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Well-defined Thermoresponsive Polymers as Injectable Gels. Dr Theoni K. Georgiou Department of Materials, ICL. Group Transfer Polymerisation. + Living polymerisation technique control of the polymer’s molecular weight, composition and architecture
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Well-defined Thermoresponsive Polymers as Injectable Gels Dr Theoni K. Georgiou Department of Materials, ICL
Group Transfer Polymerisation + Living polymerisation technique control of the polymer’s molecular weight, composition and architecture + Easy, Fast, Cost effective (RT and higher concentration) + Developed by DuPont to produce specialised polymers • - Can only use methacrylate and • acrylate monomers with R • not being an acid or alcohol group • Limitation: degree of polymerisation < 200 (depending on monomer) Webster, O. W. et al J. Am. Chem. Soc. 1983, 105, 5706-5708. Webster, O.W. Science 1991, 251, 887-893. Webster, O. W. Adv. Polym. Sci. 2004, 167, 1-34.
GTP: Choice of Monomers Hydrophobic Hydrophilic (some depending on the pH or the T) Make your own monomers! Methacryloyl chloride + R-OH
Well-Defined Polymers Polymers of narrow size distribution with defined composition and architecture Vary the composition Vary the length Vary the architecture Structure/Activity Relationships Vary the polymer’s structure
Injectable Gels Thermoresponsive Gels for Tissue Engineering 37C at body temperature the polymer will form a gel room temperature: polymer + cells in culture medium the polymer/cell mixture will be injected into a wound
Sol-Gel Thermo-transition elastic modulus (G’) viscous modulus (G’’) complex viscosity Sol – Gel Transition G’, G’’, Viscosity Temperature
Thermoresponsive Triblock Copolymers • Polymers of different molecular weights, architectures and compositions ABC triblock ABA triblock BAC triblock ACB triblock Random terpolymer
Synthesis of Triblock Copolymers THF TBABB (catalyst) MTS (initiator) PEGMA BuMA BuMA • All polymers have a molecular weight distributions, dispersity Mw/Mn < 1.19. • During polymerisation the dispersity decreased by increasing the MW as expected for a living polymerisation method. • Aqueous properties, self-assembly, micelle size is affected by the molecular weight, the architecture as well as the composition of the polymer.
20 wt% BuMA 30 wt% BuMA 40 wt% BMA Effect of MW and Composition 15000 g/mol 10000g/mol 50000g/mol Ward, M. A.; Georgiou, T. K. Soft Matter2012, 8, 2727-2745.
Effect of Architecture cmc ? ABC ACB BAC ? cmc ? multicompartment hydrogel cmc Non-ionic hydrophilic Non-ionic hydrophobic Hydrophilic, pH- and thermo-responsive
Effect of Architecture and Alkyl Side Group • The ABC is the “best” architecture – best sol-gel transition • Increasing the length of the side alkyl group lowers the gel point. • The gel stability is decreased with increasing the length of the side alkyl group. Ward, M. A.;Georgiou, T. K. Polym. Chem. 2013, 4(6), 1893-1902.
Does Asymmetry Matter? • Gels point decreases when: • The hydrophobic content increases • The triblock copolymers is more symmetric i.e. when the hydrophobic block ratio approaches one. Ward, M. A.; Georgiou, T. K. J. Polym. Sci., Part A: Polym. Chem.2013, 51(13), 2850–2859.
Summary of Main Results Aim: Fabrication of thermo-responsive triblock polymers and investigation of how the different characteristics of the polymer affect the thermoresponsive behaviour. 7000 g mol-1 30-35 wt% ↑ length ↓ gel point & stability T-response T-response T-response composition wt% hydrophobic architecture length of hydrophobic side group T-response Ward, M. A.; Georgiou, T. K. J. Polym. Sci.: Part A: Polym. Chem.2010, 48, 775-783. Ward, M. A.; Georgiou, T. K. Soft Matter2012, 8, 2727-2745. Ward, M. A.; Georgiou, T. K. Polym. Chem.2013, 4(6), 1893-1902. Ward, M. A.; Georgiou, T. K. J. Polym. Sci., Part A: Polym. Chem.2013, 51(13), 2850–2859. molecular weight
Current Investigations • Studying how the PEG side group can affect the thermoresponsive properties. Increase the side group the gelation point. • Studying how the number of blocks can affect the physical chemical properties and the thermoresponsive properties. • Investigating if these gels can be used in 3-D printing (both pH and temperature can trigger the gel formation)
Acknowledgments • Funding: • University of Hull • Engineering and Physical Science Research Council (EPSRC) • Royal Society (RS) • Department of Materials, Imperial College London • Students: • Mr Mark Ward • Miss Anna Constantinou Thank you