New Grafting Material Made from Sea Urchin Spines

Sea urchin spines possess superior material properties that could be used for the production of biodegradable artificial grafts for bone defect repair, claims a new study.

Researchers at the Institute of Metal Research (IMR) of the Chinese Academy of Sciences, the University of Science and Technology of China, and other institutions conducted a study to explore the potential applications of sea urchin (Heterocentrotus mammillatus) spines, which have a hierarchical open-cell structure similar to that of human trabecular bone, but also hold superior compressive strength (∼43.4 MPa), and are suitable for machining to a specified shape and size.

Finite element analysis revealed that compressive stress concentrates along the dense growth rings and dissipates through strut structures of the stereoms, indicating a mesostructure that plays an important role in the urchin spines high strength-to-weight ratios. Using a hydrothermal reaction, the researchers converted the spines to biodegradable magnesium-substituted tricalcium phosphate (β-TCMP) scaffolds, while still maintaining the spines' original interconnected, porous structure. The fracture strength of the hydrothermally converted β-TCMP scaffolds was ∼9.3 MPa, comparable to that of human trabecular bone.

Tests conducted on rabbits and beagles showed that bone cells and nutrients could flow through the pores and promote bone formation. Also, the scaffold degraded easily as it was replaced by the new growth. New bone formed along outer surfaces of the β-TCMP scaffolds one month after implantation, and grew into the inner open-cell spaces within three months. Fusion of the beagle lumbar facet joints using a Ti-6Al-4V cage and β-TCMP scaffold showed near complete degradation and replacement by newly formed bone ten months after implantation. The study was published on March 2, 2017, in ACS Applied Materials & Interfaces.

Marine calcium carbonate (CaCO3) skeletons have tailored architectures created by nature, which give them structural support and other functions. For example, seashells have dense lamellar structures, while coral, cuttlebone, and sea urchin spines have interconnected porous structures.