Light-induced surface structuring of azobenzene-containing films allows for creation of complex surface relief patterns with varying heights, patterns which would be difficult to create using conventional lithography tools. In order to realize the full potential of these patternable surfaces, understanding their formation dynamics and response to different types of light fields is crucial. In the present work we introduce digital holographic microscopy (DHM) for real time, in-situ observation of surface-relief grating (SRG) formation on azobenzene-containing films. This instrument allows us to measure the surface topography of films while illuminating them with two individually controlled laser beams for creating periodically varying patterns. By utilizing the information of the grating formation dynamics, we combine multiple grating patterns to create pixels with wide gamut structural colors as well as blazed grating structures on the film surface. As long as the material behaviour is linear, any Fourier optical surface can be created utilizing this multiple patterning approach. The DHM instrument presented here has the potential for creating complex 3D surface reliefs with nanometric precision.

systems interact with artificial materials, researchers have now assembled a versatile toolkit of materials and processes that allows one to fine-tune interactions at the interface, tailoring specific biological responses on demand. These strategies for biocontrol can be broadly categorized as chemical (charge, ligand presence, surface groups), material changes (moisture content, stiffness), or morphological changes (molecular orientation, surface topography, or mechanical actuation). Rational design of materials for biological interface applications has a unique set of challenges due to the unique requirements of a wide range of biological systems, since different tissues present specific compositions, with their own elasticity, structural organization, and triggering mechanisms. Even within a single organ or tissue, mechanical properties can vary widely depending on the region. A recent study of viscoelasticity in live mouse brain tissue for example found a tenfold difference within the brain depending on the region and morphological structure studied. [2] However, most biological tissues are far less stiff, and far more viscoelastic than typical artificial materials employed at their interface, especially early artificial cell culture materials, which can be much stiffer than in vivo extracellular matrix by many orders of magnitude. [3] In vivo, cells interface with a surrounding microenvironment consisting of an intricate macromolecular network of proteins and sugars swollen in an aqueous media gel. Therefore, the interaction between cells and the extracellular matrix (ECM) in the body is complex and involves a variety of cues related to topography, chemical markers, protein composition, solubility factors, and mechanical properties such as stiffness and elasticity (Figure 1a). [4] Yet much research over the past decades was focused on studying in vitro the effects of each of these signals on cell behavior, with a particular interest on the chemical factors, whereas only recently more advanced biomaterials with controlled physicomechanical properties have been developed, such as those with tunable and variable stiffness, alignment and orientation of key functional groups, and mechanical actuation. There is a large range of stiffness in human tissue, where bone (≈100 GPa) is nine orders of magnitude harder than brain tissue (≈0.1 kPa). [4] Therefore, biomaterial researchers assume a complex task of providing materials and processing technologies for controlling stiffness and micro-and nanostructures in Photoreversible optically switchable azo dye molecules in polymer-based materials can be harnessed to control a wide range of physical, chemical, and mechanical material properties in response to light, that can be exploited for optical control over the bio-interface. As a stimulus for reversibly influencing adjacent biological cells or tissue, light is an ideal triggering mechanism, since it can be highly localized (in time and space) for precise and dynamic control over a biosystem, and low-power visible light...

Surface topography is a key parameter in regulating the morphology and behavior of single cells. At multicellular level, coordinated cell displacements drive many biological events such as embryonic morphogenesis. However, the effect of surface topography on collective migration of epithelium has not been studied in detail. Mastering the connection between surface features and collective cellular behaviour is highly important for novel approaches in tissue engineering and repair. Herein, we used photopatterned microtopographies on azobenzene-containing materials and showed that smooth topographical cues with proper period and orientation can efficiently orchestrate cell alignment in growing epithelium. Furthermore, the experimental system allowed us to investigate how the orientation of the topographical features can alter the speed of wound closure in vitro. Our findings indicate that the extracellular microenvironment topography coordinates their focal adhesion distribution and alignment. These topographic cues are able to guide the collective migration of multicellular systems, even when cell–cell junctions are disrupted.

The fabrication of biomaterials whose properties are activated or inhibited on demand via light is appealing for fundamental biological studies as well as for the development of new applications in tissue engineering and regenerative medicine. One of the most widely used molecules in light-controlled systems is azobenzene for its ability to isomerise in response to light. In this minireview, the fundamental landmarks towards the application of azobenzene-containing materials as cell culture substrates will be highlighted, foreseeing their massive use as next-generation cell-instructive materials.