Switchable surfaces for regulating biomolecular and cellular interactions under complex biological conditions

Stimuli-responsive surfaces that can regulate specific biomolecular interactions are enabling novel functionalities and new device designs for a variety of biological and medical applications. In this study two different mixed self-assembled monolayers (SAMs) were used to regulate biomolecular and cellular interactions under complex biological conditions. The first part of this study was based on a well-defined biotinylated mixed SAM with an ethylene glycol group that prevented non-specific binding and used an electrical stimulus to allow control over biomolecular interactions under complex biological matrixes. This SAM system, based on switchable oligopeptides, can be dynamically modulated by an electrical potential under different commonly used biological media, ranging from Dulbecco's Modified Eagle Medium (DMEM) to DMEM supplemented with fetal bovine serum (FBS) and zwitterionic buffering agents such as HEPES. The second study involved electrically switchable mixed SAMs that were shown to be capable of exposing and concealing the RGD cell adhesion motif, to dynamically regulate the adhesion of immune macrophage cells under complex biological conditions. Macrophage cell adhesion to biomaterial surfaces plays a key role in mediating immune response to foreign materials. This system is one of the first examples of a material surface system that can control macrophage cell adhesion on demand. Hence, this study will be useful in developing more realistic dynamic extracellular matrix models and is certainly applicable in a wide variety of biological and medical applications

Switching specific biomolecular interactions on surfaces under complex biological conditions

Herein, electrically switchable mixed self-assembled monolayers based on oligopeptides have been developed and investigated for their suitability in achieving control over biomolecular interactions in the presence of complex biological conditions. Our model system, a biotinylated oligopeptide tethered to gold within a background of tri(ethylene glycol) undecanethiol, is ubiquitous in both switching specific protein interactions in highly fouling media while still offering the non-specific protein-resistance to the surface. Furthermore, the work demonstrated that the performance of the switching on the electro-switchable oligopeptide is sensitive to the characteristics of the media, and in particular, its protein concentration and buffer composition, and thus such aspects should be considered and addressed to assure maximum switching performance. This study lays the foundation for developing more realistic dynamic extracellular matrix models and is certainly applicable in a wide variety of biological and medical applications

Electrically-driven modulation of surface-grafted RGD peptides for manipulation of cell adhesion

Reported herein is a switchable surface that relies on electrically-induced conformational changes within surface-grafted arginine–glycine–aspartate (RGD) oligopeptides as the means of modulating cell adhesion

Switchable biological surfaces

The ability to control properties such as wettability and bio-molecule immobilisation onto self-assembled monolayers (SAMs) has many potential biological and medical applications. The aim of this project was to produce mixed biotinylated peptide monolayers that are responsive to an electric potential, thus providing a system in which the conformation of the biotinylated peptides could be switched. This allows for controlled protein immobilisation onto a mixed monolayer. Fluorescence images indicated that less binding took place between the neutravidin and the biotinylated peptide under a negative potential due to decreased image intensity. Control experiments were also carried out using non-biotinylated peptides to show there was minimal non-specific binding and that binding was only taking place on the biotin binding sites. Stability studies were also carried out using cyclic voltammetry on pure and mixed monolayers to further understand the stability range of the monolayers. High currents were observed in cyclic voltammograms of pure and mixed SAMs. In order to identify the cause of the high current readings, further samples were investigated of well known SAMs. Cyclic voltammograms of nitrophenolthiol and octadecanethiol suggested that a combination of polycrystalline gold and the use of PBS as an electrolyte caused excessive hydrogen evolution which overlapped with the reductive desorption peaks thus, generating high currents and unrealistic charge densities

Analysis of nonlinear polarization rotation based ASE noise reduction scheme

Light detection and ranging (LIDAR) is a remote sensing method by measuring the distance of a target. In order to do this, a pulsed laser is used as a light source and a sensor is used to capture pulses reflected from the target. Based on the time required for a pulse to return and the difference between the laser wavelength and the wavelength of light that is scattered back, digital three-dimensional representation of the target can be achieved. LIDAR driven by pulsed laser is currently a key technology for the automotive industry, developing high resolution ranging devices for self driven vehicles. Fiber lasers designed by master oscillator power amplifier configuration are effective sources for LIDAR application due to their ability to provide increasing power at eye safe wavelength and enabling a high-resolution mapping. One of the drawbacks of this configuration is that amplified spontaneous emission (ASE) noise superimposed to the pulsed signal limits the extinction ratio of the pulsed source. This ASE is most importantly observed in lasers that are pulsed with a low repetition rate, such as often required in LIDAR applications. The aim of this thesis is to develop a nonlinear switch to improve the extinction ratio of such pulsed lasers used to make high resolution maps from LIDAR. In this work, ASE noise elimination of one experimental scheme is analyzed by simulation and experiment. Simulation results of fiber amplitude discriminator (FAD) based on nonlinear polarization rotation show a promising approach to filter the pulsed signal through a nonlinear power transmission function. But the practical implementation of this FAD structure was limited. In this thesis, theoretical background of the FAD is described first. Then the simulation methodologies are stated with the obtained results. Experimental outcomes are provided next. The rest of the thesis highlights challenges and suggests possible solutions for future work with this target.La télédétection par laser (LIDAR) est une technique de qui permet de mesurer la distance d’une surface. Pour ce faire, des impulsions laser sont envoyées vers la cible et leur réflexions sont détectées par un senseur. Il est ainsi possible de construire une représentation digitale tridimensionnelle de la cible en se basant sur le délai de retour des impulsions réfléchies et leur longueur d’onde relativement à la longueur d’onde de la source. Le LIDAR basé sur les lasers pulsés est une technologie clé pour l’industrie automobile et le développement de dispositifs à haute-résolution pour la détection des objets autour de voitures sans chauffeur. Les lasers à fibre de type oscillateur maitre et amplificateur en puissance sont des sources efficaces pour les applications LIDAR, ces sources permettent d’atteindre des puissances élevées à des longueurs d’ondes sans danger pour l’oeil et permettent l’imagerie haute-résolution. Un inconvénient de ce type de source est le bruit d’émission spontanée amplifiée (ASE) qui se superpose au signal et limite ainsi le rapport d’extinction de la source. Ce phénomène d’ASE est prédominant dans les lasers qui sont pulsés à faible taux de répétition, tels que souvent requis avec les LIDARs.L’objectif de cette thèse est de développer un commutateur basé sur l’optique non linéaire pour améliorer le rapport d’extinction des sources pulsées. Dans ce rapport, les capacités d’élimination du bruit ASE d’une configuration sont analysées expérimentalement et par simulations. Les résultats de simulations du Discriminateur d’Amplitude à Fibre (FAD), basé sur la rotation de polarisation par effet non linéaire, sont prometteurs. Le FAD permettrait de filtrer le signal pulsé par une fonction de transmission non linéaire en puissance. L’implémentation pratique de la structure FAD est cependant limité. Dans cette thèse, il est d’abord question des bases théoriques derrière cette technique. La méthodologie pour les simulations numériques ainsi que les résultats de simulations sont ensuite présentés. Finalement, les résultats expérimentaux, les défis techniques et certaines suggestions possibles sont abordés

Modulation of biointeractions by electrically switchable oligopeptide surfaces: structural requirements and mechanism

Understanding the dynamic behavior of switchable surfaces is of paramount importance for the development of controllable and tailor-made surface materials. Herein, electrically switchable mixed self-assembled monolayers based on oligopeptides have been investigated in order to elucidate their conformational mechanism and structural requirements for the regulation of biomolecular interactions between proteins and ligands appended to the end of surface tethered oligopeptides. The interaction of the neutravidin protein to a surface appended biotin ligand was chosen as a model system. All the considerable experimental data, taken together with detailed computational work, support a switching mechanism in which biomolecular interactions are controlled by conformational changes between fully extended ( ON state) and collapsed ( OFF state) oligopeptide conformer structures. In the fully extended conformation, the biotin appended to the oligopeptide is largely free from steric factors allowing it to efficiently bind to the neutravidin from solution. While under a collapsed conformation, the ligand presented at the surface is partially embedded in the second component of the mixed SAM, and thus sterically shielded and inaccessible for neutravidin binding. Steric hindrances aroused from the neighboring surface-confined oligopeptide chains exert a great influence over the conformational behaviour of the oligopeptides, and as a consequence, over the switching efficiency. Our results also highlight the role of oligopeptide length in controlling binding switching efficiency. This study lays the foundation for designing and constructing dynamic surface materials with novel biological functions and capabilities, enabling their utilization in a wide variety of biological and medical applications