Solvato-morphologically controlled photo-actuated hydrogels
Dunne, Aishling and Florea, Larisa and Diamond, Dermot (2014) Solvato-morphologically controlled photo-actuated hydrogels. In: RACI National Congress, 7-12 Dec 2014, Adelaide, Australia.
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In recent years, photo-responsive hydrogels reported in the literature have been synthesised by co-polymerisation of N-isopropylacrylamide (NIPAAM) with spiropyran(SP) derivatives. This approach requires external protonation of the hydrogels in order to induce re-swelling, typically by immersing the hydrogel in strongly acidic environments1-3. Moreover, re-swelling times are long, typically up to several hours. These disadvantages have restricted the use of photo-actuated hydrogels to applications that employ single-use methods.
Recently, we reported that the addition of acrylic acid copolymerised within the hydrogel provides an internal source of protons that allows photo-actuation in neutral pH environments4.
The polymerisation solvent has been shown to directly influence the morphology of the hydrogel, by producing porous hydrogels of different pore sizes5. This has an impact on the diffusion path length for water molecules moving in/out of the hydrogel matrix, thus improving the swelling and shrinking kinetics of the hydrogel6.
In this study photo-actuator hydrogels were generated using a N-isopropylacrylamide-co-acrylated spiropyran-co-acrylic acid (p(NIPAAM-co-SP-co-AA) copolymer, in a 100-1-5 mole ratio. Different ratios of organic solvent:water (tetrahydrofran(THF), dioxane and acetone) were used as the polymerisation solvent. Varying the volume ratio of the solvent mixtures, resulted in hydrogels with different pore sizes and therefore different extent of swelling/shrinking and actuation kinetics. For example, when THF:water (4:1 v:v) was used as polymerization solvent, a remarkable contraction in hydrogel size of up to 50% was obtained after four minutes of white light irradiation.
Optimising these hydrogels by varying the polymerization solvent has resulted in faster and more reproducible shrinking and reswelling cycles.
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