Elastic Properties of Protein Functionalized Nanoporous Polymer Films

Surface-Initiated Photoinduced Iron-Catalyzed Atom Transfer Radical Polymerization with ppm Concentration of FeBr3 under Visible Light

Reversible deactivation radical polymerizations with reduced amount of organometallic catalyst are currently a field of interest of many applications. One of the very promising techniques is photoinduced atom transfer radical polymerization (photo-ATRP) that is mainly studied for copper catalysts in the solution. Recently, advantageous iron-catalyzed photo-ATRP (photo-Fe-ATRP) compatible with high demanding biological applications was presented. In response to that, we developed surface-initiated photo-Fe-ATRP (SI-photo-Fe-ATRP) that was used for facile synthesis of poly(methyl methacrylate) brushes with the presence of only 200 ppm of FeBr3/tetrabutylammonium bromide catalyst (FeBr3/TBABr) under visible light irradiation (wavelength: 450 nm). The kinetics of both SI-photo-Fe-ATRP and photo-Fe-ATRP in solution were compared and followed by 1H NMR, atomic force microscopy (AFM) and gel permeation chromatography (GPC). Brush grafting densities were determined using two methodologies. The influence of the sacrificial initiator on the kinetics of brush growth was studied. It was found that SI-photo-Fe-ATRP could be effectively controlled even without any sacrificial initiators thanks to in situ production of ATRP initiator in solution as a result of reaction between the monomer and Br radicals generated in photoreduction of FeBr3/TBABr. The optimized and simplified reaction setup allowed synthesis of very thick (up to 110 nm) PMMA brushes at room temperature, under visible light with only 200 ppm of iron-based catalyst. The same reaction conditions, but with the presence of sacrificial initiator, enabled formation of much thinner layers (18 nm).

Examining lysozyme structures on polyzwitterionic brush surfaces

Conformational structures of lysozyme at the interfaces of hydrophilic polymer poly[2-(methacryloyloxy)ethyl dimethyl-(3-sulfopropyl)ammonium hydroxide] (PMEDSAH), are examined to understand the role of protein-polymer interactions on the stability of lysozyme. This work underpins the effect of hydration layer on the structures of physically adsorbed lysozyme on PMEDSAH brushes. Hydrophilic nature and strength of hydration layers around brushes are controlled by varying the brush thickness and temperature. We measured that lysozyme is structurally less stable on 15nm thick hydrophilic PMEDSAH brushes at 75°C than at room temperature. To the contrary, 5-8nm thick brushes stretch in hydrated state by heating, hence yield higher structural stability of lysozyme. These results suggest that short polyzwitterionic brushes can facilitate improved biomaterial interactions that are essential for biosensors performing at elevated temperatures.

Confinement effect on the structure and elasticity of proteins interfacing polymers

The ordered nanostructured surfaces provide confined environments that allow functionalization of proteins. Here, we used the nanopores of poly(methyl methacrylate) films to attach fibrinogen and lysozyme, and discussed the changes in proteins' structures and elasticity upon confinement. Fourier-transform infrared spectroscopic analysis of protein secondary structures reveals that fibrinogen undergoes less structural change and behaves less stiff when the pore size is close to the protein size. Lysozyme, on the other hand, retains its native-like structure, however, it exhibits the highest modulus in 15 nm pores due to the lower macromolecular crowding effect the protein faces compared to lysozyme within larger pores. These findings manifest the effect of confinement and crowding on the conformation and elasticity of different shaped proteins tethered on surfaces.