H12 - Investigating coral cell-biomaterial interactions to drive coral reef repair

Introduction: : By mid-2030 over >95% of the world’s coral reefs could be dead, potentially impacting the livelihoods of over 1 billion people worldwide. Current approaches to repopulate reefs are too slow to match this rapid decline, relying on coral fragments to naturally grow in nurseries before ocean transplantation, necessitating new technologies to accelerate their growth. These technologies to accelerate cell and tissue growth already exist for human repair systems such as biomaterials for bone repair (i.e. Regenerative Medicine) but have yet to be translated to corals given the inherent similarities between the two (porosity, mechanical properties, chemical and inorganic skeleton compositions, others). While coral has been used for bone repair applications, we explore the alternative: can biomaterials be developed to drive coral reef repair and regeneration? Here, we derive cells from coral fragments and culture these cells in vitro. We then culture these coral cells on collagen hydrogels and examine whether coral cell activity changes due to biomaterial properties, representing a new platform for studying coral repair.

Materials and

Methods: : Live coral fragments of Candy Cane coral (genus Caulastraea) and Sunrise Montipora (genus Montipora) were purchased from a local aquarium. Cells from coral fragments were isolated in calcium and magnesium free seawater and subsequent cell straining steps, similar to primary cell isolation from human tissues. Coral cells were plated in petri dishes and maintained in 12 hr dark/light cycle with specialized coral medium (artificial seawater and nutrients). Coral cell population was verified using Sanger sequencing and coral cells were frozen in liquid-nitrogen for long-term storage. To investigate cell number, we used two assays: Alamarblue and Picogreen. To investigate the influence of biomaterials on coral cell activity, coral cells were added to type I (bovine) collagen hydrogels or glass petri dishes for 28 days and cell number (total cells and ratio of algae:coral cells) and cell morphology was visualized using confocal microscopy and scanning electron microscopy.

Results, Conclusions, and Discussions:: We successfully culture coral cells in vitro for 28 days while maintaining viability, using similar practices to mammalian cell culture. Coral cells frozen at earlier passages in liquid nitrogen demonstrated an initial decline in cell viability (~1-2 days) and by day 3 were attached to petri dishes and continued to proliferate. Coral cells could be maintained in culture for multiple passages (6+); however, we noticed a decline in cell number and attachment after multiple passages (6+). Assays used to evaluate mammalian cell health and viability were applicable to coral cell culture methodology, as we could relate cell number to AlamarBlue fluorescence linearly. Coral cells readily spread and proliferated on glass petri dishes, often forming large clusters of cells (Fig. 1. A) regardless of coral cell type. Cells could be visualized on collagen hydrogels interacting with the biomaterial (Fig. 1. B). In conclusion, we culture coral cells for 28 days in vitro and provide some of the first evidence of coral cell-biomaterial interactions. The ability to culture coral cells in biomaterials unlocks the ability to explore coral-material interactions in an unprecedented way. Similar to how advances in biomaterials design and tissue engineering have advanced bone repair applications, we expect this methodology and results to drive forward the field of coral reef repopulation and repair.

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