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Artificial enamel induced by phase transformation of amorphous nanoparticles.

ABSTRACT: Human tooth enamel has tightly packed c-axis-oriented hydroxyapatite (HAP: Ca₁₀(PO₄)₆(OH)₂) nanorods with high elastic modulus. Fabrication of an enamel architecture in vitro supports the repair of teeth using HAP; however, existing methods require complex and laborious steps to form an enamel-like structure. Here we present a very simple and effective technique for forming artificial enamel in near-physiological solution using a substrate composed of amorphous calcium phosphate (ACP) nanoparticles. Without any functionalized modification of the substrate surface, faint dissolution and successive phase transformation automatically induce formation of an intermediate layer of low-crystalline HAP nanoparticles, on which highly oriented HAP nanorods grow by geometrical selection. We also show that an enamel structure forms on a substrate of amorphous calcium carbonate when the surface nanoparticles react so as to form an intermediate layer similar to that in ACP. Our results demonstrate that there is a wide range of substrate choices for nanorod array formation. Contrary to current understanding, a stable surface designed in nanoscale is not essential for the growth of arranged guest crystals. Reactive amorphous nanoparticles and their transformation efficiently induce a nanorod array structure.

SUBMITTER: Onuma K

PROVIDER: S-EPMC5457434 | biostudies-literature | 2017 Jun

REPOSITORIES: biostudies-literature

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Artificial enamel induced by phase transformation of amorphous nanoparticles.

Onuma Kazuo K Iijima Mayumi M

Scientific reports 20170602 1

Human tooth enamel has tightly packed c-axis-oriented hydroxyapatite (HAP: Ca10(PO4)6(OH)2) nanorods with high elastic modulus. Fabrication of an enamel architecture in vitro supports the repair of teeth using HAP; however, existing methods require complex and laborious steps to form an enamel-like structure. Here we present a very simple and effective technique for forming artificial enamel in near-physiological solution using a substrate composed of ...[more]

PMID: 28578434

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Project description:Spray drying is widely used in the manufacturing of amorphous solid dispersion (ASD) systems due to its fast drying rate, enabling kinetic trapping of the drug in amorphous form. Spray-drying conditions, such as solvent composition, can have a profound impact on the properties of spray-dried dispersions. In this study, the phase behavior of spray-dried dispersions from methanol and methanol-water mixtures was assessed using ritonavir and copovidone [poly(vinylpyrrolidone-co-vinyl acetate) (PVPVA)] as dispersion components. The resultant ASDs were characterized using differential scanning calorimetry (DSC), fluorescence spectroscopy, X-ray photoelectron spectroscopy (XPS), as well as surface-normalized dissolution rate (SNDR) measurements. Quaternary phase diagrams were calculated using a four-component Flory-Huggins model. It was found that the addition of water to the solvent system can lead to phase separation during the spray-drying process. A 10:90 H2O/MeOH solvent system caused a minor extent of phase separation. Phase heterogeneity in the 50 and 75% drug loading ASDs prepared from this spray solvent can be detected using DSC but not with other techniques used. The 25% drug loading system did not show phase heterogeneity in solid-state characterization but exhibited a compromised dissolution rate compared to that of the miscible ASD prepared from H2O-free solvent. This is possibly due to the formation of slow-releasing drug-rich phases upon phase separation. ASDs prepared with a 60:40 H2O/MeOH solvent mixture showed phase heterogeneity with all analytical methods used. The surface composition of dispersion particles as measured by fluorescence spectroscopy and XPS showed good agreement, suggesting surface drug enrichment of the spray-dried ASD particles prepared from this solvent system. Calculated phase diagrams and drying trajectories were consistent with experimental observations, suggesting that small variations in solvent composition may cause significant changes in ASD phase behavior during drying. These findings should aid in spray-drying process development for ASD manufacturing and can be applied broadly to assess the risk of phase separation for spray-drying systems using mixed organic solvents or other solvent-based processes.

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Artificial enamel induced by phase transformation of amorphous nanoparticles.

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Artificial enamel induced by phase transformation of amorphous nanoparticles.

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