Solvothermal Synthesis of Magnesium Oxide-Substituted Hydroxyapatite Nanoparticles as Antibacterial Nanomaterial for Biomedical Applications Carlos Paucar Álvarez 1,d , Jeniffer S. Caballero Sarmiento 1,a * , Sidónio C. Freitas 2,b * and Claudia García 1,c* 1 Universidad Nacional de Colombia, Faculty of Science, Colombia 2 Universidad Cooperativa de Colombia, Faculty of Dentistry, Colombia a jscaballeros@unal.edu.co, b sidonio.freitas@campusucc.edu.c, c cpgarcia@unal.edu.co, d cgpaucar@unal.edu.co Keywords: hydroxyapatite, antibacterial activity, magnesium oxide, solvothermal method. Abstract. In order to generate bactericidal effects in the oral cavity, several alternatives have been studied, including the use of silver nanoparticles but presents problems such as toxicity and low biocompatibility. From human-inspired systems, the antibacterial efficiency of the hydroxyapatite nanoparticles depends strongly on the type of composites and nanoparticles size. Several types of hydroxyapatite nanoparticles and their derivatives have received much attention for their antibacterial potential effect, including magnesium oxide nanoparticles. The purpose of this research was to produce a biocompatible antimicrobial compound of nanoparticles of hydroxyapatite doped with magnesium oxide to generate antibacterial effects in the oral cavity. The solvothermal method was used to produce hydroxyapatite nanoparticles doped with magnesium oxide. Antibacterial activity of as synthesized nanopowders against cariogenic Streptococcus mutans was tested by the CLSI disk-diffusion method. As result of this research, hydroxyapatite doped with magnesium nanoparticles (nHAMg) were successfully synthetized by the solvothermal method where in structural characterization indicates magnesium substitution and FTIR analysis gives a broader spectrum of the nHAMg when compared to pure nHA and crystallite size of nHA decreased. Furthermore, results of antibacterial assays showed that nHAMg allow to inhibit the grown of S. mutans by showing a halo of inhibition around the discs. Moreover, this antibacterial activity is enhanced by the addition of silver ion in an amount below to known toxic concentration, showing a synergetic effect that can further potentiate even more these HA nanoparticles. This work demonstrates that solvothermal method is a promising synthesis way for producing antibacterial hydroxyapatites nanoparticles for biomedical applications such as oral tissue regeneration. Introduction Calcium phosphate-based biomaterials (CaPs) are used for the reconstruction of bone defects especially in the field of dentistry, orthopedics and surgery. These materials have properties of biocompatibility, osteoconductivity and osseointegration that potentiate their applications in the biomedical field [1,2]. Hydroxyapatite (HA) is one of the major constituents of the bone matrix, is the most stable, densest and least soluble of the CaPs [3], is biocompatible and bioactive; its ionic structural model can accept cationic and anionic substituents. The substitution induces modifications in the crystallinity, morphology, cell parameters and stability of the apatite structure, allowing to adapt its properties and to enhance its application [4–6]. Through nanotechnology and the materials science, it is possible to develop biomaterials with a broad spectrum of bactericidal activity not susceptible to the development of microbial resistance and nontoxic for the prevention and/or treatment of an infection. Nano and micro particles of HA with metallic nanoparticles such as Ag, silver oxide (Ag 2 O), titanium oxide (TiO 2 ), silicon (Si), copper oxide (CuO), zinc oxide (ZnO), Au, oxide Calcium (CaO) and magnesium oxide (MgO), can be a promising material to combat infectious diseases [7,8]. Defect and Diffusion Forum Submitted: 2017-08-17 ISSN: 1662-9507, Vol. 381, pp 8-14 Accepted: 2017-08-18 doi:10.4028/www.scientific.net/DDF.381.8 Online: 2017-11-30 © 2017 Trans Tech Publications, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, www.scientific.net. (#103817305-21/11/17,00:58:26)