Designing Responsive Buckled Surfaces by Halftone Gel Lithography

TLDR

Self‑actuating materials that can transform between three‑dimensional shapes find use in biomedicine, robotics, and tunable micro‑optics. The authors present a method to photopattern polymer films into temperature‑responsive gel sheets that switch between flat and prescribed 3‑D shapes. The technique employs poly(N‑isopropylacrylamide) copolymers with benzophenone groups, cross‑linking tuned by irradiation dose, and a halftone lithography process using two photomasks to embed highly cross‑linked dots in a lightly cross‑linked matrix, enabling continuous two‑dimensional swelling patterns. The method yields surfaces with constant Gaussian curvature (spherical caps, saddles, cones), zero mean curvature (Enneper’s surfaces), and more complex nearly closed shapes.

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.