Jun Park1,2,Patrick Grimes1,Henry Symons1,Mark Workentin2,Sebastien Rochat1,Pierangelo Gobbo3
University of Bristol1,The University of Western Ontario2,University of Trieste3
Jun Park1,2,Patrick Grimes1,Henry Symons1,Mark Workentin2,Sebastien Rochat1,Pierangelo Gobbo3
University of Bristol1,The University of Western Ontario2,University of Trieste3
Hydrogels have vast biomedical applications due to their highly tuneable properties, such as biocompatibility, adhesion, permeability, viscoelasticity, and stiffness. These extraordinarily adaptable materials can be engineered to be stimuli-responsive by carefully selecting the crosslinking monomers or polymers that make up the hydrogels. A stimulus that allows for excellent spatio-temporal control is light, and the translucent nature of hydrogels is complementary to its use in these materials. There are various photoactive moieties that have been incorporated into photo-responsive soft materials, however, there are very few systems utilising photo-click reactions to modify the mechanical properties of hydrogels.<br/>Click chemistry has become an established category of reactions characterized by rapid, selective, high yielding, and atom economic transformations that require minimal purification and can be carried out under mild conditions. In 2004, Bertozzi and coworkers established a bioorthogonal, click reaction called the strain-promoted alkyne-azide cycloaddition (SPAAC) by modifying the copper-assisted alkyne-azide cycloaddition (CuAAC) using strained alkynes.<sup>[1] </sup>These alkynes are more reactive and do not require cytotoxic copper catalysts due to ring strain and bond angle deformation. To circumvent degradation and unwanted side reactivity of the strained alkyne, a cyclopropenone-masked dibenzocyclooctyne (<i>hv</i>DIBO) moiety was developed, capable of facile deprotection to the strained alkyne using ultraviolet light.<sup>[2]</sup> The rapid deprotection can be performed <i>in situ</i> and the resulting alkyne is then free to selectively react with an azide <i>via</i> a SPAAC. Along with its great stability and simple deprotection, the application of <i>hv</i>DIBO onto soft materials introduces precise spatial control due to the sensitivity of the cyclopropenone group to 350 nm UV-A light.<br/>In this communication, the fabrication of photo-responsive hydrogels incorporating <i>hv</i>DIBO and azide moieties will be discussed. Photo-click crosslinking reactions between these groups to mechanically strengthen soft materials will be highlighted. The spatio-temporal control of the photo-click reaction was employed to photo-pattern the surface of hydrogels and to study the kinetics of the materials’ strengthening. A recently developed methodology designed to study the mechanical properties of soft materials with a micro-indenter was applied. Microindentation analyses were used to spatially characterize viscoelasticity and height profile changes of these hydrogels, and to determine the reaction order kinetics of the photo-click reaction.<sup>[3]</sup> These analyses aim to relate chemical processes with mechanical measurements. Overall, these photo-responsive hydrogels can be readily strengthened and patterned through clean, facile photo-click chemistry, allowing for exciting potential applications in actuation, soft robotics, biointerfacing, and biomimetic materials.<br/><br/>[1] S. T. Laughlin, J. M. Baskin, S. L. Amacher, C. R. Bertozzi, <i>Science </i><b>2008</b>, <i>320</i>, 664-667.<br/>[2] W. Luo, J. Luo, V. V. Popik, M. S. Workentin, <i>Bioconjug. Chem. </i><b>2019</b>, <i>30</i>, 1140-1149.<br/>[3] H. E. Symons, A. Galanti, J. C. Surmon, R. S. Trask, S. Rochat, P. Gobbo, <i>Soft Matter </i><b>2022</b>, <i>18</i>, 8302-8314.