27 research outputs found
Predator-Prey Interactions between Droplets Driven by Nonreciprocal Oil Exchange
Chemotactic interactions are ubiquitous in nature and can lead to
nonreciprocal and complex emergent behavior in multibody systems. Here we show
how chemotactic signaling between microscale oil droplets of different
chemistries in micellar surfactant solutions can result in predator-prey-like
chasing interactions. The interactions and dynamic self-organization result
from the net directional, micelle-mediated transport of oil between emulsion
droplets of differing composition and are powered by the free energy of mixing.
The nonreciprocal behavior occurs in a wide variety of oil and surfactant
conditions, and we systematically elucidate chemical design rules for tuning
the interactions between droplets by varying oil and surfactant chemical
structure and concentration. Through integration of experiment and simulation,
we also investigate the active behavior and dynamic reorganization of
multi-droplet clusters. Our findings demonstrate how chemically-minimal systems
can be designed with controllable, non-reciprocal chemotactic interactions to
generate emergent self-organization and collective behaviors reminiscent of
biological systems
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Direct Writing and Actuation of Three-Dimensionally Patterned Hydrogel Pads on Micropillar Supports
Freely swelling, three-dimensionally patterned responsive hydrogels fabricated by multiphoton lithography on the tips of flexible pillars provide unique capabilities for the design of adaptive systems. The resulting materials have tunable actuation direction and angle, sensitive optical response, and precise spatial integration of gels with varying pH and temperature response (see picture; scale bar: 20â
ÎŒm).Engineering and Applied Science
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Synthetic homeostatic materials with chemo-mechano-chemical self-regulation
Living organisms have unique homeostatic abilities, maintaining tight control of their local environment through interconversions of chemical and mechanical energy and self-regulating feedback loops organized hierarchically across many length scales. In contrast, most synthetic materials are incapable of continuous self-monitoring and self-regulating behaviour owing to their limited single-directional chemomechanical or mechanochemical modes. Applying the concept of homeostasis to the design of autonomous materials would have substantial impacts in areas ranging from medical implants that help stabilize bodily functions to 'smart' materials that regulate energy usage. Here we present a versatile strategy for creating self-regulating, self-powered, homeostatic materials capable of precisely tailored chemo-mechano-chemical feedback loops on the nano- or 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 into 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 are validated using computational modelling that qualitatively captures the essential features of the self-regulating behaviour and provides additional criteria for the optimization of the homeostatic function, subsequently confirmed experimentally. This design is highly customizable owing to the broad choice of chemistries, tunable mechanics and its physical simplicity, and may lead to a variety of applications in autonomous systems with chemo-mechano-chemical transduction at their core.Chemistry and Chemical Biolog
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Developmentally-Inspired Shrink-Wrap Polymers for Mechanical Induction of Tissue Differentiation
A biologically inspired thermoresponsive polymer has been developed that mechanically induces tooth differentiation in vitro and in vivo by promoting mesenchymal cell compaction as seen in each pore of the scaffold. This normally occurs during the physiological mesenchymal condensation response that triggers tooth formation in the embryo.Chemistry and Chemical Biolog
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Multiphoton Lithography of Nanocrystalline Platinum and Palladium for Site-Specific Catalysis in 3D Microenvironments
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.Engineering and Applied Science
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Chemo-Mechanically Regulated Oscillation of an Enzymatic Reaction
Chemistry and Chemical Biolog
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Microbristle in gels: Toward all-polymer reconfigurable hybrid surfaces
We report on the fabrication of biologically-inspired ââsmartââ surfaces using hybrid architectures comprising polymer microbristle embedded in a hydrogel layer. The dynamic bending of the micropostsâthe passive structural element in the designâand their return to the upright orientation are achieved during the volume-phase transition of the hydrogel layerâthe active element of the structureâupon hydration/dehydration. We compare the performance of the hybrid architectures bearing soft and stiff microposts and show that the use of soft polymeric materials results in bending actuation of the posts in cases where actuation of identically-sized posts of stiffer materials, such as silicon, would not have been possible. Modeling of the actuation process and the supporting experimental results confirm that the bending orientation of the microposts can be individually controlled by modulating the thickness gradients in the active hydrogel layer achieved by transferring micropatterns to the liquid-phase hydrogel precursor. Such procedures orchestrate coordinated actuation of the microbristle and make it possible to create elaborate reconfigurable micropatterns, such as opening/closing microflorets and microtraps. In combination with diverse hydrogel systems exhibiting response to various stimuli, these ââsmartââ hybrid all-polymer architectures open a new avenue in advanced functional materials that harness the adaptive nature of these structures for various applications.Engineering and Applied Science
Investigating oil solubilization into nonionic micelles by Raman multivariate curve resolution
Abstract Hydrophobic hydration, whereby water spontaneously structures around hydrophobic and amphiphilic molecules, plays a key role in the process of surfactant micelle formation and micellar oil solubilization. Using vibrational Raman multivariate curve resolution spectroscopy, we characterized changes in the hydrophobic hydration occurring within nonionic alkylphenol ethoxylate surfactant Tergitol NPâ12 micelles as a function of oil solubilization. We report trends in the changes of hydrophobic hydration depending on the chain length of the oil as well as the presence of a halogen atom in the oil chemical structure. Changes in hydrophobic hydration directly correlate to changes in the physical properties of the micellar solution, including cloud point and micelle hydrodynamic diameter. We compare hydrophobic hydration of Tergitol NPâ12 to nonionic linear alkyl ethoxylate surfactant Makon TDâ12 and ionic sodium dodecyl sulfate and observe similar trends; the molecular structure of the oil has the largest impact on the hydrophobic hydration. We believe these studies contribute to a fundamental understanding of the importance of hydrophobic hydration in surfactant and oil aggregates, especially as it relates to micellar oil solubilization, and provide insight into how the molecular solubilizate can impact micellar structure, size, and stability
Interfacial Polymerization on Dynamic Complex Colloids: Creating Stabilized Janus Droplets
Complex
emulsions, including Janus droplets, are becoming increasingly important
in pharmaceuticals and medical diagnostics, the fabrication of microcapsules
for drug delivery, chemical sensing, E-paper display technologies,
and optics. Because fluid Janus droplets are often sensitive to external
perturbation, such as unexpected changes in the concentration of the
surfactants or surface-active biomolecules in the environment, stabilizing
their morphology is critical for many real-world applications. To
endow Janus droplets with resistance to external chemical perturbations,
we demonstrate a general and robust method of creating polymeric hemispherical
shells via interfacial free-radical polymerization on the Janus droplets.
The polymeric hemispherical shells were characterized by optical and
fluorescence microscopy, scanning electron microscopy, and confocal
laser scanning microscopy. By comparing phase diagrams of a regular
Janus droplet and a Janus droplet with the hemispherical shell, we
show that the formation of the hemispherical shell nearly doubles
the range of the Janus morphology and maintains the Janus morphology
upon a certain degree of external perturbation (e.g., adding hydrocarbonâwater
or fluorocarbonâwater surfactants). We attribute the increased
stability of the Janus droplets to (1) the surfactant nature of polymeric
shell formed and (2) increase in interfacial tension between hydrocarbon
and fluorocarbon due to polymer shell formation. This finding opens
the door of utilizing these stabilized Janus droplets in a demanding
environment