Flexible Minerals: Self-Assembled Calcite Spicules with Extreme Bending Strength

Abstract

Silicatein-α is responsible for the biomineralization of silicates in sponges. We used silicatein-α to guide the self-assembly of calcite "spicules" similar to the spicules of the calcareous sponge Sycon sp. The self-assembled spicules, 10 to 300 micrometers (μm) in length and 5 to 10 μm in diameter, are composed of aligned calcite nanocrystals. The spicules are initially amorphous but transform into calcite within months, exhibiting unusual growth along [100]. They scatter x-rays like twinned calcite crystals. Whereas natural spicules evidence brittle failure, the synthetic spicules show an elastic response, which greatly enhances bending strength. This remarkable feature is linked to a high protein content. With nano-thermogravimetric analysis, we measured the organic content of a single spicule to be 10 to 16%. In addition, the spicules exhibit waveguiding properties even when they are bent.

Mechanism of atomic force microscopy imaging of three-dimensional hydration structures at a solid-liquid interface

“…As a substrate in this work we have chosen to use the (1014) surface of calcite (CaCO 3 ), which is an important material in biomineralization [17][18][19]. It has also been previously considered in high resolution AFM experiments [20][21][22] and simulations in liquids [23,24] due to its stability and candidacy as a benchmark system-even for some of the earliest AFM pioneers [25].…”

Anisotropic nanowire growth via a self-confined amorphous template process: A reconsideration on the role of amorphous calcium carbonate

“…Moreover, ACC emerges frequently in the formation of CaCO 3 fibers [24,28,34,38,39]. Accordingly, in immature nanowires, we found an ACC layer (Figs.…”

“…Generally, the formation of anisotropic crystals can be achieved via tuning of the surface energy of crystal faces by changing the temperature and pH, or by adding specific molecules as modifiers [21][22][23][24][25]. An alternative method is to use prefabricated templates with designed shapes and surface functional groups [26][27][28][29].…”

Cryptochrome in Sponges

“…In sponges, the individual spicules are connected either by spongin-like fibrous molecules or DUF protein ) (as in demosponges) or are even fused together, like in hexactinellids (see Wang et al 2012). Our recent studies revealed that calcareous spicules, fabricated with silicatein from siliceous sponges, are characterized by exceptionally stabile and flexible properties (Natalio et al 2013). These observations suggest that sponges can react to both exogenous light (environmental day light) and endogenous light (via the luciferase system; Müller et al 2009).…”