Calcium Carbonate Polymorphs Growing in the Presence of Sericin: A New Composite Mimicking the Hierarchic Structure of Nacre

Linda Pastero,Dino Aquilano

doi:10.3390/cryst8070263

Abstract

Bioinspired self-assembled composite materials are appealing both for their industrial applications and importance in natural sciences, and represent a stimulating topic in the area of materials science, biology, and medicine. The function of the organic matrix has been studied from the biological, chemical, crystallographic, and engineering point of view. Little attention has been paid to the effect of one of the two main components of the organic matrix, the sericin fraction, on the growth morphology of calcium carbonate polymorphs. In the present work, we address this issue experimentally, emphasizing the morphological effects of sericin on calcite and aragonite crystals, and on the formation of a sericin-aragonite-calcite self-assembled composite with a hierarchic structure comparable to that of natural nacre.

Highlights

While the structural aspects of biomineralization have been widely studied through many crystallographic techniques, the mechanisms regulating the polymorphs selection or the crystal habit modification in biomineralization need further work, mainly for their crucial importance in the field of the functionalized inorganic-organic composite materials.A critical challenge in biomineralization is the calcite/aragonite selection in mollusk and gastropod shells; in mollusks, the precipitation of these two CaCO3 polymorphs is modulated in the same shell, the polymorph selection being functional to the structural properties of the mineralized layer
We can describe many noticeable effects of sericin on the crystal growth morphology and polymorphs stability of calcium carbonate, the magnitude and significance of these effects depending on the concentration of sericin in solution
Given that the most developed form of aragonite in our spherulitic growth is represented by the (001) face, and that, experimentally, we found that calcite grows radially from the surface of the aragonite layer toward the solution with the three-fold axis almost perpendicular to the surface of the spherulite, we checked the potential coincidences between the (001)Ar and the (00.1)Cc (Tables 6 and 7)

Summary

Introduction

While the structural aspects of biomineralization have been widely studied through many crystallographic techniques, the mechanisms regulating the polymorphs selection or the crystal habit modification in biomineralization need further work, mainly for their crucial importance in the field of the functionalized inorganic-organic composite materials.A critical challenge in biomineralization is the calcite/aragonite selection in mollusk and gastropod shells; in mollusks, the precipitation of these two CaCO3 polymorphs is modulated in the same shell, the polymorph selection being functional to the structural properties of the mineralized layer. While the structural aspects of biomineralization have been widely studied through many crystallographic techniques, the mechanisms regulating the polymorphs selection or the crystal habit modification in biomineralization need further work, mainly for their crucial importance in the field of the functionalized inorganic-organic composite materials. Chitosan is converted to β-chitin by acetylation, and the matrix is mineralized by flowing Ca(HCO3 ) in the presence of polyacrylic acid and magnesium. It is well known that the protein-polysaccharide organic matrix plays a crucial role in the mechanical properties of the mineralized material. Nacre is a robust natural composite made up of of tabular calcium carbonate crystals (95%) which are intimately associated with layers of an organic matrix (5%) that is mainly built of: (i) water-soluble aspartic acid-rich proteins, (ii) glycoproteins,

Objectives

Methods

Results

Conclusion