Abstract text (incl. figure legends and references)
Introduction
Nacre, mother of pearl, is a bio-ceramic composite with excellent material characteristics (1), Using it technically is extremely limited as it is available only from animals like mussels and snails. Its beneficial properties are based on tablet-like crystal layers of CaCO3 (aragonite) 0,5 µm thin and about 15 µm in size, separated by an extreme thin layer of chitin and proteins.
Objectives
The biogenesis of native nacre is still an enigma, but nacre-like material can be produced chemically (2). Learning how nacre can be made biotechnically would make this material available for medical and other applications and can probably help to elucidate an important step in evolution.
Materials & methods
The CO2 and NH3 diffusion method was modified to observe and quantify the crystallization process. Micro-Raman-Spectroscopy was used to determine the crystal polymorphs, nanoparticles were characterized by dynamic light scattering and the surface of chitosan films were examined using white light interferometry.
Results
Pure aragonite can be produced under bio-compatible conditions by using chitosan films as nucleation surface and by inducing aragonite chrystals to release myriads of polymorph-stabile nanoparticles. These particles grow up to a confluent thin-film crystal layer as chitosan surfaces, when treated e.g. with acetate, form bursting bubbles in which the nanoparticles grow like lentils squeezing itself under the very thin chitosan layers of the bubbles.
Conclusion
The experimental results suggest that nacre-like structures can be obtained under biological conditions in repeated cycles of two steps: 1. Producing aragonite nanoparticles and 2. Seeding them on an acetate treated chitosan surface. Whether this layer by layer principle corresponds to the steps in the biogenesis of nacre in organisms is under investigation.
Literature
Nudelmann, F., Sem. Cell & Develop. Biol. 46 (2015), 2 Gao, H.L. et al., Nature Communications 8 (2017), 287