A biodegradable graphene-based paste enables secure coral attachment and mineral growth stimulation without using metal frames or toxic adhesives.
(Nanowerk Spotlight) Coral reefs form the structural foundation of diverse marine ecosystems, but their ongoing degradation threatens both biodiversity and human communities. These underwater habitats provide food, livelihoods, and coastal protection to over a billion people. Yet many reefs are in critical decline, suffering from the effects of warming seas, acidification, destructive fishing practices, and coastal development. Coral cover has declined sharply, with estimates suggesting global losses of 20–50%. If sea surface temperatures continue to rise by 1.5°C or more, most remaining reef systems may not survive through mid-century.
Efforts to restore coral reefs have centered on coral transplantation, especially through methods like coral gardening. In this approach, coral fragments are cultivated under controlled conditions—either in aquaria or underwater nurseries—before being attached to damaged reef areas. While promising, this strategy faces persistent challenges.
The first is mechanical: attaching coral fragments securely to reef surfaces is difficult in dynamic underwater environments. Common materials used for this purpose include petroleum-based epoxy pastes, cyanoacrylate glues, and marine concrete. These are often unsuited to underwater handling, pose environmental risks, or lack the durability needed for coral growth. The second challenge is biological: coral calcification and tissue regrowth proceed slowly, limiting the speed of reef recovery.
A separate restoration method known as mineral accretion technology (MAT) has been used to stimulate coral growth. This technique relies on applying an electric current across submerged electrodes, which encourages the deposition of calcium carbonate and other minerals that reinforce coral skeletons. But conventional MAT setups require large metallic frames and shore-connected power sources. The infrastructure is costly, vulnerable to corrosion, and can release harmful ions into the surrounding water once the protective mineral layers break down.
A new study by researchers at the Istituto Italiano di Tecnologia and University of Milano–Bicocca proposes a combined solution to both these limitations (Advanced Materials, “Active Biopaste for Coral Reef Restoration”). Their work introduces a biodegradable, electrically conductive paste specifically designed to anchor coral fragments underwater and simultaneously serve as an electrode for mineral accretion. This multifunctional material eliminates the need for metal supports and synthetic adhesives, while enabling growth-enhancing electrical stimulation in compact, flexible setups.
A schematic of the raw ingredients of the bicomponent conductive paste, named A and B before mixing, and its crosslinking mechanism. A and B are made with ESOA, graphene nanoplatelets (GnPs), and a solid initiator or a liquid accelerator, respectively. The crosslinked paste is named AB. (Image: reprinted from DOI:10.1002/adma.202502078, CC-BY) (click on image to enlarge)
The paste is built from a matrix of epoxidized soybean oil acrylate (ESOA), a plant-derived polymer with good chemical reactivity. To make it conductive, the researchers added graphene nanoplatelets that form percolating electrical pathways when properly dispersed. The formulation is delivered as a two-part system. One component contains a solid chemical initiator; the other includes a liquid accelerator. When the two parts are mixed, a chemical crosslinking reaction occurs, transforming the soft paste into a hardened, durable solid.
This crosslinking step is tunable: by adjusting the concentration of initiator, the paste can be made to cure faster or slower, depending on conditions. This flexibility is critical underwater, where working time and setting speed must be balanced. In strong currents or steep reef slopes, rapid hardening helps prevent coral fragments from detaching. In calmer areas, slower curing gives divers time to position larger fragments with precision.
Mechanical testing showed that the cured paste reaches a compressive strength of nearly 5 megapascals, comparable to natural coral rock. Its stiffness, measured by Young’s modulus, rises from about 0.1 MPa in the uncured state to roughly 60 MPa after curing—indicating a transition from a soft paste to a solid substrate capable of supporting coral tissue.
The electrical performance of the paste also meets the requirements for underwater use. At a graphene nanoplatelet loading of 25% by weight, the material achieves a resistivity of 0.1 ohm-meter. This level of conductivity is sufficient for low-voltage mineral accretion and remains stable over at least 30 days of continuous seawater immersion. No significant water infiltration or leaching of graphene was observed. Contact angle measurements showed that the surface becomes hydrophobic at higher filler loadings, which helps repel water and maintain cohesion. The paste retained conductivity throughout testing, even when submerged.
The researchers also evaluated the paste’s interaction with living organisms. Cytotoxicity tests on human keratinocytes and fibroblasts confirmed that the material is not harmful to skin or tissue. Coral biocompatibility was confirmed by observing the health and survival of coral fragments affixed with the paste in aquaria. The corals remained viable and showed normal growth and color.
To test the paste’s ability to support mineral accretion, the team constructed a small aquarium-based MAT system. Both anode and cathode electrodes were made from the cured paste, and coral fragments were attached directly to the cathode using additional paste. A low direct current of 5 milliamps was applied through the system, sufficient to trigger electrolysis of seawater and initiate mineral deposition.
After eight weeks, scanning electron microscopy confirmed a substantial buildup of calcium carbonate and magnesium hydroxide on the paste cathode surfaces—much higher than on control surfaces without electrical stimulation. Coral fragments exposed to the current grew in surface area by over 8% within the first two weeks, compared to only 3.6% in the control group. The difference was statistically significant and consistent with earlier studies showing that mineral accretion can accelerate coral growth at early stages.
Importantly, no structural abnormalities were observed in the coral skeletons after electrical exposure. Analysis of coral coloration showed darker pigment intensity in the test group, which may reflect higher densities of zooxanthellae—the photosynthetic algae that live symbiotically within coral tissue. Since these algae play a central role in coral health and growth, the observed color difference suggests that the electrical stimulation had a positive effect, though more investigation would be needed to confirm mechanisms.
a) Scheme showcasing mineral accretion technology (MAT) setup. b) Anode and cathode made with the crosslinked AB paste for the MAT experiments in the aquarium. c) SEM-EDS quantitative analysis results for the surface of the control mesh (CONT) versus surface of the cathode (TEST) after 8 weeks of immersion in water. Atom percentage is plotted for carbon, oxygen, magnesium, and calcium. d) Weekly percentage of growth for CONTROL and TEST for the 1st and 2nd weeks. Data are presented as mean ± SD (n = 15 for CONTROL and n = 15 for TEST; Student’s t-test *: p < 0.05; **: p < 0.01 and ***: p < 0.001). e,f) Cross-sections at SEM of one representative control e) and test f) fragment after eight weeks of the experiment. g) Pixel intensity for control and test coral fragments. (Image: reprinted from DOI:10.1002/adma.202502078, CC-BY) (click on image to enlarge)
One of the recurring problems with traditional MAT is the buildup of insulating minerals on the cathode over time, which can stop the electrochemical process. The biopaste’s moderate conductivity helps avoid this. Because the paste’s conductivity is lower than metals, the system can sustain voltage with lower current inputs, reducing the risk of overheating or electrical stress on coral tissue. This makes the technology more compatible with compact, low-power setups that could be deployed in field conditions using portable or renewable power sources.
The paste’s formulation also enables direct application to various substrates, including plastic, rock, and concrete, without requiring specialized tools. It can be applied by hand, cures in place, and supports the attachment of different coral species. The material was also shown to partially biodegrade in seawater over time, reducing environmental persistence and microplastic risks compared to petroleum-based adhesives.
The researchers suggest that this paste could be integrated into existing restoration workflows, such as microfragmentation, where coral colonies are broken into small pieces to promote faster regrowth. In combination with MAT, this could allow for faster restoration cycles and higher survival rates. Moreover, because the paste does not require metal scaffolds or bulky infrastructure, it opens the possibility of scaling coral restoration to more sites with fewer logistical barriers.
Photos taken one year after the experiment showed that coral fragments remained attached and had expanded across the paste surface. Some fragments had even fused, indicating both long-term stability and biological compatibility. This outcome supports the material’s potential as a viable substrate for sustained coral growth beyond the initial weeks following transplantation.
Compared to previously tested materials—including epoxy pastes, metal frames, marine concrete, and various biopastes—this formulation uniquely combines environmental safety, mechanical performance, electrical functionality, and ease of use. Its resistivity falls within the ideal range for MAT, its mechanical strength matches natural reef structures, and it does not release harmful chemicals or corrode in seawater.
As restoration efforts shift toward scalable and ecologically responsible methods, this biodegradable conductive paste represents a new design strategy: one that integrates attachment, support, and stimulation in a single, field-ready material. Future work will need to test the paste across more coral species, current densities, and environmental conditions, and evaluate how renewable energy sources might be used to power mineral accretion in remote reef environments. But the findings suggest a practical step forward in restoring reef ecosystems while minimizing technological and environmental compromises.
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