A gel held together entirely by interlocking DNA rings exhibits mechanical properties unlike any conventional gel, driven purely by topology.
(Nanowerk Spotlight) A chainmail shirt holds together not because its metal rings are welded shut but because each ring loops through its neighbors, creating a fabric from topology alone. In 1979, Pierre-Gilles de Gennes proposed that the same principle could work at the molecular scale, producing a gel sustained entirely by interlocking rings of polymer. The idea was elegant, the predicted properties were exotic, and the material proved elusive.
Theorists calculated that such an “Olympic gel” would behave unlike any conventional gel. Without discrete junction points, the interlocked rings could slide relative to one another, producing unusual elasticity and swelling patterns. Computer simulations confirmed these predictions repeatedly. But every laboratory attempt ran into the same chemical wall: at the concentrations needed for the rings to overlap, molecules preferentially linked end to end into linear chains rather than closing into discrete rings.
Nature hints that concatenated ring networks can exist. Parasitic microorganisms known as Kinetoplastea, which cause diseases including African sleeping sickness and Chagas disease, carry an unusual mitochondrial genome called kinetoplast DNA: several thousand concatenated DNA minicircles arranged in a flat, mesh-like sheet. Yet no one had extended this architecture into three dimensions synthetically, despite attempts using lipoic acid derivatives and the enzyme Topoisomerase II.
A study now published in Advanced Materials (“Assembling a True “Olympic Gel” From over 16000 Combinatorial DNA Rings”) reports a strategy that succeeds where previous efforts did not. The research team assembled a true Olympic gel from a library of more than 16,000 distinct DNA rings and confirmed that its elasticity arises exclusively from mechanical entanglements.
The synthesis of Olympic gels requires molecules that form concatenated rings instead of linear polymers or classical network junctions. a) Comparison between classical gels, which are crosslinked by either covalent or noncovalent junctions, and Olympic gels, which do not have distinct junctions but are held together by mechanically interlocked (concatenated) rings. b) Scheme of the key-in-lock model in which a hypothetical linear molecule with two reactive termini (a key and a lock) that bind to each other through selective recognition favors intramolecular over intermolecular binding. Given a library of molecules with a sufficient diversity of lock-and-key pairs, the polymerization of linear chains is suppressed, and the formation of an Olympic gel is thermodynamically favored. c) Design of the synthetic DLK insert for implementation of the key-in-lock model with DNA plasmid rings. Note that the scheme shows the insert in its double-stranded form, as present in the final plasmid product; Gibson assembly is conducted with the corresponding single-stranded oligonucleotide, and the complementary sequence is created in situ by the polymerase (see Methods). d) Scheme depicting the workflow in the biotechnological production of the Olympic gel. (Image: Reproduced from DOI:10.1002/adma.202520549Digital Object Identifier (DOI)
, CC BY) (click on image to enlarge)
The approach uses what the researchers call a “diversified lock and key” design. Each DNA ring is a plasmid, a naturally circular molecule used in molecular biology, carrying a synthetic insert with a 16-nucleotide combinatorial sequence. Because each position can contain any of four DNA bases, the theoretical diversity exceeds 4 billion unique sequences, though the practical library comprised more than 16,000 verified variants.
Each plasmid carries complementary sticky ends that strongly prefer to bind to each other, acting as a molecular key that fits only its own lock. Matched pairs bind roughly four times more strongly than mismatched ones, ensuring that each ring closes on itself rather than linking to a neighbor.
To activate the system, the team treated the library with a nicking enzyme that cuts one DNA strand at two flanking sites, allowing the sticky ends to open reversibly when heated to 50 °C. As the solution cools, each open ring threads through whichever neighbors overlap with it and then recloses, locking the interlocked topology in place. Because no two neighboring rings share matching sequences, linear polymerization is suppressed.
Multiple imaging techniques confirmed the gel’s structure. Atomic force microscopy of dilute samples revealed pairs and small clusters of mechanically interlocked rings but no linear multimers. Cryogenic scanning electron microscopy of concentrated samples showed an interconnected mesh with fine strands spanning across pores. Control plasmids, unable to open and reclose, formed no network under identical conditions.
DNA sequencing confirmed the library’s compositional complexity. The most abundant variant made up just 0.067% of the total, and the overall diversity exceeded the minimum threshold needed to suppress polymerization by more than two orders of magnitude.
The gel behaved as a solid rather than a liquid across a wide range of conditions, but only above the predicted critical concentration of 0.11 wt%. Its stiffness increased with concentration in a pattern characteristic of entangled networks, not of conventionally crosslinked gels. When deformed and held in place, the gel retained stored energy over thousands of seconds, while control solutions released their stress entirely in the same period.
Flow experiments revealed distinct yield points and pronounced hysteresis between consecutive shear cycles, indicating that rings open under extreme strain and require time to re-concatenate. Swelling experiments reinforced this picture. Immersed in buffer, the gel expanded and retained its shape indefinitely, while control samples dissolved within 48 hours. The swelling ratio peaked just above the gelation threshold and decreased at higher concentrations, opposite to chemically crosslinked gels but matching theoretical predictions for entangled networks.
Computer simulations of idealized concatenated ring systems reproduced the observed sub-linear stress-strain relationship, yielding an exponent of approximately 0.78, bridging the gap between the linear response expected for junction-free systems and the plateau predicted by established models of rubber elasticity.
Because the rings are functional DNA, they open a route toward applications that purely synthetic polymers cannot offer. Therapeutic sequences such as those used in mRNA vaccines could be incorporated into the plasmid backbone, enabling gel particles to act as microreactors that continuously transcribe encoded molecules. The gel’s biodegradability and permeability also make it a candidate for ultrafiltration membranes.
By merging synthetic biology, DNA nanotechnology, and polymer physics, this work transforms a 1979 conjecture into a physical material with verifiable and distinctive properties. It also shows that unusual mechanical behavior can emerge from high compositional complexity, a design principle more familiar in biology than in synthetic chemistry.
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ORCID information
Michael Lang (Leibniz Institute of Polymer Research Dresden)
, 0000-0003-3851-6670 corresponding author
Elisha Krieg (Leibniz Institute of Polymer Research Dresden)
, 0000-0002-2989-9879 corresponding author
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