Preparation Of Biomimetic Functional Materials Based On Microbial Mineralization And Self-assembly And Their Properties

The great scientific challenge of the 21st century is to develop stronger,more resilient（damage-resistant）structural materials,ideally lighter in weight,from buildings to transport to energy,to support development in strategic areas.By drawing inspiration from nature,many research groups have attempted to mimic the structure of natural materials to create composites with unique properties.Nacre（also known as mother-of-pearl）are widely concerned by researchers because of their unique"brick-and-mortar”（BM）.Although a variety of methods have been developed to prepare biomimetic structural materials,most of them have remained in the preparation of two-dimensional（2D）biomimetic composite films,and there have been few reports on three-dimensional（3D）biomimetic structural blocks.So far,this field has been largely unsuccessful in applying natural unique structures to engineering materials and design.Therefore,from the perspective of utilizing the unique structure of nature,it is necessary to find an inexpensive,simple and environmentally friendly method to realize the preparation of lightweight high-strength nanocomposites.In order to solve these problems,this paper firstly regulates the size and morphology of calcium carbonate（CaCO₃）through various polymer templates in microbial mineralization system,and studies its dissolution and recrystallization process.Then we used the crystallization of amorphous calcium carbonate（ACC）in chitosan（CS）nanocomposite film to study its mechanical properties enhancement mechanism.Then we proposed a new strategy based on biomineralization and assembly to prepare 3D artificial nacre materials,and successfully prepared 3D artificial nacre.Finally,we also prepared a biomimetic layered carbon aerogel using two-way freezing technology and applied it to electromechanical sensing,energy storage and oil-water separation.The specific research results obtained are summarized as follows:1.Silk fibroin/magnesium ion(SF/Mg²⁺)is used as a soluble additive to induce and regulate the mineralization of CaCO₃ in the microbial mineralization system,which itself acts as a nucleation site during CaCO₃ mineralization.Here,we provide a new experimental insight into the role of SF and Mg²⁺in the mineralization of CaCO₃ in microbial mineralization systems.The morphology and crystallization of CaCO₃ aggregates are affected by the self-assembly of SF molecules and the inhibition of Mg²⁺.This combination promoted the growth of a novel,rod-like superstructure of calcite crystal by aggregating/assembling behavior and crystallization kinetics.In addition,superstructures CaCO₃ crystals with the prism-shaped and hemispheres were obtained in the presence of Mg²⁺and SF,respectively.Furthermore,CaCO₃crystals with well-defined morphologies and polymorphs can be obtained by regulating the crystallization conditions（mineralization time and the amount of the additives）.This study provides some insights into the natural mineralization process of CaCO₃.2.Amorphous calcium carbonate/chitosan（ACC/CS）nanocomposites spanning the complete range of Mg-ACC content（0-100 wt%）are prepared by simple evaporation-induced assembly.Effects of Mg-ACC content on the structure and mechanical properties of nanocomposites are systematically investigated and exhibit an excellent mechanical property at Mg-ACC contents of 80 wt%compared to ordinary calcium carbonate/chitosan composites.The mechanical properties of nanocomposites films were further improved by increasing the content of Mg-ACC,and reached the maximum value at the Mg-ACC content of 80 wt%.Young’s modulus and strength of the 80%ACC-CS nanocomposite film reach 31.96 GPa and121.67 MPa,respectively,which is 5.1 times and 2.3 times higher than that of a pure CS film.When the Mg-ACC content is higher than 80 wt%,the smooth structure is transformed to tactoids through Mg-ACC crystal transformation,which deteriorate mechanical properties.Furthermore,the as-prepared ACC-CS nanocomposite films show hydrophobicity and high biocompatibilities for boosting the growth of Cell-293T.In addition,we also propose a theoretical model for the dispersion of Mg-ACC in CS matrix,which can better explain the improvement of the mechanical properties of nanocomposite films.These results offer comprehensive understanding for developing high-performance biomimetic nanocomposites with high nanofiller loading.3.Herein,we exhibited that large-scale artificial nacre with hierarchical BM structures can be easily prepared via an assembly-and-biomineralization strategy based on laminating as-prepared nacre-mimetic/calcium carbonate（CaCO₃）films.The bottom-up assembly process of the bulk artificial nacre is divided into the preparation of nacre-mimetic chitosan（CS）film,in-situ biomineralization on CS matrix and hot pressing.Among them,biomineralization on the CS matrix was discussed in detail.A novel flower clustered CaCO₃crystals were obtained under the synergistic regulation of silk fibers（SF）/Mg²⁺in Microbial mineralization system.The formation process（dissolution and recrystallization）of CaCO₃ film on CS matrix was analyzed in detail,which provides some references for future biomineralization.The obtained bulk artificial nacre exhibits impressive mechanical properties,which confirms the role of the artificial layered"BM"structure.This novel bottom-up strategy（biomineralization-assembly）can be easily expanded to other material systems because of its versatility,opening up an effective way for large-scale production of high-performance bionic structural functional materials.4.Carbon aerogels with biomimetic structures have shown excellent physicochemical properties and brought great potential applications in a wide range of fields.The utilization of renewable resources as the carbon precursor offers a low-cost and scalable way to fabricate biomimetic carbon aerogels with intriguing properties such as ultra-light weight,superelasticity and high conductivity.Inspired by the unique hierarchical mineral bridge structure of thalia dealbata stem,we fabricated an ultralight,superelastic,highly conductive carbon aerogel（KGCA）by using konjac glucomannan and graphene oxide as the carbon precursors.The unique mineral bridged layered structure not only endows the carbon aerogel with a low density of 4.2 mg cm^-3 but also a high electrical conductivity（12.9 S/m）and a high oil absorption capacity（360 g/g）.In addition,the carbon aerogel also exhibits superelastic property of 80%maximal strain and no obvious degradation after 1000 cycles of compression.We demonstrated that this Thalia dealbata-inspired carbon aerogel has potential applications in energy storage,sensors,absorbers and elastic conductors.For the current artificial mother-of-pearl structural materials,there are problems in the preparation process,the difficulty in controlling the ordered micro-nano structure,and the inability to achieve macroscopic scale and large-scale preparation.Based on the research foundation of microbial induced calcium carbonate mineralization and bionic micro/nano structural materials construction,inspired by the natural pearl layer growth mechanism,combined with the assembly process of different dimensions,the combination of assembly and biomineralization technology is proposed to construct a micro-nano layered framework-carbonate mineralized bacteria system.Microbial-induced calcium carbonate mineralization in micro/nano framework structure was carried out in order to realize the composite of organic and inorganic components and the structure of multi-stage structure,and prepare macroscopic shell-like nacre composite bionic composite structural materials under mild conditions.