A Comparative Study of the Sintering Behavior of Pure and Manganese-Substituted Hydroxyapatite.

Seamus D Thomson,Mei Wei,Michael Zilm

doi:10.3390/ma8095308

Seamus D Thomson, Mei Wei + Show 1 more

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https://doi.org/10.3390/ma8095308

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Abstract

Hydroxyapatite (HA) is a widely studied biomaterial for its similar chemical composition to bone and its osteoconductive properties. The crystal structure of HA is flexible, allowing for a wide range of substitutions which can alter bioactivity, biodegradation, and mechanical properties of the substituted apatite. The thermal stability of a substituted apatite is an indication of its biodegradation in vivo. In this study, we investigated the thermal stability and mechanical properties of manganese-substituted hydroxyapatite (MnHA) as it is reported that manganese can enhance cell attachment compared to pure HA. Pure HA and MnHA pellets were sintered over the following temperature ranges: 900 to 1300 °C and 700 to 1300 °C respectively. The sintered pellets were characterized via density measurements, mechanical testing, X-ray diffraction, and field emission electron microscopy. It was found that MnHA was less stable than HA decomposing around 800 °C compared to 1200 °C for HA. The flexural strength of MnHA was weaker than HA due to the decomposition of MnHA at a significantly lower temperature of 800 °C compared to 1100 °C for HA. The low thermal stability of MnHA suggests that a faster in vivo dissolution rate compared to pure HA is expected.

Highlights

Hydroxyapatite (HA) is an inorganic constituent of natural bone, which has been extensively studied for its biocompatible and osteo-regenerative properties, serving a scaffold for modern bone graft substitutes [1,2,3]
For temperatures greater than 700 ̋ C, HA begins to decompose into different phases such as tricalcium phosphate (TCP), calcium oxide (CaO) and water (H2 O) [16]
SPEX-milled as-synthesized HA and manganese-substituted hydroxyapatite (MnHA) powders were characterized with TEM for particle sizeSPEX-milled analysis

Summary

Introduction

Hydroxyapatite (HA) is an inorganic constituent of natural bone, which has been extensively studied for its biocompatible and osteo-regenerative properties, serving a scaffold for modern bone graft substitutes [1,2,3]. HA is brittle in nature and has a slow in vivo degradation rate which limits its applications to coatings for orthopedic implants [2,6,7,8]. To overcome these issues, HA may be densified through sintering to improve mechanical strength and or through ionic substitutions to enhance bioactivity and mechanical strength [7,8,9,10,11,12,13,14,15].

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