Sponge spicules as blueprints for the biofabrication of inorganic–organic composites and biomaterials

Abstract

While most forms of multicellular life have developed a calcium-based skeleton, a few specialized organisms complement their body plan with silica. However, of all recent animals, only sponges (phylum Porifera) are able to polymerize silica enzymatically mediated in order to generate massive siliceous skeletal elements (spicules) during a unique reaction, at ambient temperature and pressure. During this biomineralization process (i.e., biosilicification) hydrated, amorphous silica is deposited within highly specialized sponge cells, ultimately resulting in structures that range in size from micrometers to meters. Spicules lend structural stability to the sponge body, deter predators, and transmit light similar to optic fibers. This peculiar phenomenon has been comprehensively studied in recent years and in several approaches, the molecular background was explored to create tools that might be employed for novel bioinspired biotechnological and biomedical applications. Thus, it was discovered that spiculogenesis is mediated by the enzyme silicatein and starts intracellularly. The resulting silica nanoparticles fuse and subsequently form concentric lamellar layers around a central protein filament, consisting of silicatein and the scaffold protein silintaphin-1. Once the growing spicule is extruded into the extracellular space, it obtains final size and shape. Again, this process is mediated by silicatein and silintaphin-1, in combination with other molecules such as galectin and collagen. The molecular toolbox generated so far allows the fabrication of novel micro-and nanostructured composites, contributing to the economical and sustainable synthesis of biomaterials with unique characteristics. In this context, first bioinspired approaches implement recombinant silicatein and silintaphin-1 for applications in the field of biomedicine (biosilica-mediated regeneration of tooth and bone defects) or micro-optics (in vitro synthesis of light waveguides) with promising results.

Structure and mechanical properties of selected protective systems in marine organisms

“…This skeleton is made up of needle-like spicules of amorphous silica, templated by axial collagen fibers [10,11,82,[156][157][158] that are encased in a collagen net [10,156]. The structure is diagramed in Fig.…”

“…• Flexure resistant fiber optics based on strong and tough silica spicules of sponges [10,11]: the structure of the spicules is comprised of three sections: a core with a high refractive index, a low refractive index cylindrical tube and an outer portion with a progressively increasing refractive index [10]. These properties allow for effective light transmission.…”

“…2 shows some examples) offer an amazing array of traits and properties due to the design of their complex biological materials. The lessons learned from the structural biological materials of marine organisms have stimulated a number of bioinspired designs including high toughness materials inspired by abalone nacre [9], fiber optic wires inspired by sea sponge spicules [10,11] and body armor inspired by fish scales [12,13]. Given the complex structures that have already been discovered and the immense number of organisms that have yet to be investigated, the study of structural biological materials of marine organisms offers much interest to the scientific community.…”

Flashing light in sponges through their siliceous fiber network: A new strategy of “neuronal transmission” in animals

“…As an example, if animals grow under unfavorable conditions that do not allow the formation of inorganic deposits (silica or calcium biominerals), the growth of the specimens is heavily suppressed. Silica is the major constituent of sponge spicules in the classes of Demospongiae and Hexactinellida [4,5]. The spicules of these sponges are composed of hydrated, amorphous and non-crystalline silica.…”

Analysis of silicatein gene expression and spicule formation in the demosponge Amphimedon queenslandica

“…The orientation and arrangement of the biosilica lamellae by collagen fibres may also provide a platform in determining the final shape of the spicule (Ecker et al 2006;Müller et al 2007a;Müller et al 2009). …”