BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 Lecture 7: Hydrogel Biomaterials: Structure and Physical Chemistry Last Day: programmed/regulated/multifactor controlled release for drug delivery and tissue engineering Today: Applications of hydrogels in bioengineering Covalent hydrogels Physical hydrogels Synthesis of hydrogel biomaterials Synthesis of hydrogel biomaterials Physical gels Formation: Aq soln Associating hydrophobic groups synthesis in organic solvent readily assembled in situ Synthesis of pluronics? Anionic polymerization? Formation of ionic gels: coacervates, nanoparticles LCST polymer gelation: ?T Associating hydrophobic groups Thermodynamics of LCST Lecture 7 – Hydrogels 1 1 of 2 BEH.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