A team of researchers at the Wyss Institute for Biologically Inspired Engineering at Harvard University have developed a novel system for the self assembly of biological structures. Self-assembly is the coming together of a number of disordered components into an organized structure without external guidance. It is a fundamental principle which underscores developmental biology and is a principle which is being used to develop 4D printing.
Gel bricks smaller than a grain of sand (top left) can be programmed to self-assemble into complex structures. The key is attaching connector cubes coated with matching DNA glue to the gel bricks that are meant to pair up.
The present project created self assembling hydrogel cubes which are bio-compatible and biodegradable. Typically, self-assembling hydrogels systems were limited by the tendency of hydrogels to stick to each other at will. The team achieved selective adhesion by coating the sides of the cubes with DNA strands. Cube sides with matching DNA strands connected with each other without adhering to other cubes.
According to the Wyss press release, the researchers were able to program chains of fixed length, T-junctions and square shapes to self-assemble using their new technique:
When they coated hydrogel cubes with giant DNA, the cubes adhered only to partner cubes coated with matching giant DNA. Since scientists can synthesize 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 the larger cubes to self-assemble into specific shapes, including a matching pair of cubes, a linear chain, a square, and a T-shaped structure.
While the researchers believe that a number of applications may exist for their “DNA glue,” a core application for the technology is the creation of self-assembling tissue scaffolds. These scaffolds would be made up of cells embedded in the hydrogel cubes which can be injected at a site of injury and used to create a organized, functional tissue structures without the need for major surgery.
Nature Communications: DNA-directed self-assembly of shape-controlled hydrogels
Related: Skylar Tibbits: The emergence of “4D printing”
Wyss Institute: Programmable glue made of DNA directs tiny gel bricks to self-assemble