Stimuli-responsive polymer brushes for on-chip cell adhesion control

Abstract : The aim of the current Ph.D thesis was to design stimuli responsive polymer brushes in order to dynamic control cell-substrate adhesive interactions.For this purpose, Atom Transfer Radical Polymerization (ATRP) and Activators Regenerated by electron Transfer (ARGET)-ATRP were used in order to prepare thermo responsive Poly(N-isopropylacrylamide) (PNIPAM) brushes. Both the methods were applied under varying surface densities and polymerization times, and the kinetics of the brush growth using both the protocols was investigated. A well controlled chain growth was reported under ARGET-ATRP protocol, in contrast to the ATRP method. The above tested protocol was used to grow PNIPAM brushes that were patterned via deep UV photoablation strategy to design thermoresponsive patterned substrates for protein adsorption studies.The substrates showed excellent adhesive properties and reusability with long term storage capacity.The conformational changes of PNIPAM brushes, grown via the ARGET-ATRP protocol, were investigated using an original set-up based on Reflection Interference Contrast Microscopy (RICM). RICM allowed us to probe the optical response of the brushes as a function of their density profile, making it an interesting tool for brush characterization. The response of the brush was studied as a function of brush grafting density and chain length. The results provided a unique evidence for non-uniform structural changes within the brush thickness when the solvent temperature was varied across the Lower Critical Solution Temperature (LCST) of the polymer. RICM was employed to achieve the challenging task of estimating the molecular parameters of the brush and understanding the physical origin of the phenomenon of thermal hysteresis in a polymer brush.Stimuli Responsive Polymers, sensitive to non-invasive stimuli, were synthesized with an aim to address dynamic single cell adhesion studies at their physiological conditions. Free Radical Polymerization and ARGET-ATRP protocol were used to design two photo-thermo-responsive poly(DMA-AZAA) and poly(DMA-NIPAM-AZAAm) polymers. The conformational changes of the designed polymers were investigated at length by varying the overall composition of monomers in the system. The solutions of the DMA-NIPAM-AZAAm terpolymer showed a sharp phase separation at 37°C that could be reversibly switched under light irradiation, making it compatible for cell adhesion studies.
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Siddhartha Varma. Stimuli-responsive polymer brushes for on-chip cell adhesion control. Biological Physics [physics.bio-ph]. Université Grenoble Alpes, 2016. English. ⟨NNT : 2016GREAY057⟩. ⟨tel-01588155⟩

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