Lecture 2 - Hydrogel Processing Flashcards
1
Q
Hydrogel
A
- Highly hydrate polymer network
- Insoluble in water
- Water content > 30%
- Swell substantially in aqueous conditions to equilibrium condition where mass fraction of water much higher than that of polymer
2
Q
Hydrogel Backbone
A
- Hydrophilic
- Poly(ethylene glycol) —> (CH2-CH2-O)n
- Polyamide-like protein
3
Q
Hydrogel Side Groups
A
- Hydrophilic
- Hydroxyl —> (-OH)
- Carboxyl —> (-COOH)
- Amide —> (-CONH2)
- Sulfonic —> (-SO3H)
4
Q
Hydrogel Polymer Chains
A
Either chemically or physically crosslinked
5
Q
Advantages of Hydrogels as Tissue Engineering Matrices
A
- Aqueous environment for cells
- Porous to allow for nutrient transport
- Easily modified
- Usually biocompatible
6
Q
Disadvantages of Hydrogels as Tissue Engineering Matrices
A
- Hard to handle
- Physically weak
- Difficult to sterilize
7
Q
Chemical Advantages of Hydrogels as Tissue Engineering Matrices
A
- Crosslinked polymer network
- Polymer chains connected by covalent bonds to form network
- Monomer + crosslinker –copolymerize–> hydrogel network
- Macromers –copolymerize or crosslink macromers–> hydrogel network
- Water soluble polymer –crosslink polymer–> hydrogel network
8
Q
Chemical Hydrogels by Polymerization
A
- Polymerization of monofunctional vinyl monomers with difunctional vinyl monomers (act as crosslinkers)
- Acrylic acid, methacrylic acid, metacrylamide, hydroxyethyl methacrylate
9
Q
Biodegradable Hydrogels
A
- Necessary for tissue engineering applications
- Biodegradable crosslinkers often introduced
- Biodegradable after introduction of degradable PLA, PGA, PLGA et al.
10
Q
Photopolymerization
A
- Polymerization under UV light
- Includes light-induced initiation (excitation of a photoinitiator or PI) and subsequent polymerization
- Biocompatible photoinitiator is needed
11
Q
Physical Hydrogel
A
- Continuous, three-dimensional networks formed by associative force capable of forming non-covalent crosslinks
- Non-covalent crosslinks formed by weaker interactions (hydrogen bond, ionic interaction, hydrophobic association) and are reversible
- Produced without chemical reaction, more suitable for cell and biomolecules encapsulation since it avoids use of toxic chemicals
12
Q
Hydrophobic Interactions
A
- Amphiphilic polymers can self-assemble by aggregation of hydrophobic moieties among each other to form hydrogel
- Mixed hydrophilic polar group (-CONH-) and hydrophobic non-polar group [-CH(CH3)2]
- When T<32C, homogenous solution
- When T>32C, polymer solution starts to dehydrate and aggregates to form hydrogels
13
Q
Ionic Interactions
A
- Hydrogel formed by ionic interaction (cationic and anionic)
- Ex: Alginate. Alginates contain carboxylic groups, undergo reversible gelation in aqueous solution through interaction with divalent-cations such as Ca2+. Cations bind between G-blocks of adjacent alginate chains creating ionic inter-chain bridges. Forms three-dimensional network of alginate fibers (hydrogel)
14
Q
Hydrogen Bond Interactions
A
- Occur between proton donor (carboxyl -COOH and hydroxy -OH) groups and proton acceptor (O, N) groups. Polymers bearing these groups may form gels due to hydrogen bonds
15
Q
Collagen Gel
A
- Collagen dissolved in acid solution and then neutralized, becomes insoluble gel (not water soluble). This allows to incorporate cells and biomolecules in collagen gel.
