Amir, Faheem; Liles, Kevin P.; Delawder, Abigail O.; Colley, Nathan D.; Palmquist, Mark S.; Linder, Houston R.; Sell, Scott A.; Barnes, Jonathan C. published the artcile< Reversible hydrogel photopatterning: spatial and temporal control over gel mechanical properties using visible light photoredox catalysis>, Quality Control of 1592-20-7, the main research area is hydrogel photopatterning reversible photoredox catalysis viologen; artificial molecular muscles; hydrogel; photomechanical actuator; photopatterning; photoredox catalysis; redox-responsive materials; viologen.
There is a growing interest in being able to control the mech. properties of hydrogels for applications in materials, medicine, and biol. Primarily, changes in the hydrogel’s phys. properties, i.e., stiffness, toughness, etc., are achieved by modulating the network crosslinking chem. Common crosslinking strategies rely on (i) irreversible network bond degradation and reformation in response to an external stimulus, (ii) using dynamic covalent chem., or (iii) isomerization of integrated functional groups (e.g., azobenzene or spiropyran). Many of these strategies are executed using UV or visible light since the incident photons serve as an external stimulus that affords spatial and temporal control over the mech. adaptation process. Here, we describe a different type of hydrogel crosslinking strategy that uses a redox-responsive cross-linker, incorporated in poly(hydroxyethyl acrylate)-based hydrogels at three different weight percent loadings, which consists of two viologen subunits tethered by hexaethylene glycol and capped with styrene groups at each terminus. These dicationic viologen subunits (V2+) can be reduced to their monoradical cations (V•+) through a photoinduced electron transfer (PET) process using a visible light-absorbing photocatalyst (tris(bipyridine)ruthenium(II) dichloride) embedded in the hydrogel, resulting in the intramol. stacking of viologen radical cations, through radical-radical pairing interactions, while losing two pos. charges and the corresponding counteranions from the hydrogel. It is shown how this concerted process ultimately leads to collapse of the hydrogel network and significantly (p < 0.05) increases (by nearly a factor of 2) the soft material's stiffness, tensile strength, and percent elongation at break, all of which is easily reversed via oxidation of the viologen subunits and swelling in water. Application of this reversible PET process was demonstrated by photopatterning the same hydrogel multiple times, where the pattern was ""erased"" each time by turning off the blue light (∼450 nm) source and allowing for oxidation and reswelling in between patterning steps. The areas of the hydrogel that were masked exhibited lower (by 1-2 kPa) shear storage moduli (G') than the areas that were irradiated for 1.5 h. Moreover, because the viologen subunits in the functional cross-linker are electrochromic, it is possible to visualize the regions of the hydrogel that undergo changes in mech. properties. This visualization process was illustrated by photopatterning a larger hydrogel (∼9.5 cm on its longest side) with a photomask in the design of an array of stars. ACS Applied Materials & Interfaces published new progress about Acrylic polymers Role: PEP (Physical, Engineering or Chemical Process), PRP (Properties), SPN (Synthetic Preparation), TEM (Technical or Engineered Material Use), PROC (Process), PREP (Preparation), USES (Uses). 1592-20-7 belongs to class chlorides-buliding-blocks, and the molecular formula is C9H9Cl, Quality Control of 1592-20-7.
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