Date:11 September 2013
Researchers have developed programmable DNA glue that directs tiny gel bricks to self-assemble into complex structures. The new method could help create injectable components that self-assemble into intricately structured, biocompatible scaffolds at an injury site to help regrow human tissues.
The key to self-assembly was developing the world’s first programmable glue. The glue is made of DNA, and it directs specific bricks of a water-filled gel to stick only to each other, the scientists reported in the 9 September online issue of Nature Communications.
“By using DNA glue to guide gel bricks to self-assemble, we’re creating sophisticated programmable architecture,” says Peng Yin, PhD, a Core Faculty member at the Wyss Institute and senior coauthor of the study. This novel self-assembly method worked for gel cubes as small as a tiny piece of silt (30 microns diameter) to as large as a grain of sand (1 millimetre diameter), underscoring the method’s versatility.
The programmable DNA glue could also be used with other materials to create a variety of small, self-assembling devices, including lenses and reconfigurable microchips as well as surgical glue that could knit together only the desired tissues, said Ali Khademhosseini, PhD, an Associate Faculty member at the Wyss Institute who is the other senior co-author of the study.
To fabricate devices or their component parts, manufacturers often start with a single piece of material, then modify it until it has the desired properties. In other cases, they employ the same strategy as auto manufacturers, making components with the desired properties, then assembling them to produce the final device. Living organisms fabricate their tissues using a similar strategy, in which different types of cells assemble into functional building blocks that generate the appropriate tissue function.
Scientists have tried to mimic this manufacturing strategy by developing self-assembling systems to fabricate devices. For example, last year Yin, and his team reported in Science that they had developed miniscule “DNA bricks” smaller than the tiniest virus that self-assemble into complex nanoscale 3D structures.
Now, he and Khademhosseini sought to create a similar programmable, self-assembling system for mesoscale components — those with edge widths ranging from 30 microns to 1000 microns (1 millimeter). They focused first on creating a self-assembly system in which bricks of biocompatible, biodegradable gels called hydrogels assemble into complex structures. For future applications, small hydrogel bricks containing human cells could potentially be injected into the body. The bricks would assemble, then the cells would knit together to form functional tissue as the hydrogels break down.
In previous attempts to self-assemble hydrogel bricks into complex structures, scientists faced a challenge: the bricks often glom onto one another rather than assembling into the desired architecture. Yin and Khademhosseini needed a way to help each component stick only to specific partners, but not to other components. In other words, they needed programmable glue.
DNA was ideal for the task. It stores genetic information as a sequence of four chemical “letters”, or nucleotides, that bind in a specific way to complementary nucleotides (A to T, and C to G). A single strand of DNA adheres tightly to a second strand, but only if the second strand has a sequence of nucleotides that is complementary to the first. And even a short piece of DNA can have a huge number of possible sequences, which makes the glue programmable.
The researchers used enzymes to multiply a snippet of DNA into long pieces of DNA called “giant DNA” that contained multiple copies of that snippet. When they coated hydrogel cubes with giant DNA, the cubes adhered only to partner cubes coated with matching giant DNA. Since scientists can synthesise snippets of DNA with any sequence they want, this meant that giant DNA functioned as programmable DNA glue.
To assemble hydrogel cubes into larger structures, they used smaller hydrogel cubes as connectors. They coated the connector cube with their DNA glue, then attached it to one of the six faces of a larger cube. A large cube outfitted this way adhered only to other large cubes whose connectors had matching DNA glue.
By placing connector cubes on various faces of the larger cubes, they programmed larger cubes to self-assemble into specific shapes, including a matching pair of cubes, a linear chain, a square and a T-shaped structure.
The method was so specific that when the researchers placed 25 pairs of matched cubes in a single pot, all the cubes located and adhered only to their partners. This ability to assemble multiple components simultaneously is called multiplexity, and the results show that the new system has the highest degree of multiplexity of all existing mesoscale self-assembly systems.
Source: Wyss Institute