Technologies using soft, stretchable materials are increasingly important, yet we are unable to control how they stretch with much more sophistication than inflating balloons. Nature, however, demonstrates remarkable control of stretchable surfaces: for example, cephalopods can project hierarchical structures from their skin in milliseconds for a wide range of textural camouflage, run across the ocean floor, change color, and hydrojet at high speeds through the ocean. Inspired by nature, we are developing theoretical and experimental techniques that enable the design, fabrication, and control of soft robotics.
Shape transformable materials:
In this project we were inspired by cephalopod muscular morphology to develop synthetic tissue groupings that allowed programmable transformation of 2-D stretchable surfaces into target 3-D shapes. The synthetic tissue groupings consisted of elastomeric membranes embedded with inextensible textile mesh that inflated to within 10% of their target shapes using a simple fabrication method and modeling approach. These stretchable surfaces transform from flat sheets to 3-D textures that imitate natural stone and plant shapes and camouflage into their background environments.
Fig. 1. Inspiration for and description of CCOARSE. A) A conical papilla (ca. 4mm high) in Octopus rubescens that dynamically extends or retracts in ca. 220 milliseconds. This small species has numerous skin papillae that provide exceptional camouflage in shallow kelp habitats in central California. Frame grabs are from video of a live animal (R. Hanlon). B) An inflated silicone membrane showing the principal strains and resulting deformation of points on the undeformed planar membrane. The radial and circumferential strains displace the points vertically and radially, but not along theta. C) An inextensible non-woven mesh embedded in the silicone membrane constrains the circumferential strain, resulting in vertical displacement based on the radial strain. D) Fabrication of the mesh-silicone membrane. Silicone is poured into a mold. Mesh is embedded, laser cut, removed, and then the silicone is cured. A topcoat of silicone is added to fill voids and improve mesh adhesion. E) A tenstile testing specimen section with horizontal layers of mesh and LS / L silcione length fraction. F) Stress-strain measurements for specimens with multiple silicone length fractions. G) Relationship between the composite membrane strain and silicone length fraction taken from (F) at 50, 100, and 150 kPa membrane stress states. This information maps the mesh design in a silicone-mesh composite membrane to a target 3-D shape.
Fig. 4. Membranes programmed to deform into biomimetic shapes by combining axisymmetric, non-symmetric, and hierarchical shape transformations. A) A 22 cm x 22 cm membrane programmed to inflate into non-symmetric and hierarchical stone shapes. Natural river stones with the same color encircle the membrane. The mesh design is shown on the bottom. B) A membrane programmed to inflate into the shape of a Graptoveria amethorum plant. The leaves are arranged in a spiral around a center point and utilize suspended mesh supports to maintain the high aspect ratio mesh patterns. C) Digital photograph of a Graptoveria amethorum plant. D) The Gaussian curvatures of the inflated and deflated membranes. E) A topographical map with stretchable electroluminescent display that inflated to the to the landscape’s true 3-D shape using CCOARSE. The black contour lines and color-coded regions represent areas of equal elevation.
 Cameron A. Aubin, Snehashis Choudhury, Rhiannon Jerch, Lynden A. Archer, James H. Pikul, Robert F. Shepherd, “Electrolytic Vascular Systems for Energy Dense Robots”, Nature, 1, June, 2019.
 Steven Ceron, Itai Cohen, Robert F. Shepherd, James H. Pikul, Cindy Harnett, “Fiber Embroidery of Self-Sensing Soft Actuators”, Biomimetics, vol. 3, September 2018.
 T.J. Wallin, James Pikul, Robert F. Shepherd, “3D printing of soft robotic systems”, Nature Reviews Materials, May 4, 2018.
 Dean Keithly, John Whitehead, Alexandra Voinea, Diego Horna, Samantha Hollenberg, Mason Peck, James Pikul, Robert F. Shepherd, “A cephalopod-inspired combustion powered hydro-jet engine using soft actuators”, Extreme Mechanics Letters, January 6, 2018.
 James H. Pikul, Shuo Li, Hedan Bai, Roger T. Hanlon, Itai Cohen, Robert F. Shepherd, “Stretchable surfaces with programmable 3-D texture morphing for synthetic camouflaging skins”, Science, vol. 358, pp. 210-214, October 18, 2017.
 T.J. Wallin, J.H. Pikul, S. Bodkhe, B.N. Peele, B.C. Mac Murray, D. Therriault, B.W. McEnerney, R.P. Dillon, E.P. Giannelis, R.F. Shepherd, “Click chemistry stereolithography for soft robots that self-heal”, Journal of Materials Chemistry B, vol. 5, pp. 6249-6255, 2017.