BEH.462/3. 962J Molecular Principles of Biomaterials Spring 2003 Chemical structure of biodegradable hydrogels Mechanism A (non-degradable water-soluble polymers with degradable cross-links) Degradable cross-links o e.g. dextran hydrogels bacterial exo-polysaccharide branched polymer composed of a-1, 6-linked D-glucopyranose residues with a low of a-1, 2 and 1, 3 side chains Dextran with polylactide crosslinks: hydrolyzable crosslinks Figure 1, The chemical dextran dextran can be functionalized with methacrylate and then crosslinked in the presence of a small amount of vinyl monomer 2 EMA. I Lacto.2 o'o m Rootor .C EMA-lactvedl. s Figure 8. Reaction scheme for the synthesis of dex-lactateHEMA Figure 3. Schematic representation of the formation of dextran hydrogels degradable gels show first swelling then dissolution as cross-links are hydrolyzed Time(days) Figure 12. Swelling behavior of dex HEMA(O), dex-lactate-HEMA()and dex- lactate- hydrogels was 80%, the degree of methacryloyl substitution was approximate/y6 ent of the HEMA(▲) hydrogels queous solution (pH 7.2, 37C). The initial Lecture 7-Hydrogels 1 10of15BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 Chemical structure of biodegradable hydrogels Mechanism I: (non-degradable water-soluble polymers with degradable cross-links) • Degradable cross-links o e.g. dextran hydrogels9 • bacterial exo-polysaccharide • branched polymer composed of α-1,6-linked D-glucopyranose residues with a low % of α-1,2 and 1,3 side chainsDextran with polylactide crosslinks: hydrolyzable crosslinks9 • dextran can be functionalized with methacrylate and then crosslinked in the presence of a small amount of vinyl monomer: d degradable gels show first swelling then dissolution as cross-links are hydrolyzed: Lecture 7 – Hydrogels 1 10 of 15