BEH.462/3. 962J Molecular Principles of Biomaterials Spring 2003 Lecture 8: Physical Hydrogels Last Day Overview of biomedical applications of hydrogels Structure of covalent hydrogels Thermodynamics of hydrogel swelling Today Bonding in physical hydrogels Structure and thermodynamics of block copolymer hydrog Reading L.E. Bromberg and E.S. Ron, Temperature-responsive gels and thermogelling polymer matrices for protein and peptide delivery, Adv. Drug Deliv. Rev., 31, 197(1998) Associative forces in physical hydrogels Cross-link structure in physical hydrogels ·Drⅳ ing associative forces 1. Hydrophobic associations/Van der Waals forces i. LCST polymers, hydrophobic-hydrophilic block copolymers 2. Micellar packing 3. Hydrogen bonding(Rubner) 4. lonic bonding(later lecture) 5. crystallizing segments 6. Combinations of the above interactions o Peptide interactions(e.g. coiled coils)(1) Stability requires cooperative bonding interactions(2)(Guenet, Thermoreversible gelation of polymers and o Individual non-covalent bonds are relatively weak o Strength of covalent bond Hydrophobic association o lonic bond o Hydrogen bond in water o Cooperativity: lowered energy barrier for second and subsequent bonds after first has formed Used in biological associations Lecture 8 sical gels 1of12BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 Lecture 8 – Physical gels 1 of 12 Lecture 8: Physical Hydrogels Last Day: Overview of biomedical applications of hydrogels Structure of covalent hydrogels Thermodynamics of hydrogel swelling Today: Bonding in physical hydrogels Structure and thermodynamics of block copolymer hydrogels Reading: L.E. Bromberg and E.S. Ron, ‘Temperature-responsive gels and thermogelling polymer matrices for protein and peptide delivery,’ Adv. Drug Deliv. Rev., 31, 197 (1998) Associative forces in physical hydrogels Cross-link structure in physical hydrogels • Driving associative forces: 1. Hydrophobic associations/ Van der Waals forces i. LCST polymers, hydrophobic-hydrophilic block copolymers 2. Micellar packing 3. Hydrogen bonding (Rubner) 4. Ionic bonding (later lecture) 5. crystallizing segments 6. Combinations of the above interactions o Peptide interactions (e.g. coiled coils)(1) • Stability requires cooperative bonding interactions(2) (Guenet, Thermoreversible gelation of polymers and biopolymers) o Individual non-covalent bonds are relatively weak: o Strength of covalent bond: o Hydrophobic association: o Ionic bond: o Hydrogen bond in water: o o Cooperativity: lowered energy barrier for second and subsequent bonds after first has formed o Used in biological associations