What are glass sponge spicules?

Glass sponge spicules come from deep-dwelling animals called glass sponges, whose complex glass-like skeletal structures are called glass sponge spicules. Glass sponge spicules are made of silica, the same material that makes glass.

Glass sponges belong to the class Hexagonal Sponges, which are common animals in the deep sea. Their tissues contain glass-like structural particles, called spicules, which are made of silica. Some species of glass sponges produce very large spicules that fuse together in beautiful patterns to form a "glass house" - a complex skeleton that often remains intact even after the sponge itself dies. The skeleton of glass sponges, together with various chemicals, can protect against many predators. The most famous glass sponge is a species of Euplectella, known as the "Venus Flower Basket", whose skeleton is built in such a way that it can trap a certain crustacean inside for a lifetime.

Structure and mechanics of glass sponge spicules

Glass sponge spicules are known for their ability to synthesize unusually long and highly flexible fibrous spicules, which are part of their skeletal system. These spicules consist of a central core of a single block of hydrated silica surrounded by alternating layers of hydrated silica and organic materials. Upon loading, the fracturing of this layered structure results in cracking of the constituent silica and crack deflection through the thin organic layers in between, resulting in a unique step-like fracture pattern.

The crack deflection relieves the otherwise high stress concentration at the crack tip, thereby increasing the strength and toughness of the spicules. This design strategy thus prevents the structure from catastrophic failure, which is what is expected of non-laminated glass rods. Architectural designs based on the lessons learned from these studies could ultimately lead to the development of more cost-effective and energy-efficient buildings.

Biomimetic applications of glass sponge spiculules

The spicules of other sponges are tiny, but those of glass sponges can grow up to 3 meters long! These spicules have optical fiber properties comparable to commercial telecommunication optical fibers.

Spiculules are building blocks of an extremely complex glass lattice that acts as the skeleton of the sponge. Although the lattice is made of a brittle glass component, the lattice itself is extremely strong yet flexible. Materials engineers are studying their patterns, making glass sponges a favorite in the emerging field of biomimetic engineering.

Sponges are a diverse and globally distributed branch of benthic organisms that can be traced back to at least the Ediacaran-Cambrian boundary, 541 million years ago. Recently, people have discovered that glass sponge spicules have unique microstructures and good fiber properties, which have attracted the attention of scientists and researchers, and will have great potential in engineering and other fields in the future.