In the search to displace petrochemicals as feedstocks for materials, many researchers have focused on compounds from biomass that are abundant, such as sugars, proteins, and cellulose. Now, a simple and inexpensive one-step process that turns DNA into hydrogels, adhesives, and plastics could unlock DNA’s potential to make a wide variety of biomaterials (J. Am. Chem. Soc. 2020, DOI: 10.1021/jacs.0c02438).
Even though DNA on average comprises less than 1% of the biomass on Earth, there is an estimated 50 billion metric tons of it. “We don’t have a way to use it effectively now,” says Mark W. Grinstaff, a polymer scientist at Boston University, who was not involved in the work. DNA could be sourced from unwanted cellular biomass generated by industrial processes, such as the 14 million metric tons per year of bacterial residues from antibiotic manufacturing, or the 266 million metric tons of pulp waste from fruit juice production, says study coauthor Dong Wang, a postdoctoral researcher at Cornell University. Other possible DNA sources include fermentation by-products from the ethanol industry and harmful algal blooms.
Previous methods to construct bulk materials like hydrogels from DNA required well-defined DNA sequences, Grinstaff says. An approach that uses DNA in a generic way is a big step forward. “This is kind of a first; it opens up doors,” he says.
“When you treat DNA as a polymer, a lot of surprisingly good things can be made,” says Dan Luo, a bioengineer at Cornell University who led the study.
Wang and Luo read about a discovery that the amine group on guanine, one of DNA’s four bases, was nucleophilic enough to undergo an aza-Michael addition reaction to electron-poor alkenes adjacent to aldehydes (Acc. Chem. Res. 2008, DOI: 10.1021/ar700246x). They figured that the carbon-carbon double bonds of poly(ethylene glycol) diacrylate (PEGDA) could serve as an acceptor too, enabling the long strands of DNA to cross-link together and form a bulk material.
The researchers tested their idea with commercially available salmon testes DNA and PEGDA. They prepared an alkaline solution of DNA in water and stirred in PEGDA at room temperature, then they poured the mixture into a mold and allowed it to set. Within 30 min, a hydrogel formed, which grew tougher the longer it set.
The researchers then began experimenting with variations on the hydrogel. They extracted DNA from Escherichia coli, cyanobacteria, and onion slices to make similar hydrogels. They also introduced glycerol as a cosolvent in the DNA solution, which resulted in an adhesive gel that grew stickier as it got colder. At –20 °C, the gel became so sticky that a 0.4 cm2 patch placed on a piece of nonstick Teflon could support the weight of a smartphone. The researchers also made hard plastic puzzle pieces by soaking pieces of hydrogel in colored salt solutions and allowing them to dry at room temperature for 1 week.
“I think the fact that you can harvest this material from nature and then use it to create all these very different structures shown in the paper is really remarkable,” Grinstaff says.
Wang and Luo estimate the DNA biomaterials they made in the lab cost under $1 per gram of DNA gel. The researchers are now working to improve material properties such as biodegradability. Although the cross-linker PEGDA currently comes from petrochemicals, the researchers hope to use biobased substitutes in the future.