Abstract
Copper-doped hydroxyapatite (HA) of nominal composition Ca10(PO4)6[Cux(OH)2-2xOx] (0.0 ≤ x ≤ 0.8) was prepared by solid-state and wet chemical processing to explore the impact of the synthesis route and mode of crystal chemical incorporation of copper on the antibacterial efficacy against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) strains. Apatites prepared by solid-state reaction showed unit cell volume dilation from 527.17 Å3 for copper-free HA to 533.31 Å3 for material of the putative composition Ca10(PO4)6[Cu0.8(OH)0.4O0.8] consistent with Cu+ insertion into the [001] hydroxyapatite channel. This was less pronounced (528.30 Å3 to 529.3 Å3) in the corresponding wet chemical synthesised products, suggesting less complete Cu tunnel incorporation and partial tenancy of Cu in place of calcium. X-ray absorption spectroscopy suggests fast quenching is necessary to prevent oxidation of Cu+ to Cu2+. Raman spectroscopy revealed an absorption band at 630 cm−1 characteristic of symmetric O-Cu+-O units tenanted in the apatite channel while solid-state 31P magic-angle-spinning nuclear magnetic resonance (MAS NMR) supported a vacancy-Cu+ substitution model within the apatite channel. The copper doping strategy increases antibacterial efficiency by 25% to 55% compared to undoped HA, with the finer particle sizes and greater specific surface areas of the wet chemical material demonstrating superior efficacy.
Highlights
The crystallochemical formula of apatite is [AI 4 AII 6 ](MO4 )6 [X2 ], where A is a larger cation, M a smaller cation, and X an anion [1,2,3]
Powder X-ray diffraction (PXRD) patterns were collected using a Bruker D8 Advance instrument (Bruker, Billerica, USA (Bragg-Brentano geometry)) equipped with a Cu Kα (1.5406 Å) X-ray tube operating at 40 kV and 40 mA with data accumulated at a step size of 0.02◦ 2θ and dwell time of 2 s per step
A similar method was followed for S. aureus, only with the control sample, HA6WCM and HA6SS
Summary
The crystallochemical formula of apatite is [AI 4 AII 6 ](MO4 )6 [X2 ], where A is a larger cation (especially alkali, alkaline-earth, lanthanide), M a smaller cation, and X an anion [1,2,3] These structural elements are arranged as an [AI 4 ](MO4 ) framework surrounding an [AII 6 ][X2 ] channel (Figure 1). 22 of of 17 remediation of hazardous waste with the flexibility to accept a multitude of cation and anion modifying its physical, chemical and biological properties [4,5,6,7,8,9]. This study describes the incorporation of monovalent copper in HA ofdo a nominal composition sometimes conjectural, and studies of prosthetic applications usually not consider crystal. HA systems were prepared by solid-state and wet chemical deployment of as a bio-implant material for musculoskeletal surgery were considered.
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