ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Preparation, characterization, and protein adsorption properties of heat- and gamma-sterilized suspensions of nanocrystalline apatites with varying calcium deficiency

Marco Kostadinov, Petya Kovacheva, and Georgi Yordanov

Faculty of Chemistry and Pharmacy, Sofia University St. Kliment Ohridski, Sofia, Bulgaria

E-mail: g.g.yordanov@gmail.com

Received: 15 September 2025  Accepted: 31 December 2025

Abstract:

We prepared aqueous suspensions of nanocrystalline apatites with varying degrees of calcium deficiency using an improved precipitation method. These suspensions underwent physicochemical characterization, protein adsorption studies, and hemolysis testing. Sterilization of the suspensions was performed either by thermal treatment (autoclaving) or gamma irradiation. The apatite nanocrystals were analyzed by electron microscopy, X-ray powder diffraction, infrared spectroscopy, and solid state ¹H and ³¹P NMR spectroscopy. Thermal sterilization via autoclaving increased the crystallinity index of the apatites and reduced their protein adsorption efficiency. In contrast, gamma sterilization (25 kGy) of non-heated suspensions had no observable effect on nanocrystal morphology, pH, or the relatively high protein adsorption efficiency (> 90%), indicating their potential suitability for protein delivery applications in biomedicine and vaccinology. Preliminary hemolysis tests showed no measurable hemolytic activity.

Graphical abstract

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Keywords: Nanocrystals; Hydroxyapatite; Calcium phosphate; Adjuvant; Hemolysis

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-026-04643-6

Chemical Papers 80 (4) 3709–3720 (2026)