Development of an Azobenzene-Based Cell Culture Photoresponsive Platform for In Situ Modulation of Surface Topography in Wet Environments

Azopolymers are light-responsive materials that hold promise to transform in vitro cell culture systems. Through precise light illumination, they facilitate substrate pattern formation and erasure, allowing for the dynamic control and creation of active interfaces between cells and materials. However, these materials exhibit a tendency to locally detach from the supporting glass in the presence of aqueous solutions, such as cell culture media, due to the formation of blisters, which are liquid-filled cavities generated at the azopolymer film-glass interface. These blisters impede precise structurization of the surface of the azomaterial, limiting their usage for surface photoactivation in the presence of cells. In this study, we present a cost-effective and easily implementable method to improve the azopolymer-glass interface stability through silane functionalization of the glass substrate. This method proved to be efficient in preventing blister formation, thereby enabling the dynamic modulation of the azopolymer surface in situ for live-cell experiments. Furthermore, we proved that the light-illumination conditions used to induce azopolymer surface variations do not induce phototoxic effects. Consequently, this approach facilitates the development of a photoswitchable azopolymer cell culture platform for studying the impact of multiple in situ inscription and erasure cycles on cell functions while maintaining a physiological wet microenvironment.

Isomerization and reorientation of Disperse Red 1 in poly(ethyl methacrylate)

Irradiation of azobenzene-containing polymer materials with light causes cis-trans isomerization and reorientation of azobenzene moieties and thereby changes in the optical properties of the materials. In this study, the film of poly(ethyl methacrylate) doped with the azobenzene derivative Disperse Red 1 (DR1) has been irradiated with the linearly polarized light of 546 nm. The time profiles of optical anisotropy and absorbance measured during irradiation have been analyzed using a kinetic model. Based on the analysis of the time profiles, we conclude that the light-induced reorientation of DR1 molecules occurs in confined environments where trans → cis isomerization is hindered, while in roomy environments, there is no reorientation. In the confined environment, reorientation occurs due to the environmental changes caused by the isomerization attempts of the DR1 molecule. The polymer environment affects thermal cis → trans and light-induced trans → cis isomerizations of the DR1 molecule differently, suggesting that the spatial requirements for these processes to proceed are different. The thermal isomerization does not result in the reorientation of DR1 molecules in roomy environments.

Evaluation of Local Mechanical and Chemical Properties via AFM as a Tool for Understanding the Formation Mechanism of Pulsed UV Laser-Nanoinduced Patterns on Azo-Naphthalene-Based Polyimide Films

Aromatic polyimides containing side azo-naphthalene groups have been investigated regarding their capacity of generating surface relief gratings (SRGs) under pulsed UV laser irradiation through phase masks, using different fluencies and pulse numbers. The process of the material photo-fluidization and the supramolecular re-organization of the surface were investigated using atomic force microscopy (AFM). At first, an AFM nanoscale topographical analysis of the induced SRGs was performed in terms of morphology and tridimensional amplitude, spatial, hybrid, and functional parameters. Afterward, a nanomechanical characterization of SRGs using an advanced method, namely, AFM PinPoint mode, was performed, where the quantitative nanomechanical properties (i.e., modulus, adhesion, deformation) of the nanostructured azo-polyimide surfaces were acquired with a highly correlated topographic registration. This method proved to be very effective in understanding the formation mechanism of the surface modulations during pulsed UV laser irradiation. Additionally to AFM investigations, confocal Raman measurements and molecular simulations were performed to provide information about structured azo-polyimide chemical composition and macromolecular conformation induced by laser irradiation.

Design of Collective Motions from Synthetic Molecular Switches, Rotors, and Motors

Precise control over molecular movement is of fundamental and practical importance in physics, biology, and chemistry. At nanoscale, the peculiar functioning principles and the synthesis of individual molecular actuators and machines has been the subject of intense investigations and debates over the past 60 years. In this review, we focus on the design of collective motions that are achieved by integrating, in space and time, several or many of these individual mechanical units together. In particular, we provide an in-depth look at the intermolecular couplings used to physically connect a number of artificial mechanically active molecular units such as photochromic molecular switches, nanomachines based on mechanical bonds, molecular rotors, and light-powered rotary motors. We highlight the various functioning principles that can lead to their collective motion at various length scales. We also emphasize how their synchronized, or desynchronized, mechanical behavior can lead to emerging functional properties and to their implementation into new active devices and materials.