Materials, 2023,16,6397,https://doi.org/10.3390/ma16196397

Article: “Enhanced Release of Calcium Ions from Hydroxyapatite Nanoparticles with an Increase in Their Specific Surface Area”

Urszula Szałaj 1,2,* , Agnieszka Chodara 3, Stanisław Gierlotka 1, Jacek Wojnarowicz 1 and Witold Łojkowski 1

1 Laboratory of Nanostructures, Institute of High Pressure Physics, Polish Academy of Science,

Sokolowska 29/37, 01-142 Warsaw, Poland; This email address is being protected from spambots. You need JavaScript enabled to view it. (S.G.); This email address is being protected from spambots. You need JavaScript enabled to view it. (J.W.);

This email address is being protected from spambots. You need JavaScript enabled to view it. (W.Ł.)

2 Faculty of Materials Engineering, Warsaw University of Technology, Wołoska 41, 02-507 Warsaw, Poland

3 Leyton Poland Ltd., Wspólna 70, 00-687 Warsw, Poland; This email address is being protected from spambots. You need JavaScript enabled to view it.

* Correspondence: This email address is being protected from spambots. You need JavaScript enabled to view it.; Tel.: +48-22-876-04-29

 

Abstract: Synthetic calcium phosphates, e.g., hydroxyapatite (HAP) and tricalcium phosphate (TCP), are the most commonly used bone-graft materials due to their high chemical similarity to the natural hydroxyapatite—the inorganic component of bones. Calcium in the form of a free ion or bound complexes plays a key role in many biological functions, including bone regeneration. This paper explores the possibility of increasing the Ca2+-ion release from HAP nanoparticles (NPs) by reducing their size. Hydroxyapatite nanoparticles were obtained through microwave hydrothermal synthesis. Particles with a specific surface area ranging from 51 m2/g to 240 m2/g and with sizes of 39, 29, 19, 11, 10, and 9 nm were used in the experiment. The structure of the nanomaterial was also studied by means of helium pycnometry, X-ray diffraction (XRD), and transmission-electron microscopy (TEM). The calcium-ion release into phosphate-buffered saline (PBS) was studied. The highest release of Ca2+ ions, i.e., 18 mg/L, was observed in HAP with a specific surface area 240 m2/g and an average nanoparticle size of 9 nm. A significant increase in Ca2+-ion release was also observed with specific surface areas of 183 m2/g and above, and with nanoparticle sizes of 11 nm and below. No substantial size dependence was observed for the larger particle sizes.

Keywords: hydroxyapatite (HAP); nanoparticles; microwave hydrothermal synthesis; calcium-ion release; solubility; size effect; specific surface area.