Lecture 20: Gels Flashcards
(52 cards)
What is a gel?
- Non-fluid colloidal network or polymer network that is expanded throughout its whole volume by fluid
What is the characteristic of gel?
- Ability to develop a rigid molecular network
- Undergo sol-gel transition and swell when solvated
Why do gels swell and what is it constrained by?
- Due to solvent infiltration into the molecular network, thus unfolding and expanding its molecular network
- This is constrained by intermolecular interactions or cross links within the molecular network - structural rigidity
How does the rigidity of gels arise?
- A network of colloidal particles or polymer chains
What does it mean by gels are viscoelastic semi solids?
- Behave partly like a viscous liquid
- Partly like an elastic solid
- Halfway between liquid and solid
What are the 2 types of gels?
- Chemical (Type 1)
- Physical (Type 2)
What is the polymer network of type 1 (chemical) gels like?
- Irreversible polymer network
- Covalent bonds are very strong and not easily broken
What is the polymer network of type 2 (physical) gels?
- Reversible polymer network
- Start as liquid then semi-solid than liquefy again
- Electrostatic or H-bonding (weak intermolecular bonds & not permanent)
What is an example of type 1 (chemical) gel and type 2 (physical) gel?
- Polyacrylamide gel
- Agarose gel
How do type 2 (physical) gels undergo sol-gel transition?
- In response to stimulus e.g. heat, pH
What is the fluid phase of gel type: hydrogel, alcogel and organogel and hydroalcoholic?
- Water
- Alcohol
- Organic solvent
- Water and alcohol
What is the fluid phase of gel type: oleogel, Xerogel, Aerogel, cryogel?
- Oil
- None (xero = dry)
- Air
- Produced through freezing (cryo = cold)
What is a pharmaceutical gel and its administration?
- Drug entrapped in gel matrix
- Topical or parental
What are 5 indications for pharmaceutical gel and an example?
- Analgesic (ibuprofen)
- Anti-inflammatory (diclofenac)
- Anti-bacterial (Clindamycin)
- Antifungal (Miconazole)
- Local anasthetics (lidocaine)
What is dose form retention of gels?
- The semi-solid structure of the gel makes more likely to be retained at the site of admin for longer than liquid dosage
What are environmentally sensitive gels?
- Conditional drug release triggered by changes in environmental conditions e.g pH temperature
What are in situ gelling systems?
- 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
What are the 3 basic components of a gel and what is the purpose of the solvent and gelling agent?
- Drug
- solvent: dissolves drug and excipients, usually aqueous
- Gelling agent: forms molecular network, provides structural rigidity, entraps drug
What are 4 other things a gel may contain and what are the purposes of each?
- Co-solvent: enhance drug solubility
- pH regulator (buffer): enhance solubility of ionisable drugs, avoid skin irritation
- Preservative: inhibit microbial growth in aqueous gels (important for multiple use)
- Penetration enhancer: enhance drug absorption into skin
What is an example of a co-solvent used in gels?
- Alcohol
What usually doubles as a co-solvent and penetration enhancer?
- Ethanol
What is Ibuprofen gel used for?
- Relief of pain and inflammation with backache, rhematic pain, muscular ache
- Or pain/swelling from sprains and injuries
What is the purpose of hydroxyethyl cellulose in ibuprofen gel?
- Gelling agent
- It is a polymer and only polymer
What is the purpose of the sodium hydroxide, benzyl alcohol, isopropyl alcohol and purified water in the ibuprofen gel?
- pH regulator
- Antimicrobial preservative
- Cosolvent and penetration enhancer
- Solvent