The CRISPR-Cas system is regularly used to develop new gene therapies and novel diagnostic approaches, but now it is also being harnessed as a control element in a new type of stimuli-responsive "smart" materials by scientists at the Wyss Institute. Upon activation by specific natural or user-defined DNA stimuli, a CRISPR-Cas enzyme enables a variety of smart materials to release bound cargo such as fluorescent dyes and active enzymes, change their structures to deploy encapsulated nanoparticles and live cells, or regulate electric circuits thereby converting biological into electric signals.
"Our study shows that the power of CRISPR can be harnessed outside of the laboratory for controlling the behavior of DNA-responsive materials. We developed a range of materials with very different capabilities that highlight the breadth of applications enabled by programmable CRISPR-responsive smart materials," said James Collins, Ph.D., senior author of a paper published in Science today. "These applications include novel theranostic strategies, point-of-care diagnostics, and the regional monitoring of epidemic outbreaks and environmental hazards."
In the study, the team leveraged a Cas enzyme variant known as Cas12a from a Lachnospiraceae bacterium that has the same ability to recognize and cut specific DNA sequences but, activated by this event, importantly, carries on to non-specifically cleave single-stranded DNA in its vicinity at a rate of about 1250 turnovers per second.
"We incorporated single-stranded target DNA sequences into polymeric materials, either as anchors for pendant cargos, or as structural elements that maintain the materials' basic integrity, and can control different material behaviors just by providing Cas12a together with a specific gRNA as a stimulus," explained co-first author Max English.
In one variation of their concept, the researchers attached different payloads via double-stranded DNA anchor sequences to a so-called poly(ethylene glycol) hydrogel material. "The anchor sequences are targeted by nearby Cas12a enzymes in the presence of complementary gRNAs, and are then degraded," said co-first author Helena de Puig, Ph.D. "As a result, we can release payloads like fluorescent molecules and enzymes at rates that depend on the relative affinities of gRNA/target DNA pairs, as well as properties hard-coded into the gels, such as their pore sizes, and the densities of targeted anchor sequences cross-linked to the gel material." The authors think that this approach could be used, for example, to develop materials with diagnostic capabilities and for environmental monitoring.
"This breakthrough study by James Collins and his team in the Wyss Institute's Living Cellular Devices platform demonstrates the value of CRISPR technology for entirely new fields, ranging from diagnostics and theragnostics to bioelectronics, and marks yet another inspiring inflection point for biomedical developments enabled by this bioinspired technology," said Wyss Institute Founding Director Donald Ingber, M.D., Ph.D.
Image: Reminiscent of Auguste Rodin's credo 'I choose a block of marble and chop off whatever I don't need,' the Wyss Institute and MIT team used the CRISPR-Cas system (yellow-brownish structures) to alter biomaterials by selective removal of single-stranded DNA cross-linkers that are attached to hydrogels or hold them together. This approach enables the stimulus-specific release of chemical compounds, active enzymes, nanoparticles and cells, as well as materials that can convert biological into electric information. Image courtesy of Peter Q. Nguyen/Wyss Institute at Harvard University.