Fig 1.
Macroscopic and nanoscale evolution of HA upon heating.
a) sample preparation scheme; b) color changes of bone sticks as a function of temperature; scale bar 10 mm; c) SEM images showing the nanoscale heating effect on ns-HA, and compared to s-HA and β-TCP. Scale bar is 200 nm for all the images.
Fig 2.
THz absorption spectra of bone and synthetic reference calcium phosphate compounds.
a) absorption coefficients of an untreated bone sample and a series of temperature-treated samples up to 800 °C; b) absorption coefficients from a series of high-temperature (from 800 to 900 °C) treated bone samples; c) absorption coefficients of commercial ns-HA powder samples, untreated and treated at different temperatures; d) absorption coefficients from a series of reference calcium phosphate compounds: stoichiometric hydroxyapatite s-HA, TTCP, α and β-TCP, and β-CPP.
Fig 3.
X-ray diffraction patterns collected from a) untreated and heat-treated bone tissues, and b) untreated and heat-treated commercial hydroxyapatite powder (ns-HA). c) Simulated patterns for synthetic calcium phosphate compounds based on refined structures [41–44].
Fig 4.
Simulation of THz spectra (continuous lines) by calculation of the normal modes of vibrational with DFT and experimental THz absorption data (dotted lines).
In order to facilitate the visual comparison of these spectra, we adapted the experimental amplitude and frequency scales to match the 2.1 THz measured peak with the 2.8 THz calculated peak.
Fig 5.
(a) Magnification of THZ-TDS spectra of bones and HA samples around the peak at 2.1 THz (dots) and fit with a Voigt peak profile on top of the background (lines). For ns-HA, only the experimental data are shown as lines; (b) evolution of the gaussian and lorentzian contributions to the Voigt profile for the heated bone samples (left), as well as aged sample and s-HA (right, as indicated along the x-axis.); (c) evolution of the peak frequency (left axis) and Voigt width (right axis).