Dual Doping of Silicon and Manganese in Hydroxyapatites: Physicochemical Properties and Preliminary Biological Studies.

Katarzyna Szurkowska,Agata Drobniewska,Joanna Kolmas

doi:10.3390/ma12162566

Abstract

Silicated hydroxyapatite powders enriched with small amounts of manganese (Mn2+) cations were synthesized via two different methods: precipitation in aqueous solution and the solid-state method. The source of Mn2+ ions was manganese acetate, while silicon was incorporated using two different reagents: silicon acetate and sodium metasilicate. Powder X-ray diffraction (PXRD) analysis showed that the powders obtained via the precipitation method consisted of single-phase nanocrystalline hydroxyapatite. In contrast, samples obtained via the solid-state method were heterogenous and contaminated with other phases, (i.e., calcium oxide, calcium hydroxide, and silicocarnotite) arising during thermal treatment. The transmission electron microscope (TEM) images showed powders obtained via the precipitation method were nanosized and elongated, while solid-state synthesis produced spherical microcrystals. The phase identification was complemented by Fourier transform infrared spectroscopy (FTIR). An in-depth analysis via solid-state nuclear magnetic resonance (ssNMR) was carried out, using phosphorus 31P single-pulse Bloch decay (BD) (31P BD) and cross-polarization (CP) experiments from protons to silicon-29 nuclei (1H → 29Si CP). The elemental measurements carried out using wavelength-dispersive X-ray fluorescence (WD-XRF) showed that the efficiency of introducing manganese and silicon ions was between 45% and 95%, depending on the synthesis method and the reagents. Preliminary biological tests on the bacteria Allivibrio fisheri (Microtox®) and the protozoan Spirostomum ambiguum (Spirotox) showed no toxic effect in any of the samples. The obtained materials may find potential application in regenerative medicine, bone implantology, and orthopedics as bone substitutes or implant coatings.

Highlights

Among the calcium phosphates, hydroxyapatite (HA) (Ca10 (PO4 )6 (OH)2 ) has received considerable attention as a bone substitute material for orthopaedic and dental applications due to its strong affinity toward human mineralized tissues [1,2,3,4]
It should be noted that synthetic hydroxyapatites are highly susceptible to ionic substitution
Regardless of the silicon source, Si was introduced into hydroxyapatite in the form of orthosilicate SiO4 4− ions

Summary

Introduction

Hydroxyapatite (HA) (Ca10 (PO4 ) (OH)2 ) has received considerable attention as a bone substitute material for orthopaedic and dental applications due to its strong affinity toward human mineralized tissues (bone and teeth) [1,2,3,4]. It should be noted that synthetic hydroxyapatites are highly susceptible to ionic substitution. The introduction of various ions into the crystal structure of hydroxyapatite allows for obtaining material similar to bones and teeth. This is based on the concepts of biomimetics, where the greater the Materials 2019, 12, 2566; doi:10.3390/ma12162566 www.mdpi.com/journal/materials. It is important to note that ionic substitutions can change some physicochemical properties, such as the crystallographic lattice parameters, crystal morphology, and the degree of crystallinity

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Results