BEH.462/3. 962J Molecular Principles of Biomaterials Spring 2003 Covalent gels Formation: simultaneous with polymerization Approaches Free radical polymerization -+M+M+M→|+M+M+M→|-M'+M+M→|-M-M"+M Thermal initiation: Ammonium persulfate(APS) Catalyzed initiation Mechanism of APS sodium metabisulfite/ TEMED polymerization allows polymerization at room temperature or 37 C ( not a thermal initiation mechanism) Photo polymerization Mechanism Acetophenone initiation 1→"→|M→LM-M'etc. can be used in situ/in vivo during surgery DEMOS: examples of rapidity of gelation in class: APS TEMED and photopolymerization Advantages: rapid polymerization does not require organic solvents Limitations: degree of conversion typically limited Enzymatic polymerization Sperinde work with transglutaminase Hubbell work with fibrin-based hydrogels Kinetics of gelation ntn→口 conversion Lecture 7-Hydrogels 1 20f2BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 Covalent gels Formation: simultaneous with polymerization Approaches: Free radical polymerization I-I + M + M + M → I’ + M + M + M → I-M’ + M + M → I-M-M’ + M Thermal initiation: Ammonium persulfate (APS) Catalyzed initiation: Mechanism of APS + sodium metabisulfite/TEMED polymerization allows polymerization at room temperature or 37°C (not a thermal initiation mechanism) Photo polymerization Mechanism Acetophenone initiation I → I’ → I-M’ → I-M-M’ etc. can be used in situ/in vivo during surgery DEMOS: examples of rapidity of gelation in class: APS + TEMED and photopolymerization Advantages: rapid polymerization does not require organic solvents Limitations: degree of conversion typically limited Enzymatic polymerization Sperinde work with transglutaminase Hubbell work with fibrin-based hydrogels Kinetics of gelation gel point η ⇒ � η % conversion t Lecture 7 – Hydrogels 1 2 of 2