The latest news from academia, regulators
research labs and other things of interest
Posted: Jun 03, 2017
Strong hydrogels that respond to force, heat and light
(Nanowerk News) Researchers have developed novel hydrogels not only exhibited remarkable optical response from pale yellow to purple color and from green to red fluorescence under external stimuli of force, heat, and UV light, but also simply reversed its color back to the original one by white light.
Unlike other mechanoresponsive materials such as benzocyclobutene and 1,2-dioxetane, spiropyran (SP) is a multi-stimuli-responsive mechanophore, which can change its color and fluorescence in response to force, heat, and light.
Under these external stimuli, SP undergoes a reversible structural transformation between spiropyran (a ring-close) and merocyanine (MC, a ring-open) states, leading to the reversible optical property change.
However, the poor solubility of SP in aqueous solution makes it very challenging to directly incorporate SP into highly hydrophilic hydrogels (50%–90% water content), while still retaining SP mechanophore function.
More importantly, no SP-based tough hydrogels have been reported to date, thus little is known about the SP-induced mechanotransduction and toughening mechanisms in the hydrogels.
To overcome these challenges, here the resaerchers developed a new micellar-copolymerization method to incorporate highly hydrophobic SP into highly hydrated polymer network, resulting in SP-crosslinked poly(AM-co-MA/SP) (polyacrylamide-co-methylacrylate/spiropyran) hydrogels that exhibit SP-induced multimechano-responsive/recovery and mechanically strong properties.
In their paper, the authors present proof-of-concept experiments to demonstrate that their hydrogels can achieve multi-stimuli-responsive property (color and fluorescence changes under the stimuli of external force, UV light, and heat), light-induced self-recovery capacity (∼75% toughness recovery and ∼74% stiffness recovery after the first loading), and strong mechanical properties (tensile stress of 1.45 MPa, tensile strain of 570%, fracture energy of 7300 J m-2) at optimal conditions.