Designing Responsive Buckled Surfaces by Halftone Gel Lithography

Abstract

Self-actuating materials capable of transforming between three-dimensional shapes have applications in areas as diverse as biomedicine, robotics, and tunable micro-optics. We introduce a method of photopatterning polymer films that yields temperature-responsive gel sheets that can transform between a flat state and a prescribed three-dimensional shape. Our approach is based on poly(N-isopropylacrylamide) copolymers containing pendent benzophenone units that allow cross-linking to be tuned by irradiation dose. We describe a simple method of halftone gel lithography using only two photomasks, wherein highly cross-linked dots embedded in a lightly cross-linked matrix provide access to nearly continuous, and fully two-dimensional, patterns of swelling. This method is used to fabricate surfaces with constant Gaussian curvature (spherical caps, saddles, and cones) or zero mean curvature (Enneper's surfaces), as well as more complex and nearly closed shapes.

Creases on the interface between two soft materials

“…This experiment uses a photo-crosslinkable poly(N-isopropylacrylamide-co-sodium acrylate-co-acrylamidobenzophenone) polymer described in previous reports 29,35 . to dilute the swelling solution and thus increase the swelling ratio of the charged gel, while the formation of creases is monitored in situ using either an upright optical microscope (Zeiss Axiotech Vario) in reflected-light differential interference contrast mode or a laser scanning confocal fluorescence microscope (Zeiss).…”

Three-dimensional shape transformations of hydrogel sheets induced by small-scale modulation of internal stresses

“…One of the approaches to the design of such materials utilizes the generation of non-uniform internal stresses [5][6][7][8][9][10][11][12] . In the past decade, bending and folding of soft elastic sheets have been achieved by inducing gradients in swelling across the sheet thickness 11 .…”

“…In the past decade, bending and folding of soft elastic sheets have been achieved by inducing gradients in swelling across the sheet thickness 11 . Recently, in-plane differential swelling was introduced as a new concept of 3D shape transformations of thin gel sheets 5,10 . A non-uniform swelling field was prescribed to the sheet by modulating the concentration and the crosslinking density of the temperature-responsive polymer.…”

Shape control of active surfaces inspired by the movement of euglenids

“…This viewpoint has been motivated by the shapes of flowers and leaves as a result of non-uniform growth (Nechaev and Voituriez, 2001;Marder and Papanicolaou, 2006;Sharon et al, 2004;Liang and Mahadevan, 2009;Amar et al, 2012), and has been implemented in disk and tubular topologies by non-uniform swelling/shrinkage of gels (Klein et al, 2007;Kim et al, 2012) or non-uniform switching of liquid crystal elastomers (deHaan et al, 2012;Sawa et al, 2010;Urayama, 2012). In these and most references, the non-uniformity in the deformation is accomplished by patterning non-uniform swelling or nematic director fields, see also e.g.…”

“…Modes et al (2011), and applying a uniform stimulus, although it has also been accomplished by non-uniform illumination (Camacho-Lopez et al, 2004). Such programmed NEPs can therefore execute predefined shape changes, although the path between configurations can present significant variability (Kim et al, 2012).…”