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.