Emulsification is a powerful, well-known technique for mixing and dispersing immiscible components within a continuous liquid phase. Consequently, emulsions are central components of medicine, food and performance materials. Complex emulsions, including multiple emulsions and Janus droplets which contain hemispheres of differing material, are of increasing importance1 in pharmaceuticals and medical diagnostics2, in the fabrication of microparticles and capsules3–5 for food6, in chemical separations7, in cosmetics8, and in dynamic optics9. Because complex emulsion properties and functions are related to the droplet geometry and composition, the development of rapid, simple fabrication approaches allowing precise control over the droplets’ physical and chemical characteristics is critical. Significant advances in the fabrication of complex emulsions have been made using a number of procedures, ranging from large-scale, less precise techniques that give compositional heterogeneity using high-shear mixers and membranes10, to small-volume but more precise microfluidic methods11,12. However, such approaches have yet to create droplet morphologies that can be controllably altered after emulsification. Reconfigurable complex liquids potentially have greatly increased utility as dynamically tunable materials. Here we describe an approach to the one-step fabrication of three- and four-phase complex emulsions with highly controllable and reconfigurable morphologies. The fabrication makes use of the temperature-sensitive miscibility of hydrocarbon, silicone and fluorocarbon liquids, and is applied to both the microfluidic and the scalable batch production of complex droplets. We demonstrate that droplet geometries can be alternated between encapsulated and Janus configurations by varying the interfacial tensions using hydrocarbon and fluorinated surfactants including stimuli-responsive and cleavable surfactants. This yields a generalizable strategy for the fabrication of multiphase emulsions with controllably reconfigurable morphologies and the potential to create a wide range of responsive materials.

Living organisms exhibit unique homeostatic abilities, maintaining tight control of their local environment through inter-conversions of chemical and mechanical energy and selfregulating feedback loops organized hierarchically across many length scales 1-7 . In contrast, most synthetic materials are incapable of undergoing continuous self-monitoring and self-regulating behavior due to their limited single-directional chemo-mechanical 7-12 or mechano-chemical 13, 14 modes. Applying the concept of homeostasis to the design of autonomous materials 15 would have transformative impacts in areas ranging from medical implants that help stabilize bodily functions to smart materials that regulate energy usage 2, 16, 17 . Here we present a versatile strategy for creating self-regulating, self-powered, homeostatic materials capable of precisely tailored chemo-mechano-chemical feedback loops at the nano/microscale. We design a bilayer system with hydrogel-supported, catalyst-bearing microstructures, which are separated from a reactant-containing "nutrient" layer. Reconfiguration of the gel in response to a stimulus induces the reversible actuation of the microstructures in and out of the nutrient layer and serves as a highly precise "on/off" switch for chemical reactions. We apply this design to trigger organic, inorganic and biochemical reactions that undergo reversible, repeatable cycles synchronized with the motion of the microstructures and the driving external chemical stimulus. By exploiting a continuous feedback loop between various exothermic catalytic reactions in the nutrient layer and the mechanical action of the temperature-responsive gel, we then create exemplary autonomous, self-sustained homeostatic systems that maintain a user-defined parameter-temperature-in a narrow range. The experimental results were validated using computational modeling that qualitatively captured the essential features of the self-regulating behavior and provided additional criteria for the optimization of the homeostatic function, subsequently confirmed experimentally. This design is highly customizable due to the broad choice of chemistries, tunable mechanics, and physical simplicity, thus promising exciting applications in autonomous systems with chemomechano-chemical transduction at their core.The survival of organisms relies on homeostatic functions such as the maintenance of stable body temperature, blood pressure, pH, and sugar levels 1,3,[5][6][7] . This remarkable self-

No abstract

No abstract

Responsive and reversibly actuating surfaces have attracted significant attention recently due to their promising applications as dynamic materials [1] that may enable microfluidic mixing, [2] particle propulsion and fluid transport, [3] capture and release systems, [4] and antifouling. [5] Analogs in nature serve as inspiration for the design of such advanced adaptive materials systems⎯microorganisms use flagella for propulsion, [6] cilia line the human respiratory tract to sweep mucus from the lungs and prevent bacterial accumulation, [7] and echinoderms use pedicellariae for body cleaning and food capture. [8] Significant characteristics of these biological systems include functionality in a fluidic environment, controllable actuation direction or pattern, and the ability to translate chemical signals or stimulus into mechanical motion. Researchers have taken various approaches to fabricating biomimetic actuators, among which are biomorph actuators made using Micro Electromechanical Systems (MEMS) technology, [9] magnetically actuated poly(dimethylsiloxane) (PDMS) structures, [10] and artificial cilia or actuators made from responsive gel. [11,12] However, most fabricated actuators, such as MEMS or magneticallyactuated PDMS posts, must be driven by an external force or field and are not responsive to chemical stimuli. Actuating structures that have been made from responsive hydrogel are Submitted to 2 either low aspect ratio and their motion is not patternable, [11] or the movement is irreversible. [12] Microscale actuation systems which exhibit reversible chemo-mechanical response and control of actuation direction or pattern have proven difficult to achieve.Inspired by biological actuators, which can be broadly interpreted as composites consisting of an active "muscle" component coupled with a passive "bone" structure, we recently developed a hybrid actuation system in which a crosslinked acrylamide-based hydrogel, acting as an analog to muscle, drives the movement of embedded silicon [13,14] or polymer [15] microposts, serving as analogs to skeletal elements. Actuation was achieved by the swelling and contraction of the humidity-responsive gel upon hydration/drying. Actuation direction was controlled by modulating the hydrogel thickness; since thicker hydrogel exhibits a greater absolute change in volume than thin hydrogel, the forces exerted on the structures⎯and thus their actuation direction⎯can be patterned.However, a humidity responsive system will not function in the fluidic environment required for many applications such as propulsion, cargo transport, or microfluidics, and it is difficult to pattern uni-directional actuation of posts over large areas due to their lack of preferred bending direction. To enable the actuators to function in various environments, it is possible to alter the chemistry of the hydrogel muscle to make it shrink or swell while submerged in response to a range of stimuli including light, [16] temperature, [17] biomolecules (e.g. glucose), [18] or pH. [19] To gain additional ...

Micro-scale optical components play a crucial role in imaging and display technology, biosensing, beam shaping, optical switching, wavefront-analysis, and device miniaturization. Herein, we demonstrate liquid compound micro-lenses with dynamically tunable focal lengths. We employ bi-phase emulsion droplets fabricated from immiscible hydrocarbon and fluorocarbon liquids to form responsive micro-lenses that can be reconfigured to focus or scatter light, form real or virtual images, and display variable focal lengths. Experimental demonstrations of dynamic refractive control are complemented by theoretical analysis and wave-optical modelling. Additionally, we provide evidence of the micro-lenses' functionality for two potential applications—integral micro-scale imaging devices and light field display technology—thereby demonstrating both the fundamental characteristics and the promising opportunities for fluid-based dynamic refractive micro-scale compound lenses.

Mechanical forces in the cell’s natural environment have a crucial impact on growth, differentiation and behaviour. Few areas of biology can be understood without taking into account how both individual cells and cell networks sense and transduce physical stresses. However, the field is currently held back by the limitations of the available methods to apply physiologically relevant stress profiles on cells, particularly with sub-cellular resolution, in controlled in vitro experiments. Here we report a new type of active cell culture material that allows highly localized, directional and reversible deformation of the cell growth substrate, with control at scales ranging from the entire surface to the subcellular, and response times on the order of seconds. These capabilities are not matched by any other method, and this versatile material has the potential to bridge the performance gap between the existing single cell micro-manipulation and 2D cell sheet mechanical stimulation techniques.

Integration of catalytic nanostructured platinum and palladium within 3D microscale structures or fluidic environments is important for systems ranging from micropumps to microfluidic chemical reactors and energy converters. We report a straightforward procedure to fabricate microscale patterns of nanocrystalline platinum and palladium using multiphoton lithography. These materials display excellent catalytic, electrical, and electrochemical properties, and we demonstrate high-resolution integration of catalysts within 3D defined microenvironments to generate directed autonomous particle and fluid transport.