Natural Coral as a Biomaterial Revisited

Abstract

This paper first describes the state of the art of natural coral. The biocompatibility of different coral species has been reviewed and it has been consistently observed that apart from an initial transient inflammation, the coral shows no signs of intolerance in the short, medium, and long term. Immune rejection of coral implants was not found in any tissue examined. Other studies have shown that coral does not cause uncontrolled calcification of soft tissue and those implants placed under the periosteum are constantly resorbed and replaced by autogenous bone. The available studies show that the coral is not cytotoxic and that it allows cell growth. Thirdly, porosity and gradient of porosity in ceramics is explained based on far from equilibrium thermodynamics. It is known that the bone cross-section from cancellous to cortical bone is non-uniform in porosity and in pore size. Thus, it is hypothesized that a damaged bone containing both cancellous and cortical bone can be better replaced by a graded/gradient porous implant based on the idea of a biomimetic approach. The purpose of this article is to review and summarize all the pertinent work that has been published on natural coral as a bone graft during the last twenty years including in vitro, animal, and clinical human studies. In addition, as an illustration, we report the clinical experience of one of us using coral. It is a case study of complex femoral fracture (Table 1) where the essential role of vascularization and stabilization of the fracture site are underlined. The results are supported with more than 300 other femoral fractures treated using the same modus operandi. Finally, this paper overviews the ecological and ethical concerns around the use of corals as well as discussing briefly about recent impacts of nano-pollutants. Table 1: Radiographic Evolution of the Femoral Neck of the Young Patient. Pre-op t = 0 month The femoral fracture is located in the lower half of the femur. The hearth has 4 large fragments and a few small shards. t = 7 Months The reduction of the focal point is very approximate. The osteosynthesis by platelets persists an axial deviation and a stable inter-fragmentary gap prevents consolidation. Post-op t = D0 + 1 The recovery restores the diaphyseal axis and anatomically restores the diaphysis. The coral graft is distributed in contact with the shelled femoral sleeve. t = 3 months The spheres are no longer visible on a visual scale and an inhomogeneous bone callus surrounds the focal point of the fracture. t = 4 months The ends are joined. The diaphysis is reconstructed. The callus is hypertrophic, and the spinal canal is dense on the front X-ray. t = 20 months The diaphysis is anatomically reconstructed. The medullary canal is permeable.