Structure and mechanics of glass sea sponges

Structure and mechanics of glass sea sponges

Hexactinellid sponges are known for their ability to synthesize unusually long and highly flexible fibrous spicules, which serve as the building blocks of their skeletal systems. These spicules consist of a central core of monolithic hydrated silica, surrounded by alternating layers of hydrated silica and organic material. Following loading, fracture of this laminated structure involves cracking of the constituent silica and crack deflection through the intervening thin organic layers, leading to a distinctive stair step-like fracture pattern (upper image). Crack deflection mitigates the high stress concentration that would otherwise be present at the crack tip, resulting in high spicule strength and toughness. This design strategy thus prevents the structure from failing catastrophically as one would expect for a non-laminated glass rod. Architectural designs based on the lessons learned from these studies could ultimately result in the development of more cost effective and energy efficient buildings. 

In addition to the remarkable mechanical properties of their individual spicules, hexactinellid sponges are also known for their ability to form remarkably complex hierarchically-ordered skeletal systems. Using information gained from the study of these structures, we are developing new design strategies for the synthesis of robust lightweight scaffolds for load bearing applications (lower image).  Using a combination of direct mechanical testing and simulation-based strategies, they are beginning to identify specific design elements that contribute to the robustness of these unique structural materials.