Engineered Hydrophobin for Biomimetic Mineralization of Functional Calcium Carbonate Microparticles

Hanna Heinonen,Markus B Linder,Hans-Peter Hentze,Päivi Laaksonen

doi:10.4236/jbnb.2014.51001

Abstract

In this study, the modified hydrophobin, engineered for biomimetic mineralization, has been employed as a structure-directing agent for mineralization of calcium carbonate. For the first time amphiphilic calcium carbonate particles have been obtained, using engineered proteins. The mineral microparticles have been characterized by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). While mineralization in the presence of non-modified hydrophobin results in polymorph mineral structures, uniform microspheres with an average particle diameter of one micron are obtained by employing hydrophobin which has been modified with an additional ceramophilic protein sequence. Owing to the tri-functionality of the modified hydrophobin (hydrophilic, hydrophobic and ceramophilic), the obtained mineral microparticles exhibit amphiphilic properties. Potential applications are in the areas of functional fillers and pigments, like biomedical and composite materials. Pickering emulsions have been prepared as a demonstration of the emulsion-stabilizing properties of the obtained amphiphilic mineral microspheres. The structure-directing effects of the studied engineered hydrophobins are compared with those of synthetic polymers (i.e. polycarboxylates) used as crystallization and scaling inhibitors in industrial applications.

Highlights

The natural process of biomineralization enables biological materials with complex morphology and functional design
This study describes the use of engineered hydrophobins, modified with an additional protein sequence for its specific use as a structure-directing additive in biomemetic mineralization
Hydrophobin without the additional ZE-protein sequence is known to adsorb well to surfaces and to self-assemble, it is lacking the additional ceramophilic binding capacity. In contrast to the latter this study describes how the mineralization of calcium carbonate in presence of the ceramophilic modified protein results in highly regular, micronsized and amphiphilic vaterite spheres

Summary

Introduction

The natural process of biomineralization enables biological materials with complex morphology and functional design. Diatoms, bone and tooth structures are prominent examples and show how small amounts of structure-directing proteins can transform ordinary materials, like inorganic minerals, into high-performance composites [1,2,3,4,5,6,7,8]. Like other nanoparticle synthesis routes based on self-assembly, it enables morphological control of inorganic and composite particles and hierarchical structures [9]. Earlier approaches of biomimetic mineralization have been focusing on replacing natural proteins with synthetic polymers, mimicking the structural design of the natural proteins controlling the nucleation and growth of biominerals [10,11,12]. Different biopolymers have been investigated, such as dextrane, collagen-, and extracted natural proteins [10]

Methods

Discussion

Conclusion