First-Row Transition Metal Doping in Calcium Phosphate Bioceramics: A Detailed Crystallographic Study.

Guillaume Renaudin,Sandrine Gomes,Jean-Marie Nedelec

doi:10.3390/ma10010092

Abstract

Doped calcium phosphate bioceramics are promising materials for bone repair surgery because of their chemical resemblance to the mineral constituent of bone. Among these materials, BCP samples composed of hydroxyapatite (Ca10(PO4)6(OH)2) and β-TCP (Ca3(PO4)2) present a mineral analogy with the nano-multi-substituted hydroxyapatite bio-mineral part of bones. At the same time, doping can be used to tune the biological properties of these ceramics. This paper presents a general overview of the doping mechanisms of BCP samples using cations from the first-row transition metals (from manganese to zinc), with respect to the applied sintering temperature. The results enable the preparation of doped synthetic BCP that can be used to tailor biological properties, in particular by tuning the release amounts upon interaction with biological fluids. Intermediate sintering temperatures stabilize the doping elements in the more soluble β-TCP phase, which favors quick and easy release upon integration in the biological environment, whereas higher sintering temperatures locate the doping elements in the weakly soluble HAp phase, enabling a slow and continuous supply of the bio-inspired properties. An interstitial doping mechanism in the HAp hexagonal channel is observed for the six investigated cations (Mn2+, Fe3+, Co2+, Ni2+, Cu2+ and Zn2+) with specific characteristics involving a shift away from the center of the hexagonal channel (Fe3+, Co2+), cationic oxidation (Mn3+, Co3+), and also cationic reduction (Cu+). The complete crystallochemical study highlights a complex HAp doping mechanism, mainly realized by an interstitial process combined with calcium substitution for the larger cations of the series leading to potentially calcium deficient HAp.

Highlights

Biphasic Calcium Phosphates (BCP) are a promising class of bioceramics for applications in bone repair/replacement surgery
Calcium orthophosphates are present in the bones, teeth, and tendons of mammals [3]; namely the Ca10 (PO4 )6 (OH)2 hydroxyapatite phase composing the mineral part of bones (45–70 weight percent; wt %), dentine (45–70 wt %), and enamel (~95 wt %) [4]
BCP ceramics are mainly composed of hydroxyapatite (HAp) mixed with a smaller amount of beta tricalcium phosphate (Ca3 (PO4 )2, Materials 2017, 10, 92; doi:10.3390/ma10010092

Summary

Introduction

Biphasic Calcium Phosphates (BCP) are a promising class of bioceramics for applications in bone repair/replacement surgery. BCP ceramics are mainly composed of hydroxyapatite (HAp) mixed with a smaller amount of beta tricalcium phosphate (Ca3 (PO4 ) , Materials 2017, 10, 92; doi:10.3390/ma10010092 www.mdpi.com/journal/materials. BCP ceramics take advantage of the difference in solubility between β-TCP (the more soluble when implanted in the body) and HAp (less soluble, with long-term bioresorbable properties) [3]. Another interesting aspect of BCP is the possibility to prepare multi-substituted ceramics—both HAp and β-TCP structures are known to accept a large variety of atomic incorporations—in order to improve their biological and/or mechanical behavior

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