polymer science (3)

Our Flexible Molecule...


1 Soap, shampoo, and worm-like micelles Soaps and shampoos are made from amphiphilic molecules with water-loving (red) and water-hating (blue) parts that arrange themselves to form long tubes known as “worm-like micelles”. Entanglements between the tubes give these materials their pleasant, sticky feel. b The micelles can, however, disentangle themselves, just as entangled long-chain polymer molecules can slide apart too. In polymers, this process can be modeled by imagining the molecule sliding, like a snake, out of an imaginary tube formed by the surrounding spatial constraints. c Worm-like micelles can also morph their architecture by performing reconnections (left), breakages (down), and fusions (right). These operations occur randomly along the backbone, are in thermal equilibrium, and reversible. (Courtesy: Davide Michieletto)

Topics: Biology, DNA, Physics, Polymer Science, Research

DNA molecules are not fixed objects – they are constantly getting broken up and glued back together to adopt new shapes. Davide Michieletto explains how this process can be harnessed to create a new generation of “topologically active” materials.

Call me naïve, but until a few years ago I had never realized you can actually buy DNA. As a physicist, I’d been familiar with DNA as the “molecule of life” – something that carries genetic information and allows complex organisms, such as you and me, to be created. But I was surprised to find that biotech firms purify DNA from viruses and will ship concentrated solutions in the post. In fact, you can just go online and order DNA, which is exactly what I did. Only there was another surprise in store.

When the DNA solution arrived at my lab in Edinburgh, it came in a tube with about half a milligram of DNA per centimeter cube of water. Keen to experiment on it, I tried to pipette some of the solution out, but it didn’t run freely into my plastic tube. Instead, it was all gloopy and resisted the suction of my pipette. I rushed over to a colleague in my lab, eagerly announcing my amazing “discovery”. They just looked at me like I was an idiot. Of course, solutions of DNA are gloopy.

I should have known better. It’s easy to idealize DNA as some kind of magic material, but it’s essentially just a long-chain double-helical polymer consisting of four different types of monomers – the nucleotides A, T, C, and G, which stack together into base pairs. And like all polymers at high concentrations, the DNA chains can get entangled. In fact, they get so tied up that a single human cell can have up to 2 m of DNA crammed into an object just 10 μm in size. Scaled up, it’s like storing 20 km of hair-thin wire in a box no bigger than your mobile phone.

Make or break: building soft materials with DNA, Davide Michieletto is a Royal Society university research fellow in the School of Physics and Astronomy, University of Edinburgh

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Snapping Polymer Discs...


Thin polymer discs self-propel by repeated "snapping" motions. Credit: Yongjin Kim, UMass Amherst

Topics: Chemistry, Polymer Science, Materials Science, Research

A polymer-based gel made by researchers in the US and inspired by the Venus flytrap plant can snap, jump and “reset” itself autonomously. The new self-propelled material might have applications in micron-sized robots and other devices that operate without batteries or motors.

“Many plants and animals, especially small ones, use special parts that act like springs and latches to help them move really fast, much faster than animals with muscles alone,” explains team leader Alfred Crosby, a professor of polymer science and engineering in the College of Natural Sciences at UMass Amherst. “The Venus flytraps are good examples of this kind of movement, as are grasshoppers and trap-jaw ants in the animal world.”

Snapping instabilities
The Venus flytrap plant works by regulating the way its turgor pressure – that is, the swelling produced as stored water pushes against a plant cell wall – is distributed through its leaves. Beyond a certain point, this swelling leads to a condition known as snapping instability, where the tiny additional pressure of a fly’s footsteps is enough to cause the plant to snap shut. The plant then automatically regenerates its internal structures in readiness for its next meal.

Polymer gels snap and jump on their own, Isabelle Dumé, Physics World

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3D Hydrogel Polymers...


Fig. 1 Multimaterial 3D printing hydrogel with other polymers. (A) Illustration of the DLP-based multimaterial 3D printing apparatus. (B and C) Processes of printing elastomer and hydrogel structures, respectively. (D) Snapshot of a diagonally symmetric Kelvin form made of AP hydrogel and elastomer. (E) Demonstration of the high deformability of the printed diagonally symmetric Kelvin form. (F) Snapshot of a printed Kelvin foam consisting of rigid polymer, AP hydrogel, and elastomer. (G) Demonstration of the high stretchability of the printed multimaterial Kelvin foam. Scale bar, 5 mm. (Photo credit: Zhe Chen, Zhejiang University.)

Topics: Chemistry, Materials Science, Polymer Science

Hydrogel-polymer hybrids have been widely used for various applications such as biomedical devices and flexible electronics. However, the current technologies constrain the geometries of hydrogel-polymer hybrid to laminates consisting of hydrogel with silicone rubbers. This greatly limits the functionality and performance of hydrogel-polymer–based devices and machines. Here, we report a simple yet versatile multimaterial 3D printing approach to fabricate complex hybrid 3D structures consisting of highly stretchable and high–water content acrylamide-PEGDA (AP) hydrogels covalently bonded with diverse UV curable polymers. The hybrid structures are printed on a self-built DLP-based multimaterial 3D printer. We realize covalent bonding between AP hydrogel and other polymers through incomplete polymerization of AP hydrogel initiated by the water-soluble photoinitiator TPO nanoparticles. We demonstrate a few applications taking advantage of this approach. The proposed approach paves a new way to realize multifunctional soft devices and machines by bonding hydrogel with other polymers in 3D forms.

3D printing of highly stretchable hydrogel with diverse UV curable polymers, Science Advances

Qi Ge1,*,†, Zhe Chen2,*, Jianxiang Cheng1, Biao Zhang3,†, Yuan-Fang Zhang4, Honggeng Li4,5, Xiangnan He1, Chao Yuan4, Ji Liu1, Shlomo Magdassi6, and Shaoxing Qu2,†

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