Functional surfaces through biomimetic block copolymer membranes

Abstract

Fundamental scientific research was always interested by the concept of mimicking Nature because of the presence of remarkable designs. In particular, due to their importance in numerous cellular processes, biological membranes got great interest in biochemical and biophysical research. It is crucial to understand the membrane morphology, the role of individual membrane components, and also to correlate the membrane structure to its various functions. In addition to contributing to fundamental understanding, membranes are also highly attractive for industrial research and technological development. However, the complexity and fragility of natural membranes often limit their direct use. For that reason, the development of membrane models is indispensable. Suitable building blocks for model systems could be lipids or amphiphilic polymers. The versatility of polymer chemistry allows the fine-tuning of biomimetic membranes in solution and on solid supports. Methacrylate-based amphiphilic triblock copolymers poly (2-hydroxyethyl methacrylate)-b-poly (butyl methacrylate)-b-poly (2-hydroxyethyl methacrylate) PHEMA-b-PBMA-b-PHEMA were designed in solution and on gold surfaces. By varying the hydrophilic to hydrophobic ratio as well as the chain length, the polymers self-assembled into nanoparticles and micelles in solution. The micelles were used to encapsulate and release hydrophobic model payloads, showing their potential use as intracellular drug delivery systems. Also, artificial planar membranes as mimics of natural membranes were synthesized directly from gold surfaces. Upon the variations in thickness and packing density, potential incorporation of membrane proteins was shown at a determined grafting density. Upon insertion of those proteins, this system may find its application as biosensing devices. In solution, the nanostructures were characterized by using a wide range of methodologies including static and dynamic light scattering, transmission electron microscopy, ThioGlo detection, UV-vis spectroscopy, fluorescence spectroscopy and fluorescence correlation microscopy. On solid supports, atomic force microscopy and surface plasmon resonance along with neutron reflectivity were used to gain insights into morphology, homogeneity, grafting density and thickness of the layers. To demonstrate the planar membranes’ biomimetic potential, they were incubated with different channel proteins: Outer Membrane Protein F, Aquaporin Z and alpha-hemolysin. Occurring interactions were detected by in-situ ATR-FTIR and electrochemical impedance spectroscopy. In summary, this thesis might impact fundamental membrane science as well as prospective biotechnological applications.