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Fig. 1. At 37 C (top), the surface of the gel is nearly flat and functionalized regions (red) are exposed. By cooling to 25 C (bottom), folding of the surface leads to sequestration of functionalized regions. The pattern is dictated by topographic features on the substrate (inset).
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Fig. 1. At 37 C (top), the surface of the gel is nearly flat and functionalized regions (red) are exposed. By cooling to 25 C (bottom), folding of the surface leads to sequestration of functionalized regions. The pattern is dictated by topographic features on the substrate (inset). IRG II. Surfaces with dynamic chemical patterns Hayward’s group has developed hydrogel surfaces with chemical patterns that can be reversibly displayed and “erased” through changes in temperature. Films of thermally-responsive poly(N-isopropyl acrylamide) gels attached to confining substrates were designed to undergo a ‘creasing’ instability upon lowering temperature below ~ 30 C. Topographic features on the underlying substrate were used to control the spatial locations of creases, while the sharp folding of the surface within a crease was taken advantage of to translate the pattern of folds into a pattern of surface chemistry. This yielded gels with micrometer-scale surface chemical patterns that could be reversibly and reproducibly hidden by folding and regenerated by unfolding, as shown in Fig. 1. These functionalized surfaces have been used to: (i) bind, then reversibly sequester or release, microparticles; (ii) modulate the activity of surface-bound enzymes; and (iii) reversibly encapsulate adherent cells.
