilic characteristics relative to oil and water phases

Question 40

What are the five processes that determine how effective an emulsifier is?

Answer 40

1. Emulsifiers form a flexible interfacial film (physical barrier) to help prevent coalescence when globules come into contact
2. Emulsifiers provide a surface charge to globules, causing electrostatic repulsion with adjacent molecules
3. Emulsifiers reduce interfacial tension
4. Emulsifiers prevent globules coming into close contact by steric hindrance of hydrated side chains
5. Increased continuous phase viscosity slows globule movement and decreases likelihood of collision and coalescence (semi-solids = cream)

Question 41

Describe the barrier around the oil globules in o/w emulsions

Answer 41

Either due to

• electrical (polar)
• steric repulsion (non-polar) effects

Question 42

What causes repulsion between water droplets in w/o emulsions?

Answer 42

Non-polar effects from the hydrocarbon part of interfacial film

Question 43

Which groups are better barriers to coalescence in a barrier?

Answer 43

Polar groups compared to non-polar groups

Question 44

Which type of emulsions are generally more stable?

Answer 44

o/w are generally more stable than w/o