Atom Probe Tomography of Encapsulated Hydroxyapatite Nanoparticles

Abstract

Hydroxyapatite nanoparticles (HAP NPs) are important for medicine, bioengineering, catalysis, and water treatment. However, current understanding of the nanoscale phenomena that confer HAP NPs their many useful properties is limited by a lack of information about the distribution of the atoms within the particles. Atom probe tomography (APT) has the spatial resolution and chemical sensitivity for HAP NP characterization, but difficulties in preparing the required needle‐shaped samples make the design of these experiments challenging. Herein, two techniques are developed to encapsulate HAP NPs and prepare them into APT tips. By sputter‐coating gold or the atomic layer deposition of alumina for encapsulation, partially fluoridated HAP NPs are successfully characterized by voltage‐ or laser‐pulsing APT, respectively. Analyses reveal that significant tradeoffs exist between encapsulant methods/materials for HAP characterization and that selection of a more robust approach will require additional technique development. This work serves as an essential starting point for advancing knowledge about the nanoscale spatiochemistry of HAP NPs.

Developing Atom Probe Tomography to Characterize Sr-Loaded Bioactive Glass for Bone Scaffolding

“…Mass spectra peak overlap contributions were deconvoluted and the average bulk composition from six data sets of the pSrBG scaffold is shown in Table 2, which for the most part is in reasonable agreement with the nominal composition. There are also some deviations between the bulk composition measured by APT and the nominal pSrBG composition, such as overestimation of Ca, P, Mg, and a deficit of O and K. Similar discrepancies have also been reported in other studies of hydroxyapatite and nacre (Eder et al, 2019;Mosiman et al, 2020). We suspect that the origins of these are down to the atom probe measurement, as there are many factors affecting the concentration measurements.…”

Permanently polarized hydroxyapatite, an outstanding catalytic material for carbon and nitrogen fixation

“…Characterization of the HAp lattice rearrangements undergone during the polarization process is not an easy task. Although some attempts to track the OH − orientation or to directly characterize the nanoscale spatial-chemistry through HRTEM and atom probe tomography have been reported, 34 most relevant results arise from spectroscopic techniques. Among the latter, Raman spectroscopy presents significant advantages with respect to other common techniques due to the combination of two facts: (1) it provides exhaustive vibrational information of each specie in the HAp lattice ( i.e.…”

Atomically Resolved Interfacial Analysis of Bone‐Like Hydroxyapatite Nanoparticles on Titanium

“…The APT data analysis proved to be challenging due to the high number of peaks in the mass spectrum. The hydroxyapatite evaporates in various molecular species, other studies report several peaks in the range 10–50 Da as nanoHA related [ 27 ] while the chemically similar bone is reported to evaporate as many different ions with varying mass‐to‐charge‐state ratios. [ 37 ] Numerous of these overlap with the different molecular species attributed to the chromium and titanium oxides.…”

“…[ 26 ] For example, hydroxyapatite nanoparticles have successfully been studied using APT by embedding the particles in alumina and gold matrixes. [ 27 ] However, studying interfaces, especially those composed of materials with different evaporation fields, poses a significant challenge in APT, necessitating the development of novel methodologies and sample preparation techniques.…”