Porosities and pore sizes in coralline calcium carbonate

Coral is a material that recently has gained increased attention as a potential bone graft substitute material. The porosity and pore size distribution of the exoskeleton of eight different coral species were investigated by mercury intrusion and microscopy. A classification was established comprising two groups according to porosity: L-type, having low porosity (< 20 vol.%), and H-type, having high porosity (> 20 vol.%). According to literature, this value of 20 vol.% seems to be a lower porosity limit for successful surgical applications as bone graft substitution material. Pore size distributions are well-defined in three H-type species, each one having a different order of magnitude for the median pore diameter: Porites (order 2), Millepora (order 1), and Manicina (order 0). Tubular and slit pore geometries were suggested after microscopy.