Kinetics of Calcite Nucleation onto Sulfated Chitosan Derivatives and Implications for Water-Polysaccharide Interactions during Crystallization of Sparingly Soluble Salts

Anionic macromolecules are found at sites of CaCO3 biomineralization in diverse organisms, but their roles in crystallization are not well-understood. We prepared a series of sulfated chitosan derivatives with varied positions and degrees of sulfation, DS(SO3 -), and measured calcite nucleation rate onto these materials. Fitting the classical nucleation theory model to the kinetic data reveals the interfacial free energy of the calcite-polysaccharide-solution system, γnet, is lowest for nonsulfated controls and increases with DS(SO3 -). The kinetic prefactor also increases with DS(SO3 -). Simulations of Ca2+-H2O-chitosan systems show greater water structuring around sulfate groups compared to uncharged substituents, independent of sulfate location. Ca2+-SO3 - interactions are solvent-separated by distances that are inversely correlated with DS(SO3 -) of the polysaccharide. The simulations also predict SO3 - and NH3 + groups affect the solvation waters and HCO3 - ions associated with Ca2+. Integrating the experimental and computational evidence suggests sulfate groups influence nucleation by increasing the difficulty of displacing near-surface water, thereby increasing γnet. By correlating γnet and net charge per monosaccharide for diverse polysaccharides, we suggest the solvent-separated interactions of functional groups with Ca2+ influence thermodynamic and kinetic components to crystallization by similar solvent-dominated processes. The findings reiterate the importance of establishing water structure and properties at macromolecule-solution interfaces.

Effect of linearly polarized microwaves on nanomorphology of calcium carbonate mineralization using peptides

Microwaves are used for diverse applications such as mobile phones, ovens, and therapy devices. However, there are few reports on the effects of microwaves on diseases other than cancer, and on physiological processes. Here, we focused on CaCO₃ mineralization as a model of biomineralization and attempted to elucidate the effect of microwaves on CaCO₃ mineralization using peptides. We conducted AFM, ζ potential, HPLC, ICP-AES, and relative permittivity measurements. Our findings show that microwaves alter the nanomorphology of the CaCO₃ precipitate, from sphere-like particles to string-like structures. Furthermore, microwaves have little effect on the mineralization when the mineralization ability of a peptide is high, but a large effect when the precipitation ability is low. Our findings may be applicable to not only the treatment of teeth and bones but also the development of organic-inorganic nanobiomaterials. This methodology can be expanded to other molecular/atomic reactions under various microwave conditions to alter reaction activity parameters.

Chitosan as a Canvas for Studies of Macromolecular Controls on CaCO3 Biological Crystallization

A mechanistic understanding of how macromolecules, typically as an organic matrix, nucleate and grow crystals to produce functional biomineral structures remains elusive. Advances in structural biology indicate that polysaccharides (e.g., chitin) and negatively charged proteoglycans (due to carboxyl, sulfate, and phosphate groups) are ubiquitous in biocrystallization settings and play greater roles than currently recognized. This review highlights studies of CaCO₃ crystallization onto chitinous materials and demonstrates that a broader understanding of macromolecular controls on mineralization has not emerged. With recent advances in biopolymer chemistry, it is now possible to prepare chitosan-based hydrogels with tailored functional group compositions. By deploying these characterized compounds in hypothesis-based studies of nucleation rate, quantitative relationships between energy barrier to crystallization, macromolecule composition, and solvent structuring can be determined. This foundational knowledge will help researchers understand composition-structure-function controls on mineralization in living systems and tune the designs of new materials for advanced applications.

Bioinspired macromolecular templates for crystallographic orientation control of ZnO thin films through zinc hydroxide carbonate

The biomineralization-inspired preparation of inorganic hybrid materials has attracted attention. Here, we report a new approach to the orientation control of zinc oxide (ZnO) thin-film crystals through the preparation of zinc hydroxide carbonate (ZHC) by the macromolecular templates of poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(vinyl alcohol) (PVA). Using 100-nm-thick PHEMA templates, ZHC thin films with the c-axis oriented parallel to the substrate were obtained, while ZHC thin films prepared by 100-nm-thick PVA templates showed perpendicular orientation. After the thermal treatment of ZHC, the crystal orientations of the ZnO thin films were maintained. The effects of the thickness and annealing time for the polymer templates on the morphologies of the ZnO thin films were examined.

Development of biomineralization-inspired hybrids based on β-chitin and zinc hydroxide carbonate and their conversion into zinc oxide thin films

Hybrid thin films based on an environmentally friendly biopolymer, β-chitin and zinc hydroxide carbonate were developed through a biomineralization-inspired approach.

Hierarchical Microspheres Constructed from Chitin Nanofibers Penetrated Hydroxyapatite Crystals for Bone Regeneration

Chitin exists abundantly in crab and shrimp shells as the template of the minerals, which inspired us to mineralize it for fabricating bone grafting materials. In the present work, chitin nanofibrous microspheres were used as the matrix for in situ synthesis of hydroxyapatite (HA) crystals including microflakes, submicron-needles, and submicron-spheres, which were penetrated by long chitin nanofibers, leading to the hierarchical structure. The shape and size of the HA crystals could be controlled by changing the HA synthesis process. The tight interface adhesion between chitin and HA through the noncovanlent bonds occurred in the composite microspheres, and HAs were homogeneously dispersed and bounded to the chitin nanofibers. In our findings, the inherent biocompatibilities of the both chitin and HA contributed the bone cell adhesion and osteoconduction. Moreover, the chitin microsphere with submicron-needle and submicron-sphere HA crystals remarkably promoted in vitro cell adhesion and in vivo bone healing. It was demonstrated that rabbits with 1.5 cm radius defect were almost cured completely within three months in a growth factor- and cell-free state, as a result of the unique surface microstructure and biocompatibilities of the composite microspheres. The microsphere scaffold displayed excellent biofunctions and an appropriate biodegradability. This work opened up a new avenue to construct natural polymer-based organic-inorganic hybrid microspheres for bone regeneration.

Site-specific control of multiple mineralizations using a designed peptide and DNA

We have developed a site-specific method for precipitating multiple inorganic compounds using target DNA and a designed peptide consisting of a peptide nucleic acid (PNA) sequence and an inorganic compound-precipitating sequence. This system for controlled site-specific precipitation represents a powerful tool for use in nanobiotechnology and materials science.

A bio-process inspired synthesis of vaterite (CaCO3), directed by a rationally designed multifunctional protein, ChiCaSifi

A bio-process inspired synthesis of vaterite (CaCO₃) is achieved under the functions of a rationally designed multifunctional protein, ChiCaSifi.

A bio-inspired nacre-like layered hybrid structure of calcium carbonate under the control of carboxyl graphene

Schematic illustration of the fabrication of GO-COOH/CaCO₃ multilayer hybrid structures: GO-COOH, the GO-COOH/CaCl₂ multilayer hybrid structure, and the GO-COOH/CaCO₃ hybrid multilayer structure (from left to right).

Biomineralization-inspired synthesis of functional organic/inorganic hybrid materials: organic molecular control of self-organization of hybrids

Biomineralization-inspired synthesis of functional organic/inorganic hybrid materials. Molecularly controlled mechanisms of biomineralization and application of the processes towards future material synthesis are introduced.

Aragonite nanorods in calcium carbonate/polymer hybrids formed through self-organization processes from amorphous calcium carbonate solution

Nanostructured inorganic/polymer hybrid thin films comprising aragonite nanorods derived from aqueous suspensions of amorphous calcium carbonate (ACC) are prepared. For the formation of calcium carbonate (CaCO₃)/polymer hybrids, spincoated and annealed films of poly(vinyl alcohol) (PVA) that function as polymer matrices are soaked in aqueous colloidal solutions dispersing ACC stabilized by poly(acrylic acid) (PAA). In the initial stage, calcite thin films form on the surface. Subsequently, aragonite crystals start to form inside the PVA matrix that contains PVA crystallites which induce aragonite nucleation. Nanostructured hybrids composed of calcite thin films consisting of nanoparticles and assembled aragonite nanorods are formed in the matrices of PVA.