Supramolecular hierarchy among halogen and hydrogen bond donors in light-induced surface patterning

Halogen bonding, a noncovalent interaction possessing several unique features compared to the more familiar hydrogen bonding, is emerging as a powerful tool in functional materials design. Herein, we unambiguously show that one of these characteristic features, namely high directionality, renders halogen bonding the interaction of choice when developing azobenzene-containing supramolecular polymers for light-induced surface patterning. The study is conducted by using an extensive library of azobenzene molecules that differ only in terms of the bond-donor unit. We introduce a new tetrafluorophenol-containing azobenzene photoswitch capable of forming strong hydrogen bonds, and show that an iodoethynyl-containing azobenzene comes out on top of the supramolecular hierarchy to provide unprecedented photoinduced surface patterning efficiency. Specifically, the iodoethynyl motif seems highly promising in future development of polymeric optical and photoactive materials driven by halogen bonding

Linearly and circularly polarized laser photoinduced molecular order in azo dye doped polymer films

Photo-induced behavior of Azo Disperse one (AZD1) doped Poly(Methyl MethAcrylate) (PMMA) using both linear and circular polarized light is studied. The anisotropy is not erased by the circular polarization light. The circular polarization light combined with relatively long lifetime of the cis state in azo dye doped polymers activate all transverse directions of the angular hole burning through the spot in the film inducing anisotropy. Under circular polarized light, there is no orientation perpendicularly to the helex described by the rotating electric field vector, trans molecules reorients in the propagation direction of the pump beam. The polarization state of the probe beam after propagation through the pumped spot depends strongly on the angle of incidence of both pump and probe beams on the input face. In the case where circular polarized pump and probe beams are under the same angle of incidence, the probe beam “sees” anisotropic film as if it is isotropic. Results of this work shows the possibility to reorient azobenzene-type molecules in two orthogonal directions using alternately linearly and circularly polarized beams

Photopatterned antibodies for selective cell attachment

We present a phototriggerable system that allows for the spatiotemporal controlled attachment of selected cell types to a biomaterial using immobilized antibodies that specifically target individual cell phenotypes.o-Nitrobenzyl caged biotin was used to functionalize chitosan membranes and mediate site-specific coupling of streptavidin and biotinylated antibodies after light activation. The ability of this system to capture and immobilize specific cells on a surface was tested using endothelial-specific biotinylated antibodies and nonspecific ones as controls. Homogeneous patterned monolayers of human umbilical vein endothelial cells were obtained on CD31-functionalized surfaces. This is a simple and generic approach that is applicable to other ligands, materials, and cell types and shows the flexibility of caged ligands to trigger and control the interaction between cells and biomaterials.We thank Martina Knecht (MPIP) for help with the synthesis of caged biotin and Dr. Ron Unger and Prof. C. J. Kirkpatrick (University Clinic Mainz, RepairLab) for providing HUVECs. C.A.C. acknowledges funding support from the Portuguese Foundation for Science and Technology (FCT) (fellowship SFRH/BD/61390/2009) and from the International Max-Planck Research School in Mainz. The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement no. REGPOT-CT2012-316331-POLARIS

Design and validation of novel photoresponsive materials for the biological interface

This thesis makes several contributions towards tailored surfaces that can be used to guide biological growth. In Chapter 2 we synthetized and tested a new series of surfaces that can increase cell growth by 40%. Additionally, this chapter demonstrates that there is a very fine line between a cell's affinity towards the surface and the affinity of any biologically relevant ligands to their extracellular targets. Contrary to what seems intuitive, optimal control comes from regimes where cells have poor growth with ligands that possess only moderate affinity for their receptors. These are the conditions that provide the highest degree of photo-control over biological growth.To help build on the discoveries documented in Chapter 2, in Chapter 3 we designed and validated a new method of rapidly fabricating structurally diverse azobenzene chromophores. While the synthesis portion of Chapter 2 took almost a year to complete a single polymer, using the techniques developed in Chapter 3 each variant could be synthesized and purified within 48 hours, a remarkable improvement over existing techniques. We validated this with 17 derivative chromophores and showed that they retain their photophysical characteristics after functionalization, providing an additional element of control over the half-life and colour of actuation when preparing new azobenzene bio-materials. In Chapter 4 we expanded on the work of Chapter 3 in designing and testing novel faster-switching green-absorbing azo chromophores. These new ortho-nitro azobenzenes retain the characteristics that make Disperse Red 1 one of the most high-performing azo dyes in the literature and allow for the 'head' group to be easily functionalized. We tested the photophysical changes these chromophores experience in small molecule, monomer, homopolymer and copolymer forms providing important information on the trends in the colour and half-life of the chromophore in the different functionalized forms. We show that homopolymer forms experience a decrease in half-life yet show retention of their colour. The copolymer forms exhibit a bi-exponential half-life which we attribute to chain entanglement and experience a slight red-shifting in their absorbance. In all cases, the desired properties of the dyes are retained through the varied macromolecular architectures, demonstrating that this is a valid strategy to explore photomechanical issues in materials science, as well as develop new materials to guide biological growth using physical photo-induced features.In Chapter 5 we demonstrate how we developed a new surface functionalization which allows for the shedding of polymeric coatings with visible light. Using nitrobenzyl ethers we developed a new protocol to covalently attach this coating to carboxylated polystyrene beads providing a way to shed the outermost negative charge. When these beads are coated with poly-D-lysine, we show that we can trigger full release of beads adhered in cell culture. This will be useful in creating, as well as studying, tailor-made nerve connections and may hold applications for other materials.Cet ouvrage présente la conception et la préparation de molécules et de polymères photoresponsifs compatibles avec des systèmes biologiques. L'utilisation de chromophores de type azobenzene et d'éther de nitrobenzyl, en tant qu'unité structurale dans un système polymérique ou en conjonction avec des polymères biocompatibles, a permis le développement de systèmes responsifs aux stimuli de lumière et permettant de guider la croissance biologique. Après irradiation par la lumière de surfaces de polyélectrolytes multicouches, contenant des chromophores d'azobenzene fonctionnalisées avec les peptides RGD et c(RGDfK), une augmentation de 40% de la croissance cellulaire fut observée. Il s'agit de la première démonstration de l'utilisation de ces surfaces multicouches pour le contrôle réversible de la croissance cellulaire grâce aux chromophores d'azobenzene. Pour faciliter de subséquentes découvertes dans le domaine des systèmes biocompatibles, une nouvelle méthodologie synthétique basée sur la «chimie click» fut développée. Celle-ci permet de diminuer le temps nécessaire à la synthèse des chromophores d'azobenzene structurellement diversifiés. Dix-sept différents chromophores ont été synthétisés grâce à celle-ci, et ont permis de démontrer, dans tous les cas, le maintien des propriétés photo-physiques. Cette technique fut aussi utilisée pour la synthèse d'un chromophore ortho-nitro azobenzoïque à isomérisation rapide et absorbant dans la région verte du spectre lumineux. Cette dernière molécule démontre ainsi la polyvalence du procédé et son utilisation possible dans le design de nouvelles surfaces visant l'enrichissement de la science des matériaux par-delà les surfaces biocompatibles. Finalement, nous avons développé un protocole de fabrication de revêtements multicouches contenant la fonctionnalité éther de nitrobenzyl. Ce revêtement peut libérer sa surcouche de poly-D-lysine après l'adhésion d'un neurone à sa surface. La manipulation mécanique par une bille portant ce revêtement, suivi du relâchement du neurite, rend possible la construction du réseau neuronal envisagé

Enlightening materials with photoswitches

Incorporating molecular photoswitches into various materials provides unique opportunities for controlling their properties and functions with high spatiotemporal resolution using remote optical stimuli. The great and largely still untapped potential of these photoresponsive systems has not yet been fully exploited due to the fundamental challenges in harnessing geometrical and electronic changes on the molecular level to modulate macroscopic and bulk material properties. Herein, progress made during the past decade in the field of photoswitchable materials is highlighted. After pointing to some general design principles, materials with an increasing order of the integrated photoswitchable units are discussed, spanning the range from amorphous settings over surfaces/interfaces and supramolecular ensembles, to liquid crystalline and crystalline phases. Finally, some potential future directions are pointed out in the conclusion. In view of the exciting recent achievements in the field, the future emergence and further development of light-driven and optically programmable (inter)active materials and systems are eagerly anticipated

Enlightening Materials with Photoswitches

Incorporating molecular photoswitches into various materials provides unique opportunities for controlling their properties and functions with high spatiotemporal resolution using remote optical stimuli. The great and largely still untapped potential of these photoresponsive systems has not yet been fully exploited due to the fundamental challenges in harnessing geometrical and electronic changes on the molecular level to modulate macroscopic and bulk material properties. Herein, progress made during the past decade in the field of photoswitchable materials is highlighted. After pointing to some general design principles, materials with an increasing order of the integrated photoswitchable units are discussed, spanning the range from amorphous settings over surfaces/interfaces and supramolecular ensembles, to liquid crystalline and crystalline phases. Finally, some potential future directions are pointed out in the conclusion. In view of the exciting recent achievements in the field, the future emergence and further development of light-driven and optically programmable (inter)active materials and systems are eagerly anticipated. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Photoreversible Surfaces to Regulate Cell Adhesion

We report the development of a photoreversible cell culture substrate. We demonstrate the capacity to modify the adhesivity of the substrate using light, altering its capacity to support cell growth. Polyelectrolyte multilayers (PEMs) were used to produce tunable substrates of different thickness and matrix stiffness, which have different intrinsic capacities to support cell adhesion and survival. Surfaces were top-coated with a poly­(acrylic acid)-poly­(allylamine hydrochloride) polyelectrolyte bilayer functionalized with a small fraction (<1%) of an azobenzene-based photoswitchable sidegroup, which included the cell-adhesive three-amino-acid peptide RGD. Irradiation with light-induced geometric switching of the azo bond, resulting in changes to RGD exposure and consequently to cell adhesion and survival, was investigated on a variety of surfaces of different thickness and stiffness. Substrate stiffness, as modified by the thickness, had a significant influence on the adhesion of NIH 3T3 cells, consistent with previous studies. However, by disrupting the isomerization state of the azobenzene-linked RGD and exposing it to the surface, cell adhesion and survival could be enhanced up to 40% when the positioning of the RGD peptide was manipulated on the softest substrates. These findings identify permissive, yet less-than-optimal, cell culture substrate conditions that can be substantially enhanced using noninvasive modification of the substrate triggered by light. Indeed, where cell adhesion was tuned to be suboptimal under baseline conditions, the light-induced triggers displayed the most enhanced effect, and identification of this ‘Goldilocks zone’ was key to enabling light triggering