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Stage 3 Case 3 > Gels > Flashcards

Gels Flashcards

1
Q

What is a gel?

A

Non-fluid colloidal network or polymer network that is expanded throughout its whole volume by a fluid.

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2
Q

Characteristic of gel

A

Ability to develop a rigid molecular network (i.e. undergo sol-gel transition) and swell when solvated.

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3
Q

Why do gels swell?

A

Swelling is due to solvent infiltration into the molecular network, thus unfolding and expanding the molecular network.

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4
Q

How is swelling of gels constrained?

A

Constrained by intermolecular interactions or cross-links within the molecular network, which confers structural rigidity.

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5
Q

How does the rigidity of gels arise?

A

A network of colloidal particles or polymer chains.

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6
Q

What does it mean by Gels are viscoelastic semi-solids?

A

They behave partly like a viscous liquid, partly like an elastic solid.

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7
Q

What are gels semi-solid state described as?

A

Viscoelastic

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8
Q

What are the two types of gel?

A

Chemical (type I) and Physical (type II)

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9
Q

What is the polymer network of type I (chemical) gels?

A

Irreversible polymer network

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10
Q

Why is type I (chemical) gels Irreversible sol-gel transition?

A

Due to Covalently cross-linked that are not easily broken.

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11
Q

What is the polymer network of type II (physical) gels?

A

Reversible polymer network

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12
Q

Why is type II (physical) gels reversible sol-gel transition?

A

The network structure is formed from weak intermolecular bonds and are not permanent.

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13
Q

What is the molecular bonds of type I (chemical) gels?

A

Covalently cross-linked

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14
Q

What is an example of type I (chemical) gels?

A

Polyacrylamide gel

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15
Q

What is the molecular bonds of type II (physical) gels?

A

Weak intermolecular bonds (e.g. H-bonds).

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16
Q

What is an example of type II (physical) gels?

A

Agarose gel

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17
Q

How do type II (physical) gels undergo sol-gel transition?

A

In response to specific stimulus (e.g. heat, pH)

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18
Q

Fluid phase of gel type: Hydrogel

A

Water

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19
Q

Fluid phase of gel type: Alcogel

A

Alcohol

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20
Q

Fluid phase of gel type: Organogel

A

Organic solvent

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21
Q

Fluid phase of gel type: Oleogel

A

Oil

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22
Q

Fluid phase of gel type: Xerogel

A

None (xero = dry)

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23
Q

Fluid phase of gel type: Aerogel

A

Air

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24
Q

Fluid phase of gel type: Cyrogel

A

Produced though freezing (cyro = cold)

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25
Q

Fluid phase of gel type: Hydroalcoholic

A

Water and Alcohol

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26
Q

Gel type with fluid phase: Water and Alcohol

A

Hydroalcoholic

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27
Q

Gel type with fluid phase: Water

A

Hydrogel

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28
Q

Gel type with fluid phase: Alcohol

A

Alcogel

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29
Q

Gel type with fluid phase: Organic solvent

A

Organogel

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30
Q

Gel type with fluid phase: Oil

A

Oleogel

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31
Q

Gel type with fluid phase: None

A

Xerogel

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32
Q

Gel type with fluid phase: Air

A

Aerogel

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33
Q

Gel type with fluid phase: Produced though freezing

A

Cyrogel

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34
Q

What is pharmaceutical gel?

A

Drug entrapped in gel matrix.

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35
Q

What is the administration for a pharmaceutical gel?

A

Topical or parental

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36
Q

5 indications for pharmaceutical gel?

A

Analgesic

Anti-inflammatory

Anti-bacterial

Anti-fungal

Local anaesthetics

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37
Q

Analgesic Gel example

A

Ibuprofen

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38
Q

Anti-inflammatory Gel example

A

Diclofenac

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39
Q

Anti-bacterial Gel example

A

Clindamycin

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40
Q

Anti-fungal Gel example

A

Miconazole

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41
Q

Local anaesthetics Gel example

A

Lidocaine

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42
Q

Ibuprofen gel indication

A

Analgesic

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43
Q

Diclofenac gel indication

A

Anti-inflammatory

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44
Q

Clindamycin gel indication

A

Anti-bacterial

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45
Q

Miconazole gel indication

A

Anti-fungal

46
Q

Lidocaine gel indication

A

Local anaesthetics

47
Q

Dose form retention of gels

A

The semi-solid structure of the gel makes more likely to be retained at the sight of administration for longer compare to a liquid dosage form.

48
Q

Environmentally sensitive gels

A

Conditional drug release triggered by changes in environmental conditions, e.g. pH, temperature.

49
Q

In-situ gelling systems

A
  • Controlled release: administer in liquid form, drug release in semi-solid form.
  • In-situ gelling can be triggered by physiological environment, e.g. body heat.
50
Q

3 basic components of a gel

A

Drug

Solvent

Gelling agent

51
Q

Purpose of solvent in gel

A

Dissolves drug and excipients, usually aqueous.

52
Q

Purpose of gelling agent in gel

A

Forms molecular network, provides structural rigidity, entraps drug.

53
Q

4 other things a gel may contain?

A

Cosolvent

pH regulator (buffer)

Preservative

Penetration enhancer

54
Q

An example of a cosolvent used in gels

A

Alcohol

55
Q

Purpose of cosolvent in gel

A

Enhance drug solubility

56
Q

Purpose of pH regulator in gel

A

Enhance solubility of ionisable drugs, avoid skin irritation

57
Q

Purpose of preservative in gel

A

Inhibit microbial growth in aqueous gels

58
Q

Purpose of penetration enhancer in gel

A

Enhance drug absorption into skin

59
Q

What usually doubles as a co-solvent and penetration enhancer?

A

Ethanol

60
Q

What is Ibuprofen gel used for?

A

Relief of pain and inflammation associated with backache, rheumatic pain, muscular aches, pains or swellings such as sprains, strains and sports injuries.

61
Q

Hydroxyethyl cellulose purpose in ibuprofen gel

A

Gelling agent

62
Q

Sodium hydroxide purpose in ibuprofen gel

A

pH regulator

63
Q

Benzyl alcohol purpose in ibuprofen gel

A

Antimicrobial preservative

64
Q

Isopropyl alcohol purpose in ibuprofen gel

A

Cosolvent and penetration enhancer

65
Q

Purified water purpose in ibuprofen gel

A

Fluid component (Exists as a mixture containing other excipients)

66
Q

What is the sol-gel transition?

A

The transition of sol to a gel. Gels are formed from sols.

67
Q

State of sol

A

Liquid

68
Q

State of gel

A

Solid like/semi-solid

69
Q

2 properties of sol state

A
  • Colloidal dispersion (two or more components) of freely diffusing gelling agent.
  • Not a solution (single component).
70
Q

3 properties of gel state

A
  • Molecules of gelling agent interact covalently or non-covalently, polymer network develops
  • Constrained by intermolecular bonds, physical entanglement or cross-links.
  • Gelling agent not freely diffusing.
71
Q

What is the advantage of the sol state?

A

Work with liquids, measure, mix, and dissolve things evenly.

So prepare then allow it to gel.

72
Q

When does sol-gel transition happen?

A

Gel-point, but actually happened gradually over time.

73
Q

What is the gel point?

A

Point of incipient polymer network formation

74
Q

What does the gel point depend on?

A

The chemical composition of the gel formation

75
Q

Examples of chemical composition that impact the gel point (5)

A

– Molecular weight of gelling agent.

– Concentration of gelling agent.

– Concentration of other chemicals (drug, excipients).

– Ionic nature of ingredients.

– H-bonding capacity of ingredients.

76
Q

What is required for gelation occur?

A

A minimum concentration of gelling agent is required for gelation—this varies depending on the gelling agent used.

77
Q

What is the typical gelling agent used in hydrogels?

A

Polymers that can H-bond with water.

78
Q

Natural polymers

A

Cellulose

Gums (e.g. xanthan, tragacanth, carrageenan)

79
Q

Semi-synthetic polymers

A

Cellulose derivatives, e.g. methyl cellulose (MC), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), hydroxypropyl methyl cellulose (HPMC)

80
Q

Synthetic polymers

A

Carbomers (Carbopol)

Poloxamers (Pluronic)

81
Q

What are Cellulosics?

A

Cellulose polymer and its derivative

82
Q

How were cellulose derivatives formed?

A

Side chain altered to tweak polarity. They were substituted with a range of alkyl chains.

83
Q

What give different physical properties to cellulosics?

A

Different molecular weights and degrees of substitution

84
Q

What is the property of high molecular weight gels?

A

Viscous gels as they can from more extensive networks.

85
Q

What is the property of low molecular weight gels?

A

Good film-forming properties. Not as effective as forming gelling agents as they can’t form as extensive networks.

86
Q

Which cellulosics is anionic?

A

CMC

87
Q

Why is CMC anionic?

A

The COO group (carboxylate)

88
Q

When can CMC not be used in a formulation?

A

Drugs that can be ionised under the conditions that exist withing the formulation.

89
Q

What are carbomers?

A

Cross-linked polyacrylic acid polymers.

90
Q

How can gel viscosity and swelling capacity be enhanced when using carbomers?

A

By neutralisation with a base (e.g. triethanolamine) or by adding hydroxyl donors (e.g. polyols, sugar alcohols) to promote hydrogen bonding.

91
Q

Dry carbomers

A

Coiled tightly, not a gel

92
Q

Hydrated carbomers

A

ionise (—COO−) and uncoil somewhat due to

electrostatic repulsion between charged groups—low viscosity gel.

93
Q

Properties of carbomers

A

Anionic and acidic

94
Q

What is GelTears eye gel?

A

Substitution of tear fluid in the management of dry eye conditions.

95
Q

Carbomer 980 (0.2% w/w) purpose in GelTears eye gel

A

Gelling agent and Active ingredient

96
Q

How does Carbomer 980 (0.2% w/w) act as the active ingredient in GelTears eye gel?

A

Responsible for trapping moisture in the eye

97
Q

Benzalkonium chloride purpose in GelTears eye gel

A

Antimicrobial preservative

98
Q

Water for injection purpose in GelTears eye gel

A

Fluid component and solvent

99
Q

Sorbitol purpose in GelTears eye gel

A

Hydroxyl donor which promotes gel swelling

100
Q

Sodium hydroxide purpose in GelTears eye gel

A

Acidity regulator so the gel does not irritate the eye

101
Q

What usually happens when the gelling concertation is increased?

A

The more rigid the gel

102
Q

What is a property of a more rigid the gel?

A

The slower the drug release

103
Q

Sol-gel transition temperature of poloxamers depends on…

A

Chemical composition of the gel formulation

104
Q

What Chemical compositions of the gel formulation does the sol-gel transitions depend on? (poloxamers)

A

Poloxamer grade and concentration.

Solvent, drug and excipients.

105
Q

How can temperature dependence sol-gel transitions help with drug release profile?

A

The drug release is slowed down when the drug release is close to body temperature, extending its release. (i.e. in gel form)

106
Q

Poloxamers

A

Triblock copolymers of polyethylene oxide(PEO) and polypropylene oxide (PPO).

107
Q

PEO (hydrophilic)

A

homopolymer of ethylene oxide.

108
Q

PPO (hydrophobic):

A

homopolymer of propylene oxide.

109
Q

Poloxamers properties

A

Non-ionic, soluble in water, polar and non-polar solvents.

110
Q

Poloxamer and thermoreversible.

A

Form thermoreversible gels at 15–50% w/w (depending on specific grades) that are liquid at room temperature, and gel at room/body temperature.

111
Q

Different physical properties of poloxamer are formed from?

A
  • Different polymer chain lengths (average molecular weight).
  • Different ratios of ethylene oxide to propylene oxide.

Stage 3 Case 3 (8 decks)

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