Modeling growth of siliceous skeletal elements (spicules) in sponges

Abstract:

Growth of skeletal elements (spicules) is a result of biomineralization in sponges. Biomineralization is the process in which minerals deposit on an organic material and the organic part not only controls crystal nucleation but it can also control the shape of growing crystals with remarkable precision. In addition as a result of control process, biominerals have distinguished features in comparison to the minerals, so that they are produced in heterogeneous environment at ambient temperature and pressure and pH values close to neutral. In sponges for example silicate fibres (spicules) are being formed under very low temperature, surprisingly sponge spicules have superior qualities (from a material science point of view) compared to man-made optical fibres which are produced under very extreme conditions. Understanding biomineralisation has potentially a number of important applications in nanotechnology.

Recently new insights have become available in the formation of spicules in sponges. Several proteins (e.g. galactin, silicatein) are involved in this process. Here we try to understand the process by using a combination of biological data and simulations models.

One important characteristic which makes modelling of biomineralization as a challenge is that it happens at inorganic-organic interfaces and therefore some considerations for simulating both soft and hard materials are needed. Moreover, in this process meaningful behaviours happen in different temporal and spatial scales. Hence, one might consider different approaches depending which part of the dynamics is under scrutiny.

In the kind of simulation that we are currently dealing with, the growth of spicules in sponges has been modelled from the beginning of the intracellular nucleation process. It simulates the interaction of inorganic-organic materials with the view of forming an aggregate of mineral nanoparticles on an organic matrix. It is based on a random movement particle-based simulation in the first step and then a modification by adding a Poisson equation to describe the interaction of acidic sites of proteins with charged particles. The boundaries of the 3D simulation box have cylindrical symmetry, which has been chosen based on the simplified geometry of the organic matrix.