Diffusion-Controlled Crystallization of Calcium Phosphate in a Hydrogel toward a Homogeneous Octacalcium Phosphate/Agarose Composite

Abstract

Diffusion-controlled crystallization in a hydrogel has been investigated to synthesize organic/inorganic hybrid composites and obtain a fundamental understanding of the detailed mechanism of biomineralization. Although calcium phosphate/hydrogel composites have been intensively studied and developed for the application of bone substitutes, the synthesis of homogeneous and integrated composites remains challenging. In this work, diffusion-controlled systems were optimized by manipulating the calcium ion flux at the interface, concentration gradient, and diffusion coefficient to synthesize homogeneous octacalcium phosphate/hydrogel composites with respect to the crystal morphology and density. The ion flux and local pH play an important role in determining the morphology, density, and phase of the crystals. This study suggests a model system that can reveal the relation between local conditions and the resulting crystal phase in diffusion-limited systems and provides a synthetic method for homogeneously organized organic/inorganic composites.

Diffusion-Limited Processes in Hydrogels with Chosen Applications from Drug Delivery to Electronic Components

“…In particular, the great advantage of the slow and constant supply of a reagent is implemented for predictable crystal growth. Controllable ion supply through hydrogels is reported to play a primary role in carbonate biomineralization [63,64]. Apart from biomineralization, hydrogels may be used for crystal shape perfection.…”

Mineralization of Octacalcium Phosphate under Magnetic Field

“…Two-dimensional OCP particles having a range of 3-5 µm have been explored for various applications, including adsorption and as capacitors. The size and shape of OCP play important roles in some uses [12]. The 3D flower-like OCP with a size of 2-5 µm was demonstrated to be an efficient Pb 2+ adsorbent.…”

Diffusion-Controlled Crystallization of Fluorapatite Mesocrystals in a Hydrogel

“…Biominerals, such as bones, teeth, and shells, possess sophisticated structures comprising organic and inorganic components, which exhibit superior mechanical properties. , In a biological system, mineralization is meticulously controlled by the functions of biopolymers and extracellular matrices. − Inspired by biomineralization, numerous approaches have been developed to replicate biogenic structures and functionality using soluble macromolecules and insoluble matrices. − However, the aspect of mass transfer received less emphasis in the field of bioinspired crystallization, even though mass transfer in living organisms is exquisitely regulated through passive diffusion and active transport. , While the slow supply of ions benefits the growth of single crystals by maintaining low supersaturation levels, it is widely recognized that amorphous precursors, accompanied by high supersaturation levels, play crucial roles in biomineralization. , The effect of slow diffusion remains a question for a fundamental understanding in biomineralization. A hydrogel has been employed as a medium for emulating the phases and structures of biominerals because it allows for the control of ion diffusion. − Within a hydrogel, crystal structure is controlled by manipulating various factors, such as gel type, gel strength, additives, and supersaturation. ,− A hydrogel is considered a significant scaffold in the development of organic–inorganic composites for biomedical applications and serves as a simplified model in the field of crystallization for fundamental mechanism studies.…”

“…Among various biominerals, fluorapatite (FAp), including hydroxyapatite (HAp), has been intensively studied for development of dental therapy and implant materials. , The substitution of HAp in the outer layer of dental enamel with FAp prevents dental caries caused by acids because the solubility of FAp is lower than that of HAp. − Similar to other biominerals or bioinspired crystals, the crystallization of FAp has been previously controlled using soluble macromolecules and insoluble matrices. − However, the controlled supply of ions has been rarely used for synthesizing FAp or regulating its crystalline structure, although slow crystallization resulting from the controlled supply of ions is beneficial for regulating the exquisite structure of biominerals. ,− In addition to other studies, we have attempted to regulate various biominerals in a hydrogel by controlling the diffusion of ions. − Hydrogels as organic scaffolds for synthesizing bone-mimicking composites have attracted considerable attention owing to their structural similarity with the extracellular matrix in biogenic bones and excellent biocompatibility, biodegradability, and applicability in cell incorporation and proliferation. − …”