Self-assembled monolayers for biological applications: design, processing, characterization and biological studies

Abstract

Self-assembled monolayers (SAMs) on gold surfaces have been designed, processed, characterized and used for specific biological studies. The studies performed include the control of lipid bilayer diffusion, cell adhesion and vascularization studies and also the creation of antimicrobial surfaces. More specifically, dynamic SAMs on surfaces whose properties can be modified with an electrochemical external stimulus have been developed and used to interrogate biological systems. The developed platform has been applied to two different applications to overcome present challenges when performing biological studies. Firstly, in Chapter 2, the design and synthesis of all the molecules needed to develop an electroactive platform, its processing as SAMs and the optimization of the surface confined redox process between a non-reactive Hydroquinone (HQ) termination and its corresponding reactive Benzoquinone (BQ) is reported. Two different interfacial reactions taking place on the electroactivated surfaces were studied in detail; the Diels-Alder (DA) and the Michael Addition (MA) interfacial reactions, with cyclopentadiene (Cp) or thiol tagged molecules, respectively. The comparative study between DA and MA as surface functionalization strategies with a temporal control reveal that even though MA is not commonly used for this purpose it offers an attractive strategy for stimulus activated functionalization for biological applications. In Chapter 3, the developed platform has been used to achieve a temporal control of cell adhesion and in this way mimic in vivo conditions more accurately. Cell adhesion plays fundamental roles in biological functions and as such, it is important to control cell adhesion on materials used for biomedical applications. Towards this aim, the dynamic interface developed has been used to immobilize cell adhesion promoting peptides through the two different interfacial reactions, namely the DA and the MA reaction, and a comparative study has been carried out. Moreover, a study involving immobilized VEGF-mimicking peptide Qk has been conducted demonstrating the possibility of using the novel peptide for directing cell differentiation into tubular networks for in vitro platforms, by attaching them on a surface. In Chapter 4, we have used the developed electroactive interface to control the dynamics of lipid bilayers as cell membrane models, designed for transmembrane protein characterization in a more in vivo like environment. Specifically, electroactive SAMs have been used to control the moment in which tethering of lipid bilayer deposited on them occurs and consequently decrease its diffusion. In this way, proteins and lipids can maintain their fluidity until tethering is desired, a useful platform for transmembrane protein characterization. iii Finally, in Chapter 5, a surface biofunctionalization strategy also based on SAMs has been used to produce a bactericidal surface by successfully immobilizing novel antimicrobial proteins produced by recombinant DNA technology. This is relevant in view of the verge of an imminent antibiotics crisis. To confirm the antimicrobial activity and biofilm growth prevention of these surfaces, a biofilm assay was performed demonstrating that proteins retain their antimicrobial effect when immobilized. All these strategies open new possibilities for controlled biomolecule immobilization for fundamental biological studies and for applications in biotechnology, in the interface of materials science and biology.