Photoresponsive polymer hydrogel coatings that change topography

This chapter provides a brief overview of the principles as well as the potential applications of photoresponsive hydrogel films, which change surface topography. It discusses the operating mechanisms that lead to topographical changes. Changes in topography can affect the wettability of a surface, which is an interesting characteristic for making self‐cleaning coatings. The chapter also discusses polymer films that are useful for the development of self‐cleaning films. It then discusses responsive materials, for cell culturing and microfluidics applications. The chapter further shows that appealing photoresponsive polymer hydrogel coatings that change topography can be fabricated, which holds great promise in a variety of fields ranging from microfluidic devices to biomedical applications. When the structures of the topography are in the micrometer size regime, they influence the wettability of the surface. Two types of wetting can be defined: Wenzel and Cassie‐Baxter

Effect of UV illumination on perylene-doped luminescent solar concentrators:a cautionary tale

\u3cp\u3eThe luminescent solar concentrator has the potential of widespread use as a generator of electricity from sunlight well-suited for use in the urban environment owing to its adaptability in shape and coloration. The device performance is heavily dependent on the ability to transport light long distances to the edges. A common organic luminophore used in the device is based on a perylene core. In this work, we describe an overlooked effect of UV illumination on the appearance and efficiency of these devices. An additional absorption peak appears upon polymerization under intense UV in nitrogen atmosphere which significantly reduces the edge emissions from the device. The additional absorbance peak disappears after exposure to air, indicating the presence of a radical anion being formed during the UV light exposure. This suggests newly-produced LSC devices should be allowed to stand a period of time under ambient conditions before their performance characteristics are determined, which could have implications in potential future commercialization of the technology.\u3c/p\u3

Tuning microfluidic flow by pulsed light oscillating spiropyran-basedpolymer hydrogel valves

A method for microfluidic flow control based upon polymer hydrogel valves with rapid and reversible actuation properties is described. The platform allows for contactless optical flow control based upon pulsing light, resulting in a forced oscillating and control over the valve through photo-isomerisation of a spiropyran derivative, co-polymerised within an N-isopropylacrylamide (NIPAm) hydrogel. Application of pulsed light (450 nm) to the valves allows the valves to be held at an intermediate position for extended periods of time. Varying the extent of pulsing of the light source enables the flow rate to be regulated within a microfluidic flow rate range of 0–27 μL/min. Due to the pulsed light, a small period change in the flow rate is observed that corresponds to the pulse sequence as a corresponding oscillation in the hydrogel valves

Light-responsive hierarchically structured liquid crystal polymer networks for harnessing cell adhesion and migration

\u3cp\u3eExtracellular microenvironment is highly dynamic where spatiotemporal regulation of cell-instructive cues such as matrix topography tightly regulates cellular behavior. Recapitulating dynamic changes in stimuli-responsive materials has become an important strategy in regenerative medicine to generate biomaterials which closely mimic the natural microenvironment. Here, light responsive liquid crystal polymer networks are used for their adaptive and programmable nature to form hybrid surfaces presenting micrometer scale topographical cues and changes in nanoscale roughness at the same time to direct cell migration. This study shows that the cell speed and migration patterns are strongly dependent on the height of the (light-responsive) micrometer scale topographies and differences in surface nanoroughness. Furthermore, switching cell migration patterns upon in situ temporal changes in surface nanoroughness, points out the ability to dynamically control cell behavior on these surfaces. Finally, the possibility is shown to form photoswitchable topographies, appealing for future studies where topographies can be rendered reversible on demand.\u3c/p\u3

Photoresponsive passive micromixers based on spiropyran size-tunable hydrogels

\u3cp\u3eMicrofluidic devices allow the manipulation of fluids down to the micrometer scale and are receiving a lot of attention for applications where low volumes and high throughputs are required. In these micro channels, laminar flow usually dominates, which requires long residence times of the fluids, limiting the flow speed and throughput. Here a switchable passive mixer has been developed to control mixing and to easily clean microchannels. The mixer is based on a photoresponsive spiropyran based hydrogel of which the dimensions can be tuned by changing the intensity of the light. The size-tunable gels have been used to fabricate a passive slanted groove mixer that can be switched off by light allowing to change mixing of microfluidics to non-mixed flows. These findings open new possibilities for multi-purpose microfluidic devices where mixers and valves can be tuned by light. (Figure presented.).\u3c/p\u3

Dual light and temperature responsive cotton fabric functionalized with a surface-grafted spiropyran-NIPAAm-hydrogel

\u3cp\u3eA dual-responsive cotton fabric functionalized with a spiropyran-NIPAAm hydrogel, capable of dimensional changes upon irradiation with visible light or upon a temperature stimulus is reported. These volume changes are due to absorption and release of water, from and into the air, by increasing temperature above the LCST in the dark, and/or by irradiation with sunlight or white light from artificial sources. The material was obtained via grafting photo- and temperature-responsive monomers directly from the cotton fibers, using a facile controlled polymerization method, ARGET ATRP.\u3c/p\u3

Proton conductive cationic nanoporous polymers based on smectic liquid crystal hydrogen-bonded heterodimers

\u3cp\u3eThe fabrication of a cationic nanoporous smectic liquid crystal network (LCN) based on hydrogen bonded heterodimers is presented. The method relies on a supramolecular complex made from a pyridyl bearing reactive mesogen hydrogen bonded to a non-reactive benzoic acid template. Upon addition of a cross-linker, a smectic liquid crystalline phase is obtained that can be fixed by photopolymerization. It was found that the lamellar structure was maintained after template removal when 25 wt% or more cross-linker was used, yielding a nanoporous LCN. After H\u3csub\u3e3\u3c/sub\u3ePO\u3csub\u3e4\u3c/sub\u3e immobilization in the pores of the LCN, a cationic 2D nanoporous polymer is obtained showing high and anisotropic anhydrous proton conductivity.\u3c/p\u3

Re- and preconfigurable multistable visible light responsive surface topographies

Light responsive materials that are able to change their shape are becoming increasingly important. However, preconfigurable bistable or even multi-stable visible light responsive coatings have not been reported yet. Such materials will require less energy to actuate and will have a longer lifetime. Here, it is shown that fluorinated azobenzenes can be used to create rewritable and pre-configurable responsive surfaces that show multi-stable topographies. These surface structures can be formed and removed by using low intensity green and blue light, respectively. Multistable preconfigured surface topographies can also be created in the absence of a mask. The method allows for full control over the surface structures as the topographical changes are directly linked to the molecular isomerization processes. Preliminary studies reveal that these light responsive materials are suitable as adaptive biological surfaces