Natural structures such as eggs, embryos, plant seeds, vegetables like the onion, and body parts like the spinal disc, all have multiple concentric layers surrounding a central core. Each layer typically has a unique compositions and thereby a distinct function. The synthesis (morphogenesis) of these structures in nature typically proceeds in an “inside-out” fashion, where a core is formed initially, followed by a first shell and then additional shells.<br/> <br/>Taking inspiration from the above, we have developed an inside-out technique to synthesize a range of soft materials. First, we have created “onion-like” polymeric capsules with multiple concentric shells surrounding a gelled core. Each polymer shell is formed by free-radical polymerization. A given shell grows outward from the surface of the previous shell; thus, the shell thickness steadily increases with time and can be controlled. Using this technique, we can juxtapose widely different polymers next to each other in a capsule. The resulting capsules exhibit a range of unusual properties. One specific property to highlight is the ability of capsules to rapidly swell due to gas evolved from a reaction in the core; such swelling can be violent enough to eject the core.<br/> <br/>Multilayered structures in nature also exist in other geometries. Our blood vessels are examples of multilayered tubes, while many tissues in our body have outer layers of hairs called villi and microvilli. We have extended our inside-out technique to cylindrical and planar geometries to create polymeric multilayered tubes and hairy surfaces. The multilayered tubes exhibit spontaneous changes in tube diameter in response to the properties of the flowing liquid, which is reminiscent of blood vessels. The hairy surfaces absorb solutes much more efficiently than a bare surface, akin to the villi-covered surfaces of the gastrointestinal tract.

Nature-inspired elastic capsules, tubes and hairy surfaces

2019 Spring National Meeting

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