Active Biopaste for Coral Reef Restoration

Abstract

Preserving coral reefs is crucial for safeguarding marine biodiversity, global ecosystems, and coastal communities. Coral restoration focuses on farming and transplanting corals back onto reefs. However, traditional attachment methods, such as petroleum-based epoxy, pose environmental risks or provide inefficient affixation. Moreover, maximizing coral growth while farming boosts the restoration rate of the reefs. Hence, an environmentally friendly, conductive hardening bicomponent paste is developed to transplant and anchor corals, provide them with a solid growing substrate, and enable mineral accretion technology (MAT), a strategy to accelerate coral farming. The bicomponent paste consists of bio-based and biodegradable acrylate soybean oil matrix and graphene nanoplatelets fillers. The paste hardens through mixing, transitioning from a Young's modulus of ≃0.1 to ≃60 MPa and reaching a strength of ≃5 MPa. Rheological tests demonstrate the tunability of the crosslinking dynamics of the paste. The paste exhibits a resistivity of 0.1 Ω∙m, with stable electrical properties for over 40 days in seawater. MAT tests show significant enhancement of coral growth rates within two weeks, doubling those of the control group. This paste offers versatility for application in aquaria and nurseries, does not require prone-to-oxidation metallic structures underwater, and can be employed on reefs.

Keywords: biocomposite; coral reefs; coral restoration; green electronics; mineral accretion; soybean oil; underwater.

Figure 1

a) 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, GnPs, and a solid initiator or a liquid accelerator, respectively. The crosslinked paste is named AB. b) Photos of different preparations of conductive components as a function of GnPs loading (in wt.%). c–h) SEM images of cross‐sections of components A (blue) and B (orange), as well as paste AB (green) at different magnifications. All the presented SEM images display pastes with a GnPs loading of 25 wt.%.

Figure 2

a,b) Sheet resistance and resistivity as a function of GnPs loadings for the two components before mixing (A with the initiator and B with the accelerator) and after crosslinking (AB paste). c,d,e) Impedance modulus for components A, B, and AB versus GnPs by wt.%, respectively. An open circuit (OC) measurement is reported as a reference. f) Resistance variation for pastes immersed in seawater for 30 days. g) Time‐lapse demonstrating the powering of an LED through the AB paste in the air and underwater.

Figure 3

a) Complex viscosity variation during time sweep test. Different curves show results as a function of different initiator loadings. Pastes were tested during cross‐linking. b) Compressive tests’ mean curves for the two components and for the crosslinked paste. c) Mean compressive Young's moduli. d) Tensile strength comparison between different materials. e,f) Biocompatibility test on keratinocytes e) and fibroblasts f) for concentrations of 0.5 and 10 mg mL⁻¹ at 24 and 48 h, respectively. CT = control.

Figure 4

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.