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. 2024 Jan 3;25(1):621.
doi: 10.3390/ijms25010621.

Comparative In Vitro Dissolution Assessment of Calcined and Uncalcined Hydroxyapatite Using Differences in Bioresorbability and Biomineralization

Woo Young Jang  1   2 , Jae Chul Pyun  2 , Jeong Ho Chang  1
Affiliations

Comparative In Vitro Dissolution Assessment of Calcined and Uncalcined Hydroxyapatite Using Differences in Bioresorbability and Biomineralization

Woo Young Jang et al. Int J Mol Sci. .

Abstract

This study reports the effect of the not-calcining process on the bioresorption and biomineralization of hydroxyapatite through in vitro dissolution assessment. The prepared calcined hydroxyapatite (c-HAp) and uncalcined hydroxyapatite (unc-HAp) have a particle size of 2 μm and 13 μm, surface areas of 4.47 m2/g and 108.08 m2/g, and a Ca/P ratio of 1.66 and 1.52, respectively. In vitro dissolution assessments of c-HAp and unc-HAp were performed for 20 days at 37 °C in a citric acid buffer according to ISO 10993-14. During the dissolution, the c-HAp and unc-HAp confirmed an increase in weight, and the calcium and phosphorous ions were rapidly released. The calcium ions released from c-HAp formed rod-shaped particles with a longer and thinner morphology, while in unc-HAp, they appeared thicker and shorter. In the ICP-OES results, the concentrations of calcium elements were initially increased and then decreased by this formation. The rod-shaped particles identified as calcium citrate (Ca-citrate) through the XRD pattern. The calcium content of Ca-citrate particles from unc-HAp was higher than that from c-HAp. The unc-HAp demonstrated non-toxic properties in a cytotoxicity evaluation. Therefore, due to its higher bioresorption and biomineralization, unc-HAp exhibits enhanced biocompatibility compared to c-HAp.

Keywords: biomineralization; bioresorption; calcium citrate; dissolution; uncalcined hydroxyapatite.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Comparison of c-HAp and unc-HAp characterizations. (a) TEM images, (b) particle size distribution and SEM image, and (c) XRD pattern.
Figure 2
Figure 2
(a) Nitrogen adsorption–desorption isotherms, (b) BET parameters of surface areas, pore volume, and pore size, (c) contents of calcium and phosphorous elements and Ca/P molar ratios, (d) cell viability, and (e) compressive strength–stain curve and fracture strength of the c-HAp and unc-HAp.
Figure 3
Figure 3
Comparison of in vitro dissolution assessments of c-HAp and unc-HAp. (a) Weight of powder, (b) calcium and phosphorus elements concentrations in the eluted filtrate by ICP-OES analysis, (c) XRD pattern and crystallinity, (d) dissolution efficiency, (e) dissolution rate, and (f) SEM images as a function of the time.
Figure 4
Figure 4
(a) FIB-SEM images showing cross-sectional views, aspect ratio, and EDS results of rod-shaped particles, (b) XRD pattern and molecular modeling of the c-HAp and unc-HAp at 20 days, and (c) schematic representations of c-HAp and unc-HAp in citric acid.
Figure 4
Figure 4
(a) FIB-SEM images showing cross-sectional views, aspect ratio, and EDS results of rod-shaped particles, (b) XRD pattern and molecular modeling of the c-HAp and unc-HAp at 20 days, and (c) schematic representations of c-HAp and unc-HAp in citric acid.
Figure 5
Figure 5
(a) Cell viability through an MTT assay observed during in vitro dissolution assessment of c-HAp and unc-HAp at 20 days, and (b) calcium/carbon contents of Ca-citrate-1 and Ca-citrate-2.
Figure 6
Figure 6
Changes in calcium ion concentration with bioresorption and biomineralization of c-HAp and unc-HAp.
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