Photoswitchable Hydrogel Surface Topographies by Polymerisation‐Induced Diffusion

Abstract

Herein, we describe the preparation of patterned photoresponsive hydrogels by using a facile method. This polymer-network hydrogel coating consists of N-isopropylacrylamide (NIPAAM), cross-linking agent tripropylene glycol diacrylate (TPGDA), and a new photochromic spiropyran monoacrylate. In a pre-study, a linear NIPAAM copolymer (without TPGDA) that contained the spiropyran dye was synthesised, which showed relatively fast photoswitching behaviour. Subsequently, the photopolymerisation of a similar monomer mixture that included TPGDA afforded freestanding hydrogel polymer networks. The light-induced isomerisation of protonated merocyanine into neutral spiropyran under slightly acidic conditions resulted in macroscopic changes in the hydrophilicity of the entire polymer film, that is, shrinkage of the hydrogel. The degree of shrinkage could be controlled by changing the chemical composition of the acrylate mixture. After these pre-studies, a hydrogel film with spatially modulated cross-link density was fabricated through polymerisation-induced diffusion, by using a patterned photomask. The resulting smooth patterned hydrogel coating swelled in slightly acidic media and the swelling was higher in the regions with lower cross-linking densities, thus yielding a corrugated surface. Upon exposure to visible light, the surface topography flattened again, thus showing that a hydrogel coating could be created, the topography of which could be controlled by light irradiation.

Molecular Design of Light-Responsive Hydrogels, For in Situ Generation of Fast and Reversible Valves for Microfluidic Applications

“…The Sp-based derivatives 2 and 3 were synthesized according to procedures reported earlier, [9][10][11] whereas the Sp-8' derivative 1 is a novel compound and is expected to have faster isomerization kinetics to the McH + form compared to the Sp-6' derivatives, based on similar trends observed in the work of Satoh et al 26 A Fisher base and the corresponding salicylaldehyde are condensed to a Sp with a hydroxyl group at the desired 6' or 8' position. Subsequently, a Williamson ether synthesis of the Sp with 6-bromohexyl acrylate under Finkelstein conditions using potassium iodine and potassium carbonate in 2-butanone results in the corresponding Sp-ether derivatives.…”

“…[1][2][3][4][5] Photo-switching allows alteration in the dimensional and structural composition of the material with highly precise and localised actuation, without direct contact between the material and the actuating stimulus and with minimum impact on environmental conditions. [6][7][8][9][10][11] This approach is appealing for optical data storage, 12 actuators 1 and valves in microfluidics. [13][14][15][16][17][18][19][20][21] In particular, the latter application ideally requires fast and large actuation of the valve structure in order to work efficiently.…”

Light-controlled self-assembly of non-photoresponsive nanoparticles

“…1). Several recent studies demonstrated the ability to modulate the solution pH with light by means of reversible isomerization of different SP derivatives [33][34][35][36][37] . For example, Shi et al showed that a water-soluble SP derivative could be used to photoswitch reversibly the solution's acidity by as much as 2.2 pH units 38 .…”

Optical and topographic changes in water-responsive patterned cholesteric liquid crystalline polymer coatings

“…By using a mask and with the use of two subsequent photopolymerization steps, patterned polymer coatings can be prepared. 5,7 During the first step at room temperature, a mask ensures polymerization in the exposed CLC areas. The cholesteric order is fixed in these areas.…”

“…For example, thermo, pH and photoresponsive responsive hydrogel coatings have been prepared, which change their surface topography after being switched. 3,4,5,6,7 Furthermore, multi-stimulus-responsive coatings have been described, which can undergo a change between superhydrophilicity and superhydrophobicity by three different stimuli (pH, temperature and glucose concentration). 8 In most of these responsive coatings, there is an emphasis on a single property change of the coating.…”