Terminator T-1000 from DNA

A DNA-based hydrogel has a shape memory

"Nanometer" based on Cornell University materials: Organic metamaterial flows like a liquid, remembers its shapeThe new material created by researchers at Cornell University (Cornell University, USA) is a bit like the Terminator T-1000 from the cult action movie "Terminator-2.

Doomsday": It can flow like a liquid and then return to its original form.

Frame from Terminator-2: "Reincarnation" of a Terminator from a liquidHydrogels are dispersed systems consisting of two components – high-molecular substances forming a continuous three-dimensional macromolecular grid (polymer framework), and water (solvent filling the voids of this framework).

Thanks to this structure, hydrogels can absorb water in huge quantities like a sponge.

The presence of a three-dimensional polymer frame informs the gels of the mechanical properties of solids: the absence of fluidity, the ability to retain shape, strength and the ability to deform (plasticity and elasticity). However, most gels, when water is removed, are irreversibly destroyed and lose their properties. Scientists from Cornell University, led by Professor Dan Luo, have created a DNA-based hydrogel that can completely restore its shape after removing and then adding water again.

Hydrogels are used for drug delivery (voids can be filled with a target substance that is released during hydrogel degradation) or as a scaffold for tissue regeneration. The ability to form a gel of the desired shape opens up additional possibilities: for example, a gel filled with medicine can be formed in such a way as to maximally correspond to the space inside the wound.

The hydrogel obtained in Luo's laboratory is formed from synthetic DNA. As you know, DNA is a unique sequence of nucleotide bases on which genes are built, however, they can also serve as building blocks for many other self-assembling materials. Single molecular DNA chains are linked to other single chains that have complementary coding, like tiny pieces of organic Lego. Having synthesized DNA, the researchers sequentially created short segments of them, which were connected in a cross-shaped form or in the form of the letters "Y", the chains of which are complementary to each other only in certain areas. These segments, in turn, joined the ends to each other with the help of lipase enzymes, forming mesh structures like a sieve. These works were the first successful attempt to obtain a DNA-based hydrogel.

Trying to find a new approach, scientists mixed synthesized DNA with enzymes that provoke self-replication of DNA molecules and their stretching into long chains in order to obtain a hydrogel with a unique framework of the thinnest layers consisting of square cells and connected by three-dimensional fibers.

"During this process, the DNA molecules intertwine, and the interweaving leads to the formation of a 3D network," explains Luo. However, the result was not what scientists expected. "The hydrogel we obtained spread like a liquid, but when placed in water, it took the form of a container in which it was formed," says Luo, "this was not planned."

Electron microscopy studies have shown that the resulting material consists of many tiny spherical balls consisting of intertwined DNA (the authors call these structures "bird nests"), with a diameter of about 1 micron (Fig. 1). Their behavior is similar to the behavior of many rubber bands glued together. They have a hereditary form, but they cannot stretch or deform.

Fig. 1. Electronic micrography of the obtained material. You can see that the material consists of the smallest "bird's nests" - intertwined DNA spirals (left), which are connected to each other in DNA blocks (right). Such a structure creates many tiny voids that absorb water like a sponge. Source: Prof. Luo's Laboratory.

Scientists say that according to their theoretical calculations, the elastic forces that provide the shape of the hydrogel are so weak that capillary forces together with gravity easily overcome them, so the gel settles into free (unbound) droplets. But when it is immersed in water, the surface tension becomes approximately zero, so the buoyant forces exceed the action of gravity.

To demonstrate this interesting property, the researchers poured the original sol into molds in the form of the letters "D", "N" and "A". When the water was removed, the resulting hydrogel looked like an amorphous liquid, but in water it transformed back into letters (Fig. 2). See the video below.

Fig. 2. Gigdogels made in the form of the letters "D", "N" and "A" degrade themselves, passing into a liquid-like state, but return to their original form when water is added within 15 seconds. Source: Prof. Luo's Laboratory.

As a demonstration of the possible use of such a hydrogel, scientists have created a switch that reacts to water. They made a hydrogel filled with metal particles in the form of a low cylinder and placed it in an insulated tube between two electrical contacts. In liquid form, the gel could reach both ends of the tube and thereby ensure the passage of current. However, when distilled water was added, the gel shortened before reaching both contacts, and the current did not pass.

The results of this work (Lee et al., A mechanical metamaterial made from a DNA hydrogel) were published in the journal Nature Nanotechnology in December 2012.

Portal "Eternal youth" http://vechnayamolodost.ru18.12.2012