Microstructure is a critical element of many synthetic materials including materials for separations, heat transfer, and electrical energy storage. Similarly, natural systems employ microstructure for most structural and mass transfer processes. These systems achieve high-levels of performance through continuous, structural remodeling, which enables adaptation and improvement of their raw materials. In contrast, current microfabrication techniques produce static materials that do not adapt. Here, we show a fabrication process inspired by biological systems capable of adaptation. Combining the basic elements of morphogenesis, reaction and diffusion (RD), and a microvascular scaffold, we pattern microstructured materials by balancing the rates of depolymerization and inhibition of that depolymerization with a diffusive agent. As a result, the materials continuously reshape their microstructure and improve their performance. Using this system, we also recapitulate a hallmark of biological structures, formation of asymmetry from symmetric precursors. By mimicking nature's processes rather than its structure, we present a method for microfabrication that improves material performance in response to a selective pressure. ■ INTRODUCTIONMaterial microstructure is a key design element in advanced materials. Microstructure improves a material's performance for compression, mass and heat transfer, and solar energy conversion efficiency. 1−8 Shaping microstructures is also important in biological composites. Natural composites gain unmatched performance by continuously adapting their microstructure to their environment via reaction−diffusion (RD) sequences, a process termed morphogenesis. 9−14 RD is the formation of spatial micropatterns by two reactive molecules diffusing at distinct, controlled rates. 15 During lung development, for example, microstructures are morphed via RD. This action increases the efficiency of gas exchange by changing a micron-scale bud to a half-meter-long, hierarchical composite composed of thousands of identical micron-scale alveoli 16−22 (Figure 1A and B). Current RD-based synthesis of microstructures create elegant patterns 23−27 from microns to millimeters, 25,28−30 but they are not a continuous process, are incapable of adaptation, and are limited to two dimensions. Still lacking in synthetic systems is the dynamic, continuous restructuring of 3D patterns that are the key principle that biological systems use to improve performance.Here, we show a synthetic system that improves microstructure performance through RD-based microstructure change. Inspired by lung morphogenesis, we developed a synthetic depolymerization/inhibition (push/pull) method that remodels microstructures dynamically. Our method selectively improved the mass transfer performance of an experimental microcontactor and allowed us to fabricate asymmetric structures from symmetric precursors. We developed a finite element model using COMSOL to describe the function and results of the process. Microstructures dictate the properti...
Improving the efficiency of gas separation technology is a challenge facing modern industry, since existing methods for gas separation, including hollow-fiber membrane contactors, vacuum swing adsorption, and cryogenic distillation, represents a significant portion of the world’s energy consumption. Here, we report an enhancement in the release rate of carbon dioxide and oxygen of a thermal swing gas desorption unit using a counter-current amplification method inspired by fish. Differing from a conventional counter-current extraction system, counter-current amplification makes use of parallel capture fluid channels separated by a semipermeable membrane in addition to the semipermeable membrane separating the capture fluid channel and the gas release channel. The membrane separating the incoming and outgoing fluid channels allows gas that would normally exit the system to remain in the desorption unit. We demonstrate the system using both resistive heating and photothermal heating. With resistive heating, an increase in release rate of 240% was observed compared to an equivalent counter-current extraction system.
Here we show a synthetic system that uses reaction and diffusion to both grow new material via polymerization and remove material through polymer chain breakagemimicking the process of bone remodeling in a synthetic system. Researchers have explored the use of reaction/diffusion systems to pattern microstructures with success, but very little work focuses on using these processes to shape microstructures in a dynamic manner. This report provides an example of a dynamic system that can reshape itself using diffusion gradients. Mimicking this dynamic process could enable the development of materials that strengthen in response to repeated application of stress and are able to undergo remodeling after initial fabrication.
We report a technique to coat polymers onto 3D surfaces distinct from traditional spray, spin, or dip coating. In our technique, the surface of a template structure composed of poly(lactic acid) swells and entraps a soluble polymer precursor. Once entrapped, the precursor is cured, resulting in a thin, conformal membrane. The thickness of each coating depends on the coating solution composition, residence time, and template size. Thicknesses ranged from 400 nm to 4 μm within the experimental conditions we explored. The coating method was compatible with a range of polymers. Complicated 3D structures and microstructures of 10 μm thickness and separation were coated using this technique. The templates can also be selectively removed, leaving behind a hollow membrane structure in the shape of the original printed, extruded, or microporous template structures. This technique may be useful in applications that benefit from three-dimensional membrane topologies, including catalysis, separations, and potentially tissue engineering.
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